Digital Signal Processing Reference
In-Depth Information
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Fig. 7.15.
Quantization of the DCT coefficients
For this reason, the signal/noise ratio had been measured weighted, i.e.
referred to the sensitivity of the eye, even at the beginning of video testing.
It was possible to allow for much more noise in the direction of higher-
frequency image structures than with coarse, low-frequency image compo-
nents. This knowledge is utilized in JPEG and in MPEG. Low-frequency,
coarse image components are coded with finer quantization and fine image
components are coded with coarser quantization in order to save data rate.
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