Apple MA261Z/A User Manual - Page 1039

Bit Depth The number of bits used per sample determines how accurately the sample is stored, and how much intensity variation is possible within the signal. For example, a video signal with a bit depth of only 1 bit can have either a value of 0 or 1, resulting in only black or white pixels. 2 bits per sample results in four possible values: 00, 01, 10, or 11, or any of four shades of gray (or some other color) per sample. XIII Most digital video formats use a minimum of 8 bits per color channel, or 256 gradations of intensity. RGB images are traditionally described by the total bits used per pixel (8 bits per channel x 3 channels = 24 bits). 32-bit RGB images refer to 24-bit color plus 8 more bits for an alpha channel. Images with higher bit depth are becoming more common, using 16 bits per color channel, or 48 bits per RGB pixel. Video signal bit depth is usually described per channel. For example, DV and DVCPRO HD use 8 bits per color component (in other words, 8 bits for Y´, 8 bits for CR, and 8 bits for CB). Other formats, such as D-5, use 10 bits per component. This provides 1024 possible gradations instead of 256, which means much more subtle variations in intensity can be recorded. Some formats, such as Digital Betacam, record internally at 8-bit but can accept and output 10-bit video. Internally, Final Cut Express HD can do pixel calculations using 32-bit floating point precision, which allows for very accurate calculations without rounding errors. This leads to much more accurate color reproduction when applying filters and combining layers of video. This is especially important when you are going to show your movie on film or broadcast-quality video monitors. In Final Cut Express HD, the Video Processing tab in the Sequence Settings window allows you to choose the rendering bit depth for a sequence. For more information, see "Rendering" on page 877. Appendix A Video Formats 1039