jpegrepair

Repair jpeg images, by the following operations.

• Change color components: Y,Cb,Cr
• Insert blocks
• Delete blocks
• Copy relative blocks

Depends

• libjpeg

Build

make

WebAssembly

The WebAssembly build requires the Emscripten SDK, CMake, curl, and tar. It downloads and builds a pinned static copy of libjpeg-turbo, so a WebAssembly libjpeg installation is not otherwise needed.

make wasm

The output is dist/wasm/jpegrepair.js and dist/wasm/jpegrepair.wasm. The generated module works in browsers, Web Workers, and Node.js. It does not run main() automatically; put input files in Emscripten's virtual filesystem and invoke the existing command-line interface with callMain:

import createJpegRepairModule from "./dist/wasm/jpegrepair.js";

const module = await createJpegRepairModule();
module.FS.writeFile("dark.jpg", inputJpegBytes);
module.callMain(["dark.jpg", "light.jpg", "cdelta", "0", "100"]);
const outputJpegBytes = module.FS.readFile("light.jpg");

To use the browser interface, serve the project directory after building:

python3 -m http.server 8000

Then open http://localhost:8000/. The interface accepts a JPEG, builds a sequence of operations, previews the result, and provides it for download. Opening index.html directly with a file:// URL will not work because browsers restrict loading WebAssembly modules that way.

The libjpeg-turbo version and download URL can be overridden when needed:

make wasm LIBJPEG_TURBO_VERSION=3.1.1 LIBJPEG_TURBO_URL=file:///path/to/libjpeg-turbo.tar.gz

Usage

jpegrepair infile outfile OP ...

where OP is: cdelta dest insert delete copy

Operations are applied from left to right:

• dest BY BX [BN] selects the destination MCU at row BY, column BX. With BN, it selects that many consecutive MCUs. The destination remains active for following operations until another dest is encountered.
• dest BY BX BH BW selects a rectangular region of BH rows by BW columns.
• cdelta COMP DC adds DC to the DC coefficient of component COMP in the selected region. Components are normally 0 for Y (luminance), 1 for Cb, and 2 for Cr.
• insert N inserts N MCUs at the destination, shifting later coefficient blocks forward.
• delete N deletes N MCUs at the destination, shifting later coefficient blocks backward.
• copy DY DX copies coefficient blocks from the relative MCU offset DY, DX into the selected region.

JPEG DCT blocks are always 8x8 samples, but destination coordinates address MCUs. An MCU can cover multiple DCT blocks because of chroma subsampling. For example, a 4:2:2 image uses 16x8-pixel MCUs.

Examples

Increase luminance.

jpegrepair dark.jpg light.jpg cdelta 0 100

Fix blueish image.

jpegrepair blueish.jpg fixed.jpg cdelta 1 -100

Insert 2 blocks at position 50:5

jpegrepair before.jpg after.jpg dest 50 5 insert 2

Repair corrupt.jpg: delete one MCU at row 49, column 48; adjust the Y, Cb, and Cr DC coefficients in that destination region; then insert two MCUs.

jpegrepair corrupt.jpg corrupt-repaired.jpg dest 49 48 delete 1 cdelta 0 -30 cdelta 1 35 cdelta 2 -40 insert 2

Copy to position 9:35 2x2 blocks from relative block 1:-20 (1 row forward, 20 columns back).

jpegrepair before.jpg after.jpg dest 9 35 2 2 copy 1 -20

License

• jpegrepair.c - See LICENSE
• transupp.c - See README.ijg