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Where Are the Lookup Tables in the Image Pipeline?
The three lookup tables exist at different points in the image pipeline (see Figure 7-1):
- GL_COLOR_TABLE_SGI is located immediately after index lookup or RGBA to RGBA mapping, and immediately prior to the convolution operation.
- GL_POST_CONVOLUTION_COLOR_TABLE_SGI is located immediately after the convolution operation (including its scale and bias operations) and immediately prior to the color matrix operation.
- GL_POST_COLOR_MATRIX_COLOR_TABLE_SGI is located immediately after the color matrix operation (including its scale and bias operations) and immediately prior to the histogram operation.
To enable and disable color tables, call glEnable() and glDisable() with the color table name passed as the cap parameter. Color table lookup is performed only for RGBA groups, though these groups may have been specified as color indexes and converted to RGBA by an index-to-RGBA pixel map table.
When enabled, a color lookup table is applied to all RGBA pixel groups, regardless of the command that they are associated with.
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