patci-jimp

Jimp

The "JavaScript Image Manipulation Program" :-)

An image processing library for Node written entirely in JavaScript, with zero external or native dependencies.

Example usage:

var Jimp = require("jimp");

// open a file called "lenna.png"
Jimp.read("lenna.png", function (err, lenna) {
    if (err) throw err;
    lenna.resize(256, 256)            // resize
         .quality(60)                 // set JPEG quality
         .greyscale()                 // set greyscale
         .write("lena-small-bw.jpg"); // save
});

Using promises:

Jimp.read("lenna.png").then(function (lenna) {
    lenna.resize(256, 256)           // resize
         .quality(60)                // set JPEG quality
         .greyscale()                // set greyscale
         .write("lena-small-bw.jpg") // save
}).catch(function (err) {
    console.error(err);
});

Basic usage

The static Jimp.read method takes the path to a PNG, JPEG or BMP file and (optionally) a Node-style callback and returns a Promise:

Jimp.read("./path/to/image.jpg", function (err, image) {
    // do stuff with the image (if no exception)
});

Jimp.read("./path/to/image.jpg").then(function (image) {
    // do stuff with the image
}).catch(function (err) {
    // handle an exception
});

The method can also read a PNG, JPEG or BMP buffer or from a URL:

Jimp.read(lenna.buffer, function (err, image) {
    // do stuff with the image (if no exception)
});

Jimp.read("http://www.example.com/path/to/lenna.jpg", function (err, image) {
    // do stuff with the image (if no exception)
});

JPEG images with EXIF orientation data will be automatically re-orientated as appropriate.

Once the callback is filed or the promise fulfilled, the following methods can be called on the image:

image.crop( x, y, w, h );      // crop to the given region
image.invert();                // invert the image colours
image.flip( horz, vert );      // flip the image horizontally or vertically
image.gaussian( r );           // Gaussian blur the image by r pixels (VERY slow)
image.blur( r );               // fast blur the image by r pixels
image.greyscale();             // remove colour from the image
image.sepia();                 // apply a sepia wash to the image
image.opacity( f );            // multiply the alpha channel by each pixel by the factor f, 0 - 1
image.resize( w, h );          // resize the image. Jimp.AUTO can be passed as one of the values.
image.scale( f );              // scale the image by the factor f
image.rotate( deg[, resize] ); // rotate the image clockwise by a number of degrees. Unless `false` is passed as the second parameter, the image width and height will be resized appropriately.
image.blit( src, x, y );       // blit the image with another Jimp image at x, y
image.composite( src, x, y );  // composites another Jimp image over this iamge at x, y
image.brightness( val );       // adjust the brighness by a value -1 to +1
image.contrast( val );         // adjust the contrast by a value -1 to +1
image.posterize( n );          // apply a posterization effect with n level
image.mask( src, x, y );       // masks the image with another Jimp image at x, y using average pixel value
image.dither565();             // ordered dithering of the image and reduce color space to 16-bits (RGB565)
image.cover( w, h );           // scale the image so that it fills the given width and height
image.contain( w, h );         // scale the image to the largest size so that fits inside the given width and height
image.background( hex );       // set the default new pixel colour (e.g. 0xFFFFFFFF or 0x00000000) for by some operations (e.g. image.contain and image.rotate) and when writing formats that don't support alpha channels
image.mirror( horz, vert );    // an alias for flip
image.fade( f );               // an alternative to opacity, fades the image by a factor 0 - 1. 0 will haven no effect. 1 will turn the image
image.opaque();                // set the alpha channel on every pixel to fully opaque
image.clone();                 // returns a clone of the image

(Contributions of more methods are welcome!)

Writing to files and buffers

Writing to files

The image can be written to disk in PNG, JPEG or BMP format (determined by the file extension) using:

image.write( path, cb ); // Node-style callback will be fired when write is successful

Writing to Buffers

A PNG, JPEG or BMP binary Buffer of an image (e.g. for storage in a database) can to got using:

image.getBuffer( mime, cb ); // Node-style callback wil be fired with result

For convenience, supported MIME types are available as static properties:

Jimp.MIME_PNG;  // "image/png"
Jimp.MIME_JPEG; // "image/jpeg"
Jimp.BMP;       // "image/bmp"

PNG and JPEG quality

The quality of JPEGs can be set with:

image.quality( n ); // set the quality of saved JPEG, 0 - 100

The format of PNGs can be set with:

image.rgba( bool );           // set whether PNGs are saved as RGBA (true, default) or RGB (false)
image.filterType( number );   // set the filter type for the saved PNG
image.deflateLevel( number ); // set the deflate level for the saved PNG

For convenience, supported filter types are available as static properties:

Jimp.PNG_FILTER_AUTO;    // -1
Jimp.PNG_FILTER_NONE;    //  0
Jimp.PNG_FILTER_SUB;     //  1
Jimp.PNG_FILTER_UP;      //  2
Jimp.PNG_FILTER_AVERAGE; //  3
Jimp.PNG_FILTER_PAETH;   //  4

Advanced usage

Colour manipulation

Jimp supports advanced colour manipulation using a single method as follows:

image.color([
    { apply: 'hue', params: [ -90 ] },
    { apply: 'lighten', params: [ 50 ] },
    { apply: 'xor', params: [ '#06D' ] }
]);

The method supports the following modifiers:

Modifier	Description
lighten {amount}	Lighten the color a given amount, from 0 to 100. Providing 100 will always return white (works through TinyColor)
brighten {amount}	Brighten the color a given amount, from 0 to 100 (works through TinyColor)
darken {amount}	Darken the color a given amount, from 0 to 100. Providing 100 will always return black (works through TinyColor)
desaturate {amount}	Desaturate the color a given amount, from 0 to 100. Providing 100 will is the same as calling greyscale (works through TinyColor)
saturate {amount}	Saturate the color a given amount, from 0 to 100 (works through TinyColor)
greyscale {amount}	Completely desaturates a color into greyscale (works through TinyColor)
spin {degree}	Spin the hue a given amount, from -360 to 360. Calling with 0, 360, or -360 will do nothing - since it sets the hue back to what it was before. (works through TinyColor)
hue {degree}	Alias for spin
mix {color, amount}	Mixes colors by their RGB component values. Amount is opacity of overlaying color
tint {amount}	Same as applying mix with white color
shade {amount}	Same as applying mix with black color
xor {color}	Treats the two colors as bitfields and applies an XOR operation to the red, green, and blue components
red {amount}	Modify Red component by a given amount
green {amount}	Modify Green component by a given amount
blue {amount}	Modify Blue component by a given amount

Low-level manipulation ###

Jimp enables low-level manipulation of images in memory through the bitmap property of each Jimp object:

image.bitmap.data; // a Buffer of the raw bitmap data
image.bitmap.width; // the width of the image
image.bitmap.height // the height of the image

This data can be manipulated directly but remember: garbage in, garbage out.

A helper method is available to scan a region of the bitmap:

image.scan(x, y, w, h, cb); // scan a given region of the bitmap and call cb on every pixel

Example usage:

image.scan(0, 0, image.bitmap.width, image.bitmap.height, function (x, y, idx) {
    // x, y is the position of this pixel on the image
    // idx is the position start position of this rgba tuple in the bitmap Buffer
    // this is the image

    var red = this.bitmap.data[idx];
    var green = this.bitmap.data[idx+1];
    var blue = this.bitmap.data[idx+2];
    var alpha = this.bitmap.data[idx+3];

    // rgba values run from 0 - 255
    // e.g. this.bitmap.data[idx] = 0; // removes red from this pixel
});

Alternatively, you can manipulate individual pixels using the following these functions:

image.getPixelColor(x, y); // returns the colour of that pixel e.g. 0xFFFFFFFF
image.setPixelColor(hex, x, y); // sets the colour of that pixel

Two static helper functions exist to convert RGBA values into single integer (hex) values:

Jimp.rgbaToInt(r, g, b, a); // e.g. converts 255, 255, 255, 255 to 0xFFFFFFFF
Jimp.intToRGBA(hex); // e.g. converts 0xFFFFFFFF to {r: 255, g: 255, b: 255, a:255}

Creating new images

If you want to begin with an empty Jimp image, you can call the Jimp constructor passing the width and height of the image to create and (optionally) a Node-style callback:

var image = new Jimp(256, 256, function (err, image) {
    // this image is 256 x 256, every pixel is set to 0x00000000
});

You can optionally set the pixel colour as follows:

var image = new Jimp(256, 256, 0xFF0000FF, function (err, image) {
    // this image is 256 x 256, every pixel is set to 0xFF0000FF
});

Comparing images

To generate a perceptual hash of a Jimp image, based on the pHash algorithm, use:

image.hash(); // aHgG4GgoFjA

By default the hash is returned as base 64. The hash can be returned at another base by passing a number from 2 to 64 to the method:

image.hash(2); // 1010101011010000101010000100101010010000011001001001010011100100

There are 18,446,744,073,709,551,615 unique hashes. The hammering distance between the binary representation of these hashes can be used to find similar-looking images.

To calculate the hammering distance between two Jimp images based on their perceptual hash use:

Jimp.distance(image1, image2); // returns a number 0-1, where 0 means the two images are percieved to be identical

Jimp also allows the diffing of two Jimp images using PixelMatch as follows:

var diff = Jimp.diff(image1, image2, threshold); // threshold ranges 0-1 (default: 0.1)
diff.image;   // a Jimp image showing differences
diff.percent; // the proportion of different pixels (0-1), where 0 means the images are pixel identical

Using a mix of hammering distance and pixel diffing to comare images, the following code has a 99% success rate of detecting the same image from a random sample (with 1% false positives). The test this figure is drawn from attempts to match each image from sample of 120 PNGs against 120 corresponing JPEGs saved at a quality setting of 60.

var distance = Jimp.distance(png, jpeg); // percieved distance

var jpeg_r = jpeg.clone().resize(png.bitmap.width, png.bitmap.height);
var diff = Jimp.diff(png, jpeg_r);       // pixel difference

if (distance < 0.15 || diff.percent < 0.15) {
    // images match
} else {
    // not a match
}

Chaining or callbacks

Most instance methods can be chained together, for example as follows:

Jimp.read("lenna.png", function (err, image) {
    this.greyscale().scale(0.5).write("lena-half-bw.png");
});

Alternatively, methods can be passed Node-style callbacks:

Jimp.read("lenna.png", function (err, image) {
    image.greyscale(function(err, image) {
        image.scale(0.5, function (err, image) {
            image.write("lena-half-bw.png");
        });
    });
});

The Node-style callback pattern allows Jimp to be used with frameworks that expect or build on the Node-style callback pattern.

License

Jimp is licensed under the MIT license.