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This chapter is from the book

This chapter is from the book

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 is designed to look at a single horizontal scan-line of an image and plot the brightness of a pixel for each X location. This allows you to graphically see how a color correction node is affecting the image.

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  1. Select File > New Script.
  2. Answer No when prompted to save the current script.
  3. Click on the Ramp node in the Image tab.
  4. Set the width parameter to 256 and the height parameter to 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 the PlotScanline operator from the Other tab after Ramp1.

    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 the PlotScanline1.
  7. Set the value parameter to 1.5 and set the softClip parameter to 1.0.

    This 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 then PlotScanline1 in turn to see how the adjustment affects the image.

    PlotScanline is also capable of graphing the different channels of an image separately.

  9. Replace ContrastLum1 with a Gamma node located in the Color tab.
  10. Adjust the rGamma, gGamma, and bGamma parameters to be different values.

    There are now three curves representing red, green, and blue values.

  11. Place different color nodes in place of Gamma1 and see how PlotScanline reacts as the various parameters are adjusted.
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