Re: [Algorithms] Image compression

[Richard F. <ra...@gm...>]

oddly, I'm seeing better than DCT ratios. However there is something wrong
with my code as I'm not getting the same ratios as Photoshop with a JPEG
export of the same image. Can't be sure where I'm going wrong. I though it
was the huffman encoding and tried to implement jpeg standard encoder, but
found that once I had it in, it made no difference, funnily enough, my
(supposedly) naive approach to huffman encoding the DCT quantised
coefficients was bit-wise identical to the JPEG standard approach.

I recently found that some improvements in image quality can be obtained by
bleeding the colour data across any black (or very dark) colours before
compressing, thus improving the colour values of chromal sections. I wonder
if this would work even better if i included white out too?

2009/8/7 Jon Watte <jw...@gm...>

> Richard Fabian wrote:
> > notable. I took the vertical gradient, horizontal gradient, and the
> > _saddle_ (diagonal difference / Determinant), and these were then the
> > values recorded for later use in the compression. This 2D approach
> > made a small but significant difference in the compressability of the
> >
>
> Isn't that basically a lifting process, based on a 2D predicted value?
> For previous approaches, I believe that the good-old lossless JPEG
> method used almost exactly that pre-process to determine deltas, and
> then used an entropy coder to code the deltas (instead of treating the
> deltas as something to separately compress using wavelets or whatever).
> What kind of compression ratios are you seeing now, btw? And have you
> tried the smaller/embedded profiles of JPEG 2000 for comparison?
>
> Sincerely,
>
> jw
>
>
>
> --
>
>  Revenge is the most pointless and damaging of human desires.
>
>
>
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