imagejs

ImageJS

Read, manipulate and write Images

Due to a lack of pure JavaScript Image manipulation libraries available, I decided to implement one.

This is an early release supporting only jpeg and png files and only the simplest resize algorithms but there will be more to come.

Installation

npm install imagejs

New Features!

• Internal Restructuring
• Corrected Documentation
• Better Bitmap Construction
• Performance Improvements

Contents

• Interface
  • Creating Bitmaps
  • Manipulating Bitmaps
    • Set Pixel
    • Negative
    • Blur
    • Crop
    • Resize
  • Reading Images
  • Writing Images
• Release History

Interface

var ImageJS = require("imagejs");

Creating Bitmaps

// Create an uninitialized bitmap 320x200
// Note: the bitmap may be filled with random data
var bitmap = new ImageJS.Bitmap({width: 320, height: 200});

// Create a bitmap filled with green
var greenBitmap = new ImageJS.Bitmap({width: 100, height: 100, color: {r: 255, g: 255, b: 255, a: 255});

// Copy a bitmap
var copy = new ImageJS.Bitmap(otherBitmap);

// Create a bitmap and attach to supplied data structure
var attachedBitmap = new ImageJS.Bitmap({
    width: 100,
    height: 100,
    data: new Buffer(4 * 100 * 100)
});

// Create an empty (null) bitmap, ready for reading from file or stream
var nullBitmap = new ImageJS.Bitmap();

Manipulating Bitmaps

Set Pixel

// Set a pixel
// where: 0 <= x < width, 0 <= y < height, 0 <= r,g,b,a < 256
bitmap.setPixel(x,y, r,g,b,a);

// Set a pixesl using a color object
var yellow = {r:255, g:255, b:0}; // alpha defaults to 255
bitmap.setPixel(x,y, yellow);

Get Pixel

// fetch the color of a pixel
var color = bitmap.getPixel(x,y);

// to improve performance you can supply the color object
var color = {};
color = bitmap.getPixel(x,y, color);

Negative

// Create a new bitmap that is a negative of the original
var negative = bitmap.negative();

Blur

// blur with simple gaussian filter
var blurred = bitmap.blur();

Crop

// create a new bitmap from a portion of another
var cropped = bitmap.crop({top: 50, left: 30, width: 100, height: 100});

Resize

// resize to 64x64 icon sized bitmap using nearest neighbor algorithm & stretch to fit
var thumbnail = bitmap.resize({
    width: 64, height: 64,
    algorithm: "nearestNeighbor"
});

// resize to 100x150 bitmap using bilinear interpolation and cropping to fit, gravity center
var thumbnail = bitmap.resize({
    width: 100, height: 150,
    algorithm: "bilinearInterpolation",
    fit: "crop",
    gravity: {x:0.5, y:0.5} // center - note: this is the default
});

// resize to 300x200 bitmap using bicubic interpolation and padding to fit, pad color solid red
var thumbnail = bitmap.resize({
    width: 300, height: 200,
    algorithm: "bicubicInterpolation",
    fit: "pad",
    padColor: {r:255, g:0, b:0, a:255}
});

Supported Resize Algorithms

• nearestNeighbor
• bilinearInterpolation
• bicubicInterpolation
• hermiteInterpolation
• bezierInterpolation

Reading Images

// read from a file
var bitmap = new Bitmap();
bitmap.readFile(filename)
    .then(function() {
        // bitmap is ready
    });

// read JPG data from stream
var stream = createReadStream();
var bitmap = new Bitmap();
bitmap.read(stream, { type: ImageJS.ImageType.JPG })
    .then(function() {
        // bitmap is ready
    });

Writing Images

// write to a jpg file, quality 75 (default is 90)
return bitmap.writeFile("image.jpg", { quality:75 })
    .then(function() {
        // bitmap has been saved
    });

// write PNG Image to a stream
var stream = createWriteStream();
return bitmap.write(stream, {type: ImageJS.ImageType.PNG})
    .then(function() {
        // bitmap has been written and stream ended
    });

Release History

Version	Changes
0.0.1	Initial Version
0.0.2	Enhanced Resize New Resize Algorithm: Bilinear Interpolation Stretch, Crop or Pad to Fit PNG Image files supported
0.0.3	Enhanced Resize New Resize Algorithm: Bicubic Interpolation
0.0.5	Enhanced Resize New Resize Algorithm: Bezier Interpolation 2 Pass algorithm to compensate for undersampling Blur Images Crop Images
0.0.6	Internal Restructuring Corrected Documentation Better Bitmap Construction Performance Improvements