Using PlotScanline to Understand Color Corrections

To help you better understand some of Shake's color-correction functions, a useful operator called PlotScanline is included. It looks at a single horizontal scan line of an image and plots the brightness of a pixel for each X location. This lets you graphically see how a color-correction node is affecting the image.

1.	Choose File > New Script.
2.	Click No when prompted whether to save the current script.
3.	Select the Ramp node in the Image tab.
4.	Set the Res parameters to 256 by 256. The ramp is 256 pixels wide and ranges in value from 0 to 1. This provides a 1:1 correspondence between the range of possible values in an 8-bit image.
5.	Add PlotScanline from the Other tab after Ramp1, and make sure that the Res parameters are set to 256x256. The PlotScanline curve indicates that this is a linear ramp.
6.	Now insert a color-correction operator, such as ContrastLum, from the Color tab into the chain, after Ramp1 and before PlotScanline1.
7.	Set the Value parameter to 1.5 and the softClip parameter to 1.0. That will modify the gradient, and the plot will reflect this. As you adjust the values of your contrast, the plot updates to reflect any changes. The image is effectively a plot of the Contrast function.
8.	View Ramp1, ContrastLum1, and PlotScanline1 in turn to see how the adjustment affects the image. PlotScanline can also graph the different channels of an image separately.
9.	Replace ContrastLum1 with a Gamma node located on the Color tab.
10.	Adjust the rGamma, gGamma, and bGamma parameters so that they are different values. There are now three curves representing red, green, and blue values.
11.	Replace Gamma1 with different color nodes and see how PlotScanline reacts as the various parameters are adjusted.