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HTML canvas createImageData() Method

Canvas Object Reference Canvas Object

Example

Create a 100*100 pixels ImageData object where every pixel is red, and put it onto the canvas:

YourbrowserdoesnotsupporttheHTML5canvastag.

JavaScript:

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
var imgData=ctx.createImageData(100,100);
for (var i=0;i<imgData.data.length;i+=4)
  {
  imgData.data[i+0]=255;
  imgData.data[i+1]=0;
  imgData.data[i+2]=0;
  imgData.data[i+3]=255;
  }
ctx.putImageData(imgData,10,10);

Try it yourself »

Browser Support

Internet Explorer Firefox Opera Google Chrome Safari

Internet Explorer 9, Firefox, Opera, Chrome, and Safari support the createImageData() method.

Note: Internet Explorer 8 and earlier versions, do not support the <canvas> element.


Definition and Usage

The createImageData() method creates a new, blank ImageData object. The new object's pixel values are transparent black by default.

For every pixel in an ImageData object there are four pieces of information, the RGBA values:

R - The color red (from 0-255)
G - The color green (from 0-255)
B - The color blue (from 0-255)
A - The alpha channel (from 0-255; 0 is transparent and 255 is fully visible)

So, transparent black indicates: (0,0,0,0).

The color/alpha information is held in an array, and since the array contains 4 pieces of information for every pixel, the array's size is 4 times the size of the ImageData object: width*height*4. (An easier way to find the size of the array, is to use ImageDataObject.data.length)

The array containing the color/alpha information is stored in the data property of the ImageData object.

Tip: After you have manipulated the color/alpha information in the array, you can copy the image data back onto the canvas with the putImageData() method.

Examples:

The syntax for making the first pixel in the ImageData object red:

imgData=ctx.createImageData(100,100);

imgData.data[0]=255;
imgData.data[1]=0;
imgData.data[2]=0;
imgData.data[3]=255;

The syntax for making the second pixel in the ImageData object green:

imgData=ctx.createImageData(100,100);

imgData.data[4]=0;
imgData.data[5]=255;
imgData.data[6]=0;
imgData.data[7]=255;


JavaScript Syntax

There are two versions of the createImageData() method:

1. This creates a new ImageData object with the specified dimensions (in pixels):

JavaScript syntax: var imgData=context.createImageData(width,height);

2. This creates a new ImageData object with the same dimensions as the object specified by anotherImageData (this does not copy the image data):

JavaScript syntax: var imgData=context.createImageData(imageData);

Parameter Values

Parameter Description
width The width of the new ImageData object, in pixels
height The height of the new ImageData object, in pixels
imageData anotherImageData object


Canvas Object Reference Canvas Object

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