RGB color profile ignored

Hello,

There might be a bug in the way UE4 handles sRGB/RGB.
Using the color picker, I select a color. Note that the tick sRGB is on.
I desactivate sRGB. The color profile changes (my color gets darker).
When I press OK, the final color choosen is still the sRGB one, not the RGB one.
If I double click on it to open the color picker, the sRGB tick is still off.

I think whatever you do, you stay in sRGB.

26146-srgb1.jpg

26148-srgb3.jpg

Hey BZysberg -

I was aplly to reproduce this issue and have asked our engineers to continue investigating. Once I hear anything I will let you know the outcome, for reference UE-7371.

Thank You

Eric Ketchum

Hey BZysberg -

After some discussions with the engineers so I could better understand the issue: The differences between the sRGB=true and sRGB=false in the color picker is one of colorspace. The sRGB colorspace is the standard for most HDTV and CPU Monitors, with some exception in Wide Gamut systems. In this color space the color itself is mathematically computed as a series of 8 bits. This is really not ideal in terms of mathematical accuracy particularly in 3D rendering applications, but works wonderfully in representing colors on a LED/LCD screen. Typically to get around this inaccuracy, rendering engines will do a conversion between a linear RGB colorspace and a sRGB colorspace, which is what the toggle in the color picker represents.

But we find a problem here. In order for the editor to show a consistent color to all platforms and CPUs that it is supposed to run on it uses the sRGB colorspace. This is supposed to ensure that a 1,0,0,1 is always the same red when showing on various different CPUs, GPUs and Monitors. So the Color Picker attempts to show you the linear RGB colorspace but is having to render itself in sRGB, which is where the color difference in the picker comes from. It is not in error but in fact an attempt by our engineers to allow you to perceive the color in the way the rendering engine sees its HSV/RGB values in math.

I know that this can be confusing but, there is a wonderful explanation of the math behind this conversion and the human aspects over at Stackoverflow, graphics - What are the practical differences when working with colors in a linear vs. a non-linear RGB space? - Stack Overflow

Thank You

Eric Ketchum