Enhancing support with color conversion and arbitrary stretching hardware

Extended implementations of DCI provide access to display surfaces that support special hardware features. For example, some DCI clients, such as digital video codecs, may use DCI to access offscreen or overlay surfaces that support YUV color formats. The YUV color data is merged with the RGB data through the display subsystem so that both color types coexist on the same Windows screen.

In Video for Windows 1.1, compression and decompression drivers can define custom compression and bitmap formats by assigning a four-character code, known as FOURCC. The compression format four-character code must be unique. The Appendix section of this specification lists some of the registered DIB compression types. To get a complete list of all registered types or to register new ones, refer to New Multimedia Data Types Documents and the Microsoft Multimedia Registration Kit. Contact the Microsoft Developer Services fax back server line at (800) 426-9400, select option 2, option 1, and then follow instructions to retrieve the document # 950 or CompuServe® WINMM forum, document MRDK.ZIP.

For digital video, codecs must be enhanced so that they decompress to the YUV color format provided by the DCI Provider for a given surface. For example, if a specific device allows creation of an offscreen surface that has YUV 4:1:1, then a codec that decompresses to YUV 4:1:1 could offload all color conversion to the display hardware.

DCI also provides access to offscreen surfaces that support hardware stretching. This capability is provided in DCI in addition to the capabilities provided by GDI because of the additional color formats supported by DCI. These surfaces allow access to display hardware that may provide integer or arbitrary stretching of image data regardless of the color format of the image data.