ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Filtering display objects
In ActionScript, you create the matrix as a combination of an Array instance containing the values and two properties
specifying the number of rows and columns in the matrix. The following example loads an image and, when the image
finishes loading, applies a convolution filter to the image using the matrix in the previous listing:
// Load an image onto the Stage.
var loader:Loader = new Loader();
var url:URLRequest = new URLRequest("http://www.helpexamples.com/flash/images/image1.jpg");
loader.load(url);
this.addChild(loader);
function applyFilter(event:MouseEvent):void
{
// Create the convolution matrix.
var matrix:Array = [0, 0, 0,
0, 0, 1,
0, 0, 0];
}
var convolution:ConvolutionFilter = new ConvolutionFilter();
convolution.matrixX = 3;
convolution.matrixY = 3;
convolution.matrix = matrix;
convolution.divisor = 1;
loader.filters = [convolution];
loader.addEventListener(MouseEvent.CLICK, applyFilter);
Something that isn’t obvious in this code is the effect of using values other than 1 or 0 in the matrix. For example, the
same matrix, with the number 8 instead of 1 in the right-hand position, performs the same action (shifting the pixels
to the left). In addition, it affects the colors of the image, making them 8 times brighter. This is because the final pixel
color values are calculated by multiplying the matrix values by the original pixel colors, adding the values together, and
dividing by the value of the filter’s divisor property. Notice that in the example code, the divisor property is set to
1. As a general rule, if you want the brightness of the colors to stay about the same as in the original image, you should
make the divisor equal to the sum of the matrix values. So with a matrix where the values add up to 8, and a divisor of
1, the resulting image is going to be roughly 8 times brighter than the original image.
Although the effect of this matrix isn’t very noticeable, other matrix values can be used to create various effects. Here
are several standard sets of matrix values for different effects using a three by three matrix:
Basic blur (divisor 5):
0 1 0
1 1 1
0 1 0
Sharpening (divisor 1):
0, -1, 0
-1, 5, -1
0, -1, 0
Edge detection (divisor 1):
0, -1, 0
-1, 4, -1
0, -1, 0
Embossing effect (divisor 1):
Last updated 6/6/2012
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