Autotek autocad raster design 2010 ユーザーズマニュアル

If an image has many pixels that are approximately the same color or shade,
you can equalize the image to bring out more detail.

Equalization makes the darkest pixels darker and the lightest pixels lighter,
then reassigns the remaining pixels to the colors in between. This is also
known as a non-linear contrast stretch.

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 

 (page 391),

you can alter the palette of the image to include the new colors.

NOTE Raster Design uses 

 (page 396) to speed up the

editing commands.

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.

 (page 316) dialog box is displayed.

3 Click the Equalize tab.

A preview of the image is displayed. If you selected more than one image,
the histogram displays a composite of the images' values. You can view
each image by clicking its name in the list.

96 | Chapter 6   Modifying Images