The peculiar thing is that the light, flat, and dark frames are OK (all taken with AA4). It is the bias frames that PI misinterprets their value. I will try to provide an ftp link tomorrow.
Hi Tasos,
Thank you for uploading the image. The file you have uploaded is a 16-bit signed FITS image. However, its minimum sample value is 32768. This is indeed 'peculiar' for a bias frame. It is quite evident that the people who wrote the software that has created this image forgot to include the necessary BZERO and BSCALE header keywords in the main HDU of this FITS file. Another example of PixInsight being blamed for the mistakes made by other poorly coded applications
Fortunately, converting these images to the correct [0,65535] 16-bit unsigned range is very easy in PixInsight:
1. Define a PixelMath instance with the following parameters:
RGB/K expression: $T - 0.5
Rescale result disabled
Drag the blue triangle to create a PixelMath icon on your workspace.
2. Make sure that your FITS module writes unsigned integer images by default. Open the Format Explorer window and double-click the FITS item. On the FITS Preferences dialog, be sure the
Default integer signedness option is set to
Write unsigned integers.
3. Define an ImageCointainer with all your incorrect bias frames. The output template should be something like:
&filename;_u.fit
to ensure that the output images will be written in the FITS format. The _u postfix is of course optional, but I would include it to better identify the corrected files (_u stands for 'unsigned' here).
4. Drag the blue triangle from ImageContainer to the icon you created in step 1. This will convert all your bad bias frames into valid unsigned 16-bit FITS files that you can use with ImageCalibration.
As a side note, I personally would complain very seriously to the authors of the software that creates these images. I'll better stop talking at this point...
