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jimp


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Collaborators wanted: https://github.com/oliver-moran/jimp/issues/219


Jimp

The "JavaScript Image Manipulation Program" :-)

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

Installation: npm install --save jimp

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) 
});

Basic methods

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

/* Resize */
image.contain( w, h[, alignBits || mode, mode] );    // scale the image to the given width and height, some parts of the image may be letter boxed 
image.cover( w, h[, alignBits || mode, mode] );      // scale the image to the given width and height, some parts of the image may be clipped 
image.resize( w, h[, mode] );     // resize the image. Jimp.AUTO can be passed as one of the values. 
image.scale( f[, mode] );         // scale the image by the factor f 
image.scaleToFit( w, h[, mode] ); // scale the image to the largest size that fits inside the given width and height 
 
// An optional resize mode can be passed with all resize methods. 
 
/* Crop */
image.autocrop([tolerance, frames]); // automatically crop same-color borders from image (if any), frames must be a Boolean 
image.crop( x, y, w, h );         // crop to the given region 
 
/* Composing */
image.blit( src, x, y[, srcx, srcy, srcw, srch] );
                                  // blit the image with another Jimp image at x, y, optionally cropped. 
image.composite( src, x, y );     // composites another Jimp image over this image at x, y 
image.mask( src, x, y );          // masks the image with another Jimp image at x, y using average pixel value 
image.convolute( kernel );        // applies a convolution kernel matrix to the image or a region 
 
/* Flip and rotate */
image.flip( horz, vert );         // flip the image horizontally or vertically 
image.mirror( horz, vert );       // an alias for flip 
image.rotate( deg[, mode] );      // rotate the image clockwise by a number of degrees. Optionally, a resize mode can be passed. If `false` is passed as the second parameter, the image width and height will not be resized. 
image.exifRotate();               // JPEG images with EXIF orientation data will be automatically re-orientated as appropriate. 
 
/* Colour */
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.dither565();                // ordered dithering of the image and reduce color space to 16-bits (RGB565) 
image.greyscale();                // remove colour from the image 
image.invert();                   // invert the image colours 
image.normalize();                // normalize the channels in an image 
 
/* Alpha channel */
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.opacity( f );               // multiply the alpha channel by each pixel by the factor f, 0 - 1 
image.opaque();                   // set the alpha channel on every pixel to fully opaque 
image.background( hex );          // set the default new pixel colour (e.g. 0xFFFFFFFF or 0x00000000) for by some operations (e.g. image.contain and 
 
/* Blurs */
image.gaussian( r );              // Gaussian blur the image by r pixels (VERY slow) 
image.blur( r );                  // fast blur the image by r pixels 
 
/* Effects */
image.posterize( n );             // apply a posterization effect with n level 
image.sepia();                    // apply a sepia wash to the image 
image.pixelate( size[, x, y, w, h ]);  // apply a pixelation effect to the image or a region 
 
/* 3D */
image.displace( map, offset );    // displaces the image pixels based on the provided displacement map. Useful for making stereoscopic 3D images. 

Some of these methods are irreversable, so it can be useful to perform them on a clone of the original image:

image.clone();                    // returns a clone of the image 

(Contributions of more methods are welcome!)

Resize modes

The default resizing algorithm uses a bilinear method as follows:

image.resize(250, 250);           // resize the image to 250 x 250 
image.resize(Jimp.AUTO, 250);     // resize the height to 250 and scale the width accordingly 
image.resize(250, Jimp.AUTO);     // resize the width to 250 and scale the height accordingly 

Optionally, the following constants can be passed to choose a particular resizing algorithm:

Jimp.RESIZE_NEAREST_NEIGHBOR;
Jimp.RESIZE_BILINEAR;
Jimp.RESIZE_BICUBIC;
Jimp.RESIZE_HERMITE;
Jimp.RESIZE_BEZIER;

For example:

image.resize(250, 250, Jimp.RESIZE_BEZIER);

Align modes

The following constants can be passed to image.cover and image.contain methods:

Jimp.HORIZONTAL_ALIGN_LEFT;
Jimp.HORIZONTAL_ALIGN_CENTER;
Jimp.HORIZONTAL_ALIGN_RIGHT;
 
Jimp.VERTICAL_ALIGN_TOP;
Jimp.VERTICAL_ALIGN_MIDDLE;
Jimp.VERTICAL_ALIGN_BOTTOM;

For example:

image.contain(250, 250, Jimp.HORIZONTAL_ALIGN_LEFT | Jimp.VERTICAL_ALIGN_TOP);

Default align modes are :

Jimp.HORIZONTAL_ALIGN_CENTER | Jimp.VERTICAL_ALIGN_MIDDLE;

Writing text

Jimp supports basic typography using BMFont format (.fnt) bitmap fonts:

Jimp.loadFont( path ).then(function (font) { // load font from .fnt file 
    image.print(font, x, y, str);        // print a message on an image 
    image.print(font, x, y, str, width); // print a message on an image with text wrapped at width 
});
 
Jimp.loadFont( path, cb ); // using a callback pattern 

BMFont fonts are raster based and fixed in size and colour. Jimp comes with a set of fonts that can be used on images:

Jimp.FONT_SANS_8_BLACK;   // Open Sans, 8px, black 
Jimp.FONT_SANS_16_BLACK;  // Open Sans, 16px, black 
Jimp.FONT_SANS_32_BLACK;  // Open Sans, 32px, black 
Jimp.FONT_SANS_64_BLACK;  // Open Sans, 64px, black 
Jimp.FONT_SANS_128_BLACK; // Open Sans, 128px, black 
 
Jimp.FONT_SANS_8_WHITE;   // Open Sans, 8px, white 
Jimp.FONT_SANS_16_WHITE;  // Open Sans, 16px, white 
Jimp.FONT_SANS_32_WHITE;  // Open Sans, 32px, white 
Jimp.FONT_SANS_64_WHITE;  // Open Sans, 64px, white 
Jimp.FONT_SANS_128_WHITE; // Open Sans, 128px, white 

These can be used as follows:

Jimp.loadFont(Jimp.FONT_SANS_32_BLACK).then(function (font) {
    image.print(font, 10, 10, "Hello world!");
});

Online tools are also available to convert TTF fonts to BMFont format (e.g. Littera).

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 

The original extension for an image (or "png") can accessed as using image.getExtension(). The following will save an image using its original format:

var file = "new_name." + image.getExtension();
image.write(file)

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 will 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.MIME_BMP;  // "image/bmp" 

If Jimp.AUTO is passed as the MIME type then the original MIME type for the image (or "image/png") will be used. Alernatively, image.getMIME() will return the original MIME type of the image (or "image/png").

Data URI

A Base64 data URI can be generated in the same way as a Buffer, using:

image.getBase64( mime, cb ); // Node-style callback will be fired with result 

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 
Jimp.deflateStrategy( number ); // set the deflate for the saved PNG (0-3) 

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

Convolution matrix

Sum neighbor pixels weighted by the kernel matrix. You can find a nice explanation with examples at GIMP's Convolution Matrix plugin

Implement emboss effect:

  image.convolution([
    [-2,-1, 0],
    [-1, 1, 1],
    [ 0, 1, 2]
  ])

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, f); // scan a given region of the bitmap and call the function f 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 + 0 ];
    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 
});

A helper to locate a particular pixel within the raw bitmap buffer:

image.getPixelIndex(x, y); // returns the index within image.bitmap.data 

One of the following may be optionally passed as a third parameter to indicate a strategy for x, y positions that are outside of boundaries of the image:

Jimp.EDGE_EXTEND = 1;
Jimp.EDGE_WRAP = 2;
Jimp.EDGE_CROP = 3;

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 hamming distance between the binary representation of these hashes can be used to find similar-looking images.

To calculate the hamming 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 perceived 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 hamming 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 a sample of 120 PNGs against 120 corresponing JPEGs saved at a quality setting of 60.

var distance = Jimp.distance(png, jpeg); // perceived distance 
var diff = Jimp.diff(png, jpeg);         // 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. Open Sans is licensed under the Apache license.