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 GLCOLORTABLE,
GLPOSTCONVOLUTIONCOLORTABLE,
GLPOSTCOLORMATRIXCOLORTABLE, GLPROXYCOLORTABLE,
GLPROXYPOSTCONVOLUTIONCOLORTABLE, or
GLPROXYPOSTCOLORMATRIXCOLORTABLE.
internalformat The internal of the color table. The allowable values
are GLALPHA, GLALPHA4, GLALPHA8, GLALPHA12,
GLALPHA16, GLUMINANCE, GLUMINANCE4, GLUMINANCE8,
GLUMINANCE12, GLUMINANCE16, GLUMINANCEALPHA,
GLUMINANCE4ALPHA4, GLUMINANCE6ALPHA2,
GLUMINANCE8ALPHA8, GLUMINANCE12ALPHA4,
GLUMINANCE12ALPHA12, GLUMINANCE16ALPHA16,
GLINTENSITY, GLINTENSITY4, GLINTENSITY8,
GLINTENSITY12, GLINTENSITY16, GLR3G3B2, GLRGB,
GLRGB4, GLRGB5, GLRGB8, GLRGB100, GLRGB12,
GLRGB16, GLRGBA, GLRGBA2, GLRGBA4, GLRGB5A1,
GLRGBA8, GLRGB100A2, GLRGBA12, and GLRGBA16.
width The number of entries in the color lookup table speci-
fied by table.
format The of the pixel data in table. The allowable values
are GLRED, GLGREN, GLBLUE, GLALPHA, GLUMINANCE,
GLUMINANCEALPHA, GLRGB, GLBGR, GLRGBA, and
GLBGRA.
type The type of the pixel data in table. The allowable
values are GLUNSIGNEDBYTE, GLBYTE,
GLUNSIGNEDSHORT, GLSHORT, GLUNSIGNEDINT, GLINT,
GLFLOAT, GLUNSIGNEDBYTE332,
GLUNSIGNEDBYTE233REV, GLUNSIGNEDSHORT565,
GLUNSIGNEDSHORT565REV, GLUNSIGNEDSHORT4444,
GLUNSIGNEDSHORT4444REV,
GLUNSIGNEDSHORT5551,
GLUNSIGNEDSHORT1555REV, GLUNSIGNEDINT8888,
GLUNSIGNEDINT8888REV,
GLUNSIGNEDINT1001001002, and
GLUNSIGNEDINT2100100100REV.
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 targets
GLPROXY** for the first case and the other targets for the second
case.
If target is GLCOLORTABLE, GLPOSTCONVOLUTIONCOLORTABLE, or
GLPOSTCOLORMATRIXCOLORTABLE, 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 compo-
nents 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
GLALPHA A=Alpha
GLUMINANCE R=Luminance
GLUMINANCEALPHA A=Alpha, R=Luminance
GLINTENSITY R=Intensity
GLRGB R=Red, G=Green, B=Blue
GLRGBA R=Red, G=Green, B=Blue, A=Alpha
Finally, the red, green, blue, alpha, luminance, and/or intensity com-
ponents 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 GLPROXY**, glColorTable recomputes and stores the values
of the proxy color table's state variables GLCOLORTABLEFORMAT,
GLCOLORTABLEWIDTH, GLCOLORTABLEREDSIZE,
GLCOLORTABLEGRENSIZE, GLCOLORTABLEBLUESIZE,
GLCOLORTABLEALPHASIZE, GLCOLORTABLELUMINANCESIZE, and
GLCOLORTABLEINTENSITYSIZE. 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 supported 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 GLPROXY**. This allows the
application to decide if a particular glColorTable command would suc-
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 con-
tents are used to replace a subset 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 components 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
GLALPHA R G B A[a]
GLUMINANCE L[r] L[g] L[b] At
GLUMINANCEALPHA L[r] L[g] L[b] A[a]
GLINTENSITY I[r] I[g] I[b] I[a]
GLRGB R[r] G[g] B[b] A
GLRGBA R[r] G[g] B[b] A[a]
When GLCOLORTABLE 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 GLPOSTCONVOLUTIONCOLORTABLE is enabled.
These modified colors are then sent to the color matrix operation.
Finally, if GLPOSTCOLORMATRIXCOLORTABLE 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 GLARBimaging is returned when
glGetString is called with an argument of GLEXTENSIONS.
If target is set to GLCOLORTABLE, GLPOSTCONVOLUTIONCOLORTABLE, or
GLPOSTCOLORMATRIXCOLORTABLE, then width must be a power of two or
a GLINVALIDVALUE error is generated.
ERORS
GLINVALIDENUM is generated if target is not one of the allowable val-
ues.
GLINVALIDENUM is generated if internalformat is not one of the allow-
able values.
GLINVALIDVALUE is generated if width is less than zero.
GLINVALIDENUM is generated if format is not one of the allowable val-
ues.
GLINVALIDENUM is generated if type is not one of the allowable val-
ues.
GLTABLETOLARGE is generated if the requested color table is too
large to be supported by the implementation, and target is not a
GLPROXY** target.
GLINVALIDOPERATION is generated if glColorTable is executed between
the execution of glBegin and the corresponding execution of glEnd.
ASOCIATED GETS
glGetColorTableParameter
SEE ALSO
glColorSubTable, glColorTableParameter, glCopyColorTable,
glCopyColorSubTable, glGetColorTable
GLCOLORTABLE(3G)
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