XXX - Not complete.

Name

    SGIX_ycrcba

Name Strings

    GL_SGIX_ycrcba

Version

    Last Modified Date: 01/16/1998
    $Date: 1998/01/16 21:47:41 $ $Revision: 1.2 $

Number

    203

Dependencies

    This extension, combined with the subsample.spec
    (SGIX_subsample) extension obsoletes the current ycrcb.spec
    (SGIX_ycrcb) extension. Support of SGIX_ycrcb should be
    accomplished using the SGIX_subsample and SGIX_ycrcba.

    EXT_texture3D affects the definition of this extension
    EXT_subtexture affects the definition of this extension
    EXT_histogram affects the definition of this extension
    EXT_convolution affects the definition of this extension
    SGI_color_table affects the definition of this extension


Overview

    This extension provides a method for OpenGL to read and store
    images that are defined in standard YCRCB and YCRCBA video color
    spaces.  As with the CYMK extension, conversion to RGBA takes place
    immediately following the unpack pixel store, and preceding the
    pack pixel store operations, and is only available on transfers to
    and from memory.  The algorithms that convert between YCRCB and
    RGBA are "black-box" in nature, and left undefined by the
    extension, however it is recommended that conversion comply with
    the CCIR standard. This extension specifies the format of a pixel
    rectangle independent of component subsampling. Component
    subsampling is specified using a separate extension.

    Two new formats are added, YCRCB_SGIX and YCRCBA_SGIX.

    YCRCB_SGIX is defined as a 3 component format representing the Cb,
    Y, and Cr values per pixel. YCRCBA_SGIX is defined as a 4 component
    format representing Cb, Y, Cr, and A values per pixel.

    As with the CMYK extension, this extension doesn't preclude the
    possibility of other higher quality conversion methods.


New Procedures and Functions

    None

New Tokens

    Accepted by the <format> parameter of DrawPixels, ReadPixels,
    TexImage1D, TexImage2D, TexImage3DEXT, TexImage4DSGIS, TexSubImage1DEXT,
    TexSubImage2DEXT, TexSubImage3DEXT, TexSubImage4DSGIS, GetTexImage,
    ColorTableSGI, GetColorTableSGI, ConvolutionFilter1DEXT,
    ConvolutionFilter2DEXT, ConvolutionFilter3DEXT, GetConvolutionFilterEXT,
    SeparableFilter2DEXT, SeparableFilter3DEXT, GetSeparableFilterEXT,
    GetHistogramEXT, and GetMinmaxEXT:

	YCRCB_SGIX				0x8318
	YCRCBA_SGIX				0x8319

Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)

    None

Additions to Chapter 3 of the 1.0 Specification (Rasterization)

    Two entries are added to table 3.5 (DrawPixels and ReadPixels formats):

									Target
	Name			Type		Elements		Buffer
	----			----		--------		------
	YCRCB_SGIX		Component	Cb chroma value,	Color
						Y luminance value,
						Cr chroma value

	YCRCBA_SGIX		Component	Cb chroma value,	Color
						Y luminance value,
						Cr chroma value,
						A

	Table 3.5: DrawPixels and ReadPixels formats.  The third column
	gives a description of and the number and order of elements in a
	group.

    The new formats YCRCB_SGIX and YCRCBA_SGIX are added to the
    discussion of Conversion to RGB.  If the format is either of these two
    values, then the chroma and luminance values in each group are converted
    to R, G, and B values using an undefined algorithm.

Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations
and the Framebuffer)

    The new formats are added to the discussion of Obtaining Pixels from the
    Framebuffer.

    The new formats are added to the discussion of Index Lookup.

    A new section, "Conversion to YCrCb," is added immediately
    following the section "Conversion to L." Or "Conversion to L" is
    expanded to cover conversion to L, YCrCb, and CMYK


Additions to Chapter 5 of the 1.0 Specification (Special Functions)

    None

Additions to Chapter 6 of the 1.0 Specification (State and State Requests)

    None

Additions to the GLX Specification

    None

GLX Protocol

    None

Errors

    None

New State

    None

New Implementation Dependent State

    None