Autodesk 00126-050008-1640A User Guide - Page 74

WiseImage - User's Guide - or 2. Start the operation without selecting an image. 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 is displayed: 3. Use the appropriate boxes or sliders to modify the value of the following parameters: Brightness, Contrast, Hue, and Saturation. The preview window displays the effect of modifying the parameters. 4. Click Apply to run the operation. Correction by Histogram This operation is applied for precise adjustment of image brightness, hue, and contrast. The algorithm for correction by histogram requires the specification of two threshold brightness levels - the brightest and darkest pixels, and image gamma that defines the position of the middle brightness value relative to the current threshold values. The gamma defines a ratio of brightness range length between the average and the brightest value to the length of the brightness range between the dark threshold and the average value. As a result, the pixels with brightness value below the dark threshold gain zero brightness value; the pixels with a brightness value above the brightest one gain maximum brightness value (255), and the brightness values of the pixels between the darkest and the middle values, as well as between the middle and the brightest ones, are relocated evenly in conformance with their range lengths determined by the image gamma. The increase of the gamma value causes the range for brightness values in the dark range to reduce, and therefore it increases the contrast, at the same time reducing the contrast in the light hue area, and vice versa. The command enables the redistribution of both the image pixels' average brightness and brightness by separate color pixel components (Red, Green, and 76