Allows you to specify the number of distinct colors or shades of gray in the current lookup table, to reserve up to six entries for annotation and graphics, or to invert the look-up table.

Colors/Grayscales is the number of colors or shades of gray used in the current look-up table. When increasing the number of colors, the required new colors are created by interpolating between existing colors. For example, if the current color table consists of the two colors, white and black, setting the number of colors to 64 creates a grayscale palette with 64 shades of gray.

Reserved Entries allows you to allocate up to six entries in the look-up table for colors that are never altered. For example, you could reserve one entry to add color annotation to a grayscale picture. Any extra colors are displayed at the bottom of the LUT window, allowing you to edit them by double-clicking with the eyedropper tool.

Check Invert and the current look-table will be inverted when you click on OK. Unlike the Invert command in the Edit menu, pixels values are not altered, only the way the image is displayed on the screen. The first (0) and last (255) entries in the LUT, which are always white and black respectively, are never inverted since these entries are used for drawing the menu bar, title bars, dialog boxes, etc.