PNGjs-Image

JavaScript-based PNG image encoder, decoder, and manipulator

Table of Contents

• Installation
• Usage
  • Static-Methods
  • Instance-Methods
    • Pixel manipulation
    • Pixel conversion
  • Filters
• API-Documentation
• Tests
• Third-party libraries
• License

Installation

Install this module with the following command:

npm install pngjs-image

Add the module to your package.json dependencies:

npm install --save pngjs-image

Add the module to your package.json dev-dependencies:

npm install --save-dev pngjs-image

Require the module in your source-code:

var PNGImage = require('pngjs-image');

Usage

Example: Creating a new image

var image = PNGImage.createImage(100, 300);
 
// Get width and height
console.log(image.getWidth());
console.log(image.getHeight());
 
// Set a pixel at (20, 30) with red, having an alpha value of 100 (half-transparent)
image.setAt(20, 30, { red:255, green:0, blue:0, alpha:100 });
 
// Get index of coordinate in the image buffer
var index = image.getIndex(20, 30);
 
// Print the red color value
console.log(image.getRed(index));
 
// Get low level image object with buffer from the 'pngjs' package
var pngjs = image.getImage();
 
image.writeImage('path/to/file', function (err) {
    if (err) throw err;
    console.log('Written to the file');
});

Example: Loading an image

PNGImage.readImage('path/to/file', function (err, image) {
    if (err) throw err;
 
    // Get width and height
    console.log(image.getWidth());
    console.log(image.getHeight());
 
    // Set a pixel at (20, 30) with red, having an alpha value of 100 (half-transparent)
    image.setAt(20, 30, { red:255, green:0, blue:0, alpha:100 });
});

Example: Loading an image from an url

PNGImage.readImage('https://s.yimg.com/rz/l/yahoo_en-US_f_p_142x37_2x.png', function (err, image) {
    if (err) throw err;
 
    // The image is in the 'image' variable if everything went well
});

Static-Methods

• <PNGImage> = PNGImage.addFilter(key, fn) Adds the fn filter with identifier key to the filter-list
• <PNGImage> = PNGImage.createImage(width, height) Creates an image with the given size
• <PNGImage> = PNGImage.copyImage(image) Copies an image into a new container
• PNGImage.readImage(path, fn) Loads an image from the file or url, calling the fn function when done
• PNGImage.loadImage(blob, fn) Loads an image from memory, calling the fn function when done

Instance-Methods

• <pngjs> = image.getImage() Gets the pngjs instance
• <Buffer> = image.getBlob() Gets the data as a buffer object
• <int> = image.getWidth() Gets the width of the image
• <int> = image.getHeight() Gets the height of the image
• image.clip(x, y, width, height) Clips the current image; the dimensions have to be smaller than the original image
• image.fillRect(x, y, width, height, color) Fills the rectangle with the supplied color
• image.applyFilters(filters, returnResult) Applies a list of filters to the image
• <int> = image.getIndex(x, y) Converts the x and y coordinates to the sequential index of the image buffer
• image.writeImage(path, fn) Writes the image to the filesystem and calling the fn function when done
• image.toBlob(fn) Exports data to a buffer and calling the fn function when done

Pixel manipulation

• <uint32> = image.getAtIndex(idx) Gets complete 32-bit pixel at index idx
• <uint32> = image.getAt(x, y) Gets complete 32-bit pixel at the x and y coordinate
• <uint32> = image.getPixel(x, y) Gets complete 32-bit pixel at the x and y coordinate
• image.setAtIndex(idx, color) Sets a specific color at the index. A color left-off will not be modified.
• image.setAt(x, y, color) Sets a specific color at the x and y coordinate. A color left-off will not be modified.
• image.setPixel(x, y, color) Sets a specific color at the x and y coordinate. A color left-off will not be modified.
• <uint32> = image.getColorAtIndex(idx) Gets the color components of the pixel at index idx
• <uint32> = image.getColor(x, y) Gets the color components of the pixel at the x and y coordinate
• <uint8> = image.getRed(idx) Gets the red intensity at an index
• image.setRed(idx, value, opacity) Sets the red intensity at an index
• <uint8> = image.getGreen(idx) Gets the green intensity at an index
• image.setGreen(idx, value, opacity) Sets the green intensity at an index
• <uint8> = image.getBlue(idx) Gets the blue intensity at an index
• image.setBlue(idx, value, opacity) Sets the blue intensity at an index
• <uint8> = image.getAlpha(idx) Gets the alpha intensity at an index
• image.setAlpha(idx, value, opacity) Sets the alpha intensity at an index

Pixel conversion

• <uint32> = image.getBlurPixelAt(idx, funcName) Gets the blurred color of a pixel at index idx
• <uint32> = image.getYIQAtIndex(idx) Gets the YIQ-value of a pixel at index idx
• <uint32> = image.getYIQ(x, y) Gets the YIQ-value of a pixel at the x and y coordinate
• <uint32> = image.getLumaAtIndex(idx) Gets the luma of a pixel at index idx
• <uint32> = image.getLuma(x, y) Gets the luma of a pixel at the x and y coordinate
• <uint32> = image.getSepiaAtIndex(idx) Gets the sepia-color of a pixel at index idx
• <uint32> = image.getSepia(x, y) Gets the sepia-color of a pixel at the x and y coordinate
• <uint32> = image.getLuminosityAtIndex(idx) Gets the luminosity of a pixel at index idx
• <uint32> = image.getLuminosity(x, y) Gets the luminosity of a pixel at the x and y coordinate
• <uint32> = image.getLightnessAtIndex(idx) Gets the lightness of a pixel at index idx
• <uint32> = image.getLightness(x, y) Gets the lightness of a pixel at the x and y coordinate
• <uint32> = image.getGrayScaleAtIndex(idx) Gets the grayscale-value of a pixel at index idx
• <uint32> = image.getGrayScale(x, y) Gets the grayscale-value of a pixel at the x and y coordinate

Filters

Following filters can be applied to an image:

• blur
• grayScale
• lightness
• luma
• luminosity
• sepia

API-Documentation

Generate the documentation with following command:

npm run docs

The documentation will be generated in the docs folder of the module root.

Tests

Run the tests with the following command:

npm run test

The code-coverage will be written to the coverage folder in the module root.

Third-party libraries

The following third-party libraries are used by this module:

Dependencies

• pako: https://github.com/nodeca/pako
• pngjs: https://github.com/niegowski/node-pngjs
• stream-buffers: https://github.com/samcday/node-stream-buffer
• underscore: http://underscorejs.org
• request: https://github.com/request/request

Dev-Dependencies

• chai: http://chaijs.com
• coveralls: https://github.com/cainus/node-coveralls
• codeclimate-test-reporter: https://github.com/codeclimate/javascript-test-reporter
• istanbul: https://github.com/gotwarlost/istanbul
• mocha: https://github.com/visionmedia/mocha
• sinon: http://sinonjs.org
• sinon-chai: https://github.com/domenic/sinon-chai
• yuidocjs: https://github.com/yui/yuidoc

License

The MIT License

Copyright 2014-2015 Yahoo Inc.