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-debayer

stephen2615 · 85

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le: mai 12, 2019, 02:44:16 02
Greetings,

I have been looking at the various scripts and I am not sure about the use of -debayer.

It can be used with convertraw and preprocess. To me the convertraw -debayer seems to follow the GUI file conversion and when watching the YouTube video, selecting the debayer check box is very important if you want to retain the colour. If running the script  DSLR_Preprocessing_NoFlat_NoDark_NoBias, the preprocess  uses -debayer but I get the feeling that preprocessing is more about applying offset, darks and flats. I seem to get better colour with using convertraw light_ -debayer instead of leaving it to preprocessing. Am I just imagining this or does it make a difference?

Regards
Stephen



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Réponse #1 le: mai 13, 2019, 12:05:16 00
Hello, yes there's a difference. Preprocessing is indeed about using the bias, dark signal and flat field masters to reduce noise and get consistent data for the sequence, ready to be processed. The -debayer option of the preprocess command is just a commodity, because once preprocessing is done, we don't need the mosaiced version of the images, and it avoids calling the debayer on its own. We have the same in the GUI. See the commands documentation: https://free-astro.org/index.php?title=Siril:Commands#preprocess

The colours do not mean much until all the processing is finished and that colour balance or calibration is done. If you have completely wrong colours, maybe there can be a problem with the configuration or detection of the Bayer matrix type, but in general for DSLR is should be fine. Visualisation can make colours appear weird, but until it's calibrated, you cannot really tell if it's better or not. Demosaicing during conversion is not the right way to go.

Best regards,
Vincent



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Réponse #2 le: mai 13, 2019, 09:46:37 09
I have been looking at the various scripts and I am not sure about the use of -debayer.

I'm certainly not an authority on this, but consider that the Bayer pattern image sensor is only providing sparse values for each of the R, G, B color channels. That is, it's a mono image which you just happen to know was run through a bayer filter. When you debayer, what this is doing is applying some sort of interpolation function to this sparse color data to supply computed RGB values for each pixel.

When you record bias and dark current frames, you're recording the noise data from the image sensor itself, unrelated to the Bayer filter in front of it. So, when you subtract these frames, you need to do that before you do the interpolation -- otherwise, you'd be trying to remove real signal from interpolated data. Or alternatively, you'd need to debayer the calibration frames too, which wouldn't be good.



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Réponse #3 le: mai 13, 2019, 10:18:45 22
Precisely :)