Zune-JPEG

A fast, correct and safe jpeg decoder.

This crate contains a pure Rust jpeg decoder

Usage

The library provides a simple-to-use API for jpeg decoding and an ability to add options to influence decoding

Example

```Rust // Import the library use zune_jpeg::JpegDecoder; use std::fs::read; // load some jpeg data let data = read("cat.jpg").unwrap();

// create a decoder let mut decoder = JpegDecoder::new( & data); // decode the file let pixels = decoder.decode().unwrap(); ```

The decoder supports more manipulations via DecoderOptions, see additional documentation in the library.

Goals

The implementation aims to have the following goals achieved, in order of importance

1. Safety - Do not segfault on errors or invalid input, panics are okay, but should be fixed when reported. unsafe should be used sparingly
2. Speed - Get the data as quickly as possible, which means
   1. Platform intrinsics code where justifiable
   2. Carefully written platform independent code that allows the compiler to vectorize it.
   3. Regression tests.
   4. Watch the memory usage of the program
3. Usability - Provide utility functions like different color conversions functions.

Non-Goals

• Bit identical results with libjpeg/libjpeg-turbo will never be an aim of this library. Jpeg is a lossy format with very few parts specified by the standard( i.e it doesn't give a reference upsampling and color conversion algorithm)
• Error recovery - This is not a recovery library, most errors are propagated up to the caller

Features

• [x] A Pretty fast 8*8 integer IDCT.
• [x] Fast Huffman Decoding
• [x] Fast color convert functions.
• [x] Support for extended colorspaces like GrayScale and RGBA
• [X] Single-threaded decoding.
• [X] Support for four component JPEGs, and esoteric color schemes like CYMK
• [X] Support for no_std

Crate Features

| feature | on | Capabilities | |---------|-----|---------------------------------------------------------------------------------------------| | x86 | yes | Enables x86 specific instructions, specifically avx and sse for accelerated decoding. | | std | yes | Enable linking to the std crate |

Note that the x86 features are automatically disabled on platforms that aren't x86 during compile time hence there is no need to disable them explicitly if you are targeting such a platform.

Using in a no_std environment

The crate can be used in a no_std environment with the alloc feature.

But one is required to link to a working allocator for whatever environment the decoder will be running on

Debug vs release

The decoder heavily relies on platform specific intrinsics, namely AVX2 and SSE to gain speed-ups in decoding, but in debug build rust generally doesn't like platform specific intrinsics (try passing -O parameter to see optimized build) hence obviously speeds tank so bad during debug builds, and there is probably nothing we can do about that.

Benchmarks

The library tries to be at fast as [libjpeg-turbo] while being as safe as possible. Platform specific intrinsics help get speed up intensive operations ensuring we can almost match [libjpeg-turbo] speeds but speeds are always +- 10 ms of this library.

For more up-to-date benchmarks, see the online repo with benchmarks here