Converting RGB to pseudocolor

You can use a single channel with a pseudocolor table (PCT) to represent data instead of a full three-channel RGB image. This is helpful when you need to import data to software that accepts only single-channel .tif files with PCTs. Converting to PCT can to reduce an RGB file to approximately a third of its original size.

If necessary, you can also change data from a single-image channel with a PCT to full RGB representation.

When preparing color images for export to third-party software, such as a GIS system with limited color capability, RGB2PCT compresses a 24-bit color (RGB) image into a single 8-bit layer based on a PCT. A PCT colors the compressed image to look similar to the original 24-bit color image.

The input file (FILE) contains the input RGB layers (DBIC) and the target layer where the compressed result (DBOC) is saved. When enhancing image data with an LUT, it should first be applied to the RGB layers using the LUT function.

The input RGB layers and the output-compressed layer should be 8-bit. This restriction is due to the 8-bit nature of a PCT. While any type of image layer can be used, values are internally converted to 8-bit data. Using non-8-bit data may produce unexpected results.

To convert an RGB image to pseudocolor

On the Tools menu of the Focus viewer, click Algorithm Librarian, and then run the ADAPT algorithm to generate a well-distributed PCT to represent a particular image.
ADAPT takes a 24-bit RGB image and compresses it to a single 8-bit image, based on a user-supplied PCT. For each pixel, the nearest color in the supplied PCT is established and a corresponding color index is placed in the output channel.
In the Algorithm Library, open the RGB2PCT algorithm.
Select the three raster layers you want to use as your RGB channels.
Select the PCT that was created using the ADAPT algorithm.
Run the RGB2PCT algorithm, and then on the Maps tab in the Focus viewer, save the results.
If you want to convert from PCT to RGB, run the PCE algorithm from the Algorithm Library. PCE encodes an input channel into three output channels (such as red, green, and blue components) using a PCT held in a database segment.
Right-click the newly created raster layer, and then click Properties.
In the PCT Layer Properties window, click the Source Image tab.
Under PCT, in the File list, click the file containing the PCT layer, and then in the Layer list, click the PCT layer.
Save the channel and PCT with a new file name.