Select the menu Window > Histogram to open the Histogram window. This window graphically displays the frequency distribution of the color values in the image captured by the camera.
For more information on histograms see the Bit depth and digital contrast adjustment chapter.
Fig. 154: Histogram
•Red/Green/Blue
With the "Red", "Green", and "Blue" check boxes, you can enable or disable the display for each color channel. For monochrome images, the average grayscale value is displayed.