Viewing histograms and pixel values

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.

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.

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.

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

You can preview the effect on the histogram of any color and tonal adjustments.

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.

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 (CC, CS6) or the Adjustments panel (CS5), 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 (CC, CS6) or the Adjustments panel (CS5).

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 display or hide color sampler information in the Info panel, choose Color Samplers from the panel menu. A check mark indicates that the color sampler information is visible.
• To change the color space in which a color sampler displays values, move the pointer onto the color sampler icon  in the Info panel. Then, hold down the mouse button, and choose another color space from the menu.