Calibration with flat does not work

I have tried different scripts and found a problem with calibrating the image using flat. In Pixinsight, the calibration works without problem, but in Siril, the calibration with the flat field is overcorrected. I am using a standard set of image lights, biases and flats. I don’t use dark frames. I use a standard calibration script without a dark frame. I enclose light, bias and flat. Can you advise where the error maybe? Siril files

Hello, and welcome!
If you don’t use darks, you probably expect the bias to be used to calibrate the lights? This is not the case with the default script, but if you don’t use darks you cannot be using the default script either. Did you use the master bias to calibrate both the flats and the lights?
You can modify the scripts to do that automatically of course (see Scripts — Siril 1.2.0 documentation ).

And I would add a link to explain why light can be overcorrected: Calibration — Siril 1.2.0 documentation

Thanks for the information. I’m using a modified script that omits the dark frame calibration. The script runs fine and without errors. If I take one frame light and one frame flat and do the calibration in Pixel Math, everything is fine. I have no idea why the script does something different.

If you don’t remove dark, bias must be removed. The link I gave you show you the different use cases.

Yes, that’s exactly what the script does.

Convert Bias Frames to .fit files

cd biases
convert bias -out=…/process
cd …/process

Stack Bias Frames to

stack bias rej 3 3 -nonorm -out=…/masters/bias_stacked
cd …

Convert Flat Frames to .fit files

cd flats
convert flat -out=…/process
cd …/process

Calibrate Flat Frames

calibrate flat -bias=…/masters/bias_stacked

Stack Flat Frames to

stack pp_flat rej 3 3 -norm=mul -out=…/masters/pp_flat_stacked
cd …

Convert Light Frames to .fit files

cd lights
convert light -out=…/process
cd …/process

Calibrate Light Frames

calibrate light -flat=…/masters/pp_flat_stacked -cfa -equalize_cfa -debayer

Align lights

register pp_light

Stack calibrated lights to

stack r_pp_light rej 3 3 -norm=addscale -output_norm -rgb_equal -out=result

flip if required

load result
mirrorx -bottomup
save …/result_$LIVETIME:%d$s

cd …

No. You don’t remove bias from lights.

I am using the script provided with the program, where I have removed the dark frame calibration. So, I still need to do a light frame calibration using bias, if I understand correctly.

As you don’t subtract the dark, offset is still present in the light and need to be removed.
Please, have a look to my link. Everything is explained.

The line for light calibration should be:
calibrate light -bias=../masters/bias_stacked -flat=../masters/pp_flat_stacked -cfa -equalize_cfa -debayer

If you want to have a read, this section explains why: Calibration — Siril 1.2.0 documentation



Thank you for your explanation Cecile :+1:

I will use a dark frame, it will be better for the pictures.