Changing the Display Characteristics of Raster Images
Where images appear dull, or lack in contrast, you can change their contrast and brightness display settings. Additionally, you can change the Display Gamma setting. Changing any of these settings does not alter the original image. Display settings may be different for individual images and they are saved with the DGN file. Changing the Contrast and Brightness may only be carried out on one image file at a time, while the Display Gamma setting can be applied to a number of selected image files simultaneously.