blockman

Blockman is a block-based array manipulation tool that works similar to Array.map and Array.reduce, but for several elements at once. Written for image processing purposes.

$ npm install blockman
$ npm test

API

map = (data, f)

Like Array.map(), but iterates over blocks of data. The block size is inferred from the number of arguments supplied to the mapping function. The mapping function should always return an array.

var bm = require('blockman'),
    data = [1, 2, 3, 4, 5, 6];
 
bm.map(data, (x) => [x + 2]);
// [3, 4, 5, 6, 7, 8]
 
bm.map(data, (x, y) => [y, x]);
// [2, 1, 4, 3, 6, 5]
 
bm.map(data, (x, y, z) => [z, y, x]);
// [3, 2, 1, 6, 5, 4]

expand = (data, f)

Expand blocks of data. The block size is inferred from the number of arguments supplied to the expanding function. The expanding function should always return an array.

bm.expand([0], (x) => [x - 1, x, x + 1]);
// [-1, 0, 1]
 
bm.expand(data, (x, y) => [x, y, x + y]);
// [1, 2, 3, 3, 4, 7, 5, 6, 11]
 
bm.expand(data, (x, y, z) => [x, y, z, x * y * z]);
// [1, 2, 3, 6, 4, 5, 6, 120]

reduce = (data, f)

Reduce blocks of data. The block size is inferred from the number of arguments supplied to the reduction function. The reduction function should always return a Number.

bm.reduce(data, (x, y) => x + y);
// [3, 7, 11]
 
bm.reduce(data, (x, y, z) => x * y + z);
// [5, 26]

Usage

You can for example use it to easily reduce an RGBA image into a double precision grayscale bitmap array (each pixel a value from 0 to 1) and then expand it back into an RBGA array:

var fs = require('fs'),
    PNG = require('pngjs').PNG,
    bm = require('../blockman');
 
// 1. Read image into a node Buffer
var image = PNG.sync.read(fs.readFileSync('./test/test.png'));
 
// 2. Create a Float64Array view of the image data buffer
var f64 = new Float64Array(image.data);
 
// Reduce every 4 elements (R, G, B and alpha respectively).
// Resulting array will be 1/4 the size of the original.
var f64Gray = bm.reduce(f64,
  (r, g, b, a) =>
    0.2126 * (r / 255) +
    0.7152 * (g / 255) +
    0.0722 * (b / 255)
);
 
// 4. Expand the image back to its original size
f64Gray = bm.expand(
  f64Gray,
  x => [
    x * 255,
    x * 255,
    x * 255,
    255
  ]
);
 
// 5. Replace image data
image.data = new Uint8ClampedArray(f64Gray);
 
// 6. Write new image to file
fs.writeFileSync('./test/test.gray.png', PNG.sync.write(image));
console.log('wrote to ./test/test.gray.png');
console.log('---');