Autodesk 00126-050008-1620A - Autocad 2006 Essentials User Manual page 75

Blue). It enables you to correct the image pixel color, for example, to turn a pink
background to pure white.
To correct an image by histogram
1. Select an image you want to process on the screen and start the operation by
one of the following methods:
Click Equalize on the Raster Image toolbar.
Choose Equalize from the rImage menu.
- or -
2. Start the operation without selecting an image.
3. Select an image you want to process from the dialog box.
* For more detailed information on the selection procedure see "Selecting
Several Images" on page 20.
The following dialog box appears:
This dialog box represents the image histogram, displaying the averaged
number of pixels, corresponding to each brightness value. The left part of
histogram corresponds to low brightness value, and the right one corresponds to
high brightness value (the lightest tones). The sliders in the bottom part of
histogram indicate threshold values: the left black one is for the darkest value,
the grey middle one is for the middle value, and the right white one is for the
brightest pixel. The Levels box provides the numerical expression of current
threshold values. You can select one of the four histograms: Master displays
summary pixel brightness distribution, Red, Green, and Blue l display
distribution of the corresponding pixels color components. Using the Master
histogram slides, you can proportionally modify the threshold value for all
components at once. The histogram sliders Red, Green, and Blue modify
brightness threshold values separately for the corresponding color component.
The eyedroppers are used to select threshold values and gamma for an image.
If you select a color sample with the
the threshold value for the darkest (or the lightest) for all components equal to
6 Color Correction and Color Filtration
(or ) eyedropper, then it defines
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