How/when to combine synthetic lum

[ChoJin]

Hello,

I'm trying to figure out the best way to combine a synthetic lum.

My synthetic lum is computed using ImageIntegration (noise weighting) from my RGB data (DSLR) after DBE+PhotometricColorCalibration+BackgroundNeutralization+SCNR.

I did some processing on this synthetic lum (deconvolution+noise reduction) and now I'm trying to figure out how/when to merge back, with my RGB data, this processed synthetic lum without messing up my color calibration.

I stumbled upon https://pixinsight.com/forum/index.php?topic=2485.0

and I'm not sure which method is the best/less hazardous. Should I stretch both my Lsyn and RGB, Linearfit my Lsyn and LRGBCombine them, or should I go with the linear CIE XYZ space method?
Which one is best (for SNR, color balance etc.)? What are the advantages and drawbacks of both methods?

Hopefully someone can help shed some insights on this matter, because I'm having a hard time deciding

[pfile]

Should I stretch both my Lsyn and RGB, Linearfit my Lsyn and LRGBCombine them

IMO this is what most people are doing these days.

rob

[ChoJin]

Thanks Rob,

I tried to follow the RGBWorkingSpace+ChannelCombination tutorial from Juan, but I get the following error message when applying the RGBWorkingSpace process:

'Instance validation failed'

Playing with the parameters it seems to come from the values put for the chromaticity coordinates.
Any clue?

In the meantime I guess I have no other solution than doing the stretch+linearfit method then ;-)

Couple of questions though:

- Is there any need (even slightly theorical) for running PCC after LRGBCombination, or am I guaranteed to end up with the exact same correct color calibration after my LRGBCombination (assuming I used linearfit)?

- are there any benefit of using the saturation boost from LRGBCombination instead of doing it afterward using the CurveTransform/ColorSaturation processes (which have the benefit of being able to control the effect with a mask)?

[pfile]

hm, no... i am not sure what Instance validation failed means. it sounds like a pretty low-level error.

i don't think that you'd have to run PCC again, because in theory what LRGBCombination is doing is extracting and replacing the L* of the RGB image with the L image. so that should not change the color.

i usually use the saturation boost in LRGBCombination just to get the image to look right overall (comparable to the original RGB) when doing the RGB combination. hopefully the chrominance noise reduction built into LRGBCombination takes care of any oversaturation of background pixels...

rob

[ChoJin]

thank you Rob