1991-2006
Silicon Graphics, Inc.
glConvolutionFilter2D
3G

# glConvolutionFilter2D

define a two-dimensional convolution filter

## C Specification

                    void glConvolutionFilter2D
                    GLenum target
                    GLenum internalformat
                    GLsizei width
                    GLsizei height
                    GLenum format
                    GLenum type
                    const GLvoid * data

## Parameters

`target`

  Must be `GL_CONVOLUTION_2D`.

`internalformat`

  The internal format of the convolution filter kernel. The allowable values are `GL_ALPHA`, `GL_ALPHA4`, `GL_ALPHA8`, `GL_ALPHA12`, `GL_ALPHA16`, `GL_LUMINANCE`, `GL_LUMINANCE4`, `GL_LUMINANCE8`, `GL_LUMINANCE12`, `GL_LUMINANCE16`, `GL_LUMINANCE_ALPHA`, `GL_LUMINANCE4_ALPHA4`, `GL_LUMINANCE6_ALPHA2`, `GL_LUMINANCE8_ALPHA8`, `GL_LUMINANCE12_ALPHA4`, `GL_LUMINANCE12_ALPHA12`, `GL_LUMINANCE16_ALPHA16`, `GL_INTENSITY`, `GL_INTENSITY4`, `GL_INTENSITY8`, `GL_INTENSITY12`, `GL_INTENSITY16`, `GL_R3_G3_B2`, `GL_RGB`, `GL_RGB4`, `GL_RGB5`, `GL_RGB8`, `GL_RGB10`, `GL_RGB12`, `GL_RGB16`, `GL_RGBA`, `GL_RGBA2`, `GL_RGBA4`, `GL_RGB5_A1`, `GL_RGBA8`, `GL_RGB10_A2`, `GL_RGBA12`, or `GL_RGBA16`.

`width`

  The width of the pixel array referenced by `data`.

`height`

  The height of the pixel array referenced by `data`.

`format`

  The format of the pixel data in `data`. The allowable values are `GL_RED`, `GL_GREEN`, `GL_BLUE`, `GL_ALPHA`, `GL_RGB`, `GL_BGR`, `GL_RGBA`, `GL_BGRA`, `GL_LUMINANCE`, and `GL_LUMINANCE_ALPHA`.

`type`

  The type of the pixel data in `data`. Symbolic constants `GL_UNSIGNED_BYTE`, `GL_BYTE`, `GL_BITMAP`, `GL_UNSIGNED_SHORT`, `GL_SHORT`, `GL_UNSIGNED_INT`, `GL_INT`, `GL_FLOAT`, `GL_UNSIGNED_BYTE_3_3_2`, `GL_UNSIGNED_BYTE_2_3_3_REV`, `GL_UNSIGNED_SHORT_5_6_5`, `GL_UNSIGNED_SHORT_5_6_5_REV`, `GL_UNSIGNED_SHORT_4_4_4_4`, `GL_UNSIGNED_SHORT_4_4_4_4_REV`, `GL_UNSIGNED_SHORT_5_5_5_1`, `GL_UNSIGNED_SHORT_1_5_5_5_REV`, `GL_UNSIGNED_INT_8_8_8_8`, `GL_UNSIGNED_INT_8_8_8_8_REV`, `GL_UNSIGNED_INT_10_10_10_2`, and `GL_UNSIGNED_INT_2_10_10_10_REV` are accepted.

`data`

  Pointer to a two-dimensional array of pixel data that is processed to build the convolution filter kernel.

## Description

`glConvolutionFilter2D` builds a two-dimensional convolution filter kernel from an array of pixels.

The pixel array specified by `width`, `height`, `format`, `type`, and `data` is extracted from memory and processed just as if glDrawPixels were called, but processing stops after the final expansion to RGBA is completed.

If a non-zero named buffer object is bound to the `GL_PIXEL_UNPACK_BUFFER` target (see glBindBuffer) while a convolution filter is specified, `data` is treated as a byte offset into the buffer object's data store.

The R, G, B, and A components of each pixel are next scaled by the four 2D `GL_CONVOLUTION_FILTER_SCALE` parameters and biased by the four 2D `GL_CONVOLUTION_FILTER_BIAS` parameters. (The scale and bias parameters are set by glConvolutionParameter using the `GL_CONVOLUTION_2D` target and the names `GL_CONVOLUTION_FILTER_SCALE` and `GL_CONVOLUTION_FILTER_BIAS`. The parameters themselves are vectors of four values that are applied to red, green, blue, and alpha, in that order.) The R, G, B, and A values are not clamped to [0,1] at any time during this process.

Each pixel is then converted to the internal format specified by `internalformat`. This conversion simply maps the component values of the pixel (R, G, B, and A) to the values included in the internal format (red, green, blue, alpha, luminance, and intensity). The mapping is as follows:

Internal Format | Red | Green | Blue | Alpha | Luminance | Intensity
--- | --- | --- | --- | --- | --- | ---
`GL_ALPHA` |  |  |  | A |  |
`GL_LUMINANCE` |  |  |  |  | R |
`GL_LUMINANCE_ALPHA` |  |  |  | A | R |
`GL_INTENSITY` |  |  |  |  |  | R
`GL_RGB` | R | G | B |  |  |
`GL_RGBA` | R | G | B | A |  |

The red, green, blue, alpha, luminance, and/or intensity components of the resulting pixels are stored in floating-point rather than integer format. They form a two-dimensional filter kernel image indexed with coordinates i and j such that i starts at zero and increases from left to right, and j starts at zero and increases from bottom to top. Kernel location i,j is derived from the Nth pixel, where N is i+j*`width`.

Note that after a convolution is performed, the resulting color components are also scaled by their corresponding `GL_POST_CONVOLUTION_c_SCALE` parameters and biased by their corresponding `GL_POST_CONVOLUTION_c_BIAS` parameters (where c takes on the values RED, GREEN, BLUE, and ALPHA). These parameters are set by glPixelTransfer.

## Notes

`glConvolutionFilter2D` is present only if `ARB_imaging` is returned when glGetString is called with an argument of `GL_EXTENSIONS`.

## Errors

`GL_INVALID_ENUM` is generated if `target` is not `GL_CONVOLUTION_2D`.

`GL_INVALID_ENUM` is generated if `internalformat` is not one of the allowable values.

`GL_INVALID_ENUM` is generated if `format` is not one of the allowable values.

`GL_INVALID_ENUM` is generated if `type` is not one of the allowable values.

`GL_INVALID_VALUE` is generated if `width` is less than zero or greater than the maximum supported value. This value may be queried with glGetConvolutionParameter using target `GL_CONVOLUTION_2D` and name `GL_MAX_CONVOLUTION_WIDTH`.

`GL_INVALID_VALUE` is generated if `height` is less than zero or greater than the maximum supported value. This value may be queried with glGetConvolutionParameter using target `GL_CONVOLUTION_2D` and name `GL_MAX_CONVOLUTION_HEIGHT`.

`GL_INVALID_OPERATION` is generated if `height` is one of `GL_UNSIGNED_BYTE_3_3_2`, `GL_UNSIGNED_BYTE_2_3_3_REV`, `GL_UNSIGNED_SHORT_5_6_5`, or `GL_UNSIGNED_SHORT_5_6_5_REV` and `format` is not `GL_RGB`.

`GL_INVALID_OPERATION` is generated if `height` is one of `GL_UNSIGNED_SHORT_4_4_4_4`, `GL_UNSIGNED_SHORT_4_4_4_4_REV`, `GL_UNSIGNED_SHORT_5_5_5_1`, `GL_UNSIGNED_SHORT_1_5_5_5_REV`, `GL_UNSIGNED_INT_8_8_8_8`, `GL_UNSIGNED_INT_8_8_8_8_REV`, `GL_UNSIGNED_INT_10_10_10_2`, or `GL_UNSIGNED_INT_2_10_10_10_REV` and `format` is neither `GL_RGBA` nor `GL_BGRA`.

`GL_INVALID_OPERATION` is generated if a non-zero buffer object name is bound to the `GL_PIXEL_UNPACK_BUFFER` target and the buffer object's data store is currently mapped.

`GL_INVALID_OPERATION` is generated if a non-zero buffer object name is bound to the `GL_PIXEL_UNPACK_BUFFER` target and the data would be unpacked from the buffer object such that the memory reads required would exceed the data store size.

`GL_INVALID_OPERATION` is generated if a non-zero buffer object name is bound to the `GL_PIXEL_UNPACK_BUFFER` target and `data` is not evenly divisible into the number of bytes needed to store in memory a datum indicated by `type`.

`GL_INVALID_OPERATION` is generated if `glConvolutionFilter2D` is executed between the execution of glBegin and the corresponding execution of glEnd.

## Associated Gets

glGetConvolutionParameter, glGetConvolutionFilter

## See Also

glConvolutionFilter1D, glSeparableFilter2D, glConvolutionParameter, glPixelTransfer

## Copyright

Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.