openjpeg VS libjxl

mkdir ~/install cd ~/install wget https://github.com/uclouvain/openjpeg/archive/master.zip unzip master.zip cd openjpeg-master/ mkdir build cd build cmake -DCMAKE_BUILD_TYPE=Release .. make sudo make install sudo make clean cd

Details here, if you like reading bug reports. It took the cooperation of developers at all four levels to fix this. I wrote a test project to reproduce the problem, the jpeg2k developer was able to reproduce the problem under valgrind (a tool for finding bad pointer references in C, seldom needed by Rust users), an OpenJPEG developer fixed the C code, and everybody in the chain updated versions. Thanks to everyone who had a part in this.

> The whole file is effectively a write-what-where primitive2. In addition to that, the Count Info Table is not bounds checked either...

File formats like that, with many offsets in the file, are troublesome. There used to be more formats like that. Microsoft Word .doc is the classic example.

OpenJPEG 2000 has a similar problem. I just hit that yesterday.[1] Valgrind is finding references to un-initialized data which affect control flow, and running the JPEG decoder on valid but truncated files (which is allowed) is causing bad memory reference crashes and errors.

New formats like this are rare. People have learned. A modern exception is Unreal Engine 5's Nanite has much offset data, and there may be an attack surface there for hostile game content. Nanite is a way to store a graphics mesh with both multiple levels of detail and common submeshes. It's a hierarchy of directed acyclic graphs, flattened into a linear file with offsets. And, sure enough, there are many crash reports. At least Unreal provides a validator for the format.

(If only C/C++ had slices in the language. Most of the things for which pointer arithmetic is used can be done with slices. Slices really are pointer arithmetic, with sanity.)

[1] https://github.com/uclouvain/openjpeg/issues/1459

JPEG 2000 decoder crashes Trying to read files at reduced resolution crashes with memory access errors. This is jpeg2k (Rust) calling jpeg2000-sys (Rust glue to C foreign function interfaces) calling OpenJPEG (all C). The problem can now be reproduced at the C level alone, under Valgrind. The developers of the top two levels have been very helpful, but the trouble is down in the rather painful C code at the bottom. The OpenJPEG maintainers are way behind on fixes, despite being funded.

It certainly was a risk in 2013, when the open source libraries were slow and riddled with bugs. Today, there are two stable, well maintained and fast open source libraries available:

https://github.com/uclouvain/openjpeg

https://github.com/libjxl/libjxl/blob/main/doc/format_overvi... is a pretty detailed but good overview. The highlights are variable size DCT (up to 128x128), ANS entropy prediction, and chroma from luminance prediction. https://github.com/libjxl/libjxl/blob/main/doc/encode_effort... also gives a good breakdown of features by effort level.

For JPEG XL, refer to its format overview [1]. In short its lossless mode uses a combination of multiple techniques: the rANS coding with an alias table, LZ77, reversible color transforms, a general vector quantization that subsumes palettes, a modified Haar transform and a learnable meta-adaptive decision tree for context modelling.

One good thing about JPEG XL is that its lossy mode also largely uses the same tool, with a major addition of specialized quantization and context modelling for low- and high-frequenty components.

[1] https://github.com/libjxl/libjxl/blob/main/doc/format_overvi...

The cjxl source is here. If you spot any reason why -x strip=exif may not work, tell me.

The problem is that the instructions for actually running the WASM file are not that clear... the docs the author mentions shows how to compile to WASM, which is easy enough, but then here's the instructions to make that actually work in the browser:

https://github.com/libjxl/libjxl/blob/main/tools/wasm_demo/R...

Yeah, you need some mysterious Python script, a JS service worker at runtime, choose whether you want the WASM or WASM_SIMD target, use a browser that supports Threads and SIMD if you chose that, make sure to serve everything with the appropriate custom HTTP headers... just reading that, I can see that to get this stuff working on non-browser WASM targets would likely require expertise in WASM, which is the point of the OP. WASM's UX is just not there yet.

https://github.com/libjxl/libjxl#usage

> Specifically for JPEG files, the default cjxl behavior is to apply lossless recompression and the default djxl behavior is to reconstruct the original JPEG file (when the extension of the output file is .jpg).

I mean compiling a bleeding edge kicad, inkscape or jpeg-xl is easy. But will probably trash your system if you already have an older version installed.

But you look at your image viewer that could have the lossless indicator? (and there is an issue open to add this indicator to the jxl files)

https://github.com/libjxl/libjxl/issues/432

You might want to use libjxl directly, e.g. for visually lossless images: cjxl --effort 9 --brotli_effort 11 --distance 1.0 --num_threads (nproc) --lossless_jpeg 0 input.png output.jxl on linux (if you're on windows/mac, just replace the (nproc) with the number of cpu threads you have, e.g. --num_threads 16).