[Ffmpeg-devel] Re: JPEG-LS codec (original) (raw)

Kostya Shishkov kostya.shishkov
Wed Feb 1 13:10:58 CET 2006

Wed, 01 Feb 2006 03:44:45 -0500, Justin Ruggles wrote:

I haven't tested it yet, but I have some comments. First, let me say that the code is beautiful. It's clear, simple, and well-documented. Also, I am SO glad you did this.

The more I study lossless image encoders, the more I'm impressed with JPEG-LS. There are better compressors out there, but few quite so simple and fast with competitive compression to match. FFV1 looks pretty interesting, too. At a glance, it looks similar to JPEG-LS, but with a better entropy coder.

Every decent lossless encoder looks like this: context determination, prediction, error encoding. LOCO differs from JPEG-LS in two things: context-based error encoding and context determination. IIRC, JPEG-LS differs from FFV1 mostly in error encoding. The same prediction function mid_pred() used in FFV1, JPEG-LS, LOCO and HuffYUV.

I have implemented a LOCO encoder/decoder myself (not the JPEG stuff), and I have to say I like a lot of your solutions, namely to the run-mode stuff, which is a little tricky. There's SPMG implementation of JPEG-LS with source code, I got it at http://datacompression.info And a lot of testing, swearing and testing ;) I haven't seen much about JPEG-LS 2. I tried to download the spec from ITU and it didn't recognize my 3 free specs account anymore...oh well. Does anything in it look interesting or worth implementing? More coding modes (modified Golomb and arithmetic) and visual-lossless mode. SC29 site has this: http://www.itscj.ipsj.or.jp/sc29/open/29view/29n3402t.doc You can also download it as rec. ITU T.870 (ITU give you 3 free downloads it you register, but hasn't work for me last month)

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