HTML canvas createImageData() Method
Example
Create a 100*100 pixels ImageData object where every pixel is red, and put it onto the canvas:
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 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
