The pixel intensities of the monochrome images can be mapped to shades of gray between black and white. The intensities can also be mapped to different colors. The use of color enhances the eye's ability to distinguish among regions of different intensity. We provide 16 color schemes including black & white and white & black. This figure shows an image rendered in gray scale and this figure with the Rain Ramp color scheme.
Each of the tables gives the red, blue, and green (RGB) components of a color for a range of indices between 1 and 256. The pixel intensities within the contrast window are linearly mapped to the range (1, 256) and a lookup in the table gives the color.
The scheme is changed with the entries in the Color Scheme submenus of the Image and context menus. The scheme currently in effect is checked. The Options dialog contains a setting to select whether the change is applied to all images, only the active image, or all images in a 3D data set.
Mapping the intensities to 256 colors is necessary for other reasons. For gray scale images (R = G = B), the RGB components are limited to values between 0 and 255. To enhance performance, we store the image internally as a device-independent bitmap (DIB) with a color table. The DIB color table is limited to 256 entries.
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