Nuke natively works in linear RGB colour space, converting all incoming material to linear on the way in, and then before rendering, converting the output to your desired output colour space. In linear colour space the scale of brightness works on a linear scale, eg. black is 0 and 1 is twice as bright as 0.5, 2 is twice as bright as 1, etc. This makes mathematical operations on an image very simple and predictable, giving consistent results regardless or the source’s colour space. This workflow in made possible by the fact that Nuke works in floating point colour depth, making colour space conversions almost lossless (having negligible effect on image quality). Nuke also uses a viewer LUT (look up table). Computer monitors don’t expect a linear input so the viewer LUT converts the image that you’re working with into something that your monitor will understand. This can be a regular sRGB conversion, or something that has been specifically set up to mirror the way an image will look when projected in a cinema. The viewer LUT has no actual impact on the image itself, and is never ‘baked in’, it is just to help display the image correctly while it is in the Nuke