Viewing statistical information about pixel values

Statistical information about the intensity values of the pixels appears below the histogram in the Histogram palette. The Histogram palette must be in either the Expanded View or All Channels View, and Show Statistics must be chosen from the palette menu.

The statistical information includes:

Mean

Represents the average intensity value.

Standard deviation (Std Dev)

Represents how widely intensity values vary.

Median

Shows the middle value in the range of intensity values.

Pixels

Represents the total number of pixels used to calculate the histogram.

Level

Displays the intensity level of the area underneath the pointer.

Count

Shows the total number of pixels corresponding to the intensity level underneath the pointer.

Percentile

Displays the cumulative number of pixels at or below the level underneath the pointer. This value is expressed as a percentage of all the pixels in the image, from 0% at the far left to 100% at the far right.

Cache Level

Shows the current image cache used to create the histogram. If the Use Cache for Histograms option is selected in the Memory and Image Cache preferences, the histogram displays faster and is based on a representative sampling of pixels in the image (based on the magnification), rather than on all of the pixels. The original image is cache level 1. Each level above that averages four adjacent pixels below to get a single pixel, so each level is half the dimensions (1/4 the number of pixels) of the one below. When Photoshop needs to do a quick approximation, it can just use one of the upper levels. If you want to check for posterization in the image, choose Edit > Preferences > Memory & Image Cache, and then deselect the Use Cache for Histograms option.