Apple Final Cut Pro 7 - Manual (Page 1906)

Description Sample ratio
Full sample rate for each color channel, plus a fourth alpha channel
at the full sample rate. 4:4:4:4
The color channels are subsampled so that the color resolution is
halved. For example, the first pixel in a line contains Y
′
, C
B
, and C
R
samples. The next pixel contains only a Y
′
sample. This pattern
repeats. Most professional video formats use 4:2:2 color subsampling.
4:2:2
4:2:2 sample rate for each color channel, plus an alpha channel at
the full sample rate. 4:2:2:4
The color is subsampled so that the color resolution is quartered.
The first pixel in a line contains Y
′
, C
B
, and C
R
samples. The next
three pixels only contain Y
′
samples. This pattern repeats.
4:1:1
This ratio indicates that the C
B
and C
R
channels are subsampled
both horizontally (as in 4:2:2) and vertically. This reduces color
resolution in both the horizontal and vertical dimensions compared
to 4:2:2, which only reduces horizontal chroma resolution.
There are several methods for locating C
B
and C
R
samples relative
to Y
′
samples, yielding several different 4:2:0 formats.
4:2:0
The following table shows a list of color sample ratios used in various digital video formats.
Video formats Sample ratio
HDCAM SR
Most RGB computer graphics files (implicit)
4:4:4
Digital Betacam, D-1, D-5, DVCPRO HD, DVCPRO 50, and HDCAM
SR 4:2:2
HDCAM 3:1:1
NTSC DV, NTSC DVCAM, and DVCPRO 4:1:1
PAL DV, PAL DVCAM, DVD, and HDV 4:2:0
Bit Depth
The number of bits used per sample determines how accurately the sample is stored, as
well as how much intensity variation is possible within the signal. For example, a video
signal with a bit depth of only 1 bit can have a value of either 0 or 1, resulting in only
black or white pixels. Two 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 usually have 24-bit color plus 8
more bits for an alpha channel.
Note: Still images using 16 bits per color channel, or 48 bits per RGB pixel, are becoming
more common. However, most video formats use 8 or 10 bits per color channel.
1906 Appendix B Video Formats