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HistEQ

Remap colors using blended histogram weights. Figure 10.49 shows the GUI and the results in a split screen.

Figure 10.49: Control window and split screen

If the histogram is as wide as the entire range (0 - 1.0), the image is high contrast. If the range is small (i.e., the values are close together) the contrast is small. In this case HistEQ is used to distribute the few clustered values across the entire range (0 - 1.0), increasing the contrast of the frame. In order to do this HistEQ equalizes the colorspace through use of a histogram equalization algorithm. Parameters are:

Gain:
  when set to 1, the colorspace is best effort. If the gain is set to 0, the result is the entire regression line of the color map.
Blend:
  goes between a straight and a twisted line.
Split output:
  diagonally shows in the compositor, the new results on the left and old on the right.
Plot bins/lut:
  displays a plot of the result.