RGB color problem.

TheoM

Member
Greetings everyone,
I've had a lot of trouble figuring out what's happening to my image. Basically I did WBBP(latest version, with drizzle and autocrop), then BN, then doing ChannelCombination and i get a very weird color image. Last time that i did a galaxy photo there was no problem at all. I since been using the ZWO AsiAir and it's my first time using it for a galaxy.Each RGB is a stack of 51x300sec at 1x1 gain 139 (PS: I've already make sure that filters are the right ones, listed in the app). I will drop LRGB files for each channel. If you guys can take a look at the files..
Here's the drive with the files : https://drive.google.com/drive/folders/1GsdJr3ff3sJT-tE1mj8e3qWxx8wH0rUL?usp=drive_link
Theo
 
looks like the flats don't match up on R and to a lesser extent, B.

not sure what exactly you mean by a "weird" color image. is it the blotches caused by the bad flattening?
 
Just looked at your images and the red channel does not look like it flat fielded correct Large dust motes noted thrupout image.
 
Okay, so by "weird" color i mean that when doing ChannelCombination (or LRGBCombination) i get a very weird final RGB image.By weird I mean the spirals of the galaxy are pinkish and not blue, even the star have a strange color which make sense. So maybe the flats are the reason of this weird patern/color i guess ?
 
it almost seems like your filter names are mixed up, despite the fact that you have checked. if i combine RGB as GBR the image looks a little better but still not right. i didn't try all the permutations though.

i guess you can try just shooting some colored pieces of paper, maybe a paper with RGB printed onto it, and see if you get the expected results.

rob
 
it almost seems like your filter names are mixed up, despite the fact that you have checked. if i combine RGB as GBR the image looks a little better but still not right. i didn't try all the permutations though.

i guess you can try just shooting some colored pieces of paper, maybe a paper with RGB printed onto it, and see if you get the expected results.

rob
FWIW I tried several permutations (maybe all) and still got weird colors. Too much magenta, some green in the companion galaxy. And this after SPCC (which did produce an odd sort of fit distribution... something to consider here, maybe).
 
Exactly it's really strange. I've already make sure that the filters are the right ones for each channel.. I've shot new flats maybe it will change things up (which i highly doubt..). I've tried LinearFit, SPCC, PCC, ect.. and nothing seems to solve the problem. So it may come from the stacked images or maybe the filters..
 
FYI, it is since i've switched to the Asi Air that i've got this problem. Before I never had any trouble with LRGB images processing. Btw the filters are Astronomik Type 2c LRGB.
 
FYI, it is since i've switched to the Asi Air that i've got this problem. Before I never had any trouble with LRGB images processing. Btw the filters are Astronomik Type 2c LRGB.
All the better. Those are the filters I use, and I hand coded their response curves for SPCC and that's what I used to process your images. Not that the choice of specific RGB filters should make all that huge of a difference, but it's one less variable here.
 
FWIW I tried several permutations (maybe all) and still got weird colors.
Careful analysis suggests to me that both the R data and the B data are in fact blue filter data, and G is green filter data. There is no red data.
This is consistent with the SPCC white balance plots for different combinations of channels.
 
Careful analysis suggests to me that both the R data and the B data are in fact blue filter data, and G is green filter data. There is no red data.
This is consistent with the SPCC white balance plots for different combinations of channels.

that makes sense. i considered that but didn't try the analysis. i assume if you normalize the R and B and subtract them you get roughly 0?
 
Well, I guess that something may have occurred with the AsiAir then (very unusual). I re-checked my files and i've got 51 files with separated R G and B included in the files name, so, very strange. It's cloudy outside so no chance for me to take R data tonight. Might try when it clears up. I'll let you guys know. Thanks a lot.
 
i assume if you normalize the R and B and subtract them you get roughly 0?
More or less (given that one set was not properly flat corrected):
1685566973212.png

Perhaps the filter mixup is "correlated with" the flat field errors.

Update: Oops, a bit too fast. The above is (B-R*mean(B)/mean(R)), but I forgot about clipping. If I take the abs of the difference it does not cancel (because the normalised R image is almost everywhere greater than the B image). This is because the background mean is not a good normalising factor (the R background is such a mess). by using a bright reference (the max in the M51 core) the cancellation is much better- but not perfect:
1685568012879.png
 
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