Information Technology Reference
In-Depth Information
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Bit-rate (bits/s)
H.264/AVC Intra
Bit-rate (bits/s)
Motion JPEG 2000
H.264/AVC Intra
Motion JPEG 2000 Field
Motion JPEG 2000 Frame
720p50, 2
nd
encoding-decoding cycle
1080i25, 2
nd
encoding-decoding cycle
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45000000
65000000
85000000
105000000
25000000
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65000000
85000000
105000000
Bit-rate (bits/s)
H.264/AVC Intra
Bit-rate (bits/s)
Motion JPEG 2000
H.264/AVC Intra
Motion JPEG 2000 Field
Motion JPEG 2000 Frame
720p50, 4
th
encoding-decoding cycle
1080i25, 4
nd
encoding-decoding cycle
Fig. 9
Recompression loss for CrowdRun sequence
These results show that using H.264/AVC Intra, significant quality loss is in-
curred during successive encoding-decoding cycles, while the quality obtained us-
ing Motion JPEG 2000 stays more or less constant. This is likely the result of
H.264/AVCs macroblock-based coding using multi-hypothesis intra-prediction,
adaptive transform selection and adaptive frame/field coding (interlaced material).
The mode decision process, which operates based on actual distortion measure-
ments, will likely make different decisions concerning the intra-prediction mode,
transform or frame/field coding of the current macroblock since the reference used
in the distortion measurement, i.e. the input frame, is a lower quality version of the
corresponding input frame in the first encoding cycle. When the same coefficient
is quantized twice with the same quantization step-size, no additional distortion is
introduced the second time. However, when different coding options are taken for
a macroblock, compared to those used in the previous encoding-decoding cycle,
entirely different transform coefficients result, and additional noise is introduced
in the quantization stage. Additionally, errors introduced in one macroblock
propagate to neighbouring macroblocks through the intra-prediction process, con-
tributing to the overall quality degradation.
The marginal loss incurred during recompression with Motion JPEG 2000 is
largely due to rounding errors resulting from the irreversible CDF 9/7 wavelet
transform. The quantization of the wavelet coefficients which is applied in each
encoding step depends on the estimation of the distortion reduction after each
