[theora] NHW Image codec - lower quality settings
nhwcodec at gmail.com
Wed Jun 19 10:23:43 PDT 2013
I have improved a little the NHW codec.I have improved the dequantization
in the wavelet HH band, and little improved the -l2 (and lower) quality
setting.I have also added a -l3 lower quality setting (-15Ko, exp), I have
increased the quantization for this other setting, and I start to remove
higher wavelet coefficients, but this is not optimal... The artifacts start
to be noticeable for some images at -l3 setting (even if the neatness would
be still good...), really need to better modelise the wavelet coefficients
(and/or predict them) for the other lower settings (and -l3) at first.
Will certainly have to look at SPIHT and EZW algorithms.But just a very
quick question, as far as I have seen, all the codecs that use prediction
(intra block prediction or frequency domain prediction), all use a very
advanced (and impressive) context modeling, and arithmetic coding.Would
this (impressive) entropy coding scheme be required to encode the
prediction residuals effectively, as my codec does not use it?
2013/5/29 Raphael Canut <nhwcodec at gmail.com>
> I have finally added 2 lower quality settings for the NHW codec: -l1
> (-5Ko) and -l2 (-10Ko).I use a quantization of 0.935 and 0.88 (kind of
> quantization), and I decrease residual coding on the first order wavelet
> I have updated the demo page: http://nhwcodec.blogspot.com/ .
> These 2 lower quality settings are still experimental.If you could find
> time, would be interested in any opinion on this approach, and if it could
> be acceptable or not? Because lower quality settings seem quite difficult
> with my algorithm... -I prefer not remove higher wavelet coeffs for these 2
> Many thanks,
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