Julieanne Kost
The Histogram Panel in Photoshop
A histogram represents all of the pixel values in an image, plotted from 0 (black) on the left to 255 (white) on the right; the height of the column shows how many pixels in the image have that value.It can be an essential tool for managing the dynamic range of an image so that you can be sure you aren’t pushing important details in an image’s highlights or shadow areas to pure black or white without detail.