JavaScript canvas2d object method: getImageData()
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The getImageData() method of the JavaScript
DOM object
returned by the getContext("2d")
method applied to the HTML <canvas>
element returns an ImageData object characterised by the pixel data for a
specific rectangle in the canvas.
Each pixel in the
ImageData has 4 values, i.e. its RGBA values (see CSS Colours). The data is
held in an array which is 4 times the size of the ImageData object, i.e. width
x height x 4. This is stored in the data
property of the ImageDataObject.
It has the following
syntax with the following parameters.
context.getImageData(x, y, width, height)
|
Parameter
|
Required / Optional
|
Description
|
|
x
|
Required
|
x-coordinate of
upper-left corner
|
|
y
|
Required
|
y-coordinate of
upper-left corner
|
|
width
|
Required
|
Width of rectangle, in
pixels
|
|
height
|
Required
|
Height of rectangle, in
pixels
|
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