Showing Histogram

A histogram shows the distribution of color intensities in an image. The horizontal axis represents intensity values from darkest (0) at the far left to brightest (255) at the far right. The vertical axis represents the number of pixels with a given value. The histogram helps you analyze and, more importantly, correct the image contrast.

You can display five types of histograms:

• Luminosity: luminance histograms are more accurate than RGB histograms at describing the perceived brightness distribution, or "luminosity," in an image; luminance takes into account the fact that the human eye is more sensitive to green light than to red or blue light.
• RGB: intensities of the red, green, and blue color channels (colors are ignored; only their intensities are important),
• Red: intensities of the red color channel,
• Green: intensities of the green color channel,
• Blue: intensities of the blue color channel.

To show histogram:

1. Open Histogram window:

   Viewer menu:	File/Show Histogram...
   Viewer shortcut key:	Ctrl+H
   Viewer context menu:	Right-click image and choose Show Histogram...

2. Choose the Luminosity, RGB, Red, Green, or Blue channel on the toolbar.
3. You can also display all channels at once; see the Show Other Channels toolbar button.

From the Sally manual (GPL-2.0-or-later), © 1997-2023 Open Salamander Authors; © 2025-2026 Elias Bachaalany. Source: manual source (zip) · original page in the Sally repository