Adobe Photoshop CS3 - Manual (Page 158)

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Chapter 7: Making color and tonal
adjustments
Traditional photographers use different types of film or lens filters to achieve certain color and tonal results in their
photographs. They also use various tools and techniques to adjust the color and tonality of a photographic print in
the darkroom. Photoshop® CS3 provides a comprehensive set of tools for making color and tonal adjustments,
making corrections, and sharpening the overall focus of an image.
Viewing histograms and pixel values
About histograms
A histogram illustrates how pixels in an image are distributed by graphing the number of pixels at each color intensity
level. The histogram shows whether the image contains enough detail in the shadows (shown in the left part of the
histogram), midtones (shown in the middle), and highlights (shown in the right part) 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 a number of pixels in all areas.
Identifying the tonal range helps determine appropriate tonal corrections.
How to read a histogram
A. Overexposed photo B. Properly exposed photo with full tonality C. Underexposed photo
The Histogram palette 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’s histogram as an overlay in the Curves dialog box by selecting the histogram option under
Curve Display Options.
Histogram palette overview
❖ Choose Window > Histogram or click the Histogram tab to open the Histogram palette. By default, the Histogram
palette opens in Compact View with no controls or statistics, but you can adjust the view.
A B C