Choosing a Working Colour Space
In general, it's best to use a wide-gamut colour space for working. This ensures that you can properly represent as many colours as possible. For example, digital cinema (P3) contains colours that cannot be represented using the Rec. 709 primaries (used by sRGB and HD video) without using negative values.
ACES 2065-1 is an extremely wide-gamut colour space that can represent any visible colour. It can be used as a working space, but some colour operations may give unexpected results because the gamut is so wide.
ACEScg, Linear P3-D65, and Linear Rec.2020 are good in-between choices for a linear working space. ACEScct is a good choice for a log working space. They have wide gamuts, but they are not too wide. If a project is only using footage from one camera, the camera vendor log format, or its linear equivalent, may also be a good choice.
Some operations work best with colours in a specific type of space: scene-linear, video, or log-encoded. As you work, you may want to switch colour spaces to perform certain operations, and then switch back to your main working space or a different space for other operations. For these situations, it's best to use a fully invertible transform to preserve as much colour information as possible.
Operations That Work Best with Scene-linear Colours
The following operations work best with scene-linear colours (that is, with code values that are directly proportional to light energy in the scene):
- compositing and blending
- optical effects, including lens blur and defocus operations
- motion blur
- anti-aliasing
- resizing
- sub-pixel repositioning
- 3D rendering
- lighting and re-lighting
Operations That Work Best with Video or Log Colours
The following operations work best with video or log colours:
- many colour correction operations
- vectorscopes and histograms
- tracking and stabilizing
- grain and noise operations
- unsharp masking
- video transitions
- making gradients
Operations That Require Video Colours
The following operations require video colours (that is, colour values that are restricted to the range [0, 1]):
- colour inversion
- converting RGB to HLS, HSV, or YCbCr