ANNOUNCEMENT:ASTAP solver is moving from G17, G18 to the H17, H18 star databases. The stars are split in 1476 files of about 5x5 degrees instead of the usual 10x10+ degrees for the 290 files. The blind solving speed increases if your field-of-view is equal or smaller then about 1.5 degree. Blind solving speed doubles at a field-of-view of 0.5 degree compared with using the G18 star database.
There is no urgency to replace the existing G17, G18 databases. They will keep on working. In the long term I would recommend for field-of-view smaller then 1 degree to move to the H18. There is no penalty for using the H18 instead of H17, same speed only the size is larger and it goes deeper. If you install the new database, remove/uninstall the old one to activate the new one. A write-up to clarify some things in detail will follow later.
Download:
For MS Windows 64 bit:
- ASTAP installer,
version 0.9.475 dated 2021-01-13. Alternative
link, very latest development version 0.9.475 ASTAP installer
, ASTAP
executable only
- H17
star
database installer up to mag 17 (500 MB installer) or H18
star
database installer up to magn 18 (980 MB file) (at link)
for
the internal astrometric solver. Select the H18 if your FOV is less then one degree. Alternative links H17 installer, H17 zipped, H18 installer or H18 zipped, G18 rar or G17 installer. If you have both the H17 and H18 select the correct database in tab alignment. Older G17 and G18 files can be deleted.
- Optional:
- For photometry you
could download and install the V17 star database colour up
to magnitude 17. A 680 MB file. It contains the calculated
Johnson-V magnitude and colour information (GBp-GRp) for star
annotations. This one also works best for solving an image with a
FOV of more then ten degrees
- Hyperleda,
a very large galaxy database for deep sky annotation.
2.190.000
objects.
Based on extract from leda.univ-lyon1.fr/ Will be
placed in
the program
directory.
- Fpack
& Funpack,
fits image compression & decompression programs from
Nasa HEASARC.
Only required if you have files with the .fz
extension.
- ASTAP command-line version. Writes log to stdout. Not always updated to the latest version.
For MS Windows 32 bit:
- ASTAP
zipped
package
version
0.9.473 dated 2021-01-10. Extract in directory c:\ program
files\astap
or c:\astap. Note that the execution speed of the 32 bit
version is
lower then the 64 bit version. Alternative link ASTAP zipped
- H17
star
database installer up to mag 17 (500 MB installer) or H18
star
database installer up to magn 18 (980 MB file) (at link)
for
the internal astrometric solver. Select the H18 if your FOV is less then one degree. Alternative links H17 installer, H17 zipped, H18 installer or H18 zipped, G18 rar or G17 installer.
If you have both the H17 and H18 select the correct database in
tab alignment. Older G17 and G18 files can be deleted.
- Optional:
- For photometry you
could download and install the V17 star database colour up to magnitude 17. A 680 MB file. It contains the calculated Johnson-V magnitude and
colour
information (GBp-GRp) for star annotations.
- Hyperleda,
a very large galaxy database for deep sky annotation.
2.190.000
objects.
Based on extract from leda.univ-lyon1.fr/ Will be
placed in
the program
directory.
- ASTAP command-line version. Writes log to stdout.
For Linux 64 bit:
- ASTAP
debian
package or astap_amd64.tar.gz, openSUSE and Fedora support version
0.9.475 dated 2021-01-13. Alternative link, development version 0.9.473 ASTAP debian package , ASTAP tar.gz.
- H17
star
database debian package (500mb) or H18
star
database debian package (980 MB) (at link) for
internal astrometric solver. Alternatively for manual install at /opt/astap, download H17 Debian, H17 zipped, G17 zipped or H18 debian or H18 zipped or H18 rar
If you have both the H17 and H18 select the correct database
in tab alignment. Older G17 and G18 files can be deleted.
- Optional:
- dcraw support program for raw files, special version which writes camera metadata to comment section of ppm file. Will read exposure, and iso (gain) settings.
- For photometry you
could download and install the V17 star database Debian package
up to magnitude 17 . It contains the calculated Johnson-V magnitude and
colour information (GBp-GRp) for star annotations. This one also works
best for solving an image with a FOV of more then ten degrees Alternatively for manual install at /opt/astap, download V17 zipped
- For a telescope with a small field of view <30 arcmin you could download the G18 star database Debian package up to mag 18. Alternatively for manual install at /opt/astap, download the G18 zipped version or G18 as rar. Remove
the G17 files or force use of the G18 in ASTAP. tab alignment.
- Hyperleda,
a very large galaxy database for deep sky annotation.
2.1940.000
objects.
Based on extract from leda.univ-lyon1.fr/ Will be
placed in
the program
directory.
For Linux 32 bit:
For Raspberry PI, 32 bit:
For Raspberry PI, 64 bit:
For MacOS 64 bit.
- ASTAP
pkg installer
(at link)
version
0.9.475 dated 2021-01-13.
- H17
star
database pkg installer (0.5 gbyte) or H18
star
database pkg installer (1 gbyte) (at link) for
internal astrometric solver. Will be installed at /usr/local/opt/astap. The
Deepsky, HyperLeda and variable star database are included with the G17.
- Optional:
- For photometry you
could also
download and install the V17 star
database
containing 105 million stars up to Johnson-V magnitude
17. The Deepsky, HyperLeda and variable star database are
included with the V17. This one also works best for solving an
image with a FOV of more then ten degrees
- For a telescope with a small field of view <30 arcmin you could download the g18 star database installer up to mag 18 or zipped G18 star database up to mag 18 for manual install at /usr/local/opt/astap. Remove the G17 files or force use of the G18 in ASTAP. tab alignment.
Any Mac user who could assist in compiling ASTAP for
Mac on ARM using Lazarus please contact me.
ASTAP
introduction
ASTAP is a free stacking
and astrometric solver (plate solver) program for deep sky
images. In
works
with astronomical images in the FITS format, but can
import
RAW DSLR images or XISF, PGM, PPM, TIF, PNG and JPG
images.
It has a powerful FITS viewer and the native astrometric
solver can be
used by CCDCiel, NINA, APT or SGP imaging programs
to synchronise the mount based on an image taken.
Main features:
- Native
astrometric
solver, command line
compatible with PlateSolve2.
- Stacking
astronomical images including dark frame and flat field
correction.
- Filtering of
deep sky images based on HFD value and average value.
- Alignment
using an internal star match routine, internal
astrometric
solver.
- Mosaic
building covering large areas using the
astrometric linear
solution WCS or WCS+SIP polynomial.
- Background
equalizing.
- FITS viewer
with swipe functionality, deep sky and star annotation,
photometry and
CCD inspector.
- FITS
thumbnail viewer.
- Results can
be saved to 16 bit or float (-32) FITS files.
- Export to JPEG, PNG, TIFF, PFM, PPM, PGM files.
- FITS header
edit.
- FITS crop
function.
- Automatic photometry
calibration against Gaia database, Johnson -V or Gaia
Bm
- CCD inspector
- Deepsky and Hyperleda
annotation
- Solar object annotation using MPC ephemerides
- Read/writes FITS binary and reads ASCII tables.
- Some pixel
math functions and digital
development
process
- Can display images and tables from a multi-extension FITS.
- Blink routine.
- Photometry routine
- Available
for MS-Windows 32 & 64 bit, Linux 32, 64 bit,
MacOS 64 bit,
Raspberry-Pi Linux 32 and 64 bit.
Stacking of images:
Stacking
of astronomical images is done to achieve a greater signal to
noise
ratio, prevent sensor saturation and correct the images
for
dark
current and flat field. Additional imperfect images due
to
guiding, focus problems or clouds can be removed.
This is a screen short
of the stack
menu. It contains several tabs for the file list and settings.
File can
be sorted on quality and values.The image can be visually
inspected in
the
viewer by a double click on the file or using the pop-up menu.
Program requires FITS
images or RAW files as input for stacking, but it can
also
view 16 bit PGM /PPM files, XISF files
or in 8 bit PNG, TIFF or BMP
files. For importing DSLR raw images the program DCRAW from David Coffin
or LibRaw is used.
- Stacking
methods: average and sigma-clipping-average.. Internal
calculation
using
floating point numbers.
- Simple and
intuitive user interface.
- Automatic
saving of selected options and
files.
- Can create
master files for dark and flat & flat-darks to reduce
processing time.
- Limited memory
use, independent of the number of images stacked.
- Bayer
algorithm for DSLR/OSC cameras
For stacking the internal routine compares
the image star positions to align.
Astrometric
Solving:
ASTAP can be used
as
astrometric solver
to synchronise the telescope mount position with center
position
of an image taken with the telescope. Existing images can
be
solved to annotate, for
photometry
or the measure positions of unknown objects.
The
ASTAP solver aims at a robust star pattern recognition using
the
catalog star coordinates in Equinox J2000. The solution is not
corrected for
optical distortion, refraction, proper motion
of stars and other
minor effects all to be very minor.
The
process astrometric solving is often referred to as a
"plate
solve". That was a correct description in the past, but
in
modern
times there are no photographic plates involved in the
process.
Back to index
Program
installation:
MS-Windows:
The installer and separate star database will be default installed
at c:\Program Files\astap. But they can be placed anywhere as long all files are in the same directory.
Linux
installation:
The program and database are provided as a
Debian package
and will be installed at /opt/astap. The program is also a rpm
package is available. In case the executable is manually placed at
/usr/..., then the program will look for the database at /usr/share/astap/data/ (version 0.9.412b or higher)
MacOS
installation:
The program and star databases are are provide as pkg
file. The star database will be installed at /usr/local/opt/astap/
Program
operation, stacking astronomical images:
The purpose of the
stacking routine is to combine astronomical images to
reduced
noise and to flatten the image.
Ideally you should have collected
- 1a) Several light
frames. Images of deep sky object unprocessed.
- 1b) Several dark
frames
of the same temperature and exposure as the light frames. A dark frame
is a frame that represents an exposure done in total darkness. This
signal includes the bias signal, but also includes any dark current
charge accumulation, and thus any dark current noise that exists within
the dark current signal. For darks suburban area (SQM=20.4) you should
take about the same amount or more darks as lights. For a light
polluted area you could take less darks then lights since the noise in
the lights generated by the sky background will be abundant.
- 2a) Several flat
frames.
A flat frame is a frame that represents the field flatness
and taken
from an uniform light source. Ideally with a significant
signal level.
This to compensate for vignetting and dust particles.
Vignetting can
greatly darken the corners of your image and have to be
compensated.
- 2b) Flat
dark frames or bias
frames
ideally of the same temperature and exposure duration as
the flats.
Since flats are taken with very short exposure times,
either flat dark
of bias image of almost zero seconds will do.
Only light frames are essential.
The automatic stacking process in ASTAP goes through the
following
steps:
- The flats will
be combined to an average and the combined average
flat-darks will be
subtracted to have a near ideal presentation of the
vignetting
called the master flat frame.
- The darks will
be combined to an average master dark.
- Optional on the master flat a 2x2, 3x3 or 4x4 mean filter
is applied to reduce
noise.
- From each light frame the master dark will
be subtracted to extract the pure deep
sky signal.
- Each light frame will be
flattened by
dividing it by the master-flat resulting in the corrected light frames.
- The
corrected light frames are combined to the final image using the
average or sigma clip mean (to remove outliers as satellite tracks)
method.
Step 3,4,5,6 are done in memory. No intermediate results are stored on disk.
It is possible to mix different exposure times but it is not recommended.
Operation of the
stacking program
Start the ASTAP program.
Call up the stack
menu window using the ∑ button.
a)
Select frames
In tab
images select the lights. In tab dark select the corresponding darks.
Select in tab flats the flat-field images called flats and in tab
flats-darks the flat-darks/bias frames.
In most cases you could select all frames in tab images. The program
will move the fames to the corresponding tab during analyse. The light
and dark should preferable have the same exposure time and temperature.
The flats should have the same exposure time and temperature as the
flat-darks.
b)
Analyse and remove bad frames
In
tab images (for the light frames), press analyse and remove
manually
any poor image. Poor images can be detected by a too
high HFD
(Half flux diamater stars), low number of stars or high
background
value( by clouds) .
Loss of tracking could result in too low HFD value. If
required inspect
each image by double on the file name. The
list can be sorted by clicking on the corresponding columns.
Using the
pop-up menu selected bad frames can be renamed to *.bak for
deletion
later.
c)
Set parameters in tab stack method
In tab stack method
select the stacking
method, average or sigma-clip-average. For OSC camera
images
select "Convert OSC images to colour". Select the
correct Bayer
pattern
(4 options). Test the required
pattern first in the viewer with a single image. The source
images
should be raw (gray) without colour produced by
astronomical camera's.
d)
Set parameters in tab alignment
Leave this
to the default star alignment.
e) Classify by
Leave all check marks initially
unchecked. (This is an option to select automatically a master dark
with the correct temperature and exposure time for the lights. Same for
master flat selection based on filter used both in the
light and flat.)
f) Press the
Stack (..) button.
The
darks and flats & flat-darks will be combined in a master
dark
and
master flat frame. Then the program will combine the light
frames to
the final image and save it automatically to FITS. This will take some
time.
g)
Export
The stack result will be saved as FITS. The program keep a record of
all results in tab Results. Stretch the image as required.
Crop the sides if required using the pop-up menu. Equalise the
back ground if required using the tool in tab pixel
math.
Export as stretched JPG or 16 bit bit stretched/unstretched
PNG / TIFF. The stretched export follows the gamma and stretch
setting of the display. For further image processing you could
export to 32 bit float TIFF or 32 bit float PFM format.
ASTAP export types:

File formats ASTAP | 8 bit | 16 bit | 32 bit |
Import | FITS, JPEG, PNG, TIFF | FITS, PNG, TIFF, PPM, PGM, raw formats | FITS, PFM |
Export | FITS, JPEG, PNG, TIFF | FITS, PNG, TIFF, PPM, PGM | FITS, TIFF, PFM |
All the program settings and file selections will be save
by
leaving the program or click on the Stack check marked images button.
Back to index
Back to index
The stack menu:
Images, darks, flats can be added using the Browse button or can be drag dropped on the form.
For a generic description how to stack see Program operation, stacking
astronomical images
Poor images can be filtered by either 1) HFD value, 2)
Quality, 3) Star-level or 4) Background
value.
Stack multiple objects:
Several
objects can be stacked in one run. If the classify-by-object
is
check-marked, the program will stack all objects and save the
results
using
the
available darks and flats.
Analysing and removing of
the bad ones:
Before stacking the images can be analysed with the Analyse
button.
Images with a high HFD value are most likely unsharp and can
be
inspected in the viewer by double click on the filename. The
file can
be renamed to *.bak by the pop-up menu to be
removed later.
Images
with a high background indicating clouds or
twilight should be
removed/renamed to *.bak.
Sorting:
Images can be sorted on any of the columns. For example if you
click on
HFD, the images will be sorted on HFD. You could
then remove
the images with the highest value or inspect them by double
click on
the file name.
Dark classification:
If classify by exposure time and/or exposure time is
check-marked the
program will automatically select the correct darks or master
dark. So
it is possible to keep several dark files check-marked in the
darks tab
and the correct master dark will be selected automatically.
Colour stack and Colour
filter classification: If the
classify-by-filter is check-marked, the stack routine will
combine the
available filters
to a RGB image. If only Red + Green +Blue image are
available
they
will be combined in a RGB image. If Luminance images are
available
it will first stack the RGB colors and then apply a
most-common-filter
and Gaussian blur on
the RGB result. Finally the luminance image is
coloured with
the RGB result. The filter factor should be set typically
near
20.
For
nebula you could combine RGB or LRGB. If a luminance filter is
detected
the LRGB mode is used. First the RGB is combined, stars are
removed
using a most common filter, the image is then blurred with a
Gaussian
blur and and the colour is then applied luminance channel.
Star colour
is lost with this process. The filter names can be set in tab
alignment
To record star colours use RGB only.
It could be better to stack in two steps. First prepare the
Red, Green,
Blue and
Luminance stacks. Then run a stack again with the Red,
Green,
Blue and optional Luminance.
Or if you could revisit the produced interim results in the
RESULTS tab
en copy them to the IMAGES tab using the pop-up menu. You
could try different colout factors.
Image file names containing "_stacked" will be
un-checked by default to
prevent stacks by accident are re-used.
If required, just select the file and check-makr it again.
Organising images, darks,
flats and flat-darks: Images placed in the first tab
will
be organised based on the FITS header keyword
IMAGETYP.
So as soon you click on the image Analyse button, dark and
flats and
flat darks/bias images will be move to the corresponding tab.
Keyword modification:
The pop-up menu has option to update a keyword of multiple
files if
required.
OSC images (one shot
colour images): To import raw files from digital
camera,
ASTAP can execute the command line program DCRAW
from David Coffin. This program is included with the ASTAP
Windows
version. For Linux install by e.g. "sudo apt-get install
dcraw.
See import
The stacking of OSC images
works best if you start with raw image before it is converted
to
colour. The raw colour images look mono, but the program will
convert
them later in the stacking process. There are 4 different
Bayer
pattern. They are identified as 00, 1,0, 0,1, 11 and can be
set in the
stack tab "stack method".
Try emperish which will result in the correct colours. Load a
raw image
in the viewer and convert it using tools menu option "convert
bayer
matrix"(CTRL+0). If the colours are not correct, just hit
CTRL-Z to
recover and try an other bayer pattern setting in stack tab
"stack
method"
Select for OSC image 2x2 mean for flats, see tab stack method. This will
prevent
any interfering patterns due to the 2x2 Bayer matrix.
Power down option after
completion:
If stacking takes a long time you could activate this option
and the
program will be power-down the computer after completion.
Clear , button to
remove all files from the list.
||
, button to
stop blinking cycle.
>> ,
starts a continuous un-aligned blinking cycle. This is
intended to find
visually outlier images where guiding has briefly failed.
How to exclude poor images
Sort the images on quality by double clicking on the column quality and inspect visually the images with the lowest quality factor by double click on the row.
If poor, rename images with right mouse button popup menu "rename to
*.bak" for deletion later. Sort also on background and inspect visually the images with too high values on possible cloud coverage or twilight conditions by double click on the row to open.
- HFD
is the image median HFD. The lower the better. Depending on focus and
guiding. Note that low values could be result of loss of
tracking.
- Quality of the image. The higher the better. Based on the number
of star detections divided by HFD. Depending on sky transparency of the
sky and focus. Note that loss of tracking result both in a low HFD and
low star count so a low quality factor..
- Star level. The higher the better. Depending on transparency of the sky and focus. Note that a high values indicate satellite tracks.
- Background.
Depending on sky darkness and transparency. The lower the better. A
higher value means in most cases a cloud was blocking the sky.
- Sharpness.
The lower the better.Measures the change between dark and bright
pixels. The measurement is very sensitive to satellite tracks. Could be
used to detect satellite track when compared with HFD value. Could also
be used to sort images of the Moon and Sun on sharpness.(but they can't
be stacked) For correct sharpness measurement of OSC images
either the FITS header should contain the keyword BAYERPAT or
check-mark "Convert OSC to colour" in tab "Stack method".
To uncheck/untick
poor images can als be done automatically. First check mark the option "After analyse
untick worst
images". Then press button Analyse and organise images . The column quality of the images will
be
analysed statistacally and outliers can be removed using either a
standard deviation represented by the Greek lower case sigma σ letter or a percentage.
For a normal distribution you could expect the following:
Confidence interval |
Proportion
within |
1σ |
68% |
1.5σ |
87% |
2σ |
95 % |
2.5σ |
98.8% |
3σ |
99.7% |
Satellite tracks
The stack method "sigma clip average" should normally remove any satellite tracks. If after
stacking with "sigma clip average" there are still satellite tracks
visible, you could lower in tab "Stack Method". the sigma factor from 2.5 to a lower value maybe 2.2 . An other way is the blink/scroll through the
images with the >>
button. As soon you see an abnormal bright track on the image stop the
blinking by esc and inspect visually the image(s) involved by
double click on the row. Remove any poor image by using right
mouse button popup menu "rename to *.bak"
Results tab.
The
stack results are reported in the results tab. By a double
click
they can be viewed the viewer. The number of files
and
exposure times are given. With the pop-up menu it is
possible
to
copy the image file path to the clipboard for use in a file
explorer.

Back to index
Stack method tab
Master flat:
Typical setting 2x2 mean
Stacked
image: Best option is "Sigma
clip
average". For only
2 or 3 images or when you are in a hurry "average"will do.
Raw one shot colour images (OSC):
RAW
images of DSLR cameras /One shot color
cameras are monochrome and have to be converted
into colour images (after
applying darks and flats). This
converson is
called demosaic
or debayer. First set Bayer
pattern
correctly by loading a raw image (grayscale) in the viewer and
try one
of the bayer patterns till the image colours match in viewer.
If
not hit CNTRL-Z to undo and try a different Bayer pattern.
There are several methods to convert (demosaic/debayer ) the
raw
image to colour:
- AstroC,
colour for saturated stars,
as bilinear method but for saturated stars the program
tries
reconstruct the star colour. Select the range which
matches with the value of brightest stars.
- AstroM,
white stars,
as bilinear method but if there is an unbalance between
the 4 red, 4
blue or 2 green pixels it uses luminance only. Effective
for unsampled
images and stacks of a few images only. Star colour is
lossed if
undersampled but star will become white.
- AstroSimple ©, each
R,G, G, B pixel colour information is used in a 2x2 pixel range. Simple but very effective for
astro images. Works best for a little oversampled images. Stars have very few artifact if any.
- Malvar-He-Cutler
1), advanced
method for interpolation developed for terrestial images
but less suitable for OSC
astro images. The background noise is lower.
What to select:
- In general de-mosaiced OSC astro images are
suffering
from colour artifacts due to the small size of stars and
pixel saturation. If the pixels iluminated by a star are
saturated, the
red, green and blue values will have the same maximum
value and the
star centre will appear white. In most case this can be
avoid by taking
short exposures of 60 seconds or shorter.
- Best results are achieved with de-mosaic methods AstroC and Simple.
- In most cases the option "Auto level and colour smooth"
is required for the correct colour balance and colour
smooth. First the
three colour channels are adjusted to make the background
colour
neutral and the stars average white. Secondly the bright
stars are
smoothed. Both actions can be done manual in the tab pixel
math, option
"colour correction"
and "smart colur
smoothing"
- If the images are under-sampled and the
star colour is random after stacking, use AstroM, white stars. Stars will be
whiter. Star colour will be lost.
The principle of the AstroSimple demosaic method:
Auto levels: This is an option to white balance the final colour result. The stars will be average white and the background sky will be gray.
Colour smooth: This is an option to smooth the de-mosaic artifacts. The colour is smoothed while preserving the luminance signal.
The background colour noise can be removed with option
"Background colour removal" in the pixel math tab of the
stacking menu.
The
DSLR OSC images will be automatic converted to FITS files by
the DRAW
program included (Windows, MacOS) or for Linux install by
command
line "sudo apt-get install dcraw".
Oversize:
This could be 0, 100 or larger. This overlap was
introduced to
show overlapping images. If you don't want a black area around
the image set this value to zero.
If your using a monochrome filter like H-alpha, use
the viewer
Tool menu to split the images in R, G, G, B before stacking
and use the
R=red image for future processing.
The program settings will be saved automatically if your
either exit the
program or start a stack.
There is a test button for the flat filter. It will be applied
on
the image in the viewer, so load the flat first by double
click on the
fat file name.
Image stiching method (Mosaic)
Astrometric
image stiching is possible with the internal astrometric solver. The reference of each pixel is the
astronomical position. So stacking is not done against a reference
image but against an position array set by the first image.
You have to set the in tab alignment the settings for "Image
stiching (method)" correctly. If you stitch 4 images, you have set
"Mosaic width/height in tiles:" at 2. This will provide enough
space to place for the 2x2 mosaic.
Here a suggested work method:
- Stack the tiles
separately using method "SIGMA-CLIP-average" and use for the
alignment
the internal STAR alignment method.
Inspect the resulting tiles and crop them if
required. You
can
also crop them later automatically with "Mosaic skip
outside pixels"
Do this for each color separately if you have separate
files.
- In tab "stack method" select option "IMAGE STICHING METHOD" and
select
astrometic alignment using either the internal solver.
- In
tab "stack method", set the "mosaic width/height" correct and
check-mark the option "equalise background". If the input
images have poor borders, set option crop images larger then 0%.
- Select the files. Most likely the files names contain "_stacked, so you have the check-mark the files after selection.
- Click on the button Stack check marked images|
- Crop the stacked result
using the image crop option in the viewer mouse pop-up menu.
- Adjusted the stretch
range and save
as JPEG, 90% quality.
Here an example mosaic x 4 of M31 made with ASTAP:
Here an
example of a mosaic build of DSS images:

The size can be reduced by a crop function (right mouse button)
later.
Making the oversize too large could result in memory overload.
Back to index
The
alignment menu tab:
For
alignment there are four options, internal star alignment,
native astrometric solver, manual alignment or ephemeris alignment. For mosaic building you have to use
the
internal astrometric solver.
Internal star alignment

This
internal star matching alignment is the best and fastest
option to
stack images. It is not
suitable for mosaics. No settings, fully automatics alignment
for shift
in x, y, flipped or any rotation using the stars in the image.
It will
work for images of different size/camera's with some
limitations.
The
program combines four close stars into an irregular 2D
tetrahedron or
kite like figure (and
compares the six irregular tetrahedron dimensions with
irregular
tetrahedrons
of the first/reference image. It
selects at least the six best matches and uses the centre
position
of the irregular tetrahedrons in a least square fitting
routine for
alignment. The four stars are called a quad. The six distances are used to construct a hash code.
There is only two settings relevant but normally you
don't
have to change them.
- Hash code tolerance No
need to change it. Leave this at 0.005 unless you have
severe
optical distortion. If you have false detections, set this
lower at
0.003.
- Maximum
number of stars. Typically set at 500.
The following image shows the selected quads where the six distances form an irregular tetrahedrons :

The matching process is described here Background
info, how
does the ASTAP astrometric solving works internally
Astrometric alignment.
Internal
astrometric solver (plate solver). The works with
the
same four star quad as for the Star alignment option.
The quads
are compared with
the G17 star database (to be installed in the program
directory). It
has the following settings:
- Field height:
This is the square size of the star field in degrees used for
detection and will be set automatically for most FITS files. It
should equal to the image height in degrees. If unknown, you could try
initaly the option "auto".
- Radius search:
Search radius in degrees. If there is no match, the
program will
move the search field
around in a square spiral and increasing the distance
form the
initial position up to the radius specified. A
radius of 30
degrees could be searched in a few minutes.
- Maximum number of stars to use:
No need to change it. This could be set between 100
and 1000.
- Hash code tolerance:
No need to change it. Leave this at 0.005 unless you
have
severe
optical distortion. If you have false detections, set this
lower at
0.003. If you have severe optical distortion or a
low resolution image set this at 0.007
- Downsample:
For large image above 3000 pixels wide down
sampling
will speed up the solving and increase the signal noise
ration of the
stars. Also colours are combined to monochromatic so this
option is
beneficial for DSLR images
- Cropping:
For very large image above typical 3 degrees height
the
solver will only look to the center of the image.
- Force
small search steps.
This will force a 50% overlap between search fields. Use
this if
solving fails. I applied this will slow down blind
solvingC
- Calibrate prior to solving. If
your image is full of hot pixels and soling is less reliable you could
try this option. The image will be calibrated with a dark prior to
solving removing the hot pixels. Select in the darks tab, a dark or
darks with similar exposure duration as the lights you trying to solve.
If your select several darks with different exposure length,
check-mark the option classify, "Dark exposure time".
The internal plate solver works best with raw
unstretched and
sharp images of sufficient resolution where stars can be
very faint.
Exposures 5 to 300 seconds. Heavily stretched or photo
shopped images
are problematic.
For those are interested: Background
info, how
does
the ASTAP astrometric solving works internally
Manual alignment.
Manual alignment
This
option allows alignment of the images based on a single star,
asteroid
or comet. If this option is activated, the list of images in
the image
tab turns red. Double click on each image in the list and
click on the
star/comet of asteroid to be used as reference. This object is
then
marked with a little purple circle. The position will be
auto
centered. (and
the X,Y position will be added to the list) A poor lock is
indicated by
a square. If so try again till it is a circle. If all images
in
the list
are turned green, so contain a value, then click on the
Stack button .
Options:
- Star centering
- Comet centering
- No alignment
For objects which are moving in the sky, select the stack
option
"average" and not option "sigma clip".

Ephemeris alignment
Rather
then manual selecting the center point it is also possible to use the
ephemeris of an asteroid or comet. In ASTAP this is reallised by using the
annotation markers written in the header. To align go through the follow steps:
Preperation:
Stacking:
- Select ephemeris alignment
- Browse for all the images in the image tab and add if available the dark, flats.
- Press the button Analyse the selected file| in tab images .
- Select from the combobox the asteroid or comet to align on. See screenshot below.
- Hit the Stack check marked images| button.
- After the stacking is finished, it is possible to annotate the result.
Only the object selected will be sharp. The stars will form trails
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Blink tab
This tab allows to blink images and to measure variable
stars.
Blink
comparator
This
option allows rapidly cycle (blinking) through the images taken of the
same area of the sky at different times. This will allow the user to
spot easier moving objects. While blinking the result can be
demosaiced (slow) if the "auto demosaic" option in the viewer is
activated.
||
, button stops the blink
cycle.
>
, button starts one blink cycle.
>> ,
starts a continuous blink cycle.
☑ Align images.
With this option check-marked,the images will be aligned using
star
alignment. The alignment will be refreshed after pressing
"clear
alignment"
☑ Time stamp.
With this option a time stamp from the header will be written to the
bottom of the image. If the displayed image is saved as FITS, this time
stamp will be written to the saved image.
☑ Filter out stars based on first image,
With
this option check-marked,the stars will covered with a black
circle
allowing easier to spot moving objects.. The black cover size
can be
increased with option "star suppression diameter". The
star
detection can be optimised with the "σ factor".
Clear, button to
remove all files from the list.
Export video
This button will export the blink result to an uncompressed .y4m
video file (YUV4MPEG2). For OSC images, activate in the viewer
the "auto demosaic" option. The menu will ask for a video file name and
desired frame rates per seconds. Contrast will be as set in viewer.
Compression can be achieved in
an external program like VLC or leave it to YouTube. If
time-stamp is check marked then the time stamp will be written to
the video.
Export aligned This
button allow the creation of aligned FITS images. If
blinking with alignment works well, stop blinking and hit this
button All images will be copied aligned to new files
ending
_aligned.fit. Alignment will be done against the first
image in
the list. If time-stamp is check marked then the time stamp will be written to the aligned images.
Photometry tab
This tab allows measuring the magnitude change of
one
object in a series of images and detects automatically the four
most variable objects. The butttons work the
same as in
the blink tab.
Select the images to
analyse. Click
on one of the arrow buttons to cycle trough the images.
Initially it
will go a little slow till all data is analysed. The
program
will
do the following:
- Cycle 1, Find
an astrometric solution for all selected images and write the
solution
to the FITS file header.
- Cycle
2. In a second cycle, the program will identify stars in the
image and
measure the star flux against
the star database. The median flux/magnitude factor will be
used later
to measure the magnitude of any object in the image series. So
prior to
this install and use the V16, Johnson-V
version of the star Gaia database provided.
- At the end of cycle 2, it will mark the four most
variable stars with a yellow circle.
- Click on any of the stars. A purple circle will mark
the object. The measured
magnitude of each image in the series will be
written to the file list. This complete list can be exported
to a
spreadsheet using the pop-up menu allowing the creation a
magnitude curve
over time.
For maximum accuracy it is better to first to calibrate the
images with
darks, flats & flat darks. This can be
done using
the "calibration only"option in tab "stack method" and then
executing
the regular stack procedure.
Note
that the measured star flux is compared and calibrated with the
star database.
For most cases
you should either install the V16 or V17 star database containing the Johnson-V
magnitudes. After stopping the cycle it is possible to measure
any
object using the mouse pointer.
Alignment
of the images is done using the astrometric (plate) solution.
The
photometric solution is stored in seperate files. The
astrometric
solution is written to the orginal file header. You
can refresh the photometric and astrometricc calibration
using the dedicated buttons for this
.
The list contains three dates:
- Date/time (start)
in YYYY-MM-DDTHH:MM:SS. This is date & time from the
header key
word DATE-OBS. This is normally the universal time at the
start of the
exposure.
- JD (mid exposure)
This is the Julian Day of the exposure midpoint. This time
is
calculated from the key word DATE-OBS and half of the
exposure time is
added.
- HJD (helio) Heliocentric
Julian Day
at the exposure midpoint expressed in UTC. This is the event
time as
seen from the Sun center compensation the maximum ± 500
seconds time
difference depending on the positions of the Earth, the
object outside
the Solar system and Sun. For plotting purposes only the
fraction is displayed.
To convert the Julian Day to a date and time in the
spreadsheet, subtract the Julian Day by -2415018.5
and format as date or time.
For
a series of images, the standard deviation of the measured star
magnitudes is typical better then 0.02 magnitudes. The star
flux
values should be below saturation (65500) but reasonable
high.
Note that it is beneficial to de-focus an image a little to
prevent
pixel saturation and spread the flux measurement over more
pixels. It also allows longer exposure times. However
the image should reasonable focused to allow solving.

Here an example of an exoplanet transit measured using the
blink&photometry tab:

A demonstration is available at YouTube:
Measure
variable stars
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Inspector tab.
This
tab is intended to measure accurately the tilt and curvature of your
telescope & camera setup. It's done by calculating the best focus
position for each image area. To do this it requires a series of images
taken at several focuser positions.The routine will calculate from
these images the best focus point of each area. It will measure
the median HFD values of each image and area and build a table HFD as
function of the focuser position. Form this data, curve fitting will
give the transfer fucntion and the best focus position expressed in
focuser steps. The focus point differences between the image areas will
indicate the tilt of each area. The difference between the centrum
and outer areas focus point will indicate the curvature.
The usage is as follows:
-
Prepare a series of short exposure images with different focuser
positions and a lot of stars. Exposure time a few seconds. Move for each
image the focuser a small fixed step but only in one way to prevent backlash
problems. Images with stars having an hfd above 20 will not be
analysed correctly.
-
Browse with ASTAP inspector tab to the images.
-
Press curve fitting.
- The difference between the focus point of each image area will be reported in focuser steps.
The reported hfd values can be selected and copied for further analysis in a spreadsheet.
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Live stacking tab.
All file(s) in the specified directory will be stacked live. If it is finished
it will wait for new file(s). If a file is detected which is 0.2°
away from the previous files a new stack will be started
automatically. You can save the stack results from the viewer menu .
To identify files which are processed , they are renamed to the
extension *.fts. You can rename them back with the button at the bottom.

Note there is no rejection of poor images. All images are added with equal influence:
Assuming the images are A,B,C,D, E... then
Simple serial stacking:
result1:=A
result2:=(result1+B )/2
result3:=(result2*2+C)/3
result4:=(result3*3+D)/4
result5:=(result4*4+E)/5
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Pixel math1 tab.
Several options including
background equalising.
Background
equalization tool:
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Pixel math2 tab.
Several options.
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Export
FITS data to a spreadsheet:
To
analyse the relation between the HFD value, focuser position,
temperature and altitude it is possible to copy the data from a
FITS image list to the operating system clipboard.
Just
select a number of images, click on the Analyse button. Then
select all
relevant files and copy the data with right mouse button. Then
copy the
data into a spreadsheet for analysis.

Here and example of the result in a spreadheet:

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Viewer:
If
the program is associated with FITS image files or any
other
format, it
will show the image as soon you click image file. Only one
instance of
ASTAP will be allowed. After clicking on the second image it
will be
show in the first instance of ASTAP. If you want to open a
second
instance, just start ASTAP. If the program is started without
parameters, you can open more instances.
Images can be loaded from the file menu or can be drag dropped on the main form.
Besides
all FITS formats, the viewer support most image formats in
8/24 bit of
16/48 bit format. It can export to any FITS format and 16/48
bit PNG
and TIFF formats.
ASTAP
can display images and tables of MEF, multi-extension FITS. The images
of MEF can be saved as a single image. The MEF tables can copied into
the clipboard and paste to a spreadsheet. (v0.9.446)
This ASTAP version can import raw
images from almost any digital camera, For this ASTAP executes
the Libraw tool Unprocessed_raw which is included with the ASTAP
Windows
edition and can be installed in Linux by the "sudo apt-get
install
libraw-bin" command.
File formats ASTAP | 8 bit | 16 bit | 32 bit |
Import | FITS, JPEG, PNG, TIFF | FITS, PNG, TIFF, PPM, PGM, raw formats | FITS, PFM |
Export | FITS, JPEG, PNG, TIFF | FITS, PNG, TIFF, PPM, PGM | FITS, TIFF, PFM |
The
viewer has a preview function. After opening select "Preview
FITS
files".
The preview is displayed in the ASTAP viewer. The current zoom
and
position is maintained so you could study the corner of a
series images
on image quality.
The file open menu with preview selected:

Thumbnail
viewer for
FITS files
ASTAP has
a FITS thumbnail viewer (ctrl-T). This could be useful to
browse your
FITS files. By clicking on the thumbnail it will be opened in
the
viewer. With a right mouse button click some options are
available as
changing directory, copy, move, rename or rename to *.bak.
The
thumbnail size is depending on the form size. Make it larger,
the
thumbnails will follow. Thumbnails are organized in 3*X. So
the
thumbnails are pretty big by purpose. The images are fully
loaded in
memory so it will consume some memory and time. So don't try
get
thumbnails of 400 images.
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ASTAP viewer screen shot:
Astrometric
solving
the image in the viewer
With
the Solve| button it is possible to find an astrometric
solution of the
image loaded. For this the estimated celestial center
position
α, δ
should
be available. This position is normally retrieved from the
FITS header.
Secondly the estimated image height in degrees should be
specified in
the stack menu, tab alignment.
In the same tab alignment you can specify the search
radius
and down sampling. For successful solving see conditions
required for solving.
For solving JPG, PNG or RAW files it is possible to add the
object
position as center position using the deep sky database.
Double click
on RA position in
viewer and enter the object name. The position will be
retrieved from
the database. This position will be used as a start point
for
the solver.
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Batch conversion
of raw
images from digital cameras
The viewer menu tools has a batch convert option. ASTAP will
execute
DCRAW with
parameters -D -4 and this will produce 16 bit PGM raw
files. ASTAP
can read these PGM files and convert them to a 16 bit FITS.
After
conversion the intermediate PGM are no longer required and can
be
deleted manually. The FITS can be used in the stacking. The
Bayer
matrix conversion to colour will be applied later in ASTAP.
With this
method the full depth of the original RAW files will be
preserved
This conversion is not required for ASTAP. Automatic conversion
is
integrated in the menus.
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Deep
sky
annotations
If the image is solved, it is possible to add deep sky
annotations. See
pull-down menu TOOLS:
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Star
annotation
and photometry
A
second menu option is to annotate the stars and auto calibrate the
program for photometry. This can be done best with either the V16
or V17 cotaining the calculated Johnson-V magnitudes.
For a G-database the indicated magnitude
is Gaia blue. For a V-database the indicated magnitude is Johnson-V and
the following the difference between Gaia blue and red, positive for
reddish objects. All in 1/10 of a magnitude.
Below,
the image is 1) solved, 2) auto calibrated (using the V16)
The
cursor is at a star and based on the flux of all know stars, the
star
Johnson-V magnitude is estimated to be 16.1. The stars are
marked with
the Johnson-V magnitude and Bp-Rp color indication.
A
third tools option is "Annotate stars with measured magnitude".
The
measured star flux is calibrated with the star database. If the
Johnson-V version of the star database is used, the results
match very
accurate with AAVSO charts as demonstrated below. Camera was an
ASI1600
with only an UV-IR block filter:
For best accuracy the image should be monochrome and one of the
Gaia Johnson-V star databases should have been installed and
selected (V16 or V17). The image should
have taken with a Johnson-V filter or none (clear). The
measured pixel values should be below saturation.
See also
blink and photometryMark unknown stars
There
is also an option to mark nova and minor planets using the star
database. Any star like object missing from the star database will be
marked. Also if the measured magnitude is one magnitude brighter then
the database. The H18 star database up to magnitude 18 is recommended
for this option. If the H18 is selected then missing object up to magnitude
17 will be detected.
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Asteroid and comet annotation
This
option will annotate asteroids using the orbital elements taken
from the MPCORB.DAT file and for comets the ComeEls.txt from the
Minor Planet Center.
Usage:
- Solve an image.
- Go to to the viewer "Tools" menu, "Asteroid annotation".
- First time download the full
MPCORB.DAT from the minor planet center. Link is available from the blue down arrow. Set the path to MPCORB.DAT correct.
- Set the limiting magnitude and maximum number of asteroids to read.
- Press the button
Asteroid & comet annotation .
Remarks:
Renew the MPCORB.DAT and CometEls.txt files every few months.
The
observation date and time are extracted from the FITS header (date-obs,
date-avg) or for other files the file date is taken. If date
average is not available it will be calculated from the exposure time
and date-obs from the FITS header.
The
latitude and longitude of the observation location are also taken from
the header. If not available enter them manually or leave them at 0.
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CCD
inspector
The viewer has a CCD inspector under menu tools. By
reporting the median HFD value, sensor tilt and curvature the
inspector
will quickly show any problem of the imaging system.
The
image used for testing should be a single raw image
with sufficient stars and not containing a disturbing
large
and bright deep sky object. The exposure length should be
long
enough to image many stars but not too long preventing star
saturation.
The routine will detect and annotate the stars with their HFD
value and
plot a tilt indicator in the image. A star rich image containing a few hunderd stars or more gives the best accuracy.
The following will be reported:
- Image median hfd which is an
excellent indicator of the quality of focusing. The lower
the value the
better the focusing, the sharper the stars are. The value is
also
depending on the astronomical seeing and the quality of the
optics. If the image is solved it will also be indicated in arc seconds.
- Sensor tilt as the
percentage ratio between the best and worst corner
median
values. In addition as an graphical indication it draws an
trapezium in
the image based on the four median values.
There can be some variation in images of the same series, so
a tilt of
maybe 20% looks normal but anything more indicates a camera
mounting
problem. The lower the value the better. The unit if expressed in delta HFD.
- Off-axis abberation
as the delta between the HFD value in the center and in the outer areas
of the image. The stars in the outer area are normally a little larger,
oval or comet shaped due to the optics or curvature giving an higher
HFD value. The lower this value the better the optics. This value could
be a help to adjust the optimal distance between the field
flattener and the camera. This measurement is only a valid if the focus
for the center area is perfect. A more advanced measuring
method is available in tab CCD Inspector.
HFD 2D contour menu.
The star half flux diameters (HFD's) are displayed in a 2D contour.
Dark areas indicate a lower and better HFD value. This will
quickly visualise sensor tilt or other problems. To avoid
false indications by outliers the HFD values are filtered by taking the
median HFD value of the three closest stars and allocate the
result to all three stars. The HFD values are indicated numerical. They
grey levels have no direct linea relation with the HFD.
HFD
diagram menu. The star HFD values can also be represented by areas of constant HFD.
It is in principle a Voronoi diagram, but by taking the median
value of each three closest stars and allocate the median to the three
stars it looks a little different.White areas indicate a star with an
high HFD value. Darker areas indicate a lower value. The grey level is
the HFD * 100.
HFD values menu
This will only indicate the median filtered HFD values next to the
stars. The same values as in the 2D countour and HFD diagram. To avoid
false indications by outliers the HFD values are filtered by taking the
median HFD value of the three closest stars and allocate the
result to all three stars.
View
menu
This menu has the following options:
- Image clean up Ctrl+space
- Center lost windows Ctrl+F12 Use this if you have
multiple screens and once window is out of site for some
reasons.
- Flip horizontal Ctrl+H
- Flip vertical Ctrl+H
- Zoom out PgUp
- Zoom in PgDn
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Batch conversion:
With the batch routine
several FITS image
can be
"astrometric solved". Raw images
of OSC (color) sensors using a Bayer matrix can be converted
to color.
FITS tables
The
viewer has limited support for displaying FITS binary and ASCII tables.
It can read and write binary tables and read ASCII tables only. They
are displayed in the memo. Values are separated by a tab #9 and can be
selected and copied to a spreadsheet. It can display only one table and
will display the first table only. The file can be saved again but all
binary values will be all written as 4 byte float.
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Viewer
popup
menu:
Add annotation, free
text label at a x,y position. It can be connected via a line by first
holding the right mouse button and moving the mouse away. See sample
above. Persistent by annotation keyword in the FITS header. The
annotation can be switched off in pulldown menu "View". Remove by
removing the annotation line in the header.
Add marker, rectangle
marker at x,y position. Draw the rectangle first by holding the right
mouse button down and moving the mouse away. See sample above. The
Persistent by annotation keyword in the FITS header. The annotation can
be switched off in
pulldown menu "View". Remove by removing the annotation line in the
header.
Add object position,
Enabled after astrometric solve. Will add the α, δ at
the
mouse position. Orange if a lock is possible, see above sample, red if not. Not persistent after image clean up.
Add marker at α,
δ position,
will place a yellow square on an object for identification by on the
entered position. See above sample for orange star. Enabled after
astrometric solve. Will add
square marker
at α, δ position. Persistent. Position will be
save with "save settings"
Measure total magnitude within
rectangle,
Enabled after astrometric solve. The program will measure the
flux and
try to estimate the magnitude. Hold the right mouse down and
pull a
rectangle around the deep sky object, release mouse
button and then select this menu.
For best accuracy the image should be monochrome and one
of the
Johnson-V star databases should have be installed and selected
(V16 or
V17). The image could have been taken
with a
Johnson-V filter for best results or none. The measured pixel values should be below
saturation.
A demonstration is available at YouTube:
Photometry in the viewer
The measuring principle is as follows:
- Use the star database to measure the MEDIAN relation between flux of the detected stars
and star magnitude from the database. (That's why solving is required
and best result are achieved with the V16 or V17 Johnson-V star
databases based on Gaia DR2)
- Measure
the MEDIAN background 1 to 10 pixels wide outside the rectangle box.
This median measurement will ignore stars in the field.
- Measure the MEAN flux inside the box.
- Calculate the magnitude for the "inside mean flux" minus "median outside box flux" using the relation found for the stars.
You could argue that a Johnson-V filter or green channel is required
for the image but in practice the error is limited depending on the
spectrum.
Remove all markers and labels.
Will remove all none persistent labels. Persistent annotations
can be switches off in the viewer pulldown menu VIEW.
Copy image (selection) to the clipboard,
copies the displayed image or a selection of the image to the
clipboard. The orientation is depending on the selection direction..
(v0.9.417)
Copy position to clipboard,
Enabled after astrometric solve. Copies the α, δ
position to the clipboard.
Copy position to clipboard
in ° , Enabled after astrometric
solve. Copies the α, δ position in degrees to the
clipboard.
Copy position to clipboard in
radians, Enabled after astrometric solve. Copies
the α, δ position in radians to the clipboard.
Remove deep sky object.
Removes an deep sky object as part of the
pixel math tab routine
"equalise background tool". Hold the right mouse down and
pull a
rectangle around the deep sky object, release mouse
button and then and then select this menu.
Local colour smooth
Local remove colour.
Local Gaussian blur.
Local equalise tool.
Brighten a small area based on
the corner values.
Gradient removal tool
To remove
a linear gradient caused by light pollution or twilight. The
routine need two empty areas 40x40 pixels in the image to measure the
gradient. The area may contain stars but no deepsky object. The area
are selected by pressing the right mouse button(first area) and while
holding the mouse button move to the second area in the direction of
the gradient. Then select in the popup menu "Gradient removal tool".
Try to maximise the distance ideally the full image range.

Copy paste tool
Powerful
touch-up tool for cosmetic corrections. Small sections of the
image can be copied as pasted on hot pixels or artifacts. Select the
good part by holding the right mouse button and pulling a rectangle
with the mouse and move the copied part to the part to be touched up..
Set area
Set an area for the colour replacement tool in tab pixel math 1.
Remove borders. This
menu allows to remove parts of the image near de borders.
Crop fits image.
This allows the crop the image. Hold the right mouse down and
pull a
rectangle, release mouse button and then and the
select this
menu
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Usage
as astrometric solver and command
line options:
For
images in the viewer:
The simplest
way to solve an image is just to load an image in the viewer
and hit
the solve button. Some settings are available in the ∑ menu
under
tab alignment.
- Diameter
field:
This is the square size of the star
field in degrees used for detection and will be set
automatically for
most FITS files. It should be in range with the
image
diameter.
- Radius search:
Search radius in degrees. If there is no match, the program
will
move the search field
around in a square spiral and increasing the distance
form the
initial position up to the radius specified. A radius
of 30
degrees could be searched in a few minutes.
- Maximum number of stars to use:
No need to change it. This could be set between 100
and 1000. Default 500.
- Hash code tolerance:
No need to change it. Leave this at 0.003 unless you
have
severe
optical distortion. If you have severe optical
distortion or a
low resolution image set this at 0.008
- Downsampling:
For large image with a height above 3000 pixels
select downsampling factor 2 or to
speed up the solving and increase the signal noise ration of
the stars.
Also colours are combined to monochromatic so this option is
beneficial
for DSLR images
The
solution will be added to the fits header and center of the
image will
be
displayed in the log of the ∑ menu.
Click on the save button to save the FITS
file with the solution. With the solution, the status bar will
show
the astronomical position of the mouse pointer.
Conditions required
for solving:
Quick checklist for solving:
- At least 30
stars are visible. For smal field-of-view (<1°) and away from
the Milky-Way plane expose longer 30 to 300 seconds and use the H18
star database.
-
Reasonable round stars.
-
Image dimensions at least 1280x960 pixels. For smaller dimensions solving is still possible for good quality images.
- An approximate position is specified (for a spiral search). This position should be displayed in the left top of the
viewer menu. (unless you do a 180 degrees search)
-
Image is not stretched or heavily photo-shopped.
-
Correct image height in degrees specified within preferable 5% accuracy. This
height (width x height) should be displayed in the status bar of the viewer and in tab
alignment under "Field of view (height)" (Check focal length, sensor
size settings or try FOV=auto once)" You can set/force a "Field of view (height)" in tab Alignment.
If
you still have problems with solving, you could send me a link to
the file involved (FITS is preferred) and if I have time I
could have a look. Upload it e.g. to
http://nova.astrometry.net or
https://ufile.io/ and
give me the link. For privacy reasons, prior to uploading you
could remove your latitude/longitude information from the header
using the viewer "Tools", "Batch processing", "Remove longitude
latitude information" menu.
The
internal
astrometric solver works best with raw unstretched and
sharp images of sufficient resolution where stars can be very
faint.
Heavily stretched, saturated, out-of-focus or photo shopped
images are
problematic. It requires
minimum about 30 stars in the image to solve. Images
containing of a
few hundred
stars stars
are ideal. For star rich images, the program will reduce the
detection
limit to
limit the number of stars. This will only work for unstretched
images
where brighter stars have a greater intensity then fainter
stars. So ASTAP requires
three star
dimensions for solving. The star x, y coordinates and
star
intensity. Oval stars due to tracking errors or
severe optical distortion will be
ignored and solving could fail.
Check list for successful solving with ASTAP:
- Estimated
celestial center position of image should be
entered/available in
the viewer α and δ
input or passed by the command line. For FITS file
this is
normally read from the FITS file header and set
automatically. In case
you view an an JPEG, TIFF image, double click
on α
input to search for a know deep sky object position from the
database.
- Field of
view of the camera should be available. This is the height
of the image
in degrees. See ∑ window, tab alignment,
group-box astrometric
settings. For FITS images this is normally automatic
calculated from info in the file header.
- Image
height in pixels after ASTAP subsampling should be somewhere
between 1000 and 3000. If it is higher set subsample at 2. If you
specify 0 for subsampling, the program will select a subsampling factor
automatically.
- Search
radius should be set large enough. See ∑ window, tab
alignment,
group-box astrometric settings. You could set
this
at 30° or
larger up to 180°.
- Stars
in the image should be pretty round and the camera in focus. You
could
verify the star
detection
by the CCD inspector or by the Test button to show quads in the ∑ window, tab alignment). Most
stars
should be
detected.
- As
a minimum about 30 stars should be visible in the image. They can
be very faint stars, barely visible in the noise. For large
field-of-view (>1°) expose 5 to 10 seconds but for
smal field-of-view (<1°) far away from the Milky-Way plane
you have to exposure longer 30 to 300 seconds and use the H18 star
database.
- For
images filled with stars, only a small part of the stars may be
saturated. The
total exposure time could be hours as long it is possible to
separate
the
brightest stars from the faint by intensity.
- For
bayered images (OSC cameras) or large images use the
factor 2 downsample option. See ∑ window, tab alignment,
group-box astrometric settings. Save settings if modified (Viewer
pull down menu, file, exit (and save settings). You could also try auto
auto selection of binning equals 0.
- If
your image is full of hot pixels you could adjust the "Ignore stars
less then["] in tab Alignment. This is default set at 1.5" but
could be set higher for long focal length.
- An other option for hot pixels is option "calibrate
prior to solving". Select in the darks tab, a dark or darks with
similar exposure duration as the lights you trying to solve. If your
select several darks with different exposure length, check-mark
the option classify, "Dark exposure time".
- The maximum
number of stars to use should be defined. Typical set at 500. See
∑ window, tab alignment.
- Hash
code tolerance should be defined. Typical set at 0.007 especially
for long focal length telescopes which are more sensitive to the
seeing.. (In previous versions this was set at 0.005). See tab
alignment.
- For
some failures you could force in
ASTAP the option "slow" (-speed) for
more reliable solving. The
reliability will be very high but solving will be slower.
- In
case of excellent seeing and small band filter usage the imaged star
could be smaller then 1.5". Reduce the setting "Ignore stars
less then 1.5" in tab "Alignment". If the imaged star size
is about one pixel after downsampling reduce the downsampling to 1
(auto is often 2). Improvements will be reported by a increased number of quad matches.
- For
long focal length telescopes with a field of view less then
60 arc minutes it is recommend to install the H18 star database and
remove the G17 (or force use of the H18 in tab alignment).
- For long focal length telescopes with a small field
of view where objects like M13 fill the whole image ASTAP could
struggle to solve. This is caused by the fact that the database has a
better resolution then the image. Forcing option "slow" could
help.
Warnings:- In case you get regular a warning "Star database limit reached" replace
the G17 database by the H18. This could happen if your field of view
is small (<30 arcmin). Remove the G17 files to force the use of the H18.
In the plane of the Milky-way plane it is easy to image enough stars for solving as shown in this
ESA image
showing the sky star density. If you look outside the Milky-Way plane
into deep space there are less stars. The G17 will contain enough stars
if your field-of-view is 0.5 degrees or more. For a smaller
field-of-view you have to exposure longer to image fainter stars. The
H18 could work well up to a field-of-view of 0.25 degrees is exposed
enough. For large field-of-view (>1°) expose 5 to 10 seconds but for
smal field-of-view (<0.3°) you have to exposure longer 30 to
300 seconds. Expose long enough till the solver detects 30-50
stars
minimum or till the solver gives a warning
"Star database limit reached" indicating you have reached magnitude
18.
For
very long exposures and a FOV below one degree it could be required to
reduce the maximum number of stars detected. This is default set
at 500.If not stars with a magnitude fainter then the database will be detected..
Support is available via the
ASTAP
Forum
Command
line, ASTAP style
The program can be
executed using command line options to solve images astrometric
. E.g. ASTAP -f
home/test/2.fits -r 30
The program will
accept FITS files, JPG, PNG, BMP, XISF or TIF files.
|
ASTAP
astrometric
solver command line |
|
The FOV, RA,DEC options are intended for
none FITS files.
Not required for FITS files having the values in the
header. |
command
|
parameter |
unit |
remarks |
-h |
|
|
help info |
-help |
|
|
help info |
-f |
file_name |
|
File to solve astrometric. |
-f | stdin | | Will accept raw images via stdin. Raw format according INDI. See 1) |
-r |
radius_search_field |
degrees |
The program will search in a square spiral around the
start position up to this radius * |
-fov |
field_height_of_image |
degrees |
Optional. Normally calculated from FITS header. Use value 0 for auto.
If 0 is specified the fov found by solving it will be saved for next time.(learn mode) * |
-ra |
center_right_ascension |
hours |
Optional start value. Normally calculated from
FITS header. |
-spd |
center_south_pole_distance
(dec+90) |
degrees |
Normally calculated from FITS header *
The declination is given in south pole distance, so always
positive. |
-z |
down_sample_factor
|
0,1,2,3,4 |
Down sample prior to solving. Also called binning. A value "0" will result in auto selection downsampling. * |
-s |
max_number_of_stars |
|
Limits the number of star used for the solution.
Typical value 500. * |
-t |
tolerance |
|
Tolerance used to compare quads. Typical values
0.003 to 0.007. * |
-m | minimum star size | arcsec | This could be used to filter out hot pixels. |
-speed |
mode
|
slow / auto |
"slow" is forcing of reading a larger area from the star
database (more overlap) to
improve detection. * |
-o |
file
|
|
Name the output files with this base path & file
name |
-analyse | snr_minimum | | Analyse only and report in the errorlevel the median HFD * 100M + number of stars used. So the HFD is trunc(errorlevel/1M)/100 |
-extract | snr_minimum | | As analyse option but additionally write a .csv file with the detected stars info. |
-focus1 | file1.fits -focus2 file2.fits ....... | | Find best focus point for four or more images using curve fitting. Errorlevel is focuspos*1E4 + rem.error*1E3. |
-annotate | | | Produce a deep sky annotated jpeg file with same name as
input file extended with _annotated * |
-debug | | | Show GUI and stop prior to solving |
-log | | | Write solver log to file with extension .log |
-tofits | binning | 1,2,3,4 | Produce binned FITS file from input png/jpg * |
-update |
|
|
Update the fits header with the found solution * |
-wcs
|
|
|
Write a .wcs file in similar format as Astrometry.net. Else text style.
|
|
|
|
* Defaults can be set in the program. Shortcut CTRL-A,
tab alignment |
Commandline parameters have priority above fits header values. Front-end
programs
should provide access to -z and -r options. Default value for -z should be 0 (auto).
Typical command
lines:
astap.exe
-f image.fits -r 50
astap.exe
-f c:\images\image.png -ra 23.000 -spd 179.000
-fov 1.3 -r
50
For most FITS
files the command line
can be short since telescope position and field of view can be
retrieved from the FITS header. If
a FITS file is not available, preference is a non lossless
image format
like .PNG or .TIFF or RAW like .CR2. If possible in 16
bit or
original 12 bit format. Not stretched or saturated, as raw as
possible.
For formats other then FITS the RA,DEC position and -fov
(image HEIGHT
in degrees !!) should be added.
If the FOV (image height in degrees) is
unspecified in the command-line for RAW, PNG, TIFF files, ASTAP will
use the FOV as set in the program, stack menu, tab alignment. This
setting can be learned and updated automatically with the parameters
-fov 0. ASTAP will try all FOV between 10 degrees and and 0.5 degrees.
E.g.
astap.exe
-f c:\images\image.png -ra 23.000 -spd 179.000
-r
30 -fov 0
After
a successful solve, the correct FOV will be stored in the ASTAP
settings. For the next solve using images from the same source
the -fov 0 parameters can be omitted and solving will be fast.
The
debug option allows to set some solving parameters in the GUI
(graphical user interface) and to test the commandline. In debug mode
all commandline parameters are set and the specified image is shown in
the viewer. Only the solve command has to be given manually:
astap.exe
-f c:\images\image.png -ra 23.000 -spd 179.000
-r
30 -debug
or
astap.exe -debug
1) The astap -f stdin command line option
Raw
format send via stdin should start with three longwords (of 4 bytes).
The first longword contains a format identification. The second
longword contains the image width. The third longword contains the
image height followed by the image raw data.
Raw format identification:
$31574152 or RAW1, 8bit mono image
$32574152 or RAW2, 16it mono image
$33574152 or RAW3, 24bit RGB image (R,G,B,R,G,B,R.....)
$43574152 or RAW4, 32 bit mono image
$66574152 or RAWf, 32 bit float mono image
The
result is written to stdout. Only for the standard ASTAP
Windows version the stdout is blocked (unless you use the command
line version) and the result is written to a stdin.ini file at the
ASTAP program directory. Use the -o command to specify any other file
and directory. The .wcs file is always written but also here use the -o
option to specify path and file name.
The ra,dec and fov should be specified in the command line. Example using a raw file as input:
e.g. /opt/astap/astap -f stdin -ra 23 -spd 179 -fov 1.2 -r 30 <./m42.raw
raw sample file which will solve using /opt/astap/astap -f stdin -ra 6 -spd 95 -fov 2.8 -r 30 <./16bit_rosette.raw
Loading of the image can be tested by adding -debug to the command line
Command-line, output files
In command line
mode the program
produces two output files at the same location as the
input
image. In case a solution is found it will write a .wcs file 1) containing the solved FITS header
only. In any case it will write an INI file using the standard FITS keywords.
Example of the INI output
file after an successful solve:
PLTSOLVD=T
// T=true, F=false
CRPIX1= 1.1645000000000000E+003
// X of reference
& centre
pixel
CRPIX2=
8.8050000000000000E+002
// Y of reference
& centre pixel
CRVAL1= 1.5463033992314939E+002
// RA (J2000) of the reference pixel
[deg]
CRVAL2=
2.2039358425145043E+001
// DEC (J2000)of the reference pixel
[deg]
CDELT1=-7.4798001762187193E-004
// X pixel size [deg]
CDELT2=
7.4845252983311850E-004
// Y pixel size [deg]
CROTA1=-1.1668387329628058E+000
// Image twist of X
axis
[deg]
CROTA2=-1.1900321176194073E+000
// Image twist of Y
axis
[deg]
CD1_1=-7.4781868711882519E-004
// CD matrix to
convert (x,y) to (Ra, Dec)
CD1_2= 1.5241315209850368E-005
// CD matrix to
convert (x,y) to (Ra, Dec)
CD2_1= 1.5534412042060001E-005
// CD matrix to
convert (x,y) to (Ra, Dec)
CD2_2= 7.4829732842251226E-004
// CD matrix to
convert (x,y) to (Ra, Dec)
CMDLINE=......
// Text message containing command line used
WARNING=......
// Text message containing warning(s)
The reference
pixel is always specified for the centre of the image. The decimal separator is always a dot as for FITS headers.
Example of the INI output
file in case of solve failure:
PLTSOLVD=F
// T=true, F=false
CMDLINE=......
// Text message containing command line used
ERROR= .....
// Text message containing any error(s). Same as exit code errors
WARNING= .....
// Text message containing any warnings(s)
The
.wcs file contains the original FITS header with the solution added. No
data, just the header. Any warning is added to the .wcs file using the
keyword WARNING. This warning could be presented to the user for
information.
1) Note
the wcs file is default written as text file using carriage return
and line feed for each line and is not conform the FITS standard.
To have .wcs file conform the FITS standard add the command-line
option -wcs.
Command-line, error codes
In
the command-line mode errors are reported by
an error code / errorlevel {%errorlevel%}. This is the same error as reported in the .ini file in case of failure.
Error code | Describtion |
0 | No errors |
1 | No solution |
2 | Not enough stars detected |
| |
16 | Error reading image file |
| |
32 | No star database found |
33 | Error reading star database |
To analyse a FITS file you could do the following in a Windows batch file:c:\astap.fpc\astap.exe -f c:\astap.fpc\test_files\command_line_test\m16.fit -analyse 30
echo Exit Code is %errorlevel%
pause
You will get
Exit Code is 326000666
where the HFD is 3.26 using 666 stars
Finding best focus based on four or more input images:c:\astap.fpc\astap -focus1 D:\temp\FocusSample\FOCUS04689.fit
-focus2 D:\temp\FocusSample\FOCUS05039.fit -focus3
D:\temp\FocusSample\FOCUS05389.fit -focus4
D:\temp\FocusSample\FOCUS05739.fit -focus5
D:\temp\FocusSample\FOCUS06089.fit -focus6
D:\temp\FocusSample\FOCUS06439.fit -focus7
D:\temp\FocusSample\FOCUS06789.fit -focus8
D:\temp\FocusSample\FOCUS07139.fit
echo Exit Code is %errorlevel%
pause
or with the -debug option
astap.exe -debug -focus1 D:\temp\FocusSample\FOCUS04689.fit
-focus2 D:\temp\FocusSample\FOCUS05039.fit -focus3
D:\temp\FocusSample\FOCUS05389.fit -focus4
D:\temp\FocusSample\FOCUS05739.fit -focus5
D:\temp\FocusSample\FOCUS06089.fit -focus6
D:\temp\FocusSample\FOCUS06439.fit -focus7
D:\temp\FocusSample\FOCUS06789.fit -focus8
D:\temp\FocusSample\FOCUS07139.fit
Or with the special command line version:

Command-line pop-up notifier
If
the ASTAP is command-line
executed in MS-Windows, it will be shown by a small ASTAP
tray
icon on the right side of the status bar. If you move the
mouse to the
ASTAP tray icon, the hint will show the search radius reached.
To
refresh the value move the mouse away and back.
If
the search spiral has reached a distance more then 2 degrees
from
the start position then a popup notifier will show
the actual
search distance and solver
settings:

- The first line indicates the search spiral distance (8º) from the start position and the
maximum search radius (90º)
- The image height in degrees.
- Downsample
setting and the input dimensions of the image to solve.
- The α and δ of the start position.
- Speed normal (▶▶) or small steps (▶)
Tray
icons are default off in the latest Win10 version. To set
the
ASTAP tray icon on, start a solve via the imaging program, go
to
Windows "Settings",
"Taskbar", "Turn system icons on or off"
and set the ASTAP tray icon permanent "on" as shown below:

Blind solving performance
Blind solving
performance for a 90 degrees offset:
ASTAP blind solver
performance. Solving a 50 seconds exposed monochrome
image of M24, 2328x1760 pixels covering a field of 1.75
x 1.32°
starting 90 degrees more north at position
18:17, +72d
00 |
|
|
|
Maximum stars
set |
Tolerance
set |
Astrometric
solving
time |
500 |
0.005 |
147 sec. |
250 |
0.005 |
103 sec |
150 |
0.005 |
92 sec |
100 |
0.005 |
70 sec |
|
|
|
Reducing the "maximum number of
stars to use" will result in a faster
solving but also an increased risk of solve failure. |
Usage as
a
solver with other programs or as PlateSolve2 substitute
Back
to index
CCDCIEL, using ASTAP
as
solver.
ASTAP is a menu option in the CCDCIEL
program. Install both ASTAP and
the G17 star
database. Select in CCDCiel menu ASTAP as solver and follow the guidelines in the
help
file.
Progress is shown in tray icon and popup notifier.
Solving should be reliable. In
case of failure, have a look to conditions required for solving.
Back
to index
APT: using ASTAP as
solver
Since
ATP version 3.85.1, APT fully supports ASTAP. Just select
ASTAP in the APT pointcraft menu after installing both ASTAP and
the G17 star
database. For solving it is important that the correct filed of
view is
calculated from the Tools, Object calculator. So set the focal length
and "CCD width x height" correctly.
Once installed you could now test it
with a saved image. The solver needs an initial position guess.
To modify the ASTAP default settings,
see astrometric_solving
Progress is shown in tray icon and popup notifier. In case of solve failure please check the FOV indicated.
Solving should be reliable. In
case of failure, have a look to conditions required for solving.
Screenshot APT using ASTAP:

For older APT, Astro
Photography Tool use it a PlateSolve2 substitute by renaming ASTAP.EXE program as
Platesolve2.exe. and select it as PlateSolve2
Back
to index
ModelCreator:
Installation as solver for ModelCreator:
- Install ASTAP and additional install the G17 star
database.
- In ModelCreator select ASTAP as plate solver.
Back
to index
NINA, Nighttime
Imaging ‘N’ Astronomy
- Install ASTAP and additional the G17 star
database.
- Other settings as below:
To modify the ASTAP default settings,
see astrometric_solving
Solving progress is shown in tray icon and popup notifier.
Solving should be reliable. In
case of failure, have a look to conditions required for solving.
Back
to index
Back
to index
SharpCap:
Installation as solver for SharpCap:
- Install ASTAP and additional install the G17 star
database.
- In SharpCap select ASTAP as plate solver.
Back
to index
SGP,
Sequence
Generator Pro:
The
latest SGP versions support ASTAP as solver. Just install ASTAP and G17
database. Select ASTAP as solver. Set binning at 1x1 or 2x2. See conditions required for
solving.
Solving progress is shown in tray icon and popup notifier.
Solving should be reliable. In
case of failure, have a look to conditions required for
solving.
For older SGP versions: you could use ASTAP as PlateSolve2 substitute:
The orginal
PlateSolve2.exe is
located at C:\Users\you\AppData\Local\SequenceGenerator\
Where "you" is your user name. You can access this
directory also directly by %LOCALAPPDATA%\SequenceGenerator
- Install ASTAP and additional install the G17 star
database in the same directory. Typical c:\program files\astap
- Copy or move the astap.exe and all 290 files with
extension .290 to
C:\Users\you\AppData\Local\SequenceGenerator\
- Rename the original Platesolve2.exe to something
like PlateSolve2ORG.exe
- Rename ASTAP.exe to PlateSolve2.exe
- Test it with SGP. The confidence will be always 999. No
PlateSolve2 window will be shown.
Progress is shown in tray icon and popup
notifier.
If you select in SGP the PlateSolve2
setting "Max
Regions" (=3000) this will force a search up to 90 degrees
diameter.
However the solver
will be most likely stopped halfway by a SGP timeout.
Back
to index
Voyager:
The
latest Voyager versions support ASTAP as solver. Just install ASTAP and G17
database. Select ASTAP as solver.
Solving progress is shown in tray icon and popup notifier.
Solving should be reliable. In
case of failure, have a look to conditions required for
solving.
For older Voyager versions: you could use ASTAP as PlateSolve2 substitute. The original
PlateSolve2.exe is
located at C:\Program Files (x86)\Voyager
- Install ASTAP and additional install the G17 star
database in the same directory. Typical c:\program files\astap
- Copy or move the astap.exe and all 290 files with
extension .290 to C:\Program Files
(x86)\Voyager
- Rename the original Platesolve2.exe to something
like PlateSolve2ORG.exe
- Rename ASTAP.exe to PlateSolve2.exe
- Test
it with Voyager. E.g. in the OnTheFly section. Confidence will
be
reported as 999. E.g. Solved (J2000) => RA 19 59
36,167
DEC 22 42 36,31 PA 277,4 Res. 1,17 [as/px] FL 1131,77
[mm]
Star/s
999
Back
to index
Installation
of the external Astrometry.net solver:
MS-Windows:
Install a local copy
of Astrometry.net (via ANSVR or Astrotortilla)
as the astrometric
solver. Or alternatively if you have Win10, 64 bit Creation
edition you use the new Linux sub-system
ANSVR: The
ANSVR link contains a newer compilation of astrometry.net made for SGP.
It runs as a Linux program under Cygwin in MSWindows. Follow up to
installation step 9. The link you have to put in ASTAP is as follows:
C:\Users\user_name\AppData\Local\cygwin_ansvr\bin\bash.exe
Adapt "user_name" to the login name used in Windows.
The server program ANSVR is not required. Remove the ANSVR
shortcut in the startup menu. Location:
C:\Users\user_name\AppData\Roaming\Microsoft\Windows\Start
Menu\Programs\Startup
Alternative
Linux sub-system in Win10 64bit
Creators edition
Path for the astrometry.net solver program
ANSVR installation:
C:\Users\user_name\AppData\Local\cygwin_ansvr\bin\bash.exe
Astrotortilla installation:
C:\cygwin\bin\bash.exe
Win10 subsystem:
C:\Windows\System32\bash.exe
Linux installation:
The
single executable astap could be
used anywhere. Standard directory could be c:/opt/astap but also at
your home folder.
If you want to use
astrometry.net
this is described at
installation.
To get the Astrometry.net solver type: sudo apt-get
install libcairo2-dev
libnetpbm10-dev netpbm libpng-dev libjpeg-dev python-numpy
python-pyfits python-dev zlib1g-dev libbz2-dev swig libcfitsio-dev
You also have to download index files.
Path to the astrometry.net solver program "solve-field" could be:
/usr/bin/
or
/usr/local/astrometry/bin
Appendix 1, the stack
process:
The stacking process for
one shot color color camera's will be mathematically executed
as
follows:
The master flat is calculated as:
master flat: = (1/n ∑ [flat] - 1/n ∑ [flat darks] )
Where a bias image could be used as flat-dark image. The
master flat
should be averaged by a 2x2mean to remove Bayer matrix
artifacts.
Each image is calculated as:
(image- {∑ [darks]/n} ) / master flat
Then the Bayer matrix is applied and finally the images are
stacked in
mode average or sigma clipped.
So for average stack:
final image:= 1/n ∑ Bayer(image)
Back
to index
Send a message if you like this free
program. Feel free to distribute !