05-27-2020, 05:52 PM
(05-26-2020, 05:28 PM)Ofnuts Wrote: Value is max(R,G,B). So (0,255,0) (quite bright), (255,0,0) (moderately bright), (0,0,255) (not so bright), and (255,255,255) all have the same "value": 255.
When you use Levels on "Value", the range of the R/G/B channels are stretched/compressed appropriately. Ideally, Levels would use HSV, HSL or better, Lab models...
I see, might this be an answer to my prior question about reference information? If so it looks like it might take me a while to try and absorb that.
When trying to learn what "Levels" are about I found this article about how it works in Photoshop (which I do NOT use) to be quite helpful from an instructional point of view. However, I now notice that it refers to RGB as a channel selection and NOT Value. I've assumed this to mean the 3 color channels combined which I'm guilty of conflating with Value which also seemed to imply the same thing. It now sounds like RGB and Value are different even if they do something similar. Yeh? Ney?
I also work with Rawtherapee (RT) and notice that it does NOT seem to have a "Levels" tool which I've asked about here. That one didn't trigger anything like the help provided herein. Therefore, I thought it worth mentioning here. Having now spent a little more time trying to figure this out I'm now thinking that the answer is that RT is content with expecting curves to be used for such purposes. I've only yet worked with what are called Tone Curves on the Exposure tab in RT. Interestingly Rawpedia says "the histogram displayed as the curve's background shows you the levels of the data". Might that mean Value in GIMP terms?
There are also curves for Lab Adjustments on the Exposure tab. Then on the Color tab there are RBG Curves and, interestingly, something called an HSV Equalizer that might be called curves but nothing like the others. Possibly this is an even more sophisticated way to deal with Value. Yeh? Ney?