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CMOS OSC Flats Look Wrong

kirkster501

By kirkster501
in Imaging - Discussion

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ollypenrice

ollypenrice

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Top tip for finding how well your flats have corrected an image: stretch it and then run it through the Equalize filter in Photoshop (in Image-adjustments.) This is a brutal process which exaggerates all contrasts and is great for finding joints in mosaics, residual dust bunnies, etc.

Olly

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kirkster501
kirkster501

Very quick and dirty process. I did all the preprocessing manually and a quick stretch and colour boost.  But it looks OK and no vignetting.

ollypenrice
ollypenrice

Don't expect to be able to judge by eye the fall-off in a linear flat. It's really not a big fall-off. The most extreme vignetting I deal with involves a fall off of 23%. Something like 10% is far mor

kirkster501
kirkster501

Thanks Olly. Yes, maybe I am expecting to see too much of a fall off.  I have measured it and it is about 20% even though it does not look like that here. Also, should not stretch the linear flat

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kirkster501

kirkster501

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I used the SplitCFA on the master flat, equalised the levels of each and recombined with MergeCFA.  This makes a more "aggressive" flat.

I did a test preprocess to a final master of CFA adjusted flat and the regular flat and compared the two.  I looked at the pixel by pixel levels of the two final outcomes all over the image at about forty places.  There is no difference at all.

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