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PixInsight => General => Topic started by: lage on 2020 February 21 13:12:08

Title: Blue colour cast when using flats in integration
Post by: lage on 2020 February 21 13:12:08

hi.
can someone explain what's happening here?
shooting with a dslr, the preprocessed image is usually greenish. but this time, when i add flats, the preprocessed image is bright blue.
any help is appreciated.

best regards,
lage

Title: Re: Blue colour cast when using flats in integration
Post by: pfile on 2020 February 21 15:23:56

color casts with OSC cameras are common... check the histogram of your debayered master flat and you will probably find that one channel is much stronger than the other two. that is the source of the cast.

as long as the SNR of that weak channel is good, then it is fine... you can restore the color balance by doing BackgroundNeutralization and ColorCalibration to the master light, or use PhotoMetricColorCalibration.

rob

Title: Re: Blue colour cast when using flats in integration
Post by: lage on 2020 February 23 22:12:44

Quote from: pfile on 2020 February 21 15:23:56

color casts with OSC cameras are common... check the histogram of your debayered master flat and you will probably find that one channel is much stronger than the other two. that is the source of the cast.

as long as the SNR of that weak channel is good, then it is fine... you can restore the color balance by doing BackgroundNeutralization and ColorCalibration to the master light, or use PhotoMetricColorCalibration.

rob

Yes, the blue channel is stronger on the debayered master flat. But how do i restore the colour balance without debayering the master flat?

BR,
Lage

Title: Re: Blue colour cast when using flats in integration
Post by: pfile on 2020 February 24 07:42:34

you don't need to fix the flat itself. you can register and integrate your calibrated frames, then do the steps i described to the master light.

the flattening process amounts to multiplying the image by some fixed factor, so all you ever need to restore the balance is to multiply the image by some factors that restores the color balance. that's exactly what BN and CC do. (or PCC)

rob