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PixInsight produces weird colors

Matt Frepp
in PixInsight
Hello,
I thought I have PI under control (more or less) until I stumbled into a color-problem last Friday. I have 60 raw light frames of M27, plus flats and darks. The darks have not been shot at the same exposure time as the lights, but I added them anyway. No bias, forgot about them...

While I don't expect a perfect final image, I'm puzzled by the color PI produced. I did nothing more than calibrate, align and integrate. I thought these processes won't affect colors at all, but I'm obviously wrong. The light-frames show M27 in correct colors bluish/cyan with red edges, the sky is black and the stars are white. Blinking shows all in mono, but looks ok. But after calibration, alignment and integration, M27 looks yellow/whitish, the stars also yellowish, and the sky background is solid orange/brown.

Any idea what could have happened? Much appreciated.
thanks
Matt

Comments

  • Matt Frepp
    add- I used RGGB for debayering. Has always worked ok with my Nikon D850. The only difference, previously I used Nikon-lenses, this time I used a telescope. Could that have any impact? Thanks.
  • BlockHeadBlockHead
    Hi Matt,

    Weird things in...weird things out. 
    The darks really do need to be at the same time- or there will be issues (which may or may not be part of your problem). 

    The solid colored background is perfectly fine for a non-color corrected image. (Please see FastTrack Training.). You didn't say this, but it *would* be a problem if you applied an unlinked autoSTF and did not get back a reasonable result. This still would not be color corrected (the job for DBE followed by PCC). 

    So... the question is... when you do an UNLINKED AutoSTF... how do things look?

    -the Blockhead
  • Matt Frepp
    thanks Adam. I tried an unlinked STF and the results are much better. Not sure why. I think I have to rewatch some videos in FastTrack Training.

    Is it better not to include dark frames if they do not match the exposure-time of the light frames? Deal with the noise in some other way?

    Thanks again
    Matt

  • BlockHeadBlockHead
    Regarding the unlinked STF- the autoSTF can be applied to the brightness of the image (that is all three colors at the same time) or it can do an autoSTF on EACH color independently (the unlinked version). Here are the important points from FastTrack Training (and other videos):

    1. A color image is actually THREE images simultaneously. This is why linked/unlinked matters.
    2. For color images that are not color corrected- it is normal to have a color dominate- and it doesn't matter what color it is. 
    3. The unlinked autoSTF will give you a view that is sensible... but it is not color corrected- which needs to be done with something like PCC.

    Regarding dark frames... I think the answer is... "It is better to have darks frames to calibrate your data." So... no other answer is really a good one. These instruments need calibration. Comsumer cameras all calibrate their images as well.. though much of it is internal and transparent to the user. Sorry.. no short cuts. 

    -the Blockhead
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