https://github.com/lifthrasiir/j40

J40: Independent, self-contained JPEG XL decoder
https://github.com/lifthrasiir/j40

c decoder image-compression jpeg-xl single-file-library

Last synced: about 15 hours ago
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J40: Independent, self-contained JPEG XL decoder

• Host: GitHub
• URL: https://github.com/lifthrasiir/j40
• Owner: lifthrasiir
• License: other
• Created: 2022-09-13T18:15:39.000Z (over 2 years ago)
• Default Branch: main
• Last Pushed: 2022-12-09T02:18:35.000Z (about 2 years ago)
• Last Synced: 2024-12-18T21:09:10.435Z (9 days ago)
• Topics: c, decoder, image-compression, jpeg-xl, single-file-library
• Language: C
• Homepage:
• Size: 1.57 MB
• Stars: 230
• Watchers: 9
• Forks: 3
• Open Issues: 14
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.txt

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README

        
# J40: Independent, self-contained JPEG XL decoder

**J40** (Jay-forty) is a decoder for ISO/IEC 18181 [JPEG XL] image format.

It intends to be a fully compatible reimplementation to the reference implementation, [libjxl],

and also serves as a verification that the specification allows for

an independent implementation besides from libjxl.

J40 is a [single-file C99 library with zero dependencies][1file],

making it trivial to insert to your project and dependencies.

It is also a public domain software and can be used for absolutely every purpose.

[JPEG XL]: https://en.wikipedia.org/wiki/JPEG_XL

[libjxl]: https://github.com/libjxl/libjxl/

[1file]: https://github.com/nothings/single_file_libs

_**As of version 2270 (2022-09), J40 is a highly experimental software.**

Expect breakage, bug and [incomplete format support](#format-support).

In order to discourage accidental uses, you need to define an additional macro for now._

## Quick Start

The following is a simple but complete converter from JPEG XL to [Portable Arbitrary Map][pam] format,

and covers all the currently available API functions.

[pam]: http://netpbm.sourceforge.net/doc/pam.html

```c

#define J40_IMPLEMENTATION // only a SINGLE file should have this

#include "j40.h" // you also need to define a macro for experimental versions; follow the error.

#include 

#include  // for va_*

static int oops(const char *fmt, ...) {

    va_list args;

    va_start(args, fmt);

    vfprintf(stderr, fmt, args);

    va_end(args);

    return 1;

}

int main(int argc, char **argv) {

    if (argc < 3) return oops("Usage: %s input.jxl output.pam\n", argv[0]);

    FILE *out = fopen(argv[2], "wb");

    if (!out) return oops("Error: Cannot open an output file.\n");

    j40_image image;

    j40_from_file(&image, argv[1]); // or: j40_from_memory(&image, buf, bufsize, freefunc);

    j40_output_format(&image, J40_RGBA, J40_U8X4);

    // JPEG XL supports animation, so `j40_next_frame` calls can be called multiple times

    if (j40_next_frame(&image)) {

        j40_frame frame = j40_current_frame(&image);

        j40_pixels_u8x4 pixels = j40_frame_pixels_u8x4(&frame, J40_RGBA);

        fprintf(out,

            "P7\n"

            "WIDTH %d\n"

            "HEIGHT %d\n"

            "DEPTH 4\n"

            "MAXVAL 255\n"

            "TUPLTYPE RGB_ALPHA\n"

            "ENDHDR\n",

            pixels.width, pixels.height);

        for (int y = 0; y < height; ++y) {

            fwrite(j40_row_u8x4(pixels, y), 4, pixels.width, out);

        }

    }

    // J40 stops once the first error is encountered; its error can be checked at the very end

    if (j40_error(&image)) return oops("Error: %s\n", j40_error_string(&image));

    if (ferror(out)) return oops("Error: Cannot fully write to the output file.\n");

    j40_free(&image); // also frees all memory associated to j40_frame etc.

    fclose(out);

    return 0;

}

```

Alternatively, you can use a `dj40` executable to convert a JPEG XL file into a PNG file,

which can be built as follows:

```console

# if your system has make:

$ make

# otherwise, do the equivalent of:

$ cc -O3 dj40.c -o dj40

```

## Format Support

As of version 2270, J40 can decode:

* Any image encoded with [fjxl], or

* Most images encoded with [cjxl][libjxl] containing...

    * No animations or previews

    * No image features (`--dots` and `--patches`), which implies:

        * Efforts (`-e`) up to 6

        * For lossy compression, target distance (`-d`) less than 3.0

    * No progressive encoding (`-p`)

    * No lossless JPEG transcoding in use (can be disabled with `-j`)

    * No floating point samples

[fjxl]: https://github.com/libjxl/libjxl/tree/main/experimental/fast_lossless

There are some known cases where J40 and libjxl can significantly diverge:

* Restoration filters (`--epf`, `--gaborish`) are currently ignored.

* Crop retangles are currently ignored and can reveal a frame larger than the actual image.

* ICC profiles are only decoded to the point that the actual image can be decoded.