X4

MPEG glossary 393
http://pro.magix.com
Bits, not bytes are used, since the data word width has to address the
transmission restrictions.
The file size can be calculated from the average bit rate, if its length is known:
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.