Tonal values present in your image.

/ersion of CHM2PDF Pilot 2.16.100. Histogram Channel: j RGB j[v

/ersion of CHM2PDF Pilot 2.16.100. Histogram Channel: j RGB j[v

Source: | Entire Image_v I

Mean: 87,16 Level:

Std Dev: 48.49 Count:

Median: 80 Percentile:

Piaete: 1274S4 Cache Level: 2

If the Histogram Palette is not visible on your screen, you can access it by choosing Window > Histogram. The numeric display in the middle of the palette probably looks like a lot of mumbo jumbo on first glance, but as you become experienced using the Histogram Palette, you'll find this information increasingly valuable.

Among the data on display are:

• Mean. This represents the average intensity value of all the pixels in the image. If the number is very low, that will confirm that the image is rather dark; a high number means that the image is, on average, very bright.

• Standard Deviation. This is a statistical term that tells you how much the intensity values vary from each other. A low number can mean that the contrast of the image is low, while a high number can point to a high contrast image.

• Median. The median is the middle number in the range of intensity values; half the individual values are higher than the median, while half are lower.

• Pixels. This is nothing more than the number of pixels in the image.

• Level. This readout shows the intensity level of the pixels under the cursor.

• Count. This value tells you how many pixels have the same value as the pixels under the cursor. For

This documentis created with trialversion of CHM2PDF Pilot2.16.100. in an image, move the cursor to a dark area and read the count.

• Percentile. This represents the number of pixels equal to or darker than the pixels under the cursor. For example, if the Percentile reads 70, then those pixels are brighter than 70 percent of all the pixels in the image.

• Cache Level. Photoshop's Preferences include an option for caching histogram information so the program doesn't have to calculate it anew each time a histogram is displayed. When the tonal values of an image are changed, a new histogram is stored in the cache. If you've set the caching option (to improve performance, because Photoshop can check the cache rather than calculating a new histogram each time the histogram is displayed), this readout shows which Cache level is being accessed. When it has a value of 1, that means the histogram for the original image is being displayed.

To really understand the Histogram Palette, you have to use it. Figure 6.31 shows it being used in tandem with the Levels command. In the illustration, I've moved the Midtone slider slightly to the left in the Levels dialog box. The Histogram Palette mirrors this movement, but shows both the original histogram (in ghost form) and the new histogram (in solid color), as well as the changes in the red, green, and blue histograms. As you gain experience, you can see how making changes in the Levels command affects the overall image as well as individual colors.

Figure 6.31. When used with the Levels command, the Histogram Palette shows the results of your modifications in a real-time display.

[View full size image]

Figure 6.31. When used with the Levels command, the Histogram Palette shows the results of your modifications in a real-time display.

[View full size image]

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