GLCOLORTABLE(3G) GLCOLORTABLE(3G)
NAME
glColorTable - define a color lookup table
C SPECIFICATION
void glColorTable( GLenum target,
GLenum internalformat,
GLsizei width,
GLenum format,
GLenum type,
const GLvoid *table )
PARAMETERS
target Must be one of GL_COLOR_TABLE, GL_POST_CONVOLUTION_COLOR_TABLE,
GL_POST_COLOR_MATRIX_COLOR_TABLE, GL_PROXY_COLOR_TABLE,
GL_PROXY_POST_CONVOLUTION_COLOR_TABLE, or GL_PROXY_POST_COLOR_MATRIX_COLOR_TABLE.
internalformat The internal of the color table. 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, and GL_RGBA16.
width The number of entries in the color lookup table specified by table.
format The of the pixel data in table. The allowable values are GL_RED, GL_GREEN, GL_BLUE,
GL_ALPHA, GL_LUMINANCE, GL_LUMINANCE_ALPHA, GL_RGB, GL_BGR, GL_RGBA, and GL_BGRA.
type The type of the pixel data in table. The allowable values are GL_UNSIGNED_BYTE,
GL_BYTE, 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.
table Pointer to a one-dimensional array of pixel data that is processed to build the color
table.
DESCRIPTION
glColorTable may be used in two ways: to test the actual size and color resolution of a lookup table
given a particular set of parameters, or to load the contents of a color lookup table. Use the tar-gets targets
gets GL_PROXY_* for the first case and the other targets for the second case.
If target is GL_COLOR_TABLE, GL_POST_CONVOLUTION_COLOR_TABLE, or GL_POST_COLOR_MATRIX_COLOR_TABLE,
glColorTable builds a color lookup table from an array of pixels. The pixel array specified by
width, format, type, and table is extracted from memory and processed just as if glDrawPixels were
called, but processing stops after the final expansion to RGBA is completed.
The four scale parameters and the four bias parameters that are defined for the table are then used
to scale and bias the R, G, B, and A components of each pixel. (Use glColorTableParameter to set
these scale and bias parameters.)
Next, the R, G, B, and A values are clamped to the range [0, 1]. 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 Channel mapping
GL_ALPHA A=Alpha
GL_LUMINANCE R=Luminance
GL_LUMINANCE_ALPHA A=Alpha, R=Luminance
GL_INTENSITY R=Intensity
GL_RGB R=Red, G=Green, B=Blue
GL_RGBA R=Red, G=Green, B=Blue, A=Alpha
Finally, the red, green, blue, alpha, luminance, and/or intensity components of the resulting pixels
are stored in the color table. They form a one-dimensional table with indices in the range
[0, width - 1].
If target is GL_PROXY_*, glColorTable recomputes and stores the values of the proxy color table's
state variables GL_COLOR_TABLE_FORMAT, GL_COLOR_TABLE_WIDTH, GL_COLOR_TABLE_RED_SIZE,
GL_COLOR_TABLE_GREEN_SIZE, GL_COLOR_TABLE_BLUE_SIZE, GL_COLOR_TABLE_ALPHA_SIZE,
GL_COLOR_TABLE_LUMINANCE_SIZE, and GL_COLOR_TABLE_INTENSITY_SIZE. There is no effect on the image or
state of any actual color table. If the specified color table is too large to be supported, then all
the proxy state variables listed above are set to zero. Otherwise, the color table could be sup-ported supported
ported by glColorTable using the corresponding non-proxy target, and the proxy state variables are
set as if that target were being defined.
The proxy state variables can be retrieved by calling glGetColorTableParameter with a target of
GL_PROXY_*. This allows the application to decide if a particular glColorTable command would suc-ceed, succeed,
ceed, and to determine what the resulting color table attributes would be.
If a color table is enabled, and its width is non-zero, then its contents are used to replace a sub-set subset
set of the components of each RGBA pixel group, based on the internal of the table.
Each pixel group has color components (R, G, B, A) that are in the range [0.0, 1.0]. The color com-ponents components
ponents are rescaled to the size of the color lookup table to form an index. Then a subset of the
components based on the internal of the table are replaced by the table entry selected by that
index. If the color components and contents of the table are represented as follows:
Representation Meaning
r Table index computed from R
g Table index computed from G
b Table index computed from B
a Table index computed from A
L[i] Luminance value at table index i
I[i] Intensity value at table index i
R[i] Red value at table index i
G[i] Green value at table index i
B[i] Blue value at table index i
A[i] Alpha value at table index i
then the result of color table lookup is as follows:
Table Internal Resulting Texture Components
Format R G B A
GL_ALPHA R G B A[a]
GL_LUMINANCE L[r] L[g] L[b] At
GL_LUMINANCE_ALPHA L[r] L[g] L[b] A[a]
GL_INTENSITY I[r] I[g] I[b] I[a]
GL_RGB R[r] G[g] B[b] A
GL_RGBA R[r] G[g] B[b] A[a]
When GL_COLOR_TABLE is enabled, the colors resulting from the pixel map operation (if it is enabled)
are mapped by the color lookup table before being passed to the convolution operation. The colors
resulting from the convolution operation are modified by the post convolution color lookup table when
GL_POST_CONVOLUTION_COLOR_TABLE is enabled. These modified colors are then sent to the color matrix
operation. Finally, if GL_POST_COLOR_MATRIX_COLOR_TABLE is enabled, the colors resulting from the
color matrix operation are mapped by the post color matrix color lookup table before being used by
the histogram operation.
NOTES
glColorTable is present only if GL_ARB_imaging is returned when glGetString is called with an argu-ment argument
ment of GL_EXTENSIONS.
If target is set to GL_COLOR_TABLE, GL_POST_CONVOLUTION_COLOR_TABLE, or
GL_POST_COLOR_MATRIX_COLOR_TABLE, then width must be a power of two or a GL_INVALID_VALUE error is
generated.
ERRORS
GL_INVALID_ENUM is generated if target is not one of the allowable values.
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.
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_TABLE_TOO_LARGE is generated if the requested color table is too large to be supported by the
implementation, and target is not a GL_PROXY_* target.
GL_INVALID_OPERATION is generated if glColorTable is executed between the execution of glBegin and
the corresponding execution of glEnd.
ASSOCIATED GETS
glGetColorTableParameter
SEE ALSO
glColorSubTable(3G), glColorTableParameter(3G), glCopyColorTable(3G), glCopyColorSubTable(3G), glGetColorTable(3G)
GLCOLORTABLE(3G)
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