When you work with Blender and have used to work with another video editing software before, especially if you used an effect like Blender’s RGB curves, you may have noticed that the curves in the compositor (and indeed the whole color management) seem to work a bit differently. That’s because Blender works in a scene-referred linear color space.
Huh, if this sounds all G(r)eek to you, you can start here to get a little insight:
While the linear workflow has many advantages especially when working with CGI content, in some situations when you work with Videos or Images, you may want the good old gamma-corrected control back though. For example many grading tasks with the curves require an exact fine-tuning of dark tones and this gets very difficult when working in linear space!
There are two fast ways to work around the “problem”:
1. Change the input color space of your input node to linear set the Render color space in the Scene Properties to Raw.
2. (The better one) Before the Node(s) you want to use in gamma corrected space, add a gamma node (we call it g1) with the value 1/2.2 and after your correction nodes add another gamma node (g2) with the value 2.2. By doing this you linearize the already linearized values again: Applying effects in linear color space to image data that is “double-linearized” compensates the linear space and makes you work in a gamma corrected space for the moment. To put it simply ;-)
For you the second way means that you may decide which nodes in your composition shall work in linear space and which not. So you get the advantages of Blender´s cool color management without suffering from it’s drawbacks.
What I did in the screenshot: I added a value node which is directly connected to g2 and on its connection to g1 there is an inversion (1/value), so we simply put a gamma value into the Value node and control with what assumed gamma corrected space the Curves effect works. This gives us even more control.
Now have fun with that!