In this mode codecs tried to show best quality in
single-pass mode. Therefore major importance in this section is paid to graphs
of quality of compressed sequences in different metrics. All H.264 codecs used
main profile of encoding standard.
Below are some Y-PSNR/Bitrate and Delta Y-PSNR/Bitrate
graphs.
PSNR (peak-to-peak signal-to-noise ratio) is a classic
metric for video quality measurement. For two pictures xi,j and yi,j
metric's value is defined by the following formula:
Despite this metric does not generally reflect human
perception of pictures' distortion, during last decades it is commonly used as
main criterion for video codecs' performance evaluation.
Delta Y-PSNR (or Relative Y-PSNR) are comparative PSNR
graphs, where x264 codec was chosen as reference. For every measurement of each
codec the difference between this measurement and PSNR value of reference codec
with the same bitrate is plotted on these graphs. If corresponding reference
value is absent then it is linearly interpolated.
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Picture 1.
Y-PSNR. Sequence "foreman"
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Picture 2.
Delta Y-PSNR. Sequence "foreman"
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Picture 3.
Y-PSNR. Sequence "susi"
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Picture 4.
Delta Y-PSNR. Sequence "susi"
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Picture 5.
Y-PSNR. Sequence "bbc"
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Picture 6.
Delta Y-PSNR. Sequence "bbc"
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Picture 7.
Y-PSNR. Sequence "battle"
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Picture 8.
Delta Y-PSNR. Sequence "battle"
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Picture 9.
Y-PSNR. Sequence "simpsons"
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Picture 10.
Delta Y-PSNR. Sequence "simpsons"
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Picture 11.
Y-PSNR. Sequence "matrix"
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Picture 12.
Delta Y-PSNR. Sequence "matrix"
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Picture 13.
Y-PSNR. Sequence "concert"
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Picture 14.
Delta Y-PSNR. Sequence "concert"
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Conclusions:
Besides luminance component (Y-plane) sometimes it is
interesting to look at codecs' behavior on color components (U and V planes).
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Picture 15.
U-PSNR. Preset "Best quality". Sequence "foreman"
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Picture 16.
U-PSNR. Preset "Best quality". Sequence "susi"
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Picture 17.
U-PSNR. Preset "Best quality". Sequence "bbc"
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Picture 18.
V-PSNR. Preset "Best quality". Sequence "concert"
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Conclusions:
Several metrics recently appeared which aspire to be
better approximations of human perception. The most popular among them are SSIM
and VQM.
We have used them in our comparison, but they have
presented no big differences from PSNR metric.
Below are some graphs of these metrics for different
sequences.
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Picture 19.
Y-SSIM measure. Preset "Best quality". Sequence "foreman"
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Picture 20.
Y-VQM measure. Preset "Best quality". Sequence "foreman"
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Picture 21.
Y-SSIM measure. Preset "Best quality". Sequence "bbc"
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Picture 22.
Y-VQM measure. Preset "Best quality". Sequence "concert"
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During some time our laboratory is developing metrics,
which allow measuring blocking and blurring of frames in video sequences. Work
on these metrics is in progress, therefore we show only several graphs with
them.
Red horizontal line is a blocking measure (or blurring
measure) of source sequence. For blurring measure: the more is its value, the
lesser is the blurring of frame; for blocking measure: the more is its value,
the bigger is blocking of frame.
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Picture 23.
Y-Blurring measure. Preset "Best quality". Sequence
"foreman"
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Picture 24.
Y-Blocking measure. Preset "Best quality". Sequence
"foreman"
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Graph type
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Total number of graph
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Inserted in this document
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Average metric
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196
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24 (12%)
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Consider graphs showing how accurately every codec kept
requested bit rate. Grades on x-axis show target bitrates (point 0 is 100 kbps,
point 9 - 2340 kbps). Grades on y-axis show how many times codec exceeded
declared bit rate (real bit rate to requested bit rate ratio).
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Picture 25.
Bitrate handling. Preset "Best quality". Sequence "foreman"
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Picture 26.
Bitrate handling. Preset "Best quality". Sequence "susi"
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Picture 27.
Bitrate handling. Preset "Best quality". Sequence "bbc"
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Picture 28.
Bitrate handling. Preset "Best quality". Sequence "battle"
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Picture 29.
Bitrate handling. Preset "Best quality". Sequence "simpsons"
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Picture 30.
Bitrate handling. Preset "Best quality". Sequence "matrix"
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Picture 31.
Bitrate handling. Preset "Best quality". Sequence "concert"
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Conclusions:
Now let's consider graphs showing encoding time for each
sequence using "Best Quality" preset and average normalized time for this
preset.
Average normalized time is obtained as follows. At first,
for every sequence codec with largest compression time is found. Compression
times of other codecs were divided by compression time of this codec. After
this step every codec has value from 0 to 1 for each video sequence.
On the second step every codec gets evaluation calculated
as arithmetic average of obtained values for all sequences. And these
evaluations are shown on average normalized time graph.
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Picture 32.
Encoding time. Preset "Best quality". Sequence "foreman"
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Picture 33.
Encoding time. Preset "Best quality". Sequence "susi"
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Picture 34.
Encoding time. Preset "Best quality". Sequence "bbc"
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Picture 35.
Encoding time. Preset "Best quality". Sequence "battle"
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Picture 36.
Encoding time. Preset "Best quality". Sequence "simpsons"
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Picture 37.
Encoding time. Preset "Best quality". Sequence "matrix"
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Picture 38.
Encoding time. Preset "Best quality". Sequence "concert"
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Picture 39.
Normalized average encoding time. Preset "Best quality"
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Conclusions: