Question about Synthetic Lum

[Jack Harvey]

Many people use synthetic luminance frames they create from RGBs.  If one take a RGB image in PI and uses the Extract Lum function to get the luminance of the RGB do you essentially have a synthetic Lum frame.  This frame could then be additionally processed and place in the Lum slot of the LRGB tool as well as R,G,Bs of the image and now create a synL_RGB?

[mmirot]

Many people use synthetic luminance frames they create from RGBs.  If one take a RGB image in PI and uses the Extract Lum function to get the luminance of the RGB do you essentially have a synthetic Lum frame.  This frame could then be additionally processed and place in the Lum slot of the LRGB tool as well as R,G,Bs of the image and now create a synL_RGB?

I think the short answer is yes.
The question is why would want to?
Most of the modules have the capacity to operate on the luminence only.
You are merely going in a circle by extracting and recombining.
Also the RBG custom working space allows for more flexiblity if you keep it together.

Max

[Jack Harvey]

Good point! Duh!!!!

[Nocturnal]

Yes, I'm with RBA on this. Only extract L if you have no other choice. Most operations can work on just L.

[Niall Saunders]

This is one of those areas where PI scores heavily over the likes of PS - the only reason I could see for the need to extract an sLum channel from a tri-colour image is to use it as some sort of 'mask' for further processes.

Cheers,

[RBA]

Yes, I'm with RBA on this.

Are you sure about that? 

[Silvercup]

Maybe it was me 

Silvercup