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(Puschel et al. 2004), The number of low complexity
operations required to compute each multiplier box
is shown in Table 1.
Table 1: Number of operations per multiplier block.
Block Add/Sub Shift Neg
1
b 5 7 2
2
b 5 7 1
3
b 6 7 1
4
b 4 7 1
5
b 3 4 1
Table 2 shows the number of clock cycles required
by a general purpose processor (Intel, 2001) to
compute each
multiplier block, (column Mb) as well
as the conventional multiplier method (column
Mu).
As it can be seen, the number of clock cycles
required by the integer fast approximation based on
multiplier blocks is about 61% of those required by
the conventional method.
Table 2: Number of clock cycles per block operations.
Block Add/Sub Shift Neg Mb Mu
1
b 5 35 2 42 68
2
b 5 35 1 41 68
3
b 6 35 1 42 68
4
b 4 35 1 40 68
5
b 3 20 1 24 34
5 EXPERIMENTAL RESULTS
We have evaluated the error introduced by integer
approximation of the
S matrix by comparing both
methods described in previous sections.
A set of 3 different grey level images was used
(256x256, 8 bit/pel). For each one, the whole image
was transformed into
44
IT coefficient blocks.
Then, each group of four adjacent
44
IT
coefficient blocks are DCT converted by means of
two different methods: i) the full precision algorithm
described in section 2; ii) the integer approximation
described in section 4. The mean squared error
(MSE), between both resulting images (pixel
domain), was used for evaluating the error
introduced by the integer approximation method.
The results are shown in Table 3, where it can be
seen that the error due to the integer approximation
in the conversion process is actually very small. In
fact, the resulting MSE is negligible in practical
terms, which proves the usefulness of the proposed
method for fast transcoding implementations.
Table 3: MSE of the integer approximation.
Image Einstein Smandril Cameraman
MSE 0.337 0.339 0.340
6 CONCLUSIONS
In this paper, we proposed a transform domain
approach for fast conversion H.264/AVC 4x4
Integer Transform to standard
DCT. We derived the
conversion matrix and an efficient algorithm for
computing the transform, as well as, a low
complexity integer approximation method. The
presented results show that the proposed methods
are much faster than the pixel domain approach.
These methods are suitable for video transcoding
applications where fast processing is required.
REFERENCES
Chuang, S.,Vetro, A., 2005. Video Adaptation: Concepts,
Technologies, and Open Issues In
Proceedings of the
IEEE
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