13.1.4 The Imaging Subset in OpenGL 1.2

Several extensions to OpenGL 1.1 are incorporated as standard commands in OpenGL 1.2 as part of the optional imaging subset:

• Color tables (SGI_texture_color_table in 1.1)
• Convolution during pixel transfer (EXT_convolution)
• The color matrix (SGI_color_matrix)
• Histogram and minmax functions (EXT_histogram) during pixel transfer
• The blending equation and the enumerants for constant color/alpha blending, subtractive blending (EXT_blend_subtract), and blending with min and max operators (EXT_blend_minmax).

This group of extensions to the pixel transfer pipeline are useful to a class of applications that perform image processing.

The imaging subset provides color table support (glColorTable()) in the pixel transfer pipeline before the convolution operation (GL_ COLOR_TABLE), after convolution and before application of the color matrix (GL_ POST_CONVOLUTION_COLOR_TABLE), and after the color matrix (GL_ POST_COLOR_TABLE). Scale and bias are available for each color table.

The subset provides 1D, 2D and separable convolutions (glConvolutionFilter*D() and glSeparableFilter2D()) in the pixel transfer pipeline, including scale and bias parameters.

Histogram and min and max functions are provided through glHistogram() and glMinMax().

The imaging subset also provides support for glBlendEquation() and glBlendColor() and the blending modes GL_ CONSTANT_COLOR, GL_ ONE_MINUS_CONSTANT_COLOR, GL_ CONSTANT_ALPHA, and GL_ ONE_MINUS_CONSTANT_ALPHA.

If an implementation supports the imaging subset, all of the above features are supported. If the implementation doesn't support it, using these features will result in GL_ INVALID_OPERATION or GL_ INVALID_ENUM.

You can determine if an OpenGL 1.2 implementation implements the imaging subset by checking the result of glGetStringGL_ EXTENSIONS(GL_ EXTENSIONS) for the substring ``ARB_imaging''.

The imaging subset of OpenGL 1.2 is supported by the following vendors as of April, 1999:

• Silicon Graphics
• Hewlett Packard
• Sun Microsystems, Inc.
• Intergraph Computer Systems