Sdcb.SimdCodecs.Jpeg 1.2.0

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Sdcb.SimdCodecs

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Pure-managed image codecs for .NET 10: JPEG, PNG, TIFF, WebP, GIF, BMP, ICO / CUR, QOI, Netpbm (PBM / PGM / PPM / PAM / PFM), JPEG 2000 and JBIG2, plus EXIF and ICC. No native dependencies, NativeAOT-compatible, and SIMD-accelerated (AVX2, SSE, AdvSimd) with a scalar fallback. The JPEG decoder is faster than libjpeg-turbo on the benchmark corpus.

_{Every tile above was decoded by this library; the files are the LINQPad samples' images (how they were made).}

Quick start

dotnet add package Sdcb.SimdCodecs

using Sdcb.SimdCodecs;
using Sdcb.SimdCodecs.Abstractions;
using Sdcb.SimdCodecs.Jpeg;

byte[] file = File.ReadAllBytes("photo.webp");   // JPEG, PNG, TIFF, WebP, GIF, BMP, ICO, CUR, QOI, Netpbm, JPEG 2000 or JBIG2

// The facade sniffs the format from the magic bytes and decodes into a buffer you own (R G B A).
if (!SimdCodecs.TryReadInfo(file, out ImageInfo info)) throw new InvalidDataException("Not a supported image");
byte[] rgba = new byte[info.Width * info.Height * 4];
SimdCodecs.TryDecodeIntoRgba8(file, rgba);

// Encode it as a JPEG: SIMD, baseline / optimised Huffman / progressive, 4:2:0 or 4:4:4.
byte[] jpeg = JpegEncoder.Encode(rgba, info.Width, info.Height, channels: 4, new JpegEncodeOptions { Quality = 90 });
File.WriteAllBytes("photo.jpg", jpeg);

The rest of the facade:

• SimdCodecs.TryDecodeInto(file, buffer, stride, format) — BGRA (Windows / WPF / Skia), RGB, BGR (OpenCV) or grey (OCR) straight into your buffer, at any row stride. JPEG and PNG write these natively, with no RGBA frame in between; a colour JPEG's grey is its Y plane.
• SimdCodecs.TryDecode(file, out image) — the native layout: channel count (grey JPEG 1, colour JPEG 3), 8/16-bit or float samples, ICC profile.
• SimdCodecs.TryReadInfo(file, out info) — from the headers alone: format, stored bit depth, EXIF orientation (reported, never applied), frame or page count.
• SimdCodecs.DetectFormat(file) — also names formats it recognises but does not decode (HEIF, AVIF, JPEG XL, …); SimdCodecs.IsDecodable(format) tells the two apart.
• SimdCodecs.TryOpenFrames(file, out reader) — every frame, by index, in any layout: animated WebP / GIF frames with durations, multi-page TIFF pages, the images of an icon (any other image is one frame). reader.EnumerateFramesInto(buffer, stride, format) plays them in order through one buffer.

Each format is also its own package with a richer API: scaled JPEG decoding, TIFF segment reads, WebP animation seeking by timestamp, Ultra HDR, and more.

Formats

The table describes the individual format packages. The Sdcb.SimdCodecs facade intentionally exposes a narrower dispatch/display contract; for example, the separate LosslessJpeg.FromMemory API supports SOF3 directly, while JpegDecoder and the facade reject it. The other facade-specific limits are listed in docs/known-gaps.md (in Chinese).

Performance

Single-threaded, AMD Ryzen 7 5800X, .NET 10. Time relative to the native library (lower is faster):

BMP decoding writes into your buffer in any layout with no allocation and is pixel-for-pixel identical to WIC (apart from the documented decisions); every RLE, palette and mask layout decodes faster than both WIC and ImageSharp, and 5-6-5 and palette encoding are 2–6× faster than ImageSharp.

QOI and Netpbm decode into your buffer with no allocation; both match ImageMagick exactly, both ways.

The JPEG decoder is also at least as accurate as libjpeg-turbo's default (about 1 dB higher RGB PSNR against an exact reference where chroma is upsampled), and its output is bit-identical on AVX2, SSE, AdvSimd, scalar and NativeAOT. WebP output is byte-identical to libwebp. JPEG 2000 lossless decode is bit-identical to libopenjp2, and lossy decode achieves >84 dB PSNR. Full tables, corpora and methodology: JPEG, WebP, and JPEG 2000, BMP / ICO, QOI / Netpbm (on photo-like opaque lossy files WebP is on par: 0.87–1.13×; JPEG 2000 pure managed single-threaded decode is currently about 2× of libopenjp2).

Packages

All packages ship in lockstep under one version.

Package	NuGet	Contents
Sdcb.SimdCodecs		Facade: sniffs the format and dispatches to the format decoders
Sdcb.SimdCodecs.Jpeg		JPEG decoder and encoder
Sdcb.SimdCodecs.Jpeg.GainMap		Ultra HDR / Adobe gain maps
Sdcb.SimdCodecs.Jpeg.IccInjector		Splice an ICC profile into a JPEG
Sdcb.SimdCodecs.Png		PNG decoder and encoder
Sdcb.SimdCodecs.Tiff		TIFF reader and writer
Sdcb.SimdCodecs.Webp		WebP decoder, including animation
Sdcb.SimdCodecs.Gif		GIF decoder and encoder, including animation
Sdcb.SimdCodecs.Bmp		BMP / DIB decoder and encoder
Sdcb.SimdCodecs.Ico		ICO / CUR decoder and encoder
Sdcb.SimdCodecs.Qoi		QOI decoder and encoder
Sdcb.SimdCodecs.Pnm		Netpbm (PBM, PGM, PPM, PAM, PFM) decoder and encoder
Sdcb.SimdCodecs.Jpeg2000		JPEG 2000 decoder
Sdcb.SimdCodecs.Jbig2		JBIG2 decoder
Sdcb.SimdCodecs.Exif		EXIF reader and writer
Sdcb.SimdCodecs.Color.Icc		sRGB v4 ICC profile, cicp tag injector
Sdcb.SimdCodecs.Abstractions		Shared types: IImageDecoder, RasterImage, ImagePixelFormat / PixelConverter, IImageFrameReader (frames and pages), H.273 colour vocabulary

<details> <summary>Feature details per package</summary>

• Jpeg — T.81 decoder: baseline, progressive, restart intervals, any subsampling, grey / YCbCr / RGB / CMYK / YCCK, scaled 1/2–1/8 decode, lossless (SOF3). SIMD encoder: baseline, optimised Huffman or progressive; 4:4:4 / 4:2:0 / grey; embeds EXIF (APP1), XMP and an ICC profile (APP2).
• Png — every standard bit depth (including 1/2/4-bit grey and indexed), tEXt / zTXt / iTXt text chunks, PNG-3 cICP / mDCV / cLLI HDR signalling.
• Tiff — multi-page; 8/16/32-bit integer and float; Deflate / LZW (+ PackBits read); strips or tiles; chunky or planar; on-demand single strip or tile reads; reads 1/2/4-bit pages (expanded to 8-bit), CCITT fax (Group 3 1D/2D, Group 4, Modified Huffman) and the floating-point predictor.
• Webp — RFC 6386 / RFC 9649: VP8 lossy, VP8L lossless, ALPH, animation with seek, ICC / EXIF / XMP. The facade's TryDecode returns a still or frame 0 of an animation, TryOpenFrames every frame; WebpAnimationDecoder adds seeking by timestamp and the frame rectangles.
• Gif — GIF89a: global / local colour tables, interlacing, transparency, all disposal methods, NETSCAPE2.0 loop count; composited frames with seek. The decisions the spec leaves open are listed in the package README. Encoder: stills and animations, exact palettes or Wu quantization with optional Floyd–Steinberg dithering, changed-rectangle frames for opaque animations.
• Bmp — the Windows DIB and OS/2 bitmap: core, OS/2 2.x, 40-byte, V2–V5 headers; 1/2/4/8-bit palettes and 16/24/32-bit; BI_BITFIELDS / BI_ALPHABITFIELDS; RLE4 / RLE8 with deltas, OS/2 RLE24 and Huffman 1D; BI_PNG; top-down rows; V5 ICC; packed DIBs (clipboard, icon images). Decodes into any ImagePixelFormat without allocating; checked pixel for pixel against WIC. The decisions the documentation leaves open are listed in the package README.
• Ico — icons and cursors over Bmp and Png: every image, the largest and deepest by default, hotspots; encodes multi-size icons and cursors, each image PNG or a 1/4/8/24/32-bit DIB.
• Qoi — the QOI specification: 3- and 4-channel images, the colour space reported (a linear one as a linear transfer); decodes into any ImagePixelFormat without allocating; encodes from RGBA, BGRA, RGB, BGR or grey.
• Pnm — Netpbm: P1–P6 plain and raw at any maximum up to 65535 (16-bit samples above 255), PAM (P7) with 1–4 channels, PFM (Pf / PF) as float samples; only a file's first image. Encodes every format; plain output keeps lines within 70 characters. The decisions the format pages leave open are listed in the package README.
• Exif — reads JPEG, TIFF, PNG and WebP; ExifWriter builds a blob for JpegEncodeOptions.Exif.

</details>

<details> <summary>Dependency graph</summary>

Sdcb.SimdCodecs (facade)
 ├─ Abstractions
 ├─ Png ──────────┬─ Color.Icc ─ Abstractions
 │                └─ Abstractions
 ├─ Tiff ─────────┬─ Png
 │                └─ Abstractions
 ├─ Jpeg ─────────── Abstractions
 ├─ Jpeg.GainMap ─┬─ Jpeg
 │                ├─ Color.Icc
 │                └─ Abstractions
 ├─ Jbig2 ────────── Abstractions
 ├─ Jpeg2000 ─────── Abstractions
 ├─ Webp ─────────── Abstractions
 ├─ Gif ──────────── Abstractions
 ├─ Bmp ──────────┬─ Png
 │                └─ Abstractions
 ├─ Ico ──────────┬─ Bmp
 │                ├─ Png
 │                └─ Abstractions
 ├─ Qoi ──────────── Abstractions
 └─ Pnm ──────────── Abstractions

Exif ─ Tiff        Jpeg.IccInjector (no dependencies)

The MQ arithmetic decoder (JBIG2, JPEG 2000), the T.4 fax code tables (JBIG2, TIFF, BMP), Wu's palette quantizer (GIF, BMP), the stream and array writers (QOI, Netpbm) and the EXIF orientation reader (JPEG, PNG, WebP) are shared as source (src/Shared), compiled into each package that uses them: no package uses another's internals.

</details>

LINQPad samples

Each package ships runnable samples in linqpad-samples/, which LINQPad lists in its NuGet browser (source: src/<package>/linqpad-samples/):

They download their images from https://cv-public.sdcb.ai/simdcodecs/samples/v1/; how those were made and where they come from is in tools/sample-assets.

Build and test

dotnet build SimdCodecs.slnx -c Release
dotnet test  SimdCodecs.slnx -c Release

Oracle-backed tests skip when their reference tool is missing; set REQUIRE_ORACLES=1 to make a missing oracle fail instead (CI does). How to get each oracle is in AGENTS.md, which also holds the clean-room rules every contribution follows. Benchmarks are built on their own, by path: see benchmarks/README.md. Releasing: RELEASING.md.

Contact

If the WeChat group is full or the QR code has expired, join the QQ group C#/.NET Computer Vision 579060605.

License

MIT — see LICENSE. Derived from SharpAstro/Codecs (released under the Unlicense).