A histogram illustrates how pixels in an image are distributed by graphing the number of pixels at each color intensity level. The histogram shows detail in the shadows (shown in the left part of the histogram), midtones (shown in the middle), and highlights (shown in the right part) A histogram can help you determine whether an image has enough detail to make a good correction.
The histogram also gives a quick picture of the tonal range of the image, or the image key type. A low‑key image has detail concentrated in the shadows. A high‑key image has detail concentrated in the highlights. And, an average-key image has detail concentrated in the midtones. An image with full tonal range has some pixels in all areas. Identifying the tonal range helps determine appropriate tonal corrections.
A. Overexposed photo B. Properly exposed photo with full tonality C. Underexposed photo
The Histogram panel offers many options for viewing tonal and color information about an image. By default, the histogram displays the tonal range of the entire image. To display histogram data for a portion of the image, first select that portion.
You can view an image histogram as an overlay in the Curves dialog box by selecting the histogram option under Curve Display Options, and in the Curves Properties panel, or by choosing Curve Display Options from the panel menu, then Histogram.
A. Channel menu B. panel menu C. Uncached Refresh button D. Cached Data Warning icon E. Statistics
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.
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.
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.
In the All Channels View, choosing from the Channels menu affects only the topmost histogram in the panel.
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.
By default, the Histogram panel displays statistics in the Expanded View and All Channels View.
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:
Represents the average intensity value.
Std Dev (Standard deviation)
Represents how widely intensity values vary.
Shows the middle value in the range of intensity values.
Represents the total number of pixels used to calculate the histogram.
Displays the intensity level of the area underneath the pointer.
Shows the total number of pixels corresponding to the intensity level underneath the pointer.
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.
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.
Displays a histogram of the entire image, including all layers.
Displays a histogram of the layer that’s selected in the Layers panel.
Displays a histogram of an adjustment layer selected in the Layers panel, including all the layers below the adjustment layer.
You can preview the effect on the histogram of any color and tonal adjustments.
When Preview is selected, the Histogram panel shows how the adjustment affects the histogram.
When making adjustments using the Adjustments panel, changes are automatically reflected in the Histogram panel.
A. Original histogram B. Adjusted histogram C. Shadows D. Midtones E. Highlights
When a histogram is read from a cache instead of the current state of the document, the Cached Data Warning icon appears in the Histogram panel. Histograms based on the image cache are displayed faster and are based on a representative sampling of pixels in the image. You can set the maximum cache level (from 2 to 8) in the Performance preference.
A higher cache level setting will increase the redraw speed for large, multi-layer files, but requires additional usage of system RAM. If RAM is limited or you work mainly with smaller images, use lower cache level settings
Double-click anywhere in the histogram.
Click the Cached Data Warning icon .
Click the Uncached Refresh button .
Choose Uncached Refresh from the Histogram panel menu.
For information about cache level, see Histogram panel overview.
You can use the Info panel to see the color value of pixels as you make color corrections. When you work with the Properties panel, the Info panel displays two sets of color values for the pixels under the pointer. The value in the left column is the original color value. The value in the right column is the color value after the adjustment is made.
You can view the color of a single location using the Eyedropper tool . You can also use up to four Color Samplers to display color information for one or more locations in the image. These samplers are saved in the image, so you can refer to them repeatedly as you work, even if you close and reopen the image.
You can view color information for specific pixels in the image while adjusting color in the Properties panel.
Make adjustments in the Properties panel. As you make adjustments, view the before and after color values in the Info panel. Move the pointer over the image to view color values at the pointer location.
If you are using a command from the Image > Adjustments menu, the Eyedropper tool is activated (and other tools temporarily disabled) when you move the pointer over the image. You still have access to the scroll controls and to the Hand and Zoom tools using keyboard shortcuts.
Once you’ve added a color sampler, you can move or delete it, hide it, or change the color sampler information displayed in the Info panel.
To move a color sampler, drag the sampler to the new location.
To delete a color sampler, drag the sampler out of the document window. Alternatively, hold down Alt (Windows) or Option (Mac OS) until the pointer becomes a scissors and click the sampler.
To delete all color samplers, click Clear in the options bar.
To delete a color sampler while an adjustment dialog box is open, hold down Alt+Shift (Windows) or Option+Shift (Mac OS), and click the sampler.