H.261 Datasheet, PDF (7/31 Pages) List of Unclassifed Manufacturers – LINE TRANSMISSION OF NON-TELEPHONE SIGNALS

T 150 818 0-92 /d0 2
Lum inan ce sa mp le
Ch ro min ance sam ple
Block ed ge
FIGURE 2/H.261
Positioning of luminance and chrominance samples
FIGURE 2/H.261...[D02] = 10 CM
The criteria for choice of mode and transmitting a block are not subject to recommendation and may be varied dynamically as
part of the coding control strategy. Transmitted blocks are transformed and resulting coefficients are quantized and variable
length coded.
3.2.1 Prediction
The prediction is inter-picture and may be augmented by motion compensation (see 3.2.2) and a spatial filter (see 3.2.3).
3.2.2 Motion compensation
Motion compensation (MC) is optional in the encoder. The decoder will accept one vector per macroblock. Both horizontal
and vertical components of these motion vectors have integer values not exceeding ± 15. The vector is used for all four
luminance blocks in the macroblock. The motion vector for both colour difference blocks is derived by halving the
component values of the macroblock vector and truncating the magnitude parts towards zero to yield integer components.
A positive value of the horizontal or vertical component of the motion vector signifies that the prediction is formed from pels
in the previous picture which are spatially to the right or below the pels being predicted.
Motion vectors are restricted such that all pels referenced by them are within the coded picture area.
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Recommendation H.261 (03/93)