PDF (adobe.com)

Histogram panel overview



 Choose Window > Histogram or click the Histogram tab to open the Histogram panel. By default, the Histogram panel opens in Compact View with no controls or statistics, but you can adjust the view.
Histogram panel

A.
Channel menu

B.
panel menu

C.
Uncached Refresh button

D.
Cached Data Warning icon

E.
Statistics

Adjust the view of the Histogram panel

 Choose a view from the Histogram panel menu.
Expanded View
Displays the histogram with statistics. It also displays: controls for choosing the channel represented by the histogram, viewing options in the Histogram panel, refreshing the histogram to display uncached data, and choosing a specific layer in a multilayered document.

Compact View
Displays a histogram with no controls or statistics. The histogram represents the entire image.

All Channels View
Displays individual histograms of the channels in addition to all the options of the Expanded View. The individual histograms do not include alpha channels, spot channels, or masks.
Histogram panel with all channels displayed and statistics hidden

View a specific channel in the histogram

If you chose the Expanded View or All Channels View of the Histogram panel, you can choose a setting from the Channel menu. Photoshop remembers the channel setting if you switch from either Expanded View or All Channels View back to Compact View.

  • Choose an individual channel to display a histogram of the channel, including color channels, alpha channels, and spot channels.
  • Depending on the color mode of the image, choose RGB, CMYK, or Composite to view a composite histogram of all the channels.
  • If the image is RGB or CMYK, choose Luminosity to display a histogram representing the luminance or intensity values of the composite channel.
  • If the image is RGB or CMYK, choose Colors to display a composite histogram of the individual color channels in color. This option is the default view for RGB and CMYK images when you first choose Expanded View or All Channels View.

    In the All Channels View, choosing from the Channels menu affects only the topmost histogram in the panel.

View channel histograms in color

 From the Histogram panel, do one of the following:

  • In the All Channels View, choose Show Channels In Color from the panel menu.

  • In Expanded View or All Channels View, choose an individual channel from the Channel menu and choose Show Channels In Color from the panel menu. If you switch to Compact View, the channel continues to be shown in color.

  • In Expanded View or All Channels View, choose Colors from the Channel menu to show a composite histogram of the channels in color. If you switch to Compact View, the composite histogram continues to be shown in color.

View histogram statistics

By default, the Histogram panel displays statistics in the Expanded View and All Channels View.

  1. Choose Show Statistics from the Histogram panel menu.
  2. Do one of the following:

    • To view information about a specific pixel value, place the pointer in the histogram.

    • To view information about a range of values, drag in the histogram to highlight the range.

    The panel displays the following statistical information below the histogram:

    Mean
    Represents the average intensity value.

    Std Dev (Standard deviation)
    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. When the cache level is higher than 1, the histogram is displayed faster. In this case, the histogram is derived from a representative sampling of pixels in the image (based on the magnification). The original image is cache level 1. At each level above level 1, four adjacent pixels are averaged to arrive at a single pixel value. So, each level is half the dimensions (has 1/4 the number of pixels) of the lower level. When Photoshop makes a quick approximation, it can use one of the upper levels. Click the Uncached Refresh button to redraw the histogram using the actual image layer.