Autodesk 05726-091452-9060 User Guide - Page 76

WiseImage - User's Guide the corresponding components values of the selected color. If you select a color sample with the eyedropper, then it defines the position of the middle tone, and hence defines the image gamma. 2. Select a histogram corresponding to the color component to be corrected. 3. Specify the brightness value for the darkest and the brightest pixels, and for the image gamma. Use Levels or eyedroppers. Use histogram slides for precise adjustment. The preview window displays part of the image. Using the preview management tools, you can adjust the optimal correction parameters. Using the Auto button you can automatically specify the light and dark threshold values so that the brightness values of each color component not found in the image are cut off. So automatic correction tries to increase image contrast as much as possible, slightly modifying brightness values. Suppose you want to make the background tone of a map image pure white. To do so, you should select a background sample with the white eyedropper. The white triangle in the Master histogram moves to the position corresponding to the selected color brightness. All the pixels with brightness value above the defined one become white. Then suppose you want to turn outlines, which are not pure black after scanning, to black. If you select a color outline sample with the black eyedropper, then all pixels with brightness value below the defined one become black. The brightness value of the remaining pixels will be proportionally redistributed within the new tone range. As a result, the image contrast increases. Moving the grey slider (modifying gamma value) you can redistribute the contrast between the light and dark image parts. 4. Click Apply to run the operation. You can apply this operation several times, consistently modifying an image pixel brightness distribution. Gamma Correction This tool is used to enhance the overall quality of an image by changing its socalled "color profile" - i.e. it applies an "algorithm" to change the distribution of brightness. Every image has its brightest point (a "white" point) and its darkest point (a "black" point). The points having intermediate values of color intensity are usually distributed unevenly, forming a curve of an arbitrary shape. The Gamma value defines the slope of the curve halfway between the black and white. Using the Gamma Correction tool, the points that fall within in a specified range of brightness can be made either brighter or darker. The brightness of Red, Blue or Green colors can also be changed. 78