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GLHISTOGRAM(3G)			 OpenGL Manual		       GLHISTOGRAM(3G)

NAME
       glHistogram - define histogram table

C SPECIFICATION
       void glHistogram(GLenum target, GLsizei width, GLenum internalformat,
			GLboolean sink);

PARAMETERS
       target
	   The histogram whose parameters are to be set. Must be one of
	   GL_HISTOGRAM or GL_PROXY_HISTOGRAM.

       width
	   The number of entries in the histogram table. Must be a power of 2.

       internalformat
	   The format of entries in the histogram table. Must be one of
	   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_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.

       sink
	   If GL_TRUE, pixels will be consumed by the histogramming process
	   and no drawing or texture loading will take place. If GL_FALSE,
	   pixels will proceed to the minmax process after histogramming.

DESCRIPTION
       When GL_HISTOGRAM is enabled, RGBA color components are converted to
       histogram table indices by clamping to the range [0,1], multiplying by
       the width of the histogram table, and rounding to the nearest integer.
       The table entries selected by the RGBA indices are then incremented.
       (If the internal format of the histogram table includes luminance, then
       the index derived from the R color component determines the luminance
       table entry to be incremented.) If a histogram table entry is
       incremented beyond its maximum value, then its value becomes undefined.
       (This is not an error.)

       Histogramming is performed only for RGBA pixels (though these may be
       specified originally as color indices and converted to RGBA by index
       table lookup). Histogramming is enabled with glEnable() and disabled
       with glDisable().

       When target is GL_HISTOGRAM, glHistogram redefines the current
       histogram table to have width entries of the format specified by
       internalformat. The entries are indexed 0 through width - 1, and all
       entries are initialized to zero. The values in the previous histogram
       table, if any, are lost. If sink is GL_TRUE, then pixels are discarded
       after histogramming; no further processing of the pixels takes place,
       and no drawing, texture loading, or pixel readback will result.

       When target is GL_PROXY_HISTOGRAM, glHistogram computes all state
       information as if the histogram table were to be redefined, but does
       not actually define the new table. If the requested histogram table is
       too large to be supported, then the state information will be set to
       zero. This provides a way to determine if a histogram table with the
       given parameters can be supported.

NOTES
       glHistogram 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 one of the allowable
       values.

       GL_INVALID_VALUE is generated if width is less than zero or is not a
       power of 2.

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

       GL_TABLE_TOO_LARGE is generated if target is GL_HISTOGRAM and the
       histogram table specified is too large for the implementation.

       GL_INVALID_OPERATION is generated if glHistogram is executed between
       the execution of glBegin() and the corresponding execution of glEnd().

ASSOCIATED GETS
       glGetHistogramParameter()

SEE ALSO
       glGetHistogram(), glResetHistogram()

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/.

AUTHORS
       opengl.org

opengl.org			  04/29/2014		       GLHISTOGRAM(3G)

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