In order to effectively perform color manipulation on an image we need good information on what the existing values of the image are. This can be in the form of generalized visual feedback or something more specific like a set of number values. Nuke has a lot of tools that have either been designed specifically for this purpose or can be adapted to be used as such.
The Viewer window At the bottom of the Viewer window are a set of number values that represent the color values of the part of the image that lie directly under the cursor (figure 1). We can also shift drag in the viewer window to create a box from which we can get a readout of average values (click ones again in the viewer window to get rid of the red square). Still within the viewer we can press the R, G and B key (whilst our cursor hovers over the Viewer window) to see the red, green and blue channel respectively (figure 2). A press of the L key will reveal the luminance (lightness) values of the image. This is referenced when we are making lightness adjustment changes to our image and don’t want to be distracted by the hue.