Color Correction - Nuke 101: Professional Compositing and Visual Effects - page 179

Whatyoudidherewasreplace,momentarily,theblackbackgroundwithamiddle
gray background. This way you are getting rid of the black and replacing it with
a color that is not the darkest nor the lightest in the image. This new image is the
imageyouwanttogaugeusingtheCurveTool.You'llneedtomovethepipecom-
ing in to CurveTool1 ( FIGURE 4.32 ) .
Figure 4.32. Moving the pipe from Read1's output to Merge3's output.