Galaxies color issues

[JGMoreau]

Hi, Using photometric color calibration tool with average spiral galaxy as white reference, i get very yellow colors for all members
of the Leo trio :

https://www.dropbox.com/s/yb85copb82aa4im/M65-66_10F4.jpg?dl=0

Which is different from all i see on the net for these objects.

Any suggestions please ?

Thanks,

JG Moreau
Eastman, Québec

[RickS]

I've just done PCC on my data and I do get some blues.  Maybe not as much as some of the images on the web, but certainly nothing like your result.

Did the graphs created by PCC look like it got a good linear fit to the chosen stars?  What happens if you just do an unlinked stretch on a raw RGB image? (no background neutralization or colour calibration.)  Are you sure that the R, G and B channels are correctly assigned?

Cheers,
Rick.

[aworonow]

You did the calibration on an unstretched image, correct?

[JGMoreau]

Thanks Rick and aworonow for your replies.
The camera is a QHY168C and the correct pattern is RGGB if I am not mistaken.Yes i think the PCC graphs look as usual.
The PCC was done on the linear image.

Here are screen capture of the steps i did, in order :

https://www.dropbox.com/s/gxlc1ro2kkm1zg7/M65-66_integration_stf_RGGB.jpg?dl=0

https://www.dropbox.com/s/u1g4d31h2f6076c/M65-66_PCC.jpg?dl=0

https://www.dropbox.com/s/cidd801u7q04h47/M65-66_PCC_linkedSTF.jpg?dl=0

https://www.dropbox.com/s/qe4k9v14jy2zapc/M65-66_PCC_STF_stretched.jpg?dl=0

https://www.dropbox.com/s/xd3o0638aqv71os/M65-66_PCC_Color_saturation_HDR.jpg?dl=0

Thanks for your help,

Jean Guy Moreau
Eastman, Québec

[RickS]

That looks OK.  The only step that concerned me was the saturation boost.  I would apply a clipped lightness mask so that the background and dim areas are protected and I'd use the CurvesTransformation Saturation curve instead of ColorSaturation (so that the sat boost is stronger for less saturated areas and weaker for highly saturated areas.)  That may not give you much more blue but I think it will give you a more subtle result.  I suspect that these galaxies should be less blue than most images show them... including mine 

[JGMoreau]

Thank you Rick, I will try as you suggest.
I feel it is important that my images are not at odd with the accepted appearance.
I wanted to make obvious the far too yellow color with the heavy color saturation.
Happy to see that I did not make a fatal mistake with my processing.
Just a little more subtlety is required

Jean Guy Moreau