User Guide

Increasing the brightness (page 383) lightens the image and can bring out image
detail in the shadow areas, although increasing brightness too much can wash
out the light areas. Decreasing the brightness darkens the image and can bring
out details in the light areas. Likewise, decreasing brightness too much can
cause the dark areas can become almost black.
Increasing the contrast makes the differences between dark and light areas
more distinct. You can increase contrast in a grayscale image to the point
where the image becomes black and white. Decreasing the contrast makes an
image that consists mostly of mid-level grays.
In color images, you can adjust the brightness and contrast for individual
color channelscolor_channel_1 (red, green, blue, or RGB, which is a
combination of the colors). For example, if you choose red and then increase
the brightness, you see more reds. In grayscale images, you can adjust only
the single channel that represents gray.
You can limit the effect of brightness or contrast changes to a portion of the
image called a sub-region. If the image palette is Index Color (8-bit) (page 391)
you can alter the palette of the image to include the new colors.
NOTE Raster Design uses Single Image Optimization (page 396) to speed up the
editing commands.
To adjust brightness or contrast for a selected image
1 Click Image menu ➤ Image Processing ➤ Histogram.
The following prompt appears:
Press Enter for entire image or specify sub-region option [Existing/Clip
region/Window/Polygon]:
2 Do one of the following:
■ Press Enter to use the histogram on the entire image.
■ Enter e, then click a closed vector entity to use an existing entity to
define the region.
■ Enter c to use an existing image clip.
■ Enter w, then enter two points to define a rectangular sub-region.
■ Enter p, then enter several points to define a polygonal sub-region.
The Histogram (page 316) dialog box is displayed.
3 Click the Brightness/Contrast tab.
Adjusting Images with the Histogram | 93