JPEGenc

A fast JPEG-1 baseline encoder in C++17, SIMD-vectorized via Google Highway with optional multi-threading.

Features

• Full baseline JPEG encoding (DCT, quantization, Huffman coding)
• SIMD-accelerated pipeline with runtime ISA dispatch (NEON, SSE2, AVX2, AVX-512)
• Single-threaded and multi-threaded modes (producer/consumer with per-strip parallelism)
• All standard chroma subsampling modes: 4:4:4, 4:2:2, 4:1:1, 4:4:0, 4:2:0, 4:1:0, and grayscale
• Quality factor 0--100 (IJG-compatible quantization tables)
• Low memory footprint: line buffers are recycled across strips; no full-image allocation
• Reusable encoder: invoke() can be called repeatedly without reallocating internal state

Performance

Measured on Apple M3 Max (single-thread and auto-thread), 4K image (3840 x 2160, 8.3 MP), quality 75, -b benchmark mode (2 s warmup + 2 s measurement):

Mode	Subsampling	Throughput	Frame rate
1 thread	4:2:0	696 MP/s	84 fps
1 thread	4:4:4	486 MP/s	59 fps
1 thread	GRAY	965 MP/s	116 fps
auto (16 threads)	4:2:0	3595 MP/s	433 fps
auto (16 threads)	4:4:4	1961 MP/s	236 fps

Memory footprint

The encoder allocates only per-strip line buffers (16 rows), not full-image buffers. Peak RSS for the 4K image above:

Mode	Peak RSS
1 thread	~6 MB
auto (16 threads)	~12 MB

Dependencies

• C++17 compiler (Clang, GCC, MSVC)
• Google Highway (>= 1.0.6) -- included as a git submodule

Build from source

Clone with submodules:

git clone https://github.com/osamu620/JPEGenc.git --recursive
cd JPEGenc

Build with CMake (Ninja recommended):

cmake -B build -DCMAKE_BUILD_TYPE=Release -G Ninja -DBUILD_TESTING=OFF
cmake --build build

-DBUILD_TESTING=OFF suppresses Highway's own test targets.

The build produces:

• build/bin/libjpegenc_R.{so,dylib,dll} -- shared library
• build/bin/jpenc -- CLI encoder

Build types: Release (-O3), Debug (-O0 -g -fsanitize=address, executable named jpenc_dbg), RelWithDebInfo.

Usage

jpenc -i input.ppm -o output.jpg [options]

Option	Description	Default
-i FILE	Input PPM/PGM file (required)
-o FILE	Output JPEG file (required)
-q N	Quality factor (0--100)	75
-c MODE	Chroma subsampling: 444, 422, 411, 440, 420, 410, GRAY	420
-t N	Threading: 1 = single-thread, 0 = auto, N >= 2 = N workers	1
-b	Benchmark mode (2 s warmup + 2 s measurement, reports fps and MP/s)	off
-h	Print help

Examples

Encode at quality 90 with 4:4:4 subsampling:

./jpenc -i photo.ppm -o photo.jpg -q 90 -c 444

Multi-threaded encoding using all available cores:

./jpenc -i photo.ppm -o photo.jpg -t 0

Run a throughput benchmark:

./jpenc -i photo.ppm -o photo.jpg -b

Library API

The public header include/jpegenc.hpp exposes two classes:

#include <jpegenc.hpp>

FILE *fp;
// ... open and parse PPM header to get fpos, width, height, nc ...
jpegenc::im_info input(fp, fpos, width, height, nc);

int qf = 75, ycc = 5; // YUV420
jpegenc::jpeg_encoder encoder(input, qf, ycc, /*num_threads=*/1);
encoder.invoke();
std::vector<uint8_t> jpeg = encoder.get_codestream();

The encoder object is reusable -- calling invoke() again re-encodes the same image (useful for benchmarking or quality sweeps) without reallocating internal buffers.

License

See LICENSE.