| XXX - Not complete. |
| |
| Name |
| |
| SGIX_subsample |
| |
| Name Strings |
| |
| GL_SGIX_subsample |
| |
| Version |
| |
| Last Modified Date: 07/27/1999 |
| Author Revision: $Header: //depot/main/doc/registry/extensions/SGI/subsample.spec#10 $ |
| |
| Number |
| |
| 202 |
| |
| Dependencies |
| |
| Full support of SGI_ycrcb can be accomplished by using |
| SGIX_subsample and GL_COLOR_MATRIX. In addition, some |
| applications may also choose to invoke GL_CONVOLUTION |
| and GL_COLOR_TABLE to better improve the quality of both |
| the resampling and color conversion. Note however, that |
| this extension, combined with the ycrcbformat.spec |
| (SGIX_ycrcba) extension obsoletes the current ycrcb.spec |
| (SGIX_ycrcb) extension. |
| |
| 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 |
| SGI_resample affects the definition of this extension |
| SGI_subsample_4224 affects the definition of this extension |
| |
| Overview |
| |
| Many video image formats and compression techniques utilize |
| various component subsamplings, so it is necessary to provide a |
| mechanism to specify the up- and down-sampling of components as |
| pixel data is drawn from and read back to the client. Though |
| subsampled components are normally associated with the video |
| color space, YCrCb, use of subsampling in OpenGL does not imply |
| a specific color space. |
| |
| This extension defines new pixel storage modes that are used in |
| the conversion of image data to and from component subsampled |
| formats on the client side. The extension defines a new pixel |
| storage mode to specify these sampling patterns, there are |
| three legal values (PIXEL_SUBSAMPLE_4444_SGIX, |
| PIXEL_SUBSAMPLE_4242_SGIX, and |
| PIXEL_SUBSAMPLE_2424_SGIX). |
| |
| When pixel data is received from the client and an unpacking |
| upsampling mode other than PIXEL_SUBSAMPLE_4444_SGIX is |
| specified, the upsampling is performed via replication, |
| unless otherwise specified by RESAMPLE_SGIX. |
| |
| Similarly, when pixel data is read back to the client and a |
| packing downsampling mode other than |
| PIXEL_SUBSAMPLE_4444_SGIX is specified, downsampling is |
| performed via simple component decimation (point sampling), |
| unless otherwise specified by RESAMPLE_SGIX. |
| |
| Issues |
| * If we revive the ycrcbformat.spec then support for the old |
| (SGIX_ycrcb) extension can be accomplished using the the |
| SGIX_subsample and SGIX_ycrcba. |
| |
| * the enums with names like PIXEL_SUBSAMPLE_4242_SGIX and |
| PIXEL_SUBSAMPLE_2424_SGIX gives an impression that there |
| are 4 components in the subsampling. Can there be an |
| alternative name? |
| (Angela suggests: PIXEL_SUBSAMPLE_422_CbYCrY_SGIX and |
| PIXEL_SUBSAMPLE_422_YCbYCr_SGIX. This is clear, but involves |
| naming the components YCrCb. However, the term 4:2:2 basically |
| refers to the subcarrier frequency for the YCrCb transmission |
| in video signals, so 4:2:2 in a way already implies 4:2:2) |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| Accepted by the <pname> parameter of PixelStoref, PixelStorei, |
| GetBooleanv, GetIntegerv, GetFloatv and GetDoublev: |
| |
| PACK_SUBSAMPLE_RATE_SGIX 0x85A0 |
| UNPACK_SUBSAMPLE_RATE_SGIX 0x85A1 |
| |
| Accepted by the <param> parameter of PixelStoref and |
| PixelStorei when the <pname> parameter is PACK_SUBSAMPLE_RATE_SGIX or |
| UNPACK_SUBSAMPLE_RATE_SGIX: |
| |
| PIXEL_SUBSAMPLE_4444_SGIX 0x85A2 |
| PIXEL_SUBSAMPLE_2424_SGIX 0x85A3 |
| PIXEL_SUBSAMPLE_4242_SGIX 0x85A4 |
| |
| Additions to Chapter 2 of the 1.1 Specification (OpenGL Operation) |
| |
| None. |
| |
| Additions to Chapter 3 of the 1.1 Specification (Rasterization) |
| |
| 3.6.1 Pixel Storage Modes |
| |
| The following is added to Table 3.1: |
| |
| Parameter Name Type Initial Value Valid Range |
| -------------- ---- ------------- ----------- |
| UNPACK_SUBSAMPLE_RATE_SGIX integer PIXEL_SUBSAMPLE_4444_SGIX PIXEL_SUBSAMPLE_4444_SGIX |
| PIXEL_SUBSAMPLE_4242_SGIX |
| PIXEL_SUBSAMPLE_2424_SGIX |
| |
| PACK_SUBSAMPLE_RATE_SGIX integer PIXEL_SUBSAMPLE_4444_SGIX PIXEL_SUBSAMPLE_4444_SGIX |
| PIXEL_SUBSAMPLE_4242_SGIX |
| PIXEL_SUBSAMPLE_2424_SGIX |
| |
| |
| 3.6.3 Rasterization of Pixel Rectangles |
| |
| <at the end of the paragraph before the Unpacking section> |
| |
| If the PixelStore parameter UNPACK_SUBSAMPLE_RATE_SGIX is set to |
| PIXEL_SUBSAMPLE_4242_SGIX or PIXEL_SUBSAMPLE_2424_SGIX, then the |
| <format> needs to be set to a corresponding 3- or 4- component |
| pixel format or the error INVALID_OPERATION occurs. If a |
| 4-component pixel format is used, the alpha is assumed to be |
| of constant value 1.0) |
| |
| If the PixelStore parameter UNPACK_SUBSAMPLE_RATE_SGIX is set to |
| PIXEL_SUBSAMPLE_4242_SGIX or PIXEL_SUBSAMPLE_2424_SGIX, then the |
| <width> needs to be set to a multiple of 2 pixels or the error |
| INVALID_OPERATION occurs. |
| |
| <following "to form groups." at the end of the first paragraph |
| in the Unpacking section> |
| |
| If the PixelStore parameter UNPACK_SUBSAMPLE_RATE_SGIX is set to |
| something other than PIXEL_SUBSAMPLE_4444_SGIX then these elements |
| are grouped into sets of one, two, three or four values, |
| depending on the value of UNPACK_SUBSAMPLE_RATE_SGIX, to form |
| groups. |
| |
| <at the and of the paragraph> |
| |
| Table 3.5.1 summarizes the layout of groups obtained from |
| memory depending on the value of UNPACK_SUBSAMPLE_RATE_SGIX. |
| |
| Table 3.5.1: |
| |
| Value of Number of Number of Order of |
| UNPACK_SUBSAMPLE Components Values/Group components |
| _RATE_SGIX in a seq of |
| groups in memory |
| -------------------- ---------- ------- ---------- |
| PIXEL_SUBSAMPLE_4444_SGIX n n |
| PIXEL_SUBSAMPLE_4242_SGIX 3 CbYCr(rgb) 2 YCb,YCr,YCb,YCr |
| PIXEL_SUBSAMPLE_2424_SGIX 3 CbYCr(rgb) 2 CbY,CrY,CbY,CrY |
| |
| note: Cb, Y, and Cr are used to illustrate the in-memory |
| packing of pixels in the YCrCb color space. Normally, 2,3, and |
| 4 component groups are labeled LA, RGB, RGBA. |
| |
| <A new section is inserted before "Conversion to RGB"> |
| |
| Conversion to UNIFORM Sampling |
| ------------------------------ |
| |
| This step is applied only if the PixelStore parameter |
| UNPACK_SUBSAMPLE_RATE_SGIX is set to something other than |
| PIXEL_SUBSAMPLE_4444_SGIX. If UNPACK_SUBSAMPLE_RATE_SGIX |
| is set to PIXEL_SUBSAMPLE_4242_SGIX or |
| PIXEL_SUBSAMPLE_2424_SGIX then the number |
| of components per pixel is increased from two to three. |
| After upsampling, the data is treated as though it were RGB. |
| |
| 2424: |
| |
| < R0,G0> < B1,G1> < R2,G2> < B3, G3> |
| <Cb0,Y0> <Cr0,Y1> <Cb2,Y2> <Cr2, Y3> |
| | | | | | | | | |
| | | o-----o---+--o | | o-----o---+--o |
| | | | | | | | | | | |
| o--+--+-----o | | o---+--+-----o | | |
| | | | | | | | | | | | | |
| V V V V V V V V V V V V |
| <Cb0,Y0,Cr0> <Cb0,Y1,Cr0> <Cb2,Y2,Cr2> <Cb2,Y3,Cr2> |
| < R0,G0,B1 > < R0,G1,B1 > < R2,G2,B3 > < R2,G3,B3 > |
| |
| |
| 4242: |
| < G0,R0> <G1,B1 > <G2,R2 > < G3,B3 > |
| <Y0,Cb0> <Y1,Cr0> <Y2,Cb2> <Y3,Cr2> |
| | | | | | | | | |
| \ / \_____ __\__/ \ \ / \_____ __\__/ \ |
| X ___X \ | X ___X \ | |
| / \ / \ \ | / \ / \ \ | |
| | | | | | | | | | | | | |
| V V V V V V V V V V V V |
| <Cb0,Y0,Cr0> <Cb0,Y1,Cr0> <Cb2,Y2,Cr2> <Cb2,Y3,Cr2> |
| < R0,G0,B1 > < R0,G1,B1 > < R2,G2,B3 > < R2,G3,B3 > |
| |
| Additions to Chapter 4 of the 1.1 Specification (Per-Fragment |
| Operations and the Frame Buffer) |
| |
| 4.3.2 Reading Pixels |
| |
| The following is added to Table 4.5: |
| |
| Parameter Name Type Initial Value Valid Range |
| -------------- ---- ------------- ----------- |
| PACK_SUBSAMPLE_RATE_SGIX integer PIXEL_SUBSAMPLE_4444_SGIX PIXEL_SUBSAMPLE_4444_SGIX |
| PIXEL_SUBSAMPLE_4242_SGIX |
| PIXEL_SUBSAMPLE_2424_SGIX |
| |
| <A new section is inserted before "Final Conversion"> |
| |
| Conversion to Subsampled Form |
| ------------------------------ |
| |
| This step is applied only if the PixelStore parameter |
| PACK_SUBSAMPLE_RATE_SGIX is set to something other than |
| PIXEL_SUBSAMPLE_4444_SGIX. If this step is carried out its |
| operation is controlled by the values of PACK_SUBSAMPE_RATE_SGIX. |
| |
| If a filter operation is specified by RESAMPLE_SGIX, the |
| resampling filter is applied prior to the subsampling step. |
| |
| The pack mode involves dropping chroma samples. For users who |
| like to perform arbitrary filtering other than those specifiable |
| using RESAMPLE_SGIX, it could also be done prior to packing with |
| user calls to convolution function. |
| |
| If PACK_SUBSAMPLE_RATE_SGIX is set to PIXEL_SUBSAMPLE_4242_SGIX or |
| PIXEL_SUBSAMPLE_2424_SGIX then the resulting pixels has an average |
| of 2 component values per pixel. Each pixel pair are constructed |
| as follows: |
| The first destination pixel of a pair is made up of the |
| first and second component of the first source pixel. |
| The second destination pixel of a pair is made up of the |
| third component of the first source pixel, and the second |
| component of the second source pixel. |
| |
| 2424: |
| |
| <R0,G0,B0,A0> <R1,G1,B1,A1> <R2,G2,B2,A2> <R3,G3,B3,A3> |
| | | | | | | | | | | | | | | | | |
| | | | * * | * * | | | * * | * * |
| | | | | | | | | |
| V V V V V V V V |
| <R0,G0><B0 G1> <R2,G2><B2, G3> |
| <--- pixel pair ----> <--- pixel pair ----> |
| |
| 4242: |
| |
| <R0,G0,B0,A0> <R1,G1,B1,A1> <R2,G2,B2,A2> <R3,G3,B3,A3> |
| | | | * * | * * | | | * * | * * |
| \ / |____ ____| \ / |____ ____| |
| X ____X____ X ____X____ |
| / \ | | | | | | |
| V V V V V V V V |
| <G0,R0><G1 B0> <G2,R2><G3, B2> |
| <--- pixel pair ----> <--- pixel pair ----> |
| |
| <toward the end of the paragraph "Placement in Client Memory"> |
| |
| If the PixelStore parameter PACK_SUBSAMPLE_RATE_SGIX is set to |
| PIXEL_SUBSAMPLE_RATE_4242_SGIX or PIXEL_SUBSAMPLE_RATE_2424_SGIX |
| then only the corresponding two elements are written. That is, |
| only the first two components of each group are written to memory. |
| |
| Additions to Chapter 5 of the 1.1 Specification (Special Functions) |
| |
| None. |
| |
| Additions to Chapter 6 of the 1.1 Specification (State and State Requests) |
| |
| XXX |
| |
| Additions to the GLX Specification |
| |
| |
| Errors |
| |
| XXX |
| |
| |
| New State |
| |
| Get Value Get Command Type Initial Value Attribute |
| --------- ----------- ---- ------------- --------- |
| UNPACK_SUBSAMPLE_RATE_SGIX GetIntegerv Z4 PIXEL_SUBSAMPLE_4444_SGIX client |
| PACK_SUBSAMPLE_RATE_SGIX GetIntegerv Z4 PIXEL_SUBSAMPLE_4444_SGIX client |
| |
| New Implementation Dependent State |
| |
| None. |
