pixel

This project is part of the @thi.ng/umbrella monorepo.

• About
  • Packed integer pixel formats
  • Floating point pixel formats
  • Filtered image sampling and resizing
    • Filters
    • Wrap mode
  • Strided convolution & pooling
  • Normal map generation
  • Dominant color extraction
  • Status
  • Support packages
  • Related packages
• Installation
• Dependencies
• Usage examples
• API
• Authors
• License

About

Typedarray integer & float pixel buffers w/ customizable formats, blitting, dithering, convolution.

• Buffer creation from HTML image elements w/ opt resize & format conversion (browser only)
• Buffer-to-buffer blitting w/ automatic format conversion
• Buffer-to-canvas blitting
• Buffer-to-buffer blending w/ Porter-Duff operators
• Pre/post-multiply alpha
• Region / sub-image extraction
• Single-channel manipulation / extraction / replacement / conversion
• k-means based dominant color extraction (float buffers only)
• Accessors for normalized channel value
• Image sampling, resizing, pooling
  • Filters: nearest neighbor, bilinear, bicubic
  • Wrap behaviors: clamp, wrap, repeat
  • Pooling: mean/min/max
• Invert image
• Convolution w/ arbitrary shaped/sized kernels, pooling, striding
• Convolution kernel & pooling kernels presets
  • Higher order kernel generators (Gaussian, Lanczos)
• Image pyramid generation (w/ customizable kernels)
• Customizable normal map generation (i.e. X/Y gradients plus static Z component)
• XY full pixel & channel-only accessors
• 12 packed integer and 6 floating point preset formats (see table below)
• Ordered dithering w/ customizable Bayer matrix size and target color steps (int formats only)
• Declarative custom format & optimized code generation
• HTML canvas creation & ImageData utilities

Packed integer pixel formats

All packed integer formats use the canvas native ABGR 32bit format as common intermediate for conversions. During conversion to ABGR, channels with sizes smaller than 8 bits will be scaled appropriately to ensure an as full-range and as linear as possible mapping. E.g. a 4 bit channel will be scaled by 255 / 15 = 17.

Format specs can freely control channel layout within current limits:

• Channel sizes: 1 - 32 bits.
• Storage: 8, 16 or 32 bits per pixel

New formats can be defined via defPackedFormat().

Format ID	Bits per pixel	Description
ALPHA8	8	8 bit channel (alpha only)
GRAY8	8	8 bit single channel (grayscale conv)
GRAY_ALPHA8	16	8 bit single channel (grayscale conv), 8 bit alpha
GRAY16	16	16 bit single channel (grayscale conv)
GRAY_ALPHA16	32	16 bit single channel (grayscale conv), 16 bit alpha
ARGB4444	16	4 channels @ 4 bits each
ARGB1555	16	5 bits each for RGB, 1 bit alpha
RGB565	16	5 bits red, 6 bits green, 5 bits blue
RGB888	32 (24 effective)	3 channels @ 8 bits each
ARGB8888	32	4 channels @ 8 bits each
BGR888	32 (24 effective)	3 channels @ 8 bits each
ABGR8888	32	4 channels @ 8 bits each

• ALPHA8 is mapped from/to ABGR alpha channel
• GRAY8/16, GRAY_ALPHA8/16 compute grayscale/luminance when converting from ABGR and in return produce grayscale ABGR
• In all built-in formats supporting it, the alpha channel always occupies the most-significant bits (up to format size)

Floating point pixel formats

Strided floating point format presets for use with floatBuffer(). New formats can be defined via defFloatFormat().

Format ID	Channel count	Description
FLOAT_GRAY	1	Single channel / grayscale
FLOAT_GRAY_ALPHA	2	Grayscale and alpha channel
FLOAT_NORMAL	3	Normal map (signed values)
FLOAT_RGB	3	Red, Green, Blue
FLOAT_RGBA	4	Red, Green, Blue, Alpha

• All color channels are unclamped (but can be clamped via buf.clamp()). For conversion to packed int formats assumed to contain normalized data (i.e. [0..1] interval, with exception of FLOAT_NORMAL which uses [-1..1] range)
• Conversion between float formats is currently unsupported

Filtered image sampling and resizing

Available (and optimized) for both integer & floating point formats, image samplers can be created with the following filters & wrap modes:

Filters

• "nearest" - nearest neighbor
• "linear" - bilinear interpolation
• "cubic" - bicubic interpolation

Wrap mode

• "clamp" - outside values return 0
• "wrap" - infinite tiling
• "repeat" - edge pixels are repeated

const src = packedBuffer(4, 4, ABGR8888);

// fill w/ random colors
src.forEach((_,i) => 0xff000000 | Math.random() * 0xffffff);

// create bilinear sampler w/ repeated edge pixels
const sampler = defSampler(src, "linear", "repeat");

// sample at fractional positions (even outside image)
sampler(-1.1, 0.5).toString(16)
// 'ff79643a'

// resize image to 1024x256 using bicubic sampling
const img = src.resize(1024, 256, "cubic");

Filter
"nearest"
"linear"
"cubic"

Strided convolution & pooling

Floating point buffers can be processed using arbitrary convolution kernels. The following convolution kernel presets are provided for convenience:

Kernel	Size
BOX_BLUR3	3x3
BOX_BLUR5	5x5
GAUSSIAN_BLUR3	3x3
GAUSSIAN_BLUR5	5x5
GAUSSIAN(n)	2n+1 x 2n+1
HIGHPASS3	3x3
LANCZOS(a,s)	as+1 x as+1
SHARPEN3	3x3
SOBEL_X	3x3
SOBEL_Y	3x3
UNSHARP_MASK5	5x5

Custom kernels can be defined (and code generated) using an array of coefficients and a given kernel size. See above presets and defKernel() for reference.

Furthermore, convolution supports striding (i.e. only processing & keeping every nth pixel column/row, aka downscaling) and pixel pooling (e.g. for ML applications). Available pooling kernel presets (kernel sizes must be configured independently):

Kernel	Description
POOL_MEAN	Moving average
POOL_MAX	Local maximum
POOL_MIN	Local minimum
POOL_NEAREST	Nearest neighbor
POOL_THRESHOLD(bias)	Adaptive threshold

Convolution can be applied to single, multiple or all channels of a FloatBuffer. See convolveChannel() and convolveImage().

See ConvolveOpts for config options.

// convolutions are only available for float buffers (for now)
src = floatBuffer(read("test.ppm"), FLOAT_RGB);

// apply horizontal Sobel kernel preset to all channels
// downscale image by factor 2 (must be integer)
// scale kernel result values by factor 4
convolveImage(src, { kernel: SOBEL_X, stride: 2, scale: 4 });

Normal map generation

Normal maps can be created via normalMap(). This function uses an adjustable convolution kernel size to control gradient smoothness & details. Result X/Y gradients can also be scaled (uniform or anisotropic) and the Z component can be customized to (default: 1.0). The resulting image is in FLOAT_NORMAL format, using signed channel values. This channel format is auto-translating these into unsigned values when the image is converted into an integer format.

Step	Scale = 1	Scale = 2	Scale = 4	Scale = 8
0
1
2
3

import { floatBuffer, normalMap, FLOAT_GRAY, RGB888 } from "@thi.ng/pixel";
import { asPPM, read } from "@thi.ng/pixel-io-netpbm";

// read source image into a single channel floating point buffer
const src = floatBuffer(read(readFileSync("noise.pgm")), FLOAT_GRAY);

// create normal map (w/ default options)
const nmap = normalMap(src, { step: 0, scale: 1 });

// pixel lookup (vectors are stored _un_normalized)
nmap.getAt(10, 10);
// Float32Array(3) [ -0.019607841968536377, -0.04313725233078003, 1 ]

// save as 24bit PBM, conversion to RGB int format first
writeFileSync("noise-normal.ppm", asPPM(nmap.as(RGB888)));

Dominant color extraction

The dominantColors() function applies k-means clustering to extract the dominant colors from the given image. The clustering can be configured. The function returns an array of { color, area } objects (sorted by descending area), where color is a cluster's dominant color (in the format of the source image) and area the normalized cluster size (number of selected pixels over total number of pixels in the image).

Picture credit: /u/kristophershinn

// read test PPM image and convert into float RGB format
const img = floatBuffer(read(readFileSync(`test.ppm`)), FLOAT_RGB);

// extract 5 dominant color clusters
const clusters = dominantColors(img, 5);

console.log(clusters);
// [
//   {
//     color: [ 0.4000000059604645, 0.30980393290519714, 0.21176470816135406 ],
//     area: 0.3141084558823529
//   },
//   {
//     color: [ 0.21960784494876862, 0.19607843458652496, 0.1411764770746231 ],
//     area: 0.2780330882352941
//   },
//   {
//     color: [ 0.4156862795352936, 0.4745098054409027, 0.5647059082984924 ],
//     area: 0.16620710784313725
//   },
//   {
//     color: [ 0.6666666865348816, 0.7568627595901489, 0.9254902005195618 ],
//     area: 0.12385110294117647
//   },
//   {
//     color: [ 0.7176470756530762, 0.4745098054409027, 0.12941177189350128 ],
//     area: 0.11780024509803921
//   }
// ]

Status

STABLE - used in production

Search or submit any issues for this package

Support packages

• @thi.ng/pixel-io-netpbm - Multi-format NetPBM reader & writer support for @thi.ng/pixel

Related packages

• @thi.ng/porter-duff - Porter-Duff operators for packed ints & float-array alpha compositing

Installation

yarn add @thi.ng/pixel

// ES module
<script type="module" src="https://unpkg.com/@thi.ng/pixel?module" crossorigin></script>

// UMD
<script src="https://unpkg.com/@thi.ng/pixel/lib/index.umd.js" crossorigin></script>

Package sizes (gzipped, pre-treeshake): ESM: 9.20 KB / CJS: 9.49 KB / UMD: 9.20 KB

Dependencies

• @thi.ng/api
• @thi.ng/binary
• @thi.ng/checks
• @thi.ng/k-means
• @thi.ng/math
• @thi.ng/porter-duff

Usage examples

Several demos in this repo's /examples directory are using this package.

A selection:

Screenshot	Description	Live demo	Source
	Interactive image processing (adaptive threshold)	Demo	Source
	Color palette generation via dominant color extraction from uploaded images	Demo	Source
	Pixel buffer manipulations	Demo	Source
	Interactive pixel sorting tool using thi.ng/color & thi.ng/pixel	Demo	Source
	Port-Duff image compositing / alpha blending	Demo	Source
	Fork-join worker-based raymarch renderer	Demo	Source
	Textmode image warping w/ 16bit color output	Demo	Source
	Minimal multi-pass / GPGPU example	Demo	Source

API

Generated API docs

import * as pix from "@thi.ng/pixel";
import { SRC_OVER_I } from "@thi.ng/porter-duff";

import IMG from "../assets/haystack.jpg";
import LOGO from "../assets/logo-64.png";

Promise
    .all([IMG, LOGO].map(pix.imagePromise))
    .then(([img, logo]) => {

        // init 16 bit packed RGB pixel buffer from image (resized to 256x256)
        const buf = pix.PackedBuffer.fromImage(img, pix.RGB565, 256, 256);

        // create grayscale buffer for logo and use Porter-Duff operator to
        // composite with main image. Since the logo has transparency, we need
        // to premultiply alpha first...
        pix.PackedBuffer.fromImage(logo, pix.GRAY_ALPHA88)
            .premultiply()
            .blend(SRC_OVER_I, buf, {
                dx: 10,
                dy: 10
            });

        // extract sub-image
        const region = buf.getRegion(32, 96, 128, 64);
        // copy region back at new position
        region.blit(buf, { dx: 96, dy: 32 });

        // or alternatively blit buf into itself
        // buf.blit(buf, { dx: 96, dy: 32, sx: 32, sy: 96, w: 128, h: 64 });

        // create html canvas
        // (returns obj of canvas & 2d context)
        const ctx = pix.canvas2d(buf.width, buf.height * 3);

        // write pixel buffer to canvas
        buf.blitCanvas(ctx.canvas);

        // manipulate single color channel (here red)
        const id = 0;
        // obtain channel & invert
        const ch = buf.getChannel(id).invert();
        // create dot pattern
        for (let y = 0; y < ch.height; y += 2) {
            for (let x = (y >> 1) & 1; x < ch.width; x += 2) {
                ch.setAt(x, y, 0xff);
            }
        }
        // replace original channel
        buf.setChannel(id, ch);

        // write pixel buffer to new position
        buf.blitCanvas(ctx.canvas, 0, buf.height);

        // create & write grayscale version
        buf.as(GRAY8).blitCanvas(ctx.canvas, 0, buf.height * 2);

        document.body.appendChild(ctx.canvas);
});

TODO see examples & source comments for now

Authors

Karsten Schmidt

If this project contributes to an academic publication, please cite it as:

@misc{thing-pixel,
  title = "@thi.ng/pixel",
  author = "Karsten Schmidt",
  note = "https://thi.ng/pixel",
  year = 2019
}

License

© 2019 - 2021 Karsten Schmidt // Apache Software License 2.0