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Aug 29, 2011
Aug 14, 2014
Feb 17, 2014


Obscura is a small library of common image manipulation functions using canvas


First include the obscura.js file on your page

<script type="text/javascript" src="path/to/obscura.js"></script>

Obscura can be used in two different ways. You can either use it with an img element already on the page, or with an image on file.

To create a new Obscura instance do the following:

//with on page element
var camera = new obscura('#image'[,'#target']);

//with image on file
var camera = new obscura('img/my-image.gif'[,'#target']);

The second argument is optional and is the id of an on page canvas element. If this is omitted Obscura will create an internal canvas element to render to. This is generally used with the save function which returns the image as a base64 encoded string.

All methods are chainable so if you want you can just call them after the constructor, however if you are using the second method, passing a file path in, you should set the onLoad method like so:

camera.onLoad = function(){

Otherwise it won't work as it will try and call the methods before Obscura's internal image element has loaded the image.

View Demos



camera.resize(300 [,keepProportions=true[,crop=false]);
camera.resize('50%' [,keepProportions=true[,crop=false]);
camera.resize({w:300,h:250} [,keepProportions=true[,crop=false]);
camera.resize([300,250] [,keepProportions=true[,crop=false]);

Resizes image to given values. Values are specified either as a percentage string value e.g. '50%' or as a pixel value, which can be given as an integer e.g. 300 or as a string value '300px'. If only one value is given Obscura will assume you wish to resize both dimensions to that scale. There are also 2 optional parameters:

  • keepProportions A boolean value that defines whether the image will be distorted on resizing, if set to false and not cropping, it will resize to the largest of the new dimensions, or, if the new dimensions are equal, it will resize to whichever the largest original dimension is. Defaults to true.
  • crop A boolean value that defines whether to crop the image on resize if the new proportions are different. Defaults to false.

View Demo


Similar to Resize, Fit will resize an image to fit into the area defined by the width and height values provided. Priority is given to the largest original dimension.

View Demo



Crops an image to the given dimensions, from the given start co-ordinates.

View Demo



Rotates an image by the specified amount of degrees. Takes one optional parameter:

  • center Defines the center of rotation. Currently just takes a string e.g. 'top right'. The string can be formatted any way as long as it contains one of the valid x and y strings in it. Valid strings are 'top', 'bottom', 'left', 'right' and 'center'. For the exact center you can just use center once. I will be adding the facility to specify co-ordinates in the next version. Defaults to 'center'.

View Demo



Flips the image across the specified axis. If no parameter is passed it will default to 'horizontal', other option is 'vertical'.

View Demo



Adds a reflection to the image. Takes 3 optional parameters:

  • alphaStart Specifies the initial transparency percentage that the reflection will fade from. Defaults to 0.5.
  • gap Defines the distance between the bottom of the image and the start of the reflection. Defaults to 0.
  • reflectionAmount Defines the size of the reflection as a percentage of the original image. Defaults to 0.25.

View Demo



Internally used method that sets internal variables and calls the initial load of the image.



Internal method used to load the image source onto the internal canvas object for manipulation. Takes 5 optional parameters.

  • x Specifies the initial x coordinate to load from on the original image. Defaults to 0.
  • y Specifies the initial y coordinate to load from on the original image. Defaults to 0.
  • w Specifies the width of the slice to take from the inital image. Defaults to the original image width.
  • h Specifies the height of the slice to take from the inital image. Defaults to the original image height.
  • image Defines the source image to load from. Defaults to the internal target canvas object.



Internal method that renders the updated image to the target canvas. All manipulation methods call this before returning. Generally shouldn't need to be called manually.


Returns the manipulated image as a base64 encoded data url string. Can be used to load the image into an image element, or to save the image to file in conjunction with the server side solution of your choice.


camera.onLoad = function(){

Allows you to specify a callback to be called once the source image is loaded. Used when passing a file name to the constructor method instead of an image element.


Obscura uses a number of interal properties that can be accessed to give you information about the image.

  • target The target canvas that Obscura will render to. If not an on page element Obscura will create an internal object to use.
  • canvas Obscura's internal canvas object that the manipulations are performed on.
  • context The 2d context of Obscura's internal canvas object.
  • imageDimensions The current dimensions of the image. Is an object in the form {w:width,h:height}
  • dimensions The new dimensions of the image. Generally the same as imageDimensions but will be changed during the manipulation process.


Canvas Based Image Manipulation Library




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