Jimp
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The "JavaScript Image Manipulation Program" :-)
An image processing library for Node written entirely in JavaScript, with zero native dependencies.
Installation: npm install --save jimp
Example usage:
var Jimp = require("jimp");
Jimp.read("lenna.png", function (err, lenna) {
if (err) throw err;
lenna.resize(256, 256)
.quality(60)
.greyscale()
.write("lena-small-bw.jpg");
});
Using promises:
Jimp.read("lenna.png").then(function (lenna) {
return lenna.resize(256, 256)
.quality(60)
.greyscale()
.write("lena-small-bw.jpg");
}).catch(function (err) {
console.error(err);
});
Basic usage
The static Jimp.read
method takes the path to a PNG, JPEG or BMP file and returns a Promise:
Jimp.read("./path/to/image.jpg").then(function (image) {
}).catch(function (err) {
});
The method can also read a PNG, JPEG or BMP buffer or from a URL:
Jimp.read(lenna.buffer).then(function (image) {
}).catch(function (err) {
});
Jimp.read("http://www.example.com/path/to/lenna.jpg").then(function (image) {
}).catch(function (err) {
});
Basic methods
Once the promise is fulfilled, the following methods can be called on the image:
image.contain( w, h[, alignBits || mode, mode] );
image.cover( w, h[, alignBits || mode, mode] );
image.resize( w, h[, mode] );
image.scale( f[, mode] );
image.scaleToFit( w, h[, mode] );
image.autocrop([tolerance, frames]);
image.crop( x, y, w, h );
image.blit( src, x, y[, srcx, srcy, srcw, srch] );
image.composite( src, x, y );
image.mask( src, x, y );
image.convolute( kernel );
image.flip( horz, vert );
image.mirror( horz, vert );
image.rotate( deg[, mode] );
image.exifRotate();
image.brightness( val );
image.contrast( val );
image.dither565();
image.greyscale();
image.invert();
image.normalize();
image.fade( f );
image.opacity( f );
image.opaque();
image.background( hex );
image.gaussian( r );
image.blur( r );
image.posterize( n );
image.sepia();
image.pixelate( size[, x, y, w, h ]);
image.displace( map, offset );
Some of these methods are irreversable, so it can be useful to perform them on a clone of the original image:
image.clone();
(Contributions of more methods are welcome!)
Resize modes
The default resizing algorithm uses a bilinear method as follows:
image.resize(250, 250);
image.resize(Jimp.AUTO, 250);
image.resize(250, Jimp.AUTO);
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) {
image.print(font, x, y, str);
image.print(font, x, y, str, width);
});
Jimp.loadFont( path, cb );
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;
Jimp.FONT_SANS_10_BLACK;
Jimp.FONT_SANS_12_BLACK;
Jimp.FONT_SANS_14_BLACK;
Jimp.FONT_SANS_16_BLACK;
Jimp.FONT_SANS_32_BLACK;
Jimp.FONT_SANS_64_BLACK;
Jimp.FONT_SANS_128_BLACK;
Jimp.FONT_SANS_8_WHITE;
Jimp.FONT_SANS_16_WHITE;
Jimp.FONT_SANS_32_WHITE;
Jimp.FONT_SANS_64_WHITE;
Jimp.FONT_SANS_128_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 );
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 be obtained using:
image.getBuffer( mime, cb );
For convenience, supported MIME types are available as static properties:
Jimp.MIME_PNG;
Jimp.MIME_JPEG;
Jimp.MIME_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 );
PNG and JPEG quality
The quality of JPEGs can be set with:
image.quality( n );
The format of PNGs can be set with:
image.rgba( bool );
image.filterType( number );
image.deflateLevel( number );
Jimp.deflateStrategy( number );
For convenience, supported filter types are available as static properties:
Jimp.PNG_FILTER_AUTO;
Jimp.PNG_FILTER_NONE;
Jimp.PNG_FILTER_SUB;
Jimp.PNG_FILTER_UP;
Jimp.PNG_FILTER_AVERAGE;
Jimp.PNG_FILTER_PAETH;
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.convolute([
[-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;
image.bitmap.width;
image.bitmap.height
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);
Example usage:
image.scan(0, 0, image.bitmap.width, image.bitmap.height, function (x, y, idx) {
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 ];
});
If you need to do something with the image at the end of the scan:
image.scan(0, 0, image.bitmap.width, image.bitmap.height, function (x, y, idx) {
if(x == image.bitmap.width-1 &&
y == image.bitmap.height-1) {
}
});
A helper to locate a particular pixel within the raw bitmap buffer:
image.getPixelIndex(x, y);
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);
image.setPixelColor(hex, x, y);
Two static helper functions exist to convert RGBA values into single integer (hex) values:
Jimp.rgbaToInt(r, g, b, a);
Jimp.intToRGBA(hex);
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) {
});
You can optionally set the pixel colour as follows:
var image = new Jimp(256, 256, 0xFF0000FF, function (err, image) {
});
Comparing images
To generate a perceptual hash of a Jimp image, based on the pHash algorithm, use:
image.hash();
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);
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);
Jimp also allows the diffing of two Jimp images using PixelMatch as follows:
var diff = Jimp.diff(image1, image2, threshold);
diff.image;
diff.percent;
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);
var diff = Jimp.diff(png, jpeg);
if (distance < 0.15 || diff.percent < 0.15) {
} else {
}
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.
Contributing
Basicaly clone, change, test, push and pull request.
Please read de CONTRIBUTING documentation.
Testing
The test framework runs at node.js and browsers environments. Just run npm test
to test in node and browser environments.
More information at "How to Contribute" doc's "Testing" topic.
License
Jimp is licensed under the MIT license. Open Sans is licensed under the Apache license.