User Manual

Channel
This menu is used to select and display the histogram for each color channel or for the
Master channel.
Histogram Display
A histogram is a chart that represents the distribution of color values in the scene. The chart
reads from left to right, with the leftmost values representing the darkest colors in the scene
and the rightmost values representing the brightest. The more pixels in an image with the same
or similar value, the higher that portion of the chart is.
Luminance is calculated per channel; therefore, the red, green, and blue channels all have their
own histogram, and the combined result of these comprises the Master Histogram.
To scale the histogram vertically, place the mouse pointer inside the control and drag the
pointer up to zoom in or down to zoom out.
Display Selector Toolbar
The Display Selector toolbar at the top of the histogram provides a method of enabling and
disabling components of the histogram display. Hold the mouse pointer over the button to
display a tooltip that describes the button’s function.
 Input Histogram: This enables or disables the display of the input image’s histogram.
 Reference Histogram: This enables or disables the display of the reference
image’s histogram.
 Output Histogram: This enables or disables the display of the histogram from the
post-color-corrected image.
 Corrective Curve: This toggles the display of a spline used to visualize exactly how
auto color corrections applied using a reference image are affecting the image. This
can be useful when equalizing luminance between the input and reference images.
Float Images and Histogram Equalization or Matching
By using the Histogram Match or Equalize methods on a float image, the color depth of the
output image is converted to 16-bit integer. Two-dimensional histograms are not well suited to
working with the extreme dynamic range of float images, so these operations always revert to
16-bit integer processing.
Histogram Type
Each of these menu options enables a different type of color correction operation.
 Keep: Keep produces no change to the image, and the reference histogram is ignored.
 Equalize: Selecting Equalize adjusts the source image so that all the color values in
the image are equally represented—in essence, flattening the histogram so that the
distribution of colors in the image becomes more even.
 Match: The Match mode modifies the source image based on the histogram from the
reference image. It is used to match two shots with different lighting conditions and
exposures so that they appear similar.
When selected, the Equalize and Match modes reveal the following controls.
 Match/Equalize Luminance: This slider affects the degree that the Color Corrector
node attempts to affect the image based on its luminance distribution. When this
control is zero (the default), matching and equalization are applied to each color
channel independently, and the luminance, or combined value of the three color
channels, is not affected.
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