Photoshop Histogram noun Introduction tutorial

The histogram graphically represents the number of pixels in each brightness level of an image, showing the distribution of pixels in the image. The histogram shows you whether the image contains enough detail in the darkened (shown on the left), midtones (shown in the middle), and highlights (shown on the right) for better correction.

　　The histogram also provides a quick view of the image tonal range or the basic tonal type of the image. The detail of the low tone image is concentrated in the dark mediation, the detail of the tonal image is concentrated in the high light, while the details of the average tonal image are concentrated in the intermediate mediation. A full-color range of images has a large number of pixels in these areas. Identifying tonal ranges helps determine the appropriate tonal correction.

Details are not enough for the original artwork and details of the rich original artwork

Original artwork and corrected average tonal image

Original artwork and corrected bright-tone images

Original artwork and corrected dark-tone images

　　To display the histogram of an image:

1 to display the histogram data for a part of the image, select the section first. By default, the histogram displays the tonal range of the entire image.

2 Choose Image > Histogram.

To include data for spot channels and Alpha channels, hold down the ALT key (Windows) or the Option key (Mac OS) When you select Image > Histogram, and then choose the desired channel from the pop-up menu.

The horizontal axis of the histogram represents the brightness value or level, from the darkest value (0) at the leftmost end to the lightest value (255) at the far right, and the vertical axis represents the total number of pixels for the given value.

Note: Adjust the histogram of the layer to reflect the data for all visible layers under the adjustment layer.

3 for RGB, CMYK, and indexed color images, choose an option from the Channel menu. You can draw the brightness of a composite channel (using the Brightness option) or a single channel's brightness value.

4 To view information about a specific point on the histogram, place the pointer over that point. To view information about a range of values, drag in the histogram to highlight the range. When you are finished, click OK to close the histogram.

Statistics about the pixel brightness values appear below the histogram:

Averages represent average brightness values.

The standard deviation represents the range of brightness values.

An intermediate value displays the median value in the range of luminance values.

The pixel represents the total number of pixels used to compute the histogram.

Levels show the brightness level of the area below the pointer.

The quantity represents the total number of pixels that correspond to the brightness level below the pointer.

Percentile displays the level that the pointer refers to or the cumulative number of pixels below that level. The value is expressed as the percentage of all pixels in the image, from the leftmost 0% to the rightmost 100%.

The cache level displays the settings for the image cache. If the use Histogram cache option is selected in memory and image caching (Windows) or image cache (Mac OS) presets, the histogram can be displayed faster and based on a representative pixel sampling (based on magnification) in the image. Rather than all pixels (equivalent to cache level 1). Deselect this option if you want to check for tonal separations in the image. When you select Image > Histogram, press the Shift key to generate a histogram using all the pixels in the image.

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