| XXX - Not complete. |
| |
| Name |
| |
| SGIX_mpeg2 |
| |
| Name Strings |
| |
| GL_SGIX_mpeg2 |
| |
| Version |
| |
| $Date: 1997/06/07 01:24:17 $ $Revision: 1.6 $ |
| |
| Number |
| |
| ??? |
| |
| Dependencies |
| |
| SGIX_mpeg1 and SGIX_image_compression are required. |
| |
| Overview |
| |
| This extension provides support for compression and decompression |
| of MPEG2-compressed images. |
| |
| Most of the additions specified by this extension exist to permit |
| the handling of fields of images, which is required by MPEG2 but |
| not by MPEG1. This extension adds the capability to update or |
| read from only the top or bottom fields of a predictor frame. The |
| extension also allows the compression and decompression of fields |
| of an image. |
| |
| Support of this extension does not imply conformance to the MPEG2 |
| standard (ISO 13818), although the following guarantees are made: |
| |
| - During decode, the picture_structure field of the picture |
| coding extension is extracted and interpreted correctly. |
| The treatment of the resulting value is discussed below. |
| |
| - During encode, the picture_structure field of the picture |
| coding extension and the picture_type field of the picture |
| header are set correctly as determined by |
| PACK_MPEG_PICTURE_TYPE_SGIX. |
| |
| Issues |
| |
| * We guarantee that the picture_structure and picture_type |
| fields are interpreted and set correctly. We do this so that |
| we can make guarantees about which predictors will be used |
| and updated. Should we make this less restrictive? |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| Accepted by the <param> parameter of PixelStoref, PixelStorei, |
| GetBooleanv, GetIntegerv, GetFloatv, and GetDoublev: |
| |
| MPEG2_SGIX ???? |
| |
| MPEG_IFIELD_TOP_SGIX ???? |
| MPEG_IFIELD_BOTTOM_SGIX ???? |
| MPEG_PFIELD_TOP_SGIX ???? |
| MPEG_PFIELD_BOTTOM_SGIX ???? |
| MPEG_BFIELD_TOP_SGIX ???? |
| MPEG_BFIELD_BOTTOM_SGIX ???? |
| |
| Accepted by the <target> parameter of MPEGQuantTableubv and |
| GetMPEGQuantTableubv: |
| |
| PACK_MPEG_INTRA_QUANT_CHROMA ???? |
| PACK_MPEG_NON_INTRA_QUANT_CHROMA ???? |
| UNPACK_MPEG_INTRA_QUANT_CHROMA ???? |
| UNPACK_MPEG_NON_INTRA_QUANT_CHROMA ???? |
| |
| Additions to Chapter 2 of the 1.1 Specification (OpenGL Operation) |
| |
| None. |
| |
| Additions to Chapter 3 of the 1.1 Specification (Rasterization) |
| |
| The pixel storage modes are augmented to support MPEG2 compressed |
| images in memory. In Table 3.1, MPEG2_SGIX is added to the valid |
| range of UNPACK_COMPRESSION_TYPE_SGIX. |
| |
| The values PACK_MPEG_INTRA_QUANT_CHROMA, |
| PACK_MPEG_NON_INTRA_QUANT_CHROMA, UNPACK_MPEG_INTRA_QUANT_CHROMA, |
| and UNPACK_MPEG_NON_INTRA_QUANT_CHROMA are added to the list of |
| legal values for the <target> parameter of MPEGQuantTableubv. |
| |
| The following should be added to "Unpacking of Compressed Images" |
| subsection of section 3.6.3 (Rasterization of Pixel |
| Rectangles) following the information added by the MPEG1 |
| extension: MPEG2-compressed images (UNPACK_COMPRESSION_TYPE_SGIX |
| equal to MPEG2_SGIX) are classified as one of six types: I-frame, |
| P-frame, B-frame, I-field, P-field, and B-field. Fields are |
| further classified into top and bottom. The classification is |
| accomplished through extraction and interpretation of the |
| picture_type field of the picture header and the picture_structure |
| field of the picture coding extension. This extraction and |
| interpretation is performed as specified in the MPEG2 spec (ISO |
| 13818). |
| |
| Decompression of MPEG2 images is very similar to the decompression |
| of MPEG1 images described in SGIX_mpeg1, but MPEG2 decompression |
| may make use of two chrominance quantization tables: |
| UNPACK_MPEG_INTRA_QUANT_CHROMA and |
| UNPACK_MPEG_NON_INTRA_QUANT_CHROMA. These tables are set and read |
| back in the same manner and using the same commands as the |
| quantization tables introduced in SGIX_mpeg1. The chrominance |
| quantization tables may be used and changed during the |
| decompression step if UNPACK_SAMPLE_SGIX is SAMPLE_422_SGIX. |
| UNPACK_MPEG_INTRA_QUANT_CHROMA is used and updated only during the |
| decompression of I-frames and I-fields; |
| UNPACK_MPEG_NON_INTRA_QUANT_CHROMA, is used and updated only |
| during the decompression of P- and B-frames and P- and B-fields. |
| |
| Except for the use and update of UNPACK_MPEG_INTRA_QUANT_CHROMA |
| and UNPACK_MPEG_NON_INTRA_QUANT_CHROMA, MPEG2 frame pictures (I, |
| P, and B) are treated as specified in SGIX_mpeg1. MPEG2 field |
| pictures are treated as images whose height is half the height of |
| the corresponding frame. The height value, as computed in |
| image_compression_SGIX, gives the number of scan lines in the |
| field instead of the height of the frame. Fields are treated |
| identically to MPEG1 frames with two exceptions: MPEG2 fields may |
| use and update the chroma quant tables and the MPEG2 field picture |
| predictor update step is performed differently than the MPEG1 |
| predictor update step. In the predictor update step during MPEG2 |
| field decompression, only the top or bottom field of the predictor |
| is replaced. The field to be replaced is determined by the field |
| type of the current image (top fields replace the top fields of |
| the predictor). The other field of the predictor is left |
| unchanged. The predictor height must be twice the height of the |
| current image or the error INVALID_OPERATION is generated and |
| processing terminates without any change to the predictor frame |
| taking place. |
| |
| Additions to Chapter 4 of the 1.1 Specification (Per-Fragment Operations |
| and the Frame Buffer) |
| |
| In Table 4.5, the values MPEG_IFIELD_TOP_SGIX, |
| MPEG_IFIELD_BOTTOM_SGIX, MPEG_PFIELD_TOP_SGIX, |
| MPEG_PFIELD_BOTTOM_SGIX, MPEG_BFIELD_TOP_SGIX, and |
| MPEG_BFIELD_BOTTOM_SGIX are added to the valid range of |
| PACK_MPEG_PICTURE_TYPE_SGIX. |
| |
| The following should be added to the "Packing of Compressed |
| Images" subsection of section 4.3.2 following the information |
| added by the MPEG1 extension: If PACK_COMPRESSION_TYPE_SGIX is |
| equal to MPEG2_SGIX, MPEG2 compression is performed. Compression |
| of MPEG2 images is similar to compression of MPEG1 images. During |
| MPEG2 compression, the value of PACK_MPEG_PICTURE_TYPE_SGIX must |
| be equal to MPEG_IFRAME_SGIX, MPEG_PFRAME_SGIX, MPEG_BFRAME_SGIX, |
| MPEG_IFIELD_TOP_SGIX, MPEG_IFIELD_BOTTOM_SGIX, |
| MPEG_PFIELD_TOP_SGIX, MPEG_PFIELD_BOTTOM_SGIX, |
| MPEG_BFIELD_TOP_SGIX, or MPEG_BFIELD_BOTTOM_SGIX. If the value is |
| not legal, the error INVALID_ENUM is generated and no processing |
| takes place. If the image is a field, the height (as computed in |
| image_compression_SGIX) is interpreted as the number of scan lines |
| in the field, which is half the height of the corresponding frame. |
| |
| The first step of MPEG2 compression is the conversion to YCrCb. |
| If PACK_TO_RGB_SGIX is TRUE, the RGBA input image is converted to |
| a YCrCb image using an unspecified algorithm. If PACK_TO_RGB_SGIX |
| is FALSE, the input image is converted to YCrCb by setting the Y |
| equal to R, Cr equal to G, and Cb equal to B. |
| |
| The update of predictors during MPEG2 compression is identical to |
| the update of predictors during MPEG2 decompression described |
| above (including generation and possible termination of |
| processing), except that the PACK state is used in place of the |
| UNPACK state. |
| |
| During compression, the replacement of the current image by a |
| predictor is determined by the values of |
| PACK_MPEG_PREDICTOR_READ_SGIX and PACK_MPEG_PICTURE_TYPE_SGIX. If |
| PACK_MPEG_PREDICTOR_READ_SGIX is equal to NONE, the current image |
| is passed on unchanged. If PACK_MPEG_PREDICTOR_READ_SGIX is |
| PACK_MPEG_PREDICTOR_FWD_SGIX, the predictor bound to |
| PACK_MPEG_PREDICTOR_FWD_SGIX is used as the source. If |
| PACK_MPEG_PREDICTOR_READ_SGIX is PACK_MPEG_PREDICTOR_BACK_SGIX, |
| the predictor bound to PACK_MPEG_PREDICTOR_BACK_SGIX is used as |
| the source. If PACK_MPEG_PICTURE_TYPE_SGIX is MPEG_IFRAME_SGIX, |
| MPEG_PFIELD_SGIX, or MPEG_BFIELD_SGIX, the entire frame of the |
| source replaces the current image. If PACK_MPEG_PICTURE_TYPE_SGIX |
| is MPEG_IFIELD_TOP_SGIX, MPEG_PFIELD_TOP_SGIX, or |
| MPEG_BFIELD_TOP_SGIX, the top field of the predictor replaces the |
| current image. Every other scan line of the predictor is |
| extracted, beginning with the top scan line of the image. If |
| PACK_MPEG_PICTURE_TYPE_SGIX is MPEG_IFIELD_BOTTOM_SGIX, |
| MPEG_PFIELD_BOTTOM_SGIX, or MPEG_BFIELD_BOTTOM_SGIX, the bottom |
| field of the predictor replaces the current image. Every other |
| scan line of the predictor is extracted, beginning with the second |
| scan line from the top. The image extracted during the replacement |
| step replaces the current image in all subsequent processing. |
| |
| After the replacement step, downsampling of the image occurs in |
| the same manner as during the compression of MPEG1 images. |
| |
| The output of the downsampling step is converted based upon the |
| picture type specified by PACK_MPEG_PICTURE_TYPE_SGIX. In this |
| extension, we specify which quantization tables and predictors are |
| used in the conversion, but do not describe the algorithms used. |
| |
| If the picture type is MPEG_IFRAME_SGIX, MPEG_IFIELD_TOP_SGIX, or |
| MPEG_IFIELD_BOTTOM_SGIX, the quantization table |
| PACK_MPEG_INTRA_QUANT_SGIX is used. The quantization table |
| PACK_MPEG_INTRA_QUANT_CHROMA_SGIX is also used if PACK_SAMPLE_SGIX |
| is SAMPLE_422_SGIX. No predictors are used. |
| |
| If the picture type is MPEG_PFRAME_SGIX, MPEG_PFIELD_TOP_SGIX, or |
| MPEG_PFIELD_BOTTOM_SGIX, the quantization table |
| PACK_MPEG_NON_INTRA_QUANT_SGIX is used. |
| PACK_MPEG_NON_INTRA_QUANT_CHROMA_SGIX is also used if |
| PACK_SAMPLE_SGIX is SAMPLE_422_SGIX. The data is converted using |
| the predictor bound to PACK_MPEG_PREDICTOR_BACK_SGIX. If the |
| image is a frame and its size is not equal to the size of the |
| predictor bound to PACK_MPEG_PREDICTOR_BACK_SGIX, the error |
| INVALID_OPERATION is generated. If the image is a field, its |
| width must be equal to the width of the predictor and its height |
| must be equal to half the height of the predictor or the error |
| INVALID_OPERATION is generated. |
| |
| If the picture type is MPEG_BFRAME_SGIX, MPEG_PFIELD_TOP_SGIX, or |
| MPEG_PFIELD_BOTTOM_SGIX, the quantization table |
| PACK_MPEG_NON_INTRA_QUANT_SGIX is used. |
| PACK_MPEG_NON_INTRA_QUANT_CHROMA_SGIX is also used if |
| PACK_SAMPLE_SGIX is SAMPLE_422_SGIX. The image is converted using |
| the predictors bound to PACK_MPEG_PREDICTOR_BACK_SGIX and |
| PACK_MPEG_PREDICTOR_FORWARD_SGIX. If the image is a frame and its |
| size is not equal to the size of the predictors bound to |
| PACK_MPEG_PREDICTOR_BACK_SGIX and |
| PACK_MPEG_PREDICTOR_FORWARD_SGIX, the error INVALID_OPERATION is |
| generated. If the image is a field, its width must be equal to |
| the width of the predictors and its height must be equal to the |
| half the height of the predictors or the error INVALID_OPERATION |
| is generated. Error checking for this step takes place prior to |
| the predictor replacement step, so if an error is detected the |
| contents of the predictors are left unchanged. |
| |
| Further compression is applied to the image using an unspecified |
| algorithm. The output of MPEG2 decompression is a byte stream |
| containing an MPEG2 picture header followed by picture data. The |
| picture header specifies the field and frame type determined by |
| the setting of PACK_MPEG_PICTURE_TYPE_SGIX. |
| |
| 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) |
| |
| The values PACK_MPEG_INTRA_QUANT_CHROMA, |
| PACK_MPEG_NON_INTRA_QUANT_CHROMA_SGIX, |
| UNPACK_MPEG_INTRA_QUANT_CHROMA_SGIX, and |
| UNPACK_MPEG_NON_INTRA_QUANT_CHROMA_SGIX are added to the list of |
| valid values for the parameter <target> to the routine |
| GetMPEGQuantTableubv. |
| |
| Additions to the GLX Specification |
| |
| None. |
| |
| GLX Protocol |
| |
| XXX |
| |
| Errors |
| |
| INVALID_OPERATION is generated if UNPACK_MPEG_PREDICTOR_STORE_SGIX |
| is set to UNPACK_MPEG_PREDICTOR_BACK_SGIX during the download of |
| an MPEG2 field and the height of the predictor bound to |
| UNPACK_MPEG_PREDICTOR_BACK_SGIX is not equal to twice the height |
| of the field. |
| |
| INVALID_OPERATION is generated if UNPACK_MPEG_PREDICTOR_STORE_SGIX |
| is set to UNPACK_MPEG_PREDICTOR_FWD_SGIX during the download of an |
| MPEG2 field and the height of the predictor bound to |
| UNPACK_MPEG_PREDICTOR_FWD_SGIX is not equal to twice the height of |
| the field. |
| |
| INVALID_OPERATION is generated if a pixel readback operation is |
| applied, PACK_COMPRESSION_TYPE_SGIX is equal to MPEG2_SGIX, and |
| the value of PACK_MPEG_PICTURE_TYPE is not one of the legal |
| values. |
| |
| INVALID_OPERATION is generated if during MPEG2 compression of a |
| frame PACK_MPEG_PREDICTOR_STORE_SGIX is equal to a value other |
| than NONE and the width and height of the current image are not |
| equal to the width and height of the predictor bound to the |
| specified bind point. |
| |
| INVALID_OPERATION is generated if during MPEG2 compression of a |
| field PACK_MPEG_PREDICTOR_STORE_SGIX is equal to a value other |
| than NONE and the width and height of the current image are not |
| equal to the width and height of the predictor bound to the |
| specified bind point. |
| |
| New State |
| |
| Initial |
| Get Value Get Command Type Value Attrib |
| --------- ----------- ---- ------- ------ |
| PACK_MPEG_INTRA_QUANT_CHROMA GetMPEGQuantTableubv 64*Z+ XXX client |
| PACK_MPEG_NON_INTRA_QUANT_CHROMA GetMPEGQuantTableubv 64*Z+ XXX client |
| UNPACK_MPEG_INTRA_QUANT_CHROMA GetMPEGQuantTableubv 64*Z+ XXX client |
| UNPACK_MPEG_NON_INTRA_QUANT_CHROMA GetMPEGQuantTableubv 64*Z+ XXX client |
| |
| New Implementation Dependent State |
| |
| None. |
