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https://github.com/EyalAr/lwip

Light Weight Image Processor for NodeJS
https://github.com/EyalAr/lwip

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Light Weight Image Processor for NodeJS

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# Light-weight image processor for NodeJS



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0. [Overview](#overview)

  0. [Installation](#installation)

  0. [Usage](#usage)

  0. [Supported formats](#supported-formats)

  0. [Colors specification](#colors-specification)

  0. [Note on transparent images](#note-on-transparent-images)

  0. [Note on threading performance](#note-on-threading-performance)

0. [API](#api)

  0. [Open an image from file or buffer](#open-an-image)

  0. [Create a new blank image](#create-a-new-image)

  0. [Image operations](#image-operations)

    0. [Resize](#resize)

    0. [Scale](#scale)

    0. [Contain](#contain)

    0. [Cover](#cover)

    0. [Rotate](#rotate)

    0. [Crop](#crop)

    0. [Blur](#blur)

    0. [Sharpen](#sharpen)

    0. [Mirror](#mirror)

    0. [Flip](#flip)

    0. [Border](#border)

    0. [Pad](#pad)

    0. [Adjust saturation](#saturate)

    0. Adjust lightness: [lighten](#lighten) / [darken](#darken)

    0. [Adjust hue](#hue)

    0. [Fade (adjust transparency)](#fade)

    0. [Opacify](#opacify)

    0. [Paste](#paste)

    0. [Set pixel](#set-pixel)

    0. [Set metadata](#set-metadata)

  0. [Getters](#getters)

    0. [Width](#width)

    0. [Height](#height)

    0. [Pixel](#get-pixel)

    0. [Clone](#clone)

    0. [Extract / Copy](#extract)

    0. [Get as a Buffer](#get-as-a-buffer)

      0. [JPEG](#jpeg)

      0. [PNG](#png)

      0. [GIF](#gif)

    0. [Write to file](#write-to-file)

    0. [Get metadata](#get-metadata)

  0. [Batch operations](#batch-operations)

0. [Copyrights](#copyrights)



## Overview



This module provides comprehensive, fast, and simple image processing and

manipulation capabilities.



**There are no external runtime dependencies**, which means you don't have to

install anything else on your system.



**This module is in active development. [New features](https://github.com/EyalAr/lwip/issues?labels=feature+request&page=1&state=open) are being added.**



[Read the background for the development of this module.](http://eyalarubas.com/image-processing-nodejs.html)



### Installation



`npm install lwip`



Or, clone this repo and `cd lwip && npm install`.



You can run tests with `npm test`.



**Note:** Installation of this module involves compiling native code.

If `npm install lwip` failes, you probably need to setup your system.

[See instructions](https://github.com/TooTallNate/node-gyp#installation).

Building on Windows with Visual Studio requires version 2013 or higher.



### Usage



**Typical workflow:**



0. Open an image and get an image object.

0. Manipulate it.

0. Save to disk / Send image buffer over network / etc.



**Example (batch operations):**



```Javascript

// obtain an image object:

require('lwip').open('image.jpg', function(err, image){



  // check err...

  // define a batch of manipulations and save to disk as JPEG:

  image.batch()

    .scale(0.75)          // scale to 75%

    .rotate(45, 'white')  // rotate 45degs clockwise (white fill)

    .crop(200, 200)       // crop a 200X200 square from center

    .blur(5)              // Gaussian blur with SD=5

    .writeFile('output.jpg', function(err){

      // check err...

      // done.

    });



});

```



**Example (non-batch):**



```Javascript

var lwip = require('lwip');



// obtain an image object:

lwip.open('image.jpg', function(err, image){



  // check err...

  // manipulate image:

  image.scale(0.5, function(err, image){



    // check err...

    // manipulate some more:

    image.rotate(45, 'white', function(err, image){



      // check err...

      // encode to jpeg and get a buffer object:

      image.toBuffer('jpg', function(err, buffer){



        // check err...

        // save buffer to disk / send over network / etc.



      });



    });



  });



});

```



### Supported formats



**Decoding (reading):**



- JPEG, 1 & 3 channels (grayscale & RGB).

- PNG, transparency supported.

- GIF, transparency supported. Animated GIFs can be read, but only the first

  frame will be retrieved.



**Encoding (writing):**



- JPEG, 3 channels (RGB).

- PNG (lossless), 3 channels (RGB) or 4 channels (RGBA).

- GIF (no animations)



Other formats may also be supported in the future, but are probably less urgent.

Check the issues to see [which formats are planned to be supported](https://github.com/EyalAr/lwip/issues?labels=format+request&page=1&state=open).

Open an issue if you need support for a format which is not already listed.



### Colors specification



In LWIP colors are coded as RGBA values (red, green, blue and an alpha channel).



Colors are specified in one of three ways:



- As a string. possible values:



  ```Javascript

  "black"    // {r: 0, g: 0, b: 0, a: 100}

  "white"    // {r: 255, g: 255, b: 255, a: 100}

  "gray"     // {r: 128, g: 128, b: 128, a: 100}

  "red"      // {r: 255, g: 0, b: 0, a: 100}

  "green"    // {r: 0, g: 255, b: 0, a: 100}

  "blue"     // {r: 0, g: 0, b: 255, a: 100}

  "yellow"   // {r: 255, g: 255, b: 0, a: 100}

  "cyan"     // {r: 0, g: 255, b: 255, a: 100}

  "magenta"  // {r: 255, g: 0, b: 255, a: 100}

  ```



- As an array `[R, G, B, A]` where `R`, `G` and `B` are integers between 0 and

  255 and `A` is an integer between 0 and 100.

- As an object `{r: R, g: G, b: B, a: A}` where `R`, `G` and `B` are integers

  between 0 and 255 and `A` is an integer between 0 and 100.



**Note**: The `A` value (alpha channel) is always optional and defaults to

100 (completely opaque).



### Note on transparent images



0. Transparency is supported through an alpha channel which ranges between 0

   and 100. 0 is completely transparent and 100 is completely opaque.

0. Not all formats support transparency. If an image with an alpha channel is

   encoded with a format which does not support transparency, the alpha channel

   will be ignored (effectively setting it to 100% for all pixels).



### Note on threading performance



All operations are asynchronous, and processing takes place in a thread pool

managed by libuv which is part of NodeJS. This thread pool is separate from the event

loop used to process HTTP requests, so use of lwip should not significantly affect the

handling of HTTP requests by a web application. The thread pool is however shared with

other threaded native modules such as those providing database and filesystem IO.



The default thread pool size of 4 will be appropriate for most applications. However

if your application regularly processes many images concurrently and and you wish

to take full advantage of a multicore system or prevent heavy image processing work

from delaying database or filesystem IO, you may want to increase the size of the

thread pool by setting the UV_THREADPOOL_SIZE environmental variable to the NodeJS

process, e.g.:



```

UV_THREADPOOL_SIZE=8 node your_script.js

```



## API



All operations are done on an `image` object. An `image` object can be obtained

by:



0. Openning an existing image file or buffer with the [`open`](#open-an-image)

   method.

0. Creating a new image object with the [`create`](#create-a-new-image) method.

0. Cloning an existing image object with the [`image.clone`](#clone) method.

0. Extracting a sub-image from an existing image object with the

   [`image.extract`](#extract) method.



### Open an image



`lwip.open(source, type, callback)`



0. `source {String/Buffer}`: The path to the image on disk or an image buffer.

0. `type {String/Object}`: **Optional** type of the image. If omitted, the type

   will be inferred from the file extension. If `source` is a buffer, `type`

   must be specified. If `source` is an encoded image buffer, `type` must be

   a string of the image type (i.e. `"jpg"`). If `source` is a raw pixels buffer

   `type` must be an object with `type.width` and `type.height` properties.

0. `callback {Function(err, image)}`



**Note about raw pixels buffers:** `source` may be a buffer of raw pixels. The

buffer may contain pixels of 1-4 channels, where:



0. 1 channel is a grayscale image.

0. 2 channels is a grayscale image with an alpha channel.

0. 3 channels is an RGB image.

0. 4 channels is an RGBA image (with an alpha channel).



In other words, if the image in the buffer has width `W` and height `H`, the

size of the buffer can be `W*H`, `2*W*H`, `3*W*H` or `4*W*H`.



The channel values in the buffer must be stored sequentially. I.e. first all the

Red values, then all the Green values, etc.



#### Open file example



```Javascript

var lwip = require('lwip');

lwip.open('path/to/image.jpg', function(err, image){

    // check 'err'. use 'image'.

    // image.resize(...), etc.

});

```



#### Open buffer example



```Javascript

var fs = require('fs'),

    lwip = require('lwip');



fs.readFile('path/to/image.png', function(err, buffer){

  // check err

  lwip.open(buffer, 'png', function(err, image){

      // check 'err'. use 'image'.

      // image.resize(...), etc.

  });

});

```



### Create a new image



`lwip.create(width, height, color, callback)`



0. `width {Integer>0}`: The width of the new image.

0. `height {Integer>0}`: The height of the new image.

0. `color {String / Array / Object}`: **Optional** Color of the canvas. See

   [colors specification](#colors-specification). Defaults to a transparent

   canvas `{r:0, g:0, b:0, a:0}`.

0. `callback {Function(err, image)}`



**Example**:



```Javascript

var lwip = require('lwip');



lwip.create(500, 500, 'yellow', function(err, image){

  // check err

  // 'image' is a 500X500 solid yellow canvas.

});

```



### Image operations



#### Resize



`image.resize(width, height, inter, callback)`



0. `width {Integer}`: Width in pixels.

0. `height {Integer}`: **Optional** height in pixels. If omitted, `width` will

   be used.

0. `inter {String}`: **Optional** interpolation method. Defaults to `"lanczos"`.

   Possible values:

   - `"nearest-neighbor"`

   - `"moving-average"`

   - `"linear"`

   - `"grid"`

   - `"cubic"`

   - `"lanczos"`

0. `callback {Function(err, image)}`



#### Scale



`image.scale(wRatio, hRatio, inter, callback)`



0. `wRatio {Float}`: Width scale ratio.

0. `hRatio {Float}`: **Optional** height scale ratio. If omitted, `wRatio` will

   be used.

0. `inter {String}`: **Optional** interpolation method. Defaults to `"lanczos"`.

   Possible values:

   - `"nearest-neighbor"`

   - `"moving-average"`

   - `"linear"`

   - `"grid"`

   - `"cubic"`

   - `"lanczos"`

0. `callback {Function(err, image)}`



#### Contain



Contain the image in a colored canvas. The image will be resized to the largest

possible size such that it's fully contained inside the canvas.



`image.contain(width, height, color, inter, callback)`



0. `width {Integer}`: Canvas' width in pixels.

0. `height {Integer}`: Canvas' height in pixels.

0. `color {String / Array / Object}`: **Optional** Color of the canvas. See

   [colors specification](#colors-specification).

0. `inter {String}`: **Optional** interpolation method. Defaults to `"lanczos"`.

   Possible values:

   - `"nearest-neighbor"`

   - `"moving-average"`

   - `"linear"`

   - `"grid"`

   - `"cubic"`

   - `"lanczos"`

0. `callback {Function(err, image)}`



#### Cover



Cover a canvas with the image. The image will be resized to the smallest

possible size such that both its dimensions are bigger than the canvas's

dimensions. Margins of the image exceeding the canvas will be discarded.



`image.cover(width, height, inter, callback)`



0. `width {Integer}`: Canvas' width in pixels.

0. `height {Integer}`: Canvas' height in pixels.

0. `inter {String}`: **Optional** interpolation method. Defaults to `"lanczos"`.

   Possible values:

   - `"nearest-neighbor"`

   - `"moving-average"`

   - `"linear"`

   - `"grid"`

   - `"cubic"`

   - `"lanczos"`

0. `callback {Function(err, image)}`



#### Rotate



`image.rotate(degs, color, callback)`



0. `degs {Float}`: Clockwise rotation degrees.

0. `color {String / Array / Object}`: **Optional** Color of the canvas. See

   [colors specification](#colors-specification).

0. `callback {Function(err, image)}`



#### Crop



#### Crop with rectangle coordinates



`image.crop(left, top, right, bottom, callback)`



0. `left, top, right, bottom {Integer}`: Coordinates of the crop rectangle.

0. `callback {Function(err, image)}`



#### Crop a rectangle from center



`image.crop(width, height, callback)`



0. `width, height {Integer}`: Width and height of the rectangle to crop from the

   center of the image.

0. `callback {Function(err, image)}`



#### Blur



Gaussian blur.



`image.blur(sigma, callback)`



0. `sigma {Float>=0}`: Standard deviation of the Gaussian filter.

0. `callback {Function(err, image)}`



#### Sharpen



Inverse diffusion shapren.



`image.sharpen(amplitude, callback)`



0. `amplitude {Float}`: Sharpening amplitude.

0. `callback {Function(err, image)}`



#### Mirror



Mirror an image along the 'x' axis, 'y' axis or both.



`image.mirror(axes, callback)`



0. `axes {String}`: `'x'`, `'y'` or `'xy'` (case sensitive).

0. `callback {Function(err, image)}`



#### Flip



Alias of [`mirror`](#mirror).



#### Border



Add a colored border to the image.



`image.border(width, color, callback)`



0. `width {Integer}`: Border width in pixels.

0. `color {String / Array / Object}`: **Optional** Color of the border. See

   [colors specification](#colors-specification).

0. `callback {Function(err, image)}`



#### Pad



Pad image edges with colored pixels.



`image.pad(left, top, right, bottom, color, callback)`



0. `left, top, right, bottom {Integer}`: Number of pixels to add to each edge.

0. `color {String / Array / Object}`: **Optional** Color of the padding. See

   [colors specification](#colors-specification).

0. `callback {Function(err, image)}`



#### Saturate



Adjust image saturation.



`image.saturate(delta, callback)`



0. `delta {Float}`: By how much to increase / decrease the saturation.

0. `callback {Function(err, image)}`



**Examples**:



0. `image.saturate(0, ...)` will have no effect on the image.

0. `image.saturate(0.5, ...)` will increase the saturation by 50%.

0. `image.saturate(-1, ...)` will decrease the saturation by 100%, effectively

   desaturating the image.



#### Lighten



Adjust image lightness.



`image.lighten(delta, callback)`



0. `delta {Float}`: By how much to increase / decrease the lightness.

0. `callback {Function(err, image)}`



**Examples**:



0. `image.lighten(0, ...)` will have no effect on the image.

0. `image.lighten(0.5, ...)` will increase the lightness by 50%.

0. `image.lighten(-1, ...)` will decrease the lightness by 100%, effectively

   making the image black.



#### Darken



Adjust image lightness.



`image.darken(delta, callback)`



Equivalent to `image.lighten(-delta, callback)`.



#### Hue



Adjust image hue.



`image.hue(shift, callback)`



0. `shift {Float}`: By how many degrees to shift each pixel's hue.

0. `callback {Function(err, image)}`



**Examples**:



0. `image.lighten(0, ...)` will have no effect on the image.

0. `image.lighten(100, ...)` will shift pixels' hue by 100 degrees.



**Note:** The hue is shifted in a circular manner in the range [0,360] for each

pixel individually.



#### Fade



Adjust image transperancy.



`image.fade(delta, callback)`



0. `delta {Float}`: By how much to increase / decrease the transperancy.

0. `callback {Function(err, image)}`



**Note:** The transparency is adjusted independently for each pixel.



**Examples**:



0. `image.fade(0, ...)` will have no effect on the image.

0. `image.fade(0.5, ...)` will increase the transparency by 50%.

0. `image.fade(1, ...)` will make the image completely transparent.



#### Opacify



Make image completely opaque.



`image.opacify(callback)`



0. `callback {Function(err, image)}`



#### Paste



Paste an image on top of this image.



`image.paste(left, top, img, callback)`



0. `left, top {Integer}`: Coordinates of the top-left corner of the pasted

   image.

0. `img {Image object}`: The image to paste.

0. `callback {Function(err, image)}`



**Notes:**



0. If the pasted image exceeds the bounds of the base image, an exception

   is thrown.

0. `img` is pasted in the state it was at the time `image.paste( ... )` was

   called, eventhough `callback` is called asynchronously.

0. For transparent images, alpha blending is done according to the equations

   described [here](http://en.wikipedia.org/wiki/Alpha_compositing#Alpha_blending).

0. Extra caution is required when using this method in batch mode, as the images

   may change by the time this operation is called.



#### Set Pixel



Set the color of a pixel.



`image.setPixel(left, top, color, callback)`



0. `left, top {Integer}`: Coordinates of the pixel from the left-top corner of

   the image.

0. `color {String / Array / Object}`: Color of the pixel to set.

   See [colors specification](#colors-specification).

0. `callback {Function(err, image)}`



**Notes:**



0. If the coordinates exceed the bounds of the image, an exception is thrown.

0. Extra caution is required when using this method in batch mode, as the

  dimensions of the image may change by the time this operation is called.



#### Set metadata



Set the metadata in an image. This is currently only supported for PNG files.

Sets a tEXt chunk with the key `lwip_data` and comment as the given string. If

called with a `null` parameter, removes existing metadata from the image,

if present.



`image.setMetadata(metadata)`



0. `metadata {String}`: a string of arbitrary length, or null.



### Getters



#### Width



`image.width()` returns the image's width in pixels.



#### Height



`image.height()` returns the image's height in pixels.



#### Get Pixel



`image.getPixel(left, top)` returns the color of the pixel at the `(left, top)`

coordinate.



0. `left {Integer>=0}`

0. `top {Integer>=0}`



Color is returned as an object. See [colors specification](#colors-specification).



#### Clone



Clone the image into a new image object.



`image.clone(callback)`



0. `callback {Function(err, newImage)}`



**Example**: See [`examples/clone.js`](examples/clone.js)



**Note**: The image is cloned to the state it was at the time

`image.clone( ... )` was called, eventhough `callback` is called asynchronously.



```Javascript

image.width(); // 500

image.clone(function(err, clone){

    clone.width(); // 500

});

image.resize(100, 100, function(err, image){

    image.width(); //100

});

```



#### Extract



Copy an area of the image into a new image object.



`image.extract(left, top, right, bottom, callback)`



0. `left, top, right, bottom {Integer}`: Coordinates of the area to copy.

0. `callback {Function(err, newImage)}`



**Example**: See [`examples/extract.js`](examples/extract.js)



**Note**: The sub-image is extracted from the original image in the state it was

at the time `image.extract( ... )` was called, eventhough `callback` is called

asynchronously.



#### Get as a Buffer



Get encoded binary image data as a NodeJS

[Buffer](http://nodejs.org/api/buffer.html).



When opening an image, it is decoded and stored in memory as an uncompressed

image. All manipulations are done on the uncompressed data in memory. This

method allows to encode the image to one of the specified formats and get the

encoded data as a NodeJS Buffer object.



`image.toBuffer(format, params, callback)`



0. `format {String}`: Encoding format. Possible values:

  - `"jpg"`

  - `"png"`

  - `"gif"`

0. `params {Object}`: **Optional** Format-specific parameters (See below).

0. `callback {Function(err, buffer)}`



**Supported encoding formats:**



##### JPEG



The `params` object should have the following fields:



- `quality {Integer}`: Defaults to `100`.



Note that when encoding to JPEG the alpha channel is discarded.



##### PNG



The `params` object should have the following fields:



- `compression {String}`: Defaults to `"fast"`. Possible values:

  - `"none"` - No compression. Fastest.

  - `"fast"` - Basic compression. Fast.

  - `"high"` - High compression. Slowest.

- `interlaced {Boolean}`: Defaults to `false`.

- `transparency {true/false/'auto'}`: Preserve transparency? Defaults to

  `'auto'`. Determines if the encoded image will have 3 or 4 channels. If

  `'auto'`, the image will be encoded with 4 channels if it has transparent

  components, and 3 channels otherwise.



##### GIF



The `params` object should have the following fields:



- `colors {Integer}`: Defaults to `256`. Number of colors in the color table

  (at most). Must be between 2 and 256.

- `interlaced {Boolean}`: Defaults to `false`.

- `transparency {true/false/'auto'}`: Preserve transparency? Defaults to

  `'auto'`. Determines if the encoded image will have 3 or 4 channels. If

  `'auto'`, the image will be encoded with 4 channels if it has transparent

  components, and 3 channels otherwise.

- `threshold {Integer}` - Between 0 and 100. Pixels in a gif image are either

  fully transparent or fully opaque. This value sets the alpha channel

  threshold to determine if a pixel is opaque or transparent. If the alpha

  channel of the pixel is above this threshold, this pixel will be considered

  as opaque; otherwise it will be transparent.



#### Write to file



Write encoded binary image data directly to a file.



`image.writeFile(path, format, params, callback)`



0. `path {String}`: Path of file to write.

0. `format {String}`: **Optional** Encoding format. If omitted, will be inferred

   from `path` extension. Possible values are specified in

   [Get as a Buffer](#get-as-a-buffer) section.

0. `params {Object}`: **Optional** Format-specific parameters.

0. `callback {Function(err)}`



#### Get Metadata



Get the textual metadata from an image. This is currently only supported for

tEXt chunks in PNG images, and will get the first tEXt chunk found with the key

`lwip_data`. If none is found, returns null.



`image.getMetadata()`



### Batch operations



Each of the [image operations](#image-operations) above can be done as part of

a batch of operations. Operations can be queued, and executed as a batch at any

time.



Each one of the [image operations](#image-operations) has a batch equivalent

which takes the same arguments, except the callback, which is not needed.



When all batch operations had been queued, they can be executed in one of

several methods, as explained below.



#### Obtaining a batch object



In order to start queueing operations, a batch object first needs to be obtained

from the image.



```Javascript

// obtain a batch object from the image:

var batch = image.batch();

```



#### Using a batch object



Use the batch object to queue [image operations](#image-operations). Each of the

operations above has a batch equivalent. Operations can be chained.



**Remember, the batch manipulation methods do not take a callback.**



**Example:**



```Javascript

batch.rotate(45, 'white').scale(0.5).blur(5);

```



#### Executing a batch



There are several methods which start the execution of a batch. Once a batch

finishes an execution, it becomes empty and can be resued to queue additional

operations.



##### Execute batch and obtain the manipulated image object



When all desired operations had been queued, execute the batch with the `exec()`

method. `exec` takes a `callback` argument; `callback` is a function which

receives an error object and the manipulated image object:



`batch.exec(callback)`



  - `callback {Function(err, image)}`:

    - `err`: An error object or `null` when no error.

    - `image`: An image object of the manipulated image.



```Javascript

batch.exec(function(err, image){

  // check err, use image

});

```



##### Execute batch and obtain a Buffer object



Batch objects have a `toBuffer` convenience method.



`batch.toBuffer(format, params, callback)`



See parameters of [`image.toBuffer()`](#get-as-a-buffer).



##### Execute batch and write to file



Batch objects have a `writeFile` convenience method.



`batch.writeFile(path, format, params, callback)`



See parameters of [`image.writeFile()`](#write-to-file).



#### Notes on batch operations



An image can have more than one batch object, but all batch objects modify the

same underlying image. This means the order of execution matters.



```Javascript

var batch1 = image.batch().rotate('45', 'black');

var batch2 = image.batch().border(15, 'black');

```



This will rotate the image 45degs and then add a black border:



```Javascript

batch1.exec(function(err, image){

    batch2.exec(function(err, image){

        // ...

    });

});

```



While this will add a black border and then rotate the image 45degs:



```Javascript

batch2.exec(function(err, image){

    batch1.exec(function(err, image){

        // ...

    });

});

```



## Copyrights



The native part of this module is compiled from source which uses the following:



- Independent JPEG Group's free JPEG software:

  - [Website](http://www.ijg.org/)

  - [Readme](https://github.com/EyalAr/lwip/blob/master/src/lib/jpeg/README)

- libpng:

  - [Website](http://www.libpng.org/)

  - [Readme](https://github.com/EyalAr/lwip/blob/master/src/lib/png/README)

- zlib:

  - [Website](http://www.zlib.net/)

  - [Readme](https://github.com/EyalAr/lwip/blob/master/src/lib/zlib/README)

- The CImg Library

  - [Website](http://cimg.sourceforge.net/)

  - [Readme](https://github.com/EyalAr/lwip/blob/master/src/lib/cimg/README.txt)

- giflib

  - [Website](http://giflib.sourceforge.net/)

  - [Readme](https://github.com/EyalAr/lwip/blob/master/src/lib/gif/README)