The Histogram controls help you visualize how the individual pixel RGB values are distributed across the image.

The histogram is a visual representation of all the color values contained in the image as they are distributed over the range of pixel values (0–255). The color values depend on the bit depth (255 is the highest value for 8-bit).

You can view histograms for the red, green, or blue channels, or you can view the histogram for the entire image (RGB).