A 3-page overview of everything relevant

What is digital color

Digital color refers to the digital data representation of a real-life color. Since real life color work fundamentally different from digital color, we need to use all kinds of tricks and systems to represent them accurately.

Important vocabulary

Working space and display space

It’s important to distinguish the color space of the file/software versus the color space of the display:

Working space (sometimes called Color Settings)	The color space used inside the application to blend texture, paint, etc.
Display transform (sometimes called View Transform or Proof Setup)	Display transform converts the linear colors from the working space to the color space of the monitor to display colors perceptually (to be seen by the human eyes). Display transforms often include a tonemapping pass to compress colors to fit the limited range of values allowed by a screen.
File space	An image can carry meta-data that communicates which display transform should be used (by defining a color space) to display the raw color data in that image. Not all displays, viewers and software support all color spaces (see chapter on File types).

Most modern software has options to adjust the Display (or View) Transform. However, this does not change the working space of your DCC.

Photoshop proof setup

Painter viewport color management

Changing the working space can also be done in the software. Note that changing the working space changes your color picker and other color-related tools, for the simple reason that you can now “choose” colors from a wider (or narrower) selection of colors.

Photoshop working spaces setup (also when you create a new file)

Painter color spaces settings

Unreal Engine’s working color space

You can write your working color space into the file (depending on file type); like in Photoshop in the save dialogue:

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Scene referred and display referred

In game/rendering engines, the brightness of a color can be many times more than 1, thousands of times more. The brightness of a color inside the engine is unclamped, meaning it can be as high as computationally possible. But how to we display that brightness to a display which only has one level of brightness?

With Unreal’s current implementation, the full processing of the rendered scene is handled through what is known as the ACES Viewing Transform (other renderers might use different Transforms). This process works by using scene-referred and display-referred images.

Scene-referred images maintain the original linear light values of the source materials without limiting the exposure range. Scene-referred is also often in Linear Light, which while suitable for computer graphic rendering, is not suitable for grading workflows.
Display-referred is the final image transformed into the color space of the display being used.

This transformation works in three steps in the following order:

Look Modification Transform (LMT) - This part of the process takes the ACES color-encoded image that has had a creative "look" (color grading and correction) applied to it and then outputs the images rendered with ACES in combination with the Reference Rendering Transform (RRT) and an Output Device Transform (ODT).