TLDR: Editing software does never indicate clearly how effects operate in terms of color spaces, gamma ramps and whitepoints. Why?
Since I learned a lot about colorspaces, whitepoints, gamma ramps, with all the glorious details, I started wondering about pretty much every single application, in what color space and with what gamma ramp they operate.
For example in Photoshop / Premiere Pro / GIMP / Lightroom:
- Curves, Levels
- Blending modes (like Add)
- Channel Mixer
- HSL / HSV (these are transformations of an RGB colorspace, but which one?)
- The color picker (aka eyedropper) tools (particularly in Lightroom)
All of these operations happen in a colorspace, with a gamma ramp. Why do applications not indicate this? This information is very important to me.
Some examples to support why this is important (skip these if you know why):
- Stupid artificial example: you want to add a sun to a picture. The physically correct way to do this is to make sure the picture of the sun and the background picture are in the same additive colorspace using both a linear gamma ramp and add the corresponding values together. Doing this in a mismatched colorspace or with an sRGB gamma ramp would make the effect physically incorrect.
- Due to the lack of a Lightroom-like-camera-calibration effect in Premiere, I was trying to recreate this effect using a channel mixer effect, which does a matrix transformation on the color. But again: I don't have a clue wether or not this effect first converts the color to a linear additive colorspace or not. Do I have to add in gamma correction before and after the effect?
- When examining a color in Lightroom with the eyedropper. The indicated values: what color space are they in? The RAW RGB from the camera (most likely not when examining values)? sRGB? ProPhoto RGB? Are these gamma corrected?
- Imagine you have a hazy (aka foggy) photo and want to reduce/remove haze. First thing to ask yourself is: what is haze? I would argue it is light reflected from water particles and add extra light to the sensor of your camera. Meanwhile, it is blocking out some of the original light from the landscape. So, the fix would be to subtract the corresponding RGB values of the spectrum of the light reflected by the fog, and finally increasing exposure. But... what colorspace do I have to project the light spectrum to? Does the tool I am using (typically "Curves" or "Levels") to subtract this value do gamma correction (aka: are the color values in linear light, like I need for this effect)?
In general, often when I am editing, I'm thinking about how the look I want to achieve would have manifested itself when it happened spontaneously in nature. Thinking about this gives me an idea of what I want to try to make an effect. But then comes the problem: what do all these effects exactly do, in which colorspace and with or without gamma correction. Then I haven't even talked about whitepoints yet.
I know that some effects are unaffected by the colorspace or gamma ramp of the color values (like exposure), but there are many effects where this is very important. But for a fact, up to this day, I still don't know wether or not Photoshop performs the Add blending mode in physical linear light, or in sRGB gamma light.
So the question is: Why is this so unclear in these applications? Is there documentation for at least one application that explicitly talks about this? Meta question: would any of you be interested in knowing all this information, in order to know exactly what you are doing to your photo or video?