A histogram shows the total distribution of color intensities in the image. The horizontal axis represents the intensity values from darkest (0) at the far left to brightest (255) at the far right. The vertical axis represents the total number of pixels with a given value. The histogram helps us analyze, and more importantly, correct the contrast of the image.
You can display five types of histograms:
- Luminosity: luminance histograms are more accurate than RGB histograms at describing the perceived brightness distribution or "luminosity" within an image; luminance takes into account the fact that the human eye is more sensitive to green light than red or blue light,
- RGB: intensities of red, green, and blue color channels (colors are ignored, only their intensities are important),
- Red: intensities of red color channel,
- Green: intensities of green color channel,
- Blue: intensities of blue color channel.
To show histogram:
- Open Histogram window:
Viewer menu: File/Show Histogram... Viewer shortcut key: Ctrl+H Viewer context menu: Right-click image and choose Show Histogram...
- Choose Luminosity, RGB, Red, Green, or Blue channel on toolbar.
- You can also display all channels at once, see toolbar button Show Other Channels.