Apple Final Cut Pro 5 - Manual (Page 1714)

Appendix A Video Formats 363
V
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.
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 C
R
,
and 8 bits for C
B
). 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 Pro 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 Pro, the Video Processing tab in the
Sequence Settings window allows you to choose the rendering bit depth for a
sequence. For more information, see Volume III, Chapter 24, “Rendering.”