[theora] NHW Image codec - improvement of precision

Raphael Canut nhwcodec at gmail.com
Wed Oct 17 07:25:22 PDT 2012


I don't have really advanced on my codec at the moment, but a very
interesting thing I have read recently, is that there is normally no reason
that frequency prediction would be more difficult than (2-D) spatial
prediction (for image).For my codec, I have tried to predict little wavelet
(hf) coefficients, but it is really very difficult and I don't have
results.It is maybe more difficult to predict little wavelet coeffs as most
of them are certainly related with noise parts of image (and are then
random and not predictable), but for the others, not related to noise, even
if it is 5% of them and if there would be an algorithm to predict them,
please do not hesitate to point me out.

I have also not compiled the Linux binaries for my codec, and if someone
has managed to compile them, please do not hesitate to let me know, would
be just great, and could add them on my demo page.

Very quickly to finish, I have also not worked on the other quality
settings.For the next higher ones, I could start to add residual coding,
correct errors on the 512x256 wavelet "high-resolution" part (for a 512x512
image), but higher quality settings is maybe not the most difficult..., the
most difficult is to remove data and the lower quality settings.As I would
like to keep a good neatness of image, maybe add, for the lower quality
settings, a segmentation and denoising function, that will first remove
data, even if the image will be then more "flat"? But is it generally a
good idea, or not? I don't know the current state of segmentation (and
geometric) image compression, and I am really not skilled enough.

So there is really a big amount of work to do on my codec, and really
(really) too much for me, and of course I can not spend this time if there
is not any intended usage for my codec... -My codec doesn't seem to have
reached a lot of interest for now-...

Many thanks again for your time,

2012/7/25 Raphael Canut <nhwcodec at gmail.com>

> Hi again,
> I have improved precision of my codec (on the encoder and decoder).I have
> also improved the -h1 quality setting.-Source code and binaries at
> http://nhwcodec.blogspot.com/ -.
> I am still trying to improve precision of my codec, with keeping my
> low-complexity (fast) approach.
> I do not totally use the reference (and impressive) block prediction with
> different modes + residual coding scheme, but I just apply residual coding
> on the first order wavelet "image" (for example for a 512x512 image, I just
> code the errors on the 256x256 wavelet "high-resolution" part), hence the
> lack of precision.I try to compensate it with a little more neatness of the
> wavelet 5/3 filterbank, but that's right that precision seems visually more
> important.
> Any opinion on this approach or on the codec in general is very welcome.
> Many thanks again,
> Raphael
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