Original vs Intended Color Temp Means What?

[ajax]

I think the "Color>Color Temperature" control (menu selection) is a new tool in GIMP 2.10.  The term "Color Temperature" arises in other image processing software in the context of "White Balance" which as best I can tell is something that needs to be taken into account in order to develop the RAW image data available from some cameras.  I believe it is the way to advise the software about the light conditions of the scene when the image was shot.  While this provides a way to develop the RAW data in a manner that provides a more faithful/realistic reproduction of the original scene the software also allows for adjustments to be made that can alter an image to suite the artist intent of the photographer.

Insofar as GIMP does not develop RAW data it would seem that the later is what GIMP could do.  Other image processing software commonly use the term "White Balance" for a control from which "Color Temperature" can be adjusted.  This tool in GIMP 2.10 is the only one where I've noticed 2 rather than 1 adjustment.  In my mind, it's always been thought of as a way to increase or decrease the temperature from what it is to start with.  From experimentation it appears as though the same results can be achieved by either lowering what GIMP calls the "Original Temperature" or increasing what GIMP calls the "Intended Temperature" or visa versa.  In that, the only thing that matters is the difference between the 2 settings.  There is no need for 2 values (i.e., Original and Intended) to do this.

What am I missing?  Is there some reason for supplying 2 values verses 1 (which would simply be the amount to increase or decrease)?

[rich2005]

You need one of the clever guys to answer that long question, maybe a re-post on pixls.us

However, roughly as I suspected, Guess the original colour temperature, (say tungsten lighting 3500) and rebalance to standard RGB daylight (5500)

Amazingly, a search did bring up a Gimp help page https://docs.gimp.org/2.9/en/gimp-filter...ature.html
and I did learn something, did not know about the standard value drop down, but then not a tool I use

[Ofnuts]

(08-14-2018, 02:30 AM)ajax Wrote: I think the "Color>Color Temperature" control (menu selection) is a new tool in GIMP 2.10.  The term "Color Temperature" arises in other image processing software in the context of "White Balance" which as best I can tell is something that needs to be taken into account in order to develop the RAW image data available from some cameras.  I believe it is the way to advise the software about the light conditions of the scene when the image was shot.  While this provides a way to develop the RAW data in a manner that provides a more faithful/realistic reproduction of the original scene the software also allows for adjustments to be made that can alter an image to suite the artist intent of the photographer.

Insofar as GIMP does not develop RAW data it would seem that the later is what GIMP could do.  Other image processing software commonly use the term "White Balance" for a control from which "Color Temperature" can be adjusted.  This tool in GIMP 2.10 is the only one where I've noticed 2 rather than 1 adjustment.  In my mind, it's always been thought of as a way to increase or decrease the temperature from what it is to start with.  From experimentation it appears as though the same results can be achieved by either lowering what GIMP calls the "Original Temperature" or increasing what GIMP calls the "Intended Temperature" or visa versa.  In that, the only thing that matters is the difference between the 2 settings.  There is no need for 2 values (i.e., Original and Intended) to do this.

What am I missing?  Is there some reason for supplying 2 values verses 1 (which would simply be the amount to increase or decrease)?

If there were no setting for Original temperature, the other setting would be a relative color change, -2000K to +2000K or something. Besides the possibly wrong assumption, that going fro 5000 to 4000 it exactly the same as going from 400 to 3000, iIn practice there is no way to know from the picture the "color temperature" it was taken with... take a shot of a sunset, and despite a "tungsten" color temp in you camera it will still be pretty red. Is the sky blue because that's how it is or because you mistakenly left the camera in "tungsten" WB?

Luca de Alfaro's "Auto white balance" work a bit differently by being given something that should have been pure gray (or white) and then computing the color balance delta from that. But that requires such a color to exist in the picture: white sheet of paper, fridge, cloth/garment and even then you can be off because paper and garments are actually slightly blue to look "whiter than white", and an old fridge can be a bit yellow.