feature request: RawTherapee RGB White Balance Multipliers

(Elle Stone) #1

Many, well actually most raw processors display the resulting RGB channel multipliers when setting a raw file white balance, and also provide an option to directly set the white balance using RGB multipliers. RawTherapee doesn’t.

Could RGB Multipliers be added to RawTherapee, preferably both as “displayed” regardless of how the white balance is actually set, and also as a way to directly set and modify the white balance?

(Stefan Chirila) #2

@Elle that sounds like an interesting feature. I’ve not personally encountered it before, but then again my experience is only with RawTherapee, Lightroom, and a negligible amount with DarkTable.

I assume you don’t mean the individual RGB channels in RT, nor the RGB white point setting, since those are already in.

(Elle Stone) #3

I’m not sure what you mean. I often fail to see what’s right there in plain sight. But I don’t see in RawTherapee any equivalent to setting the R/G1/B/G2 multipliers, as can be done at the command line using dcraw using the “-r” switch.

Most raw processors somehow manage to munge G1 and G2 together, giving the user access only to R, G, and B, which for my own cameras hasn’t ever been a problem. I imagine for some cameras G1 and G2 might need to be specified separately. And for cameras that don’t use the Bayer array, well, who knows whether a simple “R/G/B” is sufficient.

But putting possible complications to one side, and to show what I mean, here’s a screenshot of the RT raw white balance options:

For comparison, here’s a screenshot of darktable’s raw white balance options:

And here’s UFRAW, which uses the terminology “Channel multipliers” to refer to the RGB(G) multipliers:

And etc. If RawTherapee already has such an option, then that’s wonderful! but if so, where in the user interface is it located?

(Stefan Chirila) #4

@Elle Here’s the settings I was referring to.

The RGB channel mixer - allows you to set how much of each colour is in the given channel

Also check out this tab in the menu, youll find black points and white point compensation in there as well. I’m not at home, so I need to make do with the screenshots I am able to scavange off off Google :slight_smile:

(Elle Stone) #5

@stefan.chirila - thanks! for the screenshots.

Channel Mixer isn’t the same as using the RGB multipliers to set a white balance. I’m assuming that Channel Mixer operations are done after the image is already white balanced, and also after converting the image from the camera input profile to one of the RawTherapee working spaces.

The Raw Black Points sliders are somewhat the “black point” equivalent of RGB(G) “white balance” multipliers, and if RawTherapee already had RGB(G) white balance multipliers, then the white balance multipliers could be set to 1/1/1/(1) and then the white balance could be set using the Raw Black Points slider, at least in theory.

Sometimes I do use the Raw Black Points sliders in RawTherapee to pull the “noise floor” down a bit. But to avoid adding a color cast to the image, it’s necessary to move the Raw Black Points sliders proportionately to the white balance multipliers, which RawTherapee doesn’t supply.

Right now when I want to move RT’s Raw Black Points sliders, I use a spreadsheet, inputting white balance multipliers obtained from UFRAW, which produces colors that look more or less right. But I’d feel more comfortable if I knew for sure what white balance multipliers RT is using, if indeed RT really does use white balance multipliers to set the white balance.

Though this brings up another question: How is the white balance in RT actually calculated? I have a feeling it’s more complicated than just adjusting the RGB(G) multipliers.

(Stefan Chirila) #6

@Morgan_Hardwood @paperdigits @patdavid do you guys have any good input on this ?