Creating new segments

On the Edit menu, you can select a command to create a new lookup-table (LUT) segment, pseudocolor-table (PCT) segment, or text segment, as applicable.

A LUT segment stores numerical tables that map image gray levels to new gray levels. The segment consists of 256 8-bit values, between 0 and 255. You use a LUT to apply enhancements to raster data. You can also use a LUT to encode thematic class mapping.

A PCT segment stores numerical tables that map image DN values to a specific color. Colors are defined by an intensity value (between 0 and 255) for each of a red, green, and blue component. A PCT segment contains an array of 256 colors and assigns color values to 8-bit images. A PCT always contains exactly 256 entries. File formats such as TIFF, which can have color tables with less than 256 colors, assign a value of zero to unused colors. There is no support for alpha channels in the table.

A text segment stores attribute data linked to the gray levels of a particular image channel or free-form text, such as legend information used during map generation or commands to implement an analysis model.

To create a new segment