Gimp - 2.4 ユーザーガイド
GNU Image Manipulation Program
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14.10.22.2
‘Equalize Layer’ example
Figure 14.91: Original image
The active layer and its Red, Green, Blue histograms before Equalize.
Figure 14.92: Image after the command
The active layer and its Red, Green, Blue histograms after treatment. Histogram stretching creates gaps between pixel columns
giving it a striped look.
14.10.23
White Balance
The White Balance command automatically adjusts the colors of the active layer by stretching the Red, Green and Blue channels
separately. To do this, it discards pixel colors at each end of the Red, Green and Blue histograms which are used by only 0.05%
of the pixels in the image and stretches the remaining range as much as possible. The result is that pixel colors which occur
very infrequently at the outer edges of the histograms (perhaps bits of dust, etc.) do not negatively influence the minimum and
maximum values used for stretching the histograms, in comparison with
separately. To do this, it discards pixel colors at each end of the Red, Green and Blue histograms which are used by only 0.05%
of the pixels in the image and stretches the remaining range as much as possible. The result is that pixel colors which occur
very infrequently at the outer edges of the histograms (perhaps bits of dust, etc.) do not negatively influence the minimum and
maximum values used for stretching the histograms, in comparison with
. Like ‘Stretch Contrast’, however, there
may be hue shifts in the resulting image.
This command suits images with poor white or black. Since it tends to create pure white (and black), it may be useful e.g. to
enhance photographs.
enhance photographs.
White Balance operates on layers from RGB images. If the image is Indexed or Grayscale, the menu item is insensitive and
grayed out.
grayed out.
14.10.23.1
Activating the Command
• You can access this command from the image menubar through Layer → Colors → Auto → White Balance.