YAPF — Yet Another Picture Format

Lossless images that decode several times faster than PNG — on one core.

YAPF is a lossless image format for photos, UI and game assets, built for decode speed first. There is no entropy coder, no bit reader and no context model: every structure is byte aligned, and the decoder runs short loops that modern CPUs execute at memory speed — with SSE / NEON where available. The encoder does the hard work, so the decoder only follows instructions.

• 6–10× faster decoding than PNG (stb_image), single-threaded; a 4K image decodes in about 6 ms (5.6 GB/s). Multithreaded decoding is optional.
• Smaller than PNG on UI, icons and screenshots; 20–45 % larger on photos and natural textures — the price of having no entropy coder.
• Made for games and tools too: mipmaps, GPU format hint, sRGB / premultiplied flags, and random access to 64×64 tiles.
• Tiny and portable: two C99 files, no dependencies. Plus a CLI, Python, JavaScript and plugins for the tools you already use.

This is YAPF version 1, the first stable format.

---

Use it in…

Where	What you get	Guide	Status
C / C++	yapf.h + yapf.c, drop into any project	below	✅ tested on Linux x64, Windows x64, Linux ARM64
Command line	convert PNG/JPG/TGA/BMP/PSD/GIF ↔ YAPF, info, bench, thumbnail	below	✅ tested on Linux, Windows
GIMP 3	open, export (with mipmaps)	extensions/gimp	✅ tested in GIMP 3.0.8
Blender 4.2+	import, export, drag & drop, image as plane	extensions/blender	✅ tested in Blender 5.1
VS Code	image preview with zoom and mip picker	extensions/vscode	✅ packaged, preview tested in Chromium
Figma	import .yapf, export selection as .yapf	extensions/figma	✅ plugin UI tested in Chromium
Photoshop	File → Scripts → Open YAPF / Save as YAPF	extensions/photoshop	⚠️ not yet tested inside Photoshop
Linux desktop	file type + thumbnails in GNOME Files, Nemo, Caja, Thunar	extensions/linux	⚠️ thumbnailer tested, not in a file manager
Python	yapf.load() / yapf.save()	bindings/python	✅ tested
JavaScript	browsers, Node.js, workers	bindings/js	✅ tested, byte-identical to C

Pre-built downloads (command-line tool and libraries for Windows, macOS and Linux, plus the plugin packages) are published on the Releases page; everything can also be built from source as described below.

---

Command line

yapf photo.png photo.yapf             # encode (formats by file extension)
yapf texture.png texture.yapf --mips  # with a full mip chain
yapf photo.yapf photo.png             # decode to PNG / JPG / BMP / TGA
yapf texture.yapf mip2.png --mip 2    # export one mip level
yapf info photo.yapf                  # size, channels, mips, flags, ratio
yapf bench photo.yapf                 # decode speed, 1 thread and all cores
yapf thumbnail photo.yapf thumb.png 256

Options when writing .yapf: --mips, --linear (pixels are not sRGB), --premult (alpha is premultiplied).

---

Benchmark

Single core, AMD Ryzen 7 5700G, gcc -O2. PNG is decoded with stb_image; the PNG files are the ones shipped with the respective projects. "Plain C" is the library built with -DYAPF_NO_SIMD; the default build uses SSE / NEON.

Image	Raw	PNG	YAPF	vs PNG	PNG decode	YAPF, plain C	YAPF (default)
Wallpaper 3840×2160	32400 K	1812 K	2267 K	125 %	44.7 ms¹	10.3 ms	5.9 ms (5.6 GB/s)
UI screenshot 261×430	438 K	176 K	143 K	81 %	1.6 ms	0.31 ms	0.17 ms
UI screenshot 305×529	630 K	201 K	185 K	92 %	2.1 ms	0.45 ms	0.24 ms
App icon 128×128	64 K	24 K	23 K	93 %	0.26 ms	0.06 ms	0.03 ms
Rock texture 512×512	768 K	182 K	221 K	121 %	1.4 ms	0.35 ms	0.16 ms
Wood texture 512×512	768 K	185 K	234 K	126 %	1.4 ms	0.46 ms	0.16 ms
Canvas texture 512×512	768 K	171 K	245 K	143 %	1.0 ms	0.35 ms	0.15 ms
Pixel art 512×512	1024 K	—	66 K	—	—	0.74 ms	0.32 ms
Random noise 512×512	1024 K	—	1024 K	—	—	0.1 ms	0.1 ms

¹ PNG decode of the wallpaper measured between 44.7 and 66 ms depending on the harness; the table uses the fastest. -O2 and -O3 builds of YAPF perform the same.

---

C / C++

The library is two files. Add them to your project:

yapf.h    — public API and the complete format specification
yapf.c    — encoder and decoder

#include "yapf.h"

yapf_image_t *img = yapf_load("texture.yapf");      /* or yapf_load_memory(buf, len) */
if (img) {
    /* img->pixels: width × height × channels bytes, rows top to bottom */
    upload_texture(img->width, img->height, img->channels, img->pixels);
    yapf_free(img);
}

yapf_image_t out = { .width = w, .height = h, .channels = 4,
                     .mip_levels = 1, .pixels = rgba, .flags = YAPF_FLAG_SRGB };
yapf_save("out.yapf", &out);

Compile with any C99 compiler (-pthread on Unix for the _mt loaders):

cc -O2 -std=c99 main.c yapf.c -o app -pthread

SIMD is on by default: SSSE3 on x86 / x64 (chosen at run time with CPUID, so binaries still run on older CPUs) and NEON on ARM64, with GCC, Clang, MSVC and MinGW.

Define	Effect
-DYAPF_NO_SIMD	plain C only
-DYAPF_NO_THREADS	no threads; the _mt loaders decode on the calling thread, and only the C standard library is needed

API Reference

Types

typedef struct {
    uint32_t  width;       /* pixels per row                             */
    uint32_t  height;      /* rows                                       */
    uint8_t   channels;    /* 1 gray / 2 gray+alpha / 3 RGB / 4 RGBA     */
    uint8_t   gpu_format;  /* YAPF_GPU_* hint                            */
    uint8_t   flags;       /* YAPF_FLAG_* (premultiplied alpha, sRGB)    */
    uint8_t   mip_levels;  /* 1 = base only, up to 16                    */
    uint8_t  *pixels;      /* base level, malloc-owned                   */
    uint8_t **mips;        /* mips[0] == pixels, mips[1..] smaller levels */
} yapf_image_t;

pixels is a tightly packed, row-major byte array of width × height × channels bytes. Mip level m is max(1, width >> m) × max(1, height >> m). The layout per pixel matches the channels value:

channels	Layout per pixel
1	Y
2	Y A
3	R G B
4	R G B A

Functions

yapf_image_t *yapf_load(const char *filename);
yapf_image_t *yapf_load_memory(const void *buffer, size_t size);

Decode a YAPF file from disk or from memory (e.g. a game archive). Return a heap-allocated image on success, NULL on any failure (file not found, invalid or corrupt data, out of memory). Corrupt input is rejected, never read out of bounds.

yapf_image_t *yapf_load_mt(const char *filename, int threads);
yapf_image_t *yapf_load_memory_mt(const void *buffer, size_t size, int threads);

Same, decoding tiles on up to threads threads (0 = one per CPU core). The output is identical to the single-threaded loaders.

int yapf_save(const char *filename, const yapf_image_t *img);

Encodes an image to disk. Writes img->mip_levels levels; img->mips may be NULL when mip_levels == 1. Returns YAPF_OK (0) on success or a negative YAPF_ERR_* code on failure.

void yapf_free(yapf_image_t *img);

Releases memory returned by the loaders. Passing NULL is safe.

Return codes

Constant	Value	Meaning
YAPF_OK	0	Success
YAPF_ERR_INVALID	–1	NULL or logically invalid argument
YAPF_ERR_IO	–2	File could not be opened or written
YAPF_ERR_OOM	–3	Out of memory

Channel constants

YAPF_CHANNELS_GRAY        1
YAPF_CHANNELS_GRAY_ALPHA  2
YAPF_CHANNELS_RGB         3
YAPF_CHANNELS_RGBA        4

---

Building

System	Command	Output
Linux, macOS, BSD	make · make test · sudo make install	build/: libyapf.a, libyapf.so / .dylib, yapf
Linux, macOS (LLVM)	./build.sh	dist/<platform>/ incl. macOS universal binaries
Windows (LLVM)	build.bat	dist\windows-x64\, dist\windows-arm64\: yapf.dll, yapf.lib, libyapf.a, yapf.exe
Windows (Visual Studio)	cl /O2 /c yapf.c and add yapf.obj to your project
All platforms at once	tools/build_release.sh (needs zig)	dist/release/: every download on the Releases page

The command-line tool is tools/yapf_cli.c + yapf.c; it uses the public domain stb headers in third_party/.

---

How it works

1. Two colour transforms — per 64×64 tile, YCoCg-R or subtract-green (G, R−G, B−G), whichever codes smaller. Both run mod 256, so every plane stays one byte per sample.
2. Twelve row filters — per band of 8 rows: Left, Gradient (L + A − D), Up-right, Up-average, or the row 1–8 rows above (catches repeating textures and dither patterns). None depends on the previous sample by more than one add, and the vertical ones decode as plain vector code.
3. Groups of 8 — residuals are packed in groups of 8 at the group's bit width: 8 values × w bits = exactly w bytes, so every group is byte aligned and unpacks with one 64-bit load (or one SIMD shuffle).
4. 4-bit control codes — one per group, or one per run of up to 64 groups repeating the previous width; the encoder picks the cheapest sequence with a small dynamic program.
5. Validate first, then run — all sizes in a tile are checked before the hot loops start, so the loops need no bounds checks. Corrupt files are rejected, never read out of bounds.
6. Constant and stored tiles — a plane that is constant in a tile costs one byte; a tile that would not shrink is stored raw (noise never grows).
7. Independent tiles — any tile can be decoded on its own, in any order, on any thread.

The complete specification is the comment at the top of yapf.h:

HEADER (20 bytes)   "YAPF", version 1, channels, GPU hint, mip count,
                    flags, 3 reserved, width u32, height u32
MIP INDEX           per level: offset u32, size u32
LEVEL DATA          tile_size u32 × tile_count, then the tiles
TILE (64×64)        header byte: stored raw, or constant-plane mask + colour transform
                    per plane: filter byte per 8 rows, control nibbles,
                               w bytes per group of 8 values

---

Testing

make test                      # C suite: 784 checks, plus JavaScript if node is installed
node bindings/js/test.js       # JavaScript: round-trips, sample file, corrupt input

What has been verified for this release:

• exact round-trips for 1–4 channels, odd sizes from 1×1 up, mip chains, single- and multi-threaded decoding;
• the same tests pass on Linux x64, Windows x64 (MinGW, run under Wine), Linux ARM64 (NEON, run under qemu), with and without SIMD, and under AddressSanitizer, UndefinedBehaviorSanitizer and ThreadSanitizer;
• thousands of corrupted and truncated files are rejected without crashing;
• the JavaScript and Python versions produce byte-identical files to C;
• the GIMP plugin and the Blender extension in the real applications.

The macOS builds are cross-compiled and not yet run on a Mac.

---

Project layout

yapf.h, yapf.c          the library (format spec in yapf.h)
tools/yapf_cli.c        the `yapf` command-line tool
tools/build_release.sh  builds every download for all platforms
tests/test_yapf.c       C test suite
bindings/js/            JavaScript encoder / decoder
bindings/python/        Python module
extensions/gimp/        GIMP 3 plugin
extensions/blender/     Blender extension
extensions/vscode/      VS Code preview
extensions/figma/       Figma plugin
extensions/photoshop/   Photoshop scripts
extensions/linux/       MIME type and thumbnailer
third_party/            stb_image / stb_image_write (public domain, CLI only)
other/YAPF.YAPF         sample image (the YAPF logo)

---

License

Apache License 2.0 — see LICENSE. third_party/ contains stb_image and stb_image_write by Sean Barrett (public domain / MIT).