Kopf-Lischinski "Depixelizing Pixel Art" for Node.js

Based on the following paper:

• Depixelizing Pixel Art by Johannes Kopf & Dani Lischinski

And the source code included with this paper:

• Depixelizing Pixel Art on GPUs by Felix Kreuzer

Improvements upon original GPU version:

• Add a threshold parameter to adjust how close two colors need to be to be consider similar
• Better handle alpha channels (treat as dissimilar from non-transparent pixels)
• Fix stretching/scaling due to texel misalignment
• Add option to pass in a similarity map
  • Relatedly, outputSimilarityMask outputs a scaled up similarity map (for use in post-processing, etc)

Notes

• Original GPU code is MIT licensed, the same license may apply here, all original code in this project is additionally released under the MIT License
• Most GPU code semi-automatically converted to JavaScript by Codex (AI)
• Example below is expanded to 12x via Depixel and then shrunk by 2x with linear filtering (e.g. 2xAA)

API

type Image = {
  data: Buffer; // Or Uint8Array - pixels in RGBA byte order
  width: number;
  height: number;
  similarityData?: Buffer;
};

type Opts = {
  height: number;
  threshold?: number; // 0..255, lower = fewer similarity edges; default 255
  // borderPx - pad input with this many pixels (1-2) - useful with
  //   `threshold=0` for complete hard edges
  borderPx?: number;
  // if `similarity` specified, uses values here instead or RGBA values to
  //   determine similarity.  Note: `threshold` (default 3) is used against sum
  //   of RGB differences in this buffer instead the default of using a
  //   perceptual threshold based on color
  // note: color still impacts shape of splines
  similarity?: Buffer;
  // if `outputSimilarityMask` and `similarity` is specified,
  //   then `similarityData` in the return will contain a scaled up version of
  //   the `similarity` mask (for use in post-processing, etc
  outputSimilarityMask?: boolean; // default false
  renderMode?: 'splines' | 'default'; // default default
  doOpt?: boolean; // default true
}

function scaleImage(src: Image, opts: Opts): Image;

Example usage

const { scaleImage } = require('depixel');

let src = new Uint32Array([
  // White on black "x"
  0xFFFFFFFF, 0x000000FF, 0xFFFFFFFF,
  0x000000FF, 0xFFFFFFFF, 0x000000FF,
  0xFFFFFFFF, 0x000000FF, 0xFFFFFFFF,
]);

let result = scaleImage({
  data: src,
  width: 3,
  height: 3,
}, {
  height: 3 * 6,
});

See test/test.js for an example including reading and writing from a PNG file.

Links

• https://johanneskopf.de/publications/pixelart/
• https://github.com/falichs/Depixelizing-Pixel-Art-on-GPUs
• https://www.cg.tuwien.ac.at/research/publications/2014/KREUZER-2014-DPA/