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FAQ: Why can't bilinear or bicubic pyramids be built on a colormap image?

Question

Why can't bilinear or bicubic pyramids be built on a colormap image?

Answer

The only valid interpolation method to be used with a color mapped image is Nearest Neighbor. Color mapped images require that the pixels values of the generated pyramid layers remain within a discrete set of values. The pixel values are actually indexes into a color lookup table (colormap), only Nearest Neighbor guarantees that no non-existant indexes are being created during the interpolation; bilinear or bicubic will most likely generate index values that do not exist in the colormap.

Code:
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C:\>sderaster -o pyramid -l andy44,image -v 1 -L -1 -I bilinear -i 5161 -u raster -p raster -D raster

Connecting to server Thorne, port 5161, as user raster

Updating pyramid...
Error: SE_stream_execute (-66)
Error: Invalid parameter value passed to function
Incomplete...

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C:\>sderaster -o pyramid -l andy44,image -v 1 -L -1 -I bicubic -i 5161 -u raster -p raster -D raster

Connecting to server Thorne, port 5161, as user raster

Updating pyramid...
Error: SE_stream_execute (-66)
Error: Invalid parameter value passed to function
Incomplete...

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C:\>sderaster -o pyramid -l andy44,image -v 1 -L -1 -I nearest -i 5161 -u raster -p raster -D raster

Connecting to server Thorne, port 5161, as user raster

Updating pyramid...
Raster ID : 1

Total Time: 00:00:00
Complete...

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