How does the Color Management Curve work?

How does the Color Management Curve work?
I mean it doesent work like in Photoshop or even the Node-Editor for Shaders.

The C is for contrast, the R red, G green, B blue. If you select one and then click on the line in the curves it will place an adjustment point, anything dragged to the bottom will be reducing the color spectrum of that shade you have selected above C,R,G,B

Here is some example shots of what zero value does for a contrast setting vs the default, and likewise for the red as well.

This is the default settings


This is with the contrast “C” selected and dropped to zero the point to the right of the graph


As with the contrast this is setting the red “R” to zero


These curve settings only apply to a rendered image. Otherwise if you are wanting to adjust a specific image you may be using for example a background image that would need to be done in the node editor.

I assume you are using it to adjust colors in viewport cycles with filmic color management:
if i remember correctly, when using filmic, which works “logarithmic” it’s normal that the curve works differently, just as it does with Log.
That’s why Filmic comes with contrast presets

Yes with Filmic, i dont undestand the way blender interprets the curves.

Post some screens for further help

Think of it this way – all curves define some kind of mathematical function: y = f(x) for some f(). The “inputs,” if you will, are taken from the X-axis and the outputs from the Y. A straight diagonal line is a null function which passes its inputs to its outputs without modification. The shape of the curve is a smooth interpolation between whatever control points you put on it, passing exactly through those points. How the output-value described by the curve is actually used, depends on the situation. Some are linear; some are logarithmic. Such curves are used everywhere in Blender.

yeah, but with Filmic you’re dealing with a different set of values, where half of the curve isn’t mapped to half the pixels value intensity

This is a problem with Blender in that the UI isn’t colour managed.

The curves UI adjusts the scene referred data, making it mostly useless, regardless as to the view applied.

The X axis is input, the Y axis is output.

Need more people to scream about colour managing the UI; sometimes pixel pushers need a linear response, sometimes a linear response across a chosen domain, sometimes a log-like response, sometimes a particular transfer function. This doesn’t even being to scratch the tip of the iceberg. Good on you for spotting the (in hindsight) glaring deficiency.

@Troy what should the 2.8 team consider when reworking the UI/UX elements

It is super simple:

Colour manage all UI elements.

Try it. Try to isolate a particular value such as middle grey (0.18 scene referred) and try to isolate it. This impacts every area of Blender, even albedo adjustments etc.

In the case of middle grey, you will find that it is represented at around 18% along the bottom X axis of the curves. Even if you were aware of it (most folks would infer 50% is about 50% of the visible range), it isn’t easily manipulated. It is even worse for the half of your image below middle grey, and at least as bad moving up.

Moving up, if you are dealing with a display referred encode such as the sRGB OE transfer function, the maximum that ends up on the display post view is mapped to the far right of the X axis of the Curves UI, top right corner. If you are using Filmic or any other reasonably correct scene referred transform? It isn’t even graphically on the curve without unlocking the curve constraints and manually scrolling to the position. In Filmic’s case, this is about 16.291 scene referred, meaning you have to scroll about 17 grid panels up and right.

There are other vast implications via Color Ramps, albedo picking, and other such intensity based factors. In terms of the actual colour of UI elements, that too isn’t managed, so you have no real clue what you are picking in a number of the UI elements. This is challenging to demonstrate using configurations that use REC.709 based primaries such as Filmic. Alternate reference spaces such as ACES, REC.2020, etc. become very apparent quickly.

Given that the UI isn’t colour managed, this means what folks are looking at on an Apple product post 2015, or any other wider gamut display, is absolutely wrong.