User manual

MPEG glossary 129
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F = (BRV + BRA) * t
F=File size BRV=
Video bit rate
BRA=
Audio bit rate
t=Length in s
Block
For almost all image file editing techniques the image is subdivided
into 8 x 8 pixel blocks (image points). This should be noted if you
would like to used user-defined image resolutions (width/height), and
they should always be a multiple of 8.
Chroma format
The color value of each image point consists of the color values for
the primary colors red, green, and blue (RGB), and for traditional and
technical reasons it is transformed into one brightness value (Y =
0.299*R = 0.587*G + 0.114*B) and two color difference values (U = R
- Y, V = G -Y).
The Y value alone produces the black and white picture. These signal
components allow brightness and color information to be handled
separately. The first data reduction occurs when single rows
comprising a picture are read. Because the human eye has a lower
color resolution than a brightness resolution, the color components
are recorded only for every other point of a row (4:2:2) for each four
pixels grouped (4:1:0), i.e. color signal under-reading.
4:2:2 This corresponds to the established TV standard. One piece of
color information is transmitted per row for two pixels which
corresponds to a 2/3 compression of the output data.
4:1:0 This is the color coding used for DVDs and most other
consumer video applications. For each 4 pixels grouped together on
two rows, one unit of color information is saved. This corresponds to
a output data compression of 1/2.
Field
A half-image, i.e. two halves which combine to produce a frame (see
de-interlacing (view page 131)).