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U. Glaeser

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FIGURE 42.29 150th Frame of original: (a) “Suzie” sequence and its compressed version at 64 kbit/s using, (b) H.261,<br />

(c) baseline H.263, and (d) Full-option H.263.<br />

FIGURE 42.30 PSNR values for Suzie sequence compressed at 64 kbit/s (a) baseline H.263 (b) Full-option H.263<br />

(c) H.261.<br />

Objectively, the video quality is measured by using some mathematical criteria, the most common of<br />

which is the peak-to-peak signal-to-noise ratio (PSNR) defined in Eq. (42.2).<br />

© 2002 by CRC Press LLC<br />

PSNR 10 log10 1<br />

---------------<br />

M × N ( x( i, j)<br />

– xˆ ( i, j)<br />

) 2<br />

---------------------------------------------------------------------------------<br />

=<br />

M−1 N−1<br />

∑ ∑ i=0 j=0<br />

(42.2)<br />

For a fair comparison of perceptual quality between two video coding algorithms, the objective and<br />

subjective results must be evaluated at the same target bit rates. Because the bit rate in kbit/s is directly<br />

proportional to the number of frames coded per unit of time, the frame rate (f/s) has also to be mentioned<br />

in the evaluation process.<br />

Figures 42.29 and 42.30 show the subjective and objective results, respectively, for coding 150 frames<br />

of the sequence “Suzie” at a bit rate of 64 kbit/s and a frame rate of 25 f/s.<br />

255 2

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