PictureSharp.Jxl 0.8.6

PictureSharp.Jxl

JPEG XL for PictureSharp, in pure C# with no native dependencies. Requires .NET 10+ and PictureSharp 0.9.0+.

Install from NuGet:

dotnet add package PictureSharp.Jxl

Usage

Register the format once, then load and save .jxl files like any other image:

using PictureSharp;
using PictureSharp.Formats.Jxl;

ImageConfiguration.Default = ImageConfiguration.Default.ToBuilder().AddFormat(new JxlFormat()).Build();

using var image = Image.Load("photo.jxl", new DecoderOptions { ApplyExifOrientation = true });
image.Mutate(x => x.Resize(1600, 0));
image.SaveAsJxl("small.jxl");

Loading keeps the ICC profile, EXIF and XMP; saving writes them back. Saving is lossy at distance 1.0 like cjxl by default; new JxlEncoderOptions { Quality = 100 } (or Distance = 0) saves losslessly. Image.EditMetadata changes the metadata without touching the frames.

To preserve an existing JPEG exactly, use the separate transcoder without loading its pixels:

JxlTranscoder.FromJpeg("original.jpg", "archived.jxl");
JxlTranscoder.ToJpeg("archived.jxl", "restored.jpg"); // byte-identical to original.jpg
// Stream and buffer overloads are also available, e.g. FromJpeg(jpegStream, jxlStream).

Keep 16-bit samples

using Image scan = Image.Load("scan.png", new DecoderOptions { PreserveBitDepth = true });
scan.SaveAsJxl("scan.jxl", new JxlEncoderOptions { Distance = 0 });

This preserves every 16-bit sample, including alpha. Default loading returns 8-bit pixels; enable PreserveBitDepth when reading the result too.

Support

• Read: still images as cjxl produces them: lossy (VarDCT) and lossless (Modular), recompressed JPEGs, progressive files, patches; RGB and grayscale with alpha, up to 16 bits per sample (Rgba64 with PreserveBitDepth, otherwise reduced to 8).
• Write: lossy VarDCT with Quality/Distance and Effort 1–9, about as small as cjxl at the same settings (patches included); lossless 8-bit or 16-bit gray or RGB with alpha, with libjxl's effort tiers and about as small as cjxl -d 0 at the same effort.
• Metadata: ICC, EXIF, XMP (also Brotli-compressed), colour description and orientation; read, written and edited in place (editing files with JPEG reconstruction data is unsupported).
• JPEG transcoding: JxlTranscoder.FromJpeg stores sequential or progressive 8-bit Huffman JPEG (gray or YCbCr 4:4:4/4:2:2/4:2:0); ToJpeg reconstructs the original JPEG byte for byte, including metadata.
• Not supported yet: animations, layers, photon noise and splines, float samples, CMYK (NotSupportedException); writing animations; transcoding RGB, CMYK/YCCK, arithmetic or 12-bit JPEG.

Pixels match djxl (libjxl 0.12.0): lossless images exactly, lossy ones within 1 of 255 in a few samples. Files this package writes decode with djxl the same way.

Status: early development (0.8.6). Not for production use yet; the API may change. CI runs on Linux, including a Native AOT build.

Guides: decoding · encoding · JPEG transcoding · metadata · architecture · release notes

Performance

• SIMD: AVX2/FMA and SSE4.1 kernels with a scalar fallback; all paths produce identical output.
• Native AOT: publish with -p:IlcInstructionSet=x86-64-v3 (or native) to get the AVX2/FMA kernels; the default target uses SSE4.1 only.
• Threads: decoding, encoding and JPEG transcoding run independent groups in parallel. Set MaxDegreeOfParallelism (-1 = all cores, the default; 1 = single-threaded) on DecoderOptions, JxlEncoderOptions or JxlTranscoderOptions. The output does not depend on it.
• Encoding effort: lower Effort is faster; lossless efforts 1–3 are several times faster than 7.
• Memory: a 12 MP image needs about 180 MiB (JPEG-recompressed decode) to 860 MiB (lossless encode) at its peak, including the 48 MB output or input image.

Measurements: speed.

License

MIT. Ported libjxl sources are listed in THIRD-PARTY-NOTICES.txt.

Build

dotnet build -c Release
dotnet test -c Release
dotnet pack src/PictureSharp.Jxl -c Release --no-build -o artifacts
bash scripts/verify-package-consumer.sh