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`).

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 `glGetString GL_EXTENSIONS(GL_EXTENSIONS)`
for the substring ``

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