Issue with SCNR noise reduction

[johnrt]

When I use the SCNR tool to remove green pixels the process does the opposite - adds green - preserve lum check box has no effect. The red and blue still seem to function correctly.
I am on a mac running 64bit.

[Carlos Milovic]

Do you have the last version, with all upgrades?

[johnrt]

Yes I am running ver. 0652 with all the updates downloaded.

[johnrt]

Is nobody else having issues with this?

[Simon Hicks]

Are you using Green / Average Neutral as the settings? These work for me.

[Juan Conejero]

Hi John,

The problem is in the "Preserve luminance" option of SCNR. Just don't use it when you are removing green.

If you enable that option, you can easily end with more green than before applying SCNR. The reason is that green's contribution to luminance is about 70% in perceptual RGB color spaces (such as the default sRGB color space), so to preserve the original luminance after neutralizing a significant part of the green pixels the process has to inject more green in the image. Then we enter an endless loop: remove some green and then reinject it to satisfy the luminance preservation constraint... ad infinitum

I'm considering the possibility of dropping the preserve luminance option of SCNR precisely for this reason.

[Carlos Milovic]

Juan, you may just disable it as default, but keep the option.

[johnrt]

Thanks for the explanation on this.