Color image processing has arrived!

American Association of Variable Star Observers (AAVSO)
Wed, 04/03/2024 - 15:49

VPhot can now accept color images and automatically demosaic them into separate monochrome fits files. This feature is added with the help and hard work of Geoff Stone. Thanks Geoff!

A color image file named xyz will be translated into xyz-B, xyz-G and xyz-R with filters set to TB, TG and TR

The conversion rules:
- FITS files that are layered (ie, NAXIS==3) will have the layers read out in R, G, B order.

- Bayered FITS files with a valid BAYERPAT will be debayered (demosaiced is the proper term) into 3 images.
     Note that there should also be a ROWORDER key in the file: this is needed to interpret the BAYERPAT. If the image is from a ZWO SeeStar the ROWORDER is known to be BOTTOM-UP. Otherwise, if ROWORDER is not supplied it will be assumed to be TOP-DOWN.

- If you do not want VPhot to demosaic the file or you have done it with some other tool, make sure the BAYERPAT is removed or set to INVALID. Because a monochrome image is by definition not bayered.

- Color images from Canon or Nikon cameras with file extensions like CR2 or RAW or NEF or what ever should work too. Try it and check the result as we were not able to test all the possible color image file formats that exist. If you have a problem, contact

As in the case of any new feature, trust but verify. If the result is wrong, contact me.

This feature is part of version 45.