Documentation for XFree86 - glSeparableFilter2D - define a separable two-dimensional convolution filter

Name

glSeparableFilter2D - define a separable two-dimensional convolution filter

C Specification

void glSeparableFilter2D( GLenum target,

    GLenum internalformat,
    GLsizei width,
    GLsizei height,
    GLenum format,
    GLenum type,
    const GLvoid *row,
    const GLvoid *column )

Parameters

target: Must be GL_SEPARABLE_2D.
internalformat: The internal 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 number of elements in the pixel array referenced by row. (This is the width of the separable filter kernel.)
height: The number of elements in the pixel array referenced by column. (This is the height of the separable filter kernel.)
format: The of the pixel data in row and column. The allowable values are GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_BGR, GL_RGBA, GL_BGRA, GL_INTENSITY, GL_LUMINANCE, and GL_LUMINANCE_ALPHA.
type: The type of the pixel data in row and column. 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.
row: Pointer to a one-dimensional array of pixel data that is processed to build the row filter kernel.
column: Pointer to a one-dimensional array of pixel data that is processed to build the column filter kernel.

Description

glSeparableFilter2D builds a two-dimensional separable convolution filter kernel from two arrays of pixels.

The pixel arrays specified by (width, format, type, row) and (height, format, type, column) are processed just as if they had been passed to glDrawPixels, but processing stops after the final expansion to RGBA is completed.

Next, the R, G, B, and A components of all pixels in both arrays are scaled by the four separable 2D GL_CONVOLUTION_FILTER_SCALE parameters and biased by the four separable 2D GL_CONVOLUTION_FILTER_BIAS parameters. (The scale and bias parameters are set by glConvolutionParameter using the GL_SEPARABLE_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 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 (red, green, blue, alpha, luminance, and intensity). The mapping is as follows:

Internal Format Red Green Blue Alpha Luminance Intensity

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 They form two one-dimensional filter kernel images. The row image is indexed by coordinate i starting at zero and increasing from left to right. Each location in the row image is derived from element i of row. The column image is indexed by coordinate j starting at zero and increasing from bottom to top. Each location in the column image is derived from element j of column.

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

glSeparableFilter2D is present only if GL_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_SEPARABLE_2D.

GL_INVALID_ENUM is generated if internalformat 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_SEPARABLE_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_SEPARABLE_2D and name GL_MAX_CONVOLUTION_HEIGHT.

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_OPERATION is generated if glSeparableFilter2D is executed between the execution of glBegin and the corresponding execution of glEnd.

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.

Associated Gets

glGetConvolutionParameter, glGetSeparableFilter