
5,9 The Rate-Distortion Function
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this "lows" picture can be represented by many fewer samples than would
have been needed for the original picture. The "highs" signal is obtained by
taking either the gradient or the Laplacian of the picture (Sections 6.3.1 and
6.3.2) and consists of essentially the edges in the picture. A two-dimensional
high-frequency picture (also called the "synthetic highs") can be synthesized
from this edge information. This high-frequency information, when combined
with the "lows" picture, gives back essentially the original picture. The "highs"
picture may be efficiently transmitted by contour coding the edge informatio ...