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New forum on-line

Post by han.k » 23 Nov 2017, 15:55

The new forum is on-line:


Program describtion:

ASTAP, Astrometric Stacking Program and FITS viewer.

ASTAP is a free stacking program for deep sky images. This program can view and stack astronomical FITS images using an astrometric solution. It uses a local version of or PlateSolve2 to find the astrometric solution. With the solution the astronomical position of each pixel can be calculated.
astap_stack_menu.png (39.91 KiB) Viewed 4492 times
Main features:

Stacking images including Dark Frame and Flat Field correction
Filtering of deep sky images based on HFD value and average value.
Automatic call to local or Platesolve2 for the astrometric solution.
FITS viewer with swipe functionality.
Results can be saved to 16 bit or float (-32) FITS file
Export to 16 or 32 bit integer TIFF files, grayscale or color or simple PNG or JPEG.
Mosaic building covering large areas using the astrometric linear solution.
Some pixel math functions and digital development process

Double click on one of the selected files to see it in the viewer:

Program requires FITS images as input It can also process PNG, TIFF or BMP files but only in 8 bit resolution. No import facility for DSLR raw files.

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 OSC cameras
Available for MS-Windows and in the near future Linux

ASTAP is not:
A post processing software with advanced options like noise reduction and unsharp mask. It is only intended for convenient stacking of astronomical deep sky images.

Program installation:

The single executable astap.exe can be used anywhere.

Install a local copy of (preferred option via ANSVR or Astrotortilla) or Platesolve2 including star database as the astrometric solver.

The ANSVR link contains a newer compilation of made for ASP. 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:


Adapt "user_name" to the login name used in Windows.

Start the ASTAP program. (astap.exe)

Enter the approximate location of the images taken and the image dimensions unless the location and dimension are already contained in the FITS file header. You can test this by just opening one FITS file.

Call up the stack window. Select the images, dark, flats, flat darks (bias)

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.

Press the stack button.

Save result as FITS ( IEEE float (-32) or 16 bit format), or export as 16 bit stretched, 16 bit or 32 bit TIFF. The stretched export folllows the gamma and stretch setting of the display.
astap_stack_menu2.png (31.3 KiB) Viewed 4492 times
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. If the oversize is set from the default 100 pixels to a large value lets say 2000 pixels, the array is on all sides 2000 pixels larger then the first image. If the first image is 2000x1500 pixels, the stacking array will be 6000 x 5500 pixels large. So any following image will be placed in this 6000x5500 pixel array. If the images are taken from different areas of the sky, the stacking will result in a mosaic as long the proceeding images are within this 6000x5500 pixels. Here an example of a mosaic build:

The size can be reduced by a crop function (right mouse button) later. Making the oversize too large could result in memory overload.

De stack menu:

The astrometry menu:

Some guidelines:

Show solving: shows the solving console. You better keep this on to see what happening.
Keep console open: This should be off and is only required to see an solving error.
Search area: This can be large 10 degrees or so.
Pixel tolerance: Can be off.
Extra options: Can be blank. --downsample 2 or --downsample 4 helps sometimes with solving. For noisy images you could experiment with --sigma 10 or higher.

Typical cold CMOS master dark:

Application of Gaussian blur under sigma 5:

Gaussian blur under sigma 5 and hot pixel removed:

Additional functionality:

The FITS viewer can call PlateSolve2 and add the plate solution to the FITS header. Also PNG and JPEG files can be plate solved. The program will convert them to the FITS format. With the batch routine several FITS image can be "plate solved". The viewer can convert raw images of sensors with a Bayer matrix to color.

ASTAP viewer screen shot:

PlateSolve2 is a good plate solver but can’t write the plate solution to the FITS header using standard keywords. HNS_FV can call the PlateSolve2 program and writes the found plate solution to the FITS file header using standard keywords.

Working of the program:

Load the FITS file in the viewer
Press the “Solve” button
Is the solution found press “Save” button.

In principle it should be possible to rename the program as Platesolve2 and call it instead of PlateSolve2. The solution will then written automatically to the FITS file. The plate solution is read from the APM file produced by PlateSolve2.

There is a big variation in FITS file keywords. If this version doesn't work, please send me the FITS file for testing.

Send a message if you like this free program. Feel free to distribute !