[XviD-devel] quality settings
Michael Militzer
michael at xvid.org
Thu Jun 30 10:08:56 CEST 2005
Hi,
quality 0: keyframes only, performs no motion estimation. (fastest)
quality 1: performs simple motion estimation at full-pixel accuracy only,
just one motion vector per macroblock.
quality 2: like quality 1 plus performs motion estimation at half-pixel
accuracy, which results in significantly higher picture quality.
quality 3: like quality 2 plus enables 'four vector mode'. Hence, not just
one but also four motion vectors can be assigned to a macroblock
in order to more accurately track motion and raise image quality.
quality 4: like quality 3 plus enables 'chroma motion estimation'. In all
quality modes < 4, the motion estimation algorithm determines
motion vectors based on the luminance image plane only whereas
with chroma ME the chrominance information is considered also.
quality 5: like quality 4 plus enables 'trellis quantization', which is an
R-D optimized quantization approach. Here, the dct coefficients
are 'intelligently' quantized to yield the best trade-off
between the introduced distortion and required bits for coding.
quality 6: like quality 5 plus enables R-D optimized AC prediction and
extended search strategies. Here, the ME algorithm performs
additional search steps to further improve the accuracy of the
motion vectors. R-D optimized AC prediction enhances the quality
of non-temporally predicted (INTRA) macroblocks. (slowest)
Rgds,
Michael
Quoting Tom Jacobs <T.R.Jacobs at lboro.ac.uk>:
>
> hi
>
> i have been looking for a brief description of what each of the quality (-q)
> settings do. from that i can tell they switch on functionality like
> halfpelrefine16/8, earlystop16/8, inter4v and changes the quantization
> matrix.
>
> what i am slightly unsure of is what these actually mean.
>
> if anyone could help me out with a short (one line) desciption of each that
> would be much appreciated since i have to add a very small section into a
> paper just so i can explain what each line on the graph represents instrad
> of just sayin 1, 2, 3 etc
>
> many thanks
>
> Tom
>
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