Adobe® Flex® 4 Language Reference
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flash.filters 
ConvolutionFilter 
Packageflash.filters
Classpublic class ConvolutionFilter
InheritanceConvolutionFilter Inheritance BitmapFilter Inheritance Object

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

The ConvolutionFilter class applies a matrix convolution filter effect. A convolution combines pixels in the input image with neighboring pixels to produce an image. A wide variety of image effects can be achieved through convolutions, including blurring, edge detection, sharpening, embossing, and beveling. You can apply the filter to any display object (that is, objects that inherit from the DisplayObject class), such as MovieClip, SimpleButton, TextField, and Video objects, as well as to BitmapData objects.

To create a convolution filter, use the syntax new ConvolutionFilter(). The use of filters depends on the object to which you apply the filter:

  • To apply filters to movie clips, text fields, buttons, and video, use the filters property (inherited from DisplayObject). Setting the filters property of an object does not modify the object, and you can remove the filter by clearing the filters property.
  • To apply filters to BitmapData objects, use the BitmapData.applyFilter() method. Calling applyFilter() on a BitmapData object takes the source BitmapData object and the filter object and generates a filtered image as a result.

If you apply a filter to a display object, the value of the cacheAsBitmap property of the object is set to true. If you clear all filters, the original value of cacheAsBitmap is restored.

A filter is not applied if the resulting image exceeds the maximum dimensions. In AIR 1.5 and Flash Player 10, the maximum is 8,191 pixels in width or height, and the total number of pixels cannot exceed 16,777,215 pixels. (So, if an image is 8,191 pixels wide, it can only be 2,048 pixels high.) In Flash Player 9 and earlier and AIR 1.1 and earlier, the limitation is 2,880 pixels in height and 2,880 pixels in width. For example, if you zoom in on a large movie clip with a filter applied, the filter is turned off if the resulting image exceeds maximum dimensions.

View the examples

See also



Public Properties
 PropertyDefined By
  alpha : Number
The alpha transparency value of the substitute color.
ConvolutionFilter
  bias : Number
The amount of bias to add to the result of the matrix transformation.
ConvolutionFilter
  clamp : Boolean
Indicates whether the image should be clamped.
ConvolutionFilter
  color : uint
The hexadecimal color to substitute for pixels that are off the source image.
ConvolutionFilter
 Inheritedconstructor : Object
A reference to the class object or constructor function for a given object instance.
Object
  divisor : Number
The divisor used during matrix transformation.
ConvolutionFilter
  matrix : Array
An array of values used for matrix transformation.
ConvolutionFilter
  matrixX : Number
The x dimension of the matrix (the number of columns in the matrix).
ConvolutionFilter
  matrixY : Number
The y dimension of the matrix (the number of rows in the matrix).
ConvolutionFilter
  preserveAlpha : Boolean
Indicates if the alpha channel is preserved without the filter effect or if the convolution filter is applied to the alpha channel as well as the color channels.
ConvolutionFilter
 Inheritedprototype : Object
[static] A reference to the prototype object of a class or function object.
Object
Public Methods
 MethodDefined By
  
ConvolutionFilter(matrixX:Number = 0, matrixY:Number = 0, matrix:Array = null, divisor:Number = 1.0, bias:Number = 0.0, preserveAlpha:Boolean = true, clamp:Boolean = true, color:uint = 0, alpha:Number = 0.0)
Initializes a ConvolutionFilter instance with the specified parameters.
ConvolutionFilter
  
[override] Returns a copy of this filter object.
ConvolutionFilter
 Inherited
Indicates whether an object has a specified property defined.
Object
 Inherited
Indicates whether an instance of the Object class is in the prototype chain of the object specified as the parameter.
Object
 Inherited
Indicates whether the specified property exists and is enumerable.
Object
 Inherited
Sets the availability of a dynamic property for loop operations.
Object
 Inherited
Returns the string representation of this object, formatted according to locale-specific conventions.
Object
 Inherited
Returns the string representation of the specified object.
Object
 Inherited
Returns the primitive value of the specified object.
Object
Property Detail

alpha

property
alpha:Number

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

The alpha transparency value of the substitute color. Valid values are 0 to 1.0. The default is 0. For example, .25 sets a transparency value of 25%.



Implementation
    public function get alpha():Number
    public function set alpha(value:Number):void

bias

property 
bias:Number

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

The amount of bias to add to the result of the matrix transformation. The bias increases the color value of each channel, so that dark colors appear brighter. The default value is 0.



Implementation
    public function get bias():Number
    public function set bias(value:Number):void

clamp

property 
clamp:Boolean

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

Indicates whether the image should be clamped. For pixels off the source image, a value of true indicates that the input image is extended along each of its borders as necessary by duplicating the color values at each respective edge of the input image. A value of false indicates that another color should be used, as specified in the color and alpha properties. The default is true.



Implementation
    public function get clamp():Boolean
    public function set clamp(value:Boolean):void

Example  ( How to use this example )
The following example creates two boxes using the BitmapData class, one of which is half the size of the other. When the example first loads, the larger box is drawn inside mc using the attachBitmap(). When mc is clicked and the applyFilter() method is called, the largeBox instance of BitmapData is redrawn with smallBox as a source bitmap. Since applyFilter() draws smallBox over a Rectangle whose width and height is specified as those of largeBox, the source bitmap is smaller than the drawing area. The clamp property of ConvolutionFilter in this case is set to false and the area which is not covered by the source bitmap, smallBox, is a solid red as determined by the clampColor and clampAlpha variables.
 package {
    import flash.display.Sprite;
    import flash.display.BitmapData;
    import flash.filters.ConvolutionFilter;
    import flash.text.TextField;
    import flash.geom.Rectangle;
    import flash.geom.Point;

    public class ConvolutionClampExample extends Sprite {
        // Variables that affect clamping:
        var clamp:Boolean = false;
        var clampColor:Number = 0xFF0000;
        var clampAlpha:Number = 1;
        
        // For illustration, keep other ConvolutionFilter variables neutral:
        var bias:Number = 0;
        var preserveAlpha:Boolean = false;
        // Also, construct a neutral matrix
        var matrixCols:Number = 3;
        var matrixRows:Number = 3;
        var matrix:Array = [ 1,1,1,
                             1,1,1,
                             1,1,1 ];
        
        var filter:ConvolutionFilter = new ConvolutionFilter(matrixCols, matrixRows, matrix, matrix.length, bias, preserveAlpha, clamp, clampColor, clampAlpha);
        
        var largeBoxWidth:Number = 100;
        var largeBoxHeight:Number = 100;
        var largeBox:BitmapData = new BitmapData(largeBoxWidth, largeBoxWidth, true, 0xCC00FF00);
        var smallBoxWidth:Number = largeBoxWidth / 2;
        var smallBoxHeight:Number = largeBoxHeight / 2;
        var smallBox:BitmapData = new BitmapData(smallBoxWidth, smallBoxWidth, true, 0xCC0000FF);
            
        var mc:MovieClip = this.createEmptyMovieClip("mc", this.getNextHighestDepth());
        mc.attachBitmap(largeBox, this.getNextHighestDepth());
        
        mc.onPress = function() {
            largeBox.applyFilter(smallBox,
                                 new Rectangle(0,0, largeBoxWidth, largeBoxHeight),
                                 new Point(0,0),
                                 filter);
        }
    }
}

color

property 
color:uint

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

The hexadecimal color to substitute for pixels that are off the source image. It is an RGB value with no alpha component. The default is 0.



Implementation
    public function get color():uint
    public function set color(value:uint):void

divisor

property 
divisor:Number

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

The divisor used during matrix transformation. The default value is 1. A divisor that is the sum of all the matrix values smooths out the overall color intensity of the result. A value of 0 is ignored and the default is used instead.



Implementation
    public function get divisor():Number
    public function set divisor(value:Number):void

matrix

property 
matrix:Array

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

An array of values used for matrix transformation. The number of items in the array must equal matrixX * matrixY.

A matrix convolution is based on an n x m matrix, which describes how a given pixel value in the input image is combined with its neighboring pixel values to produce a resulting pixel value. Each result pixel is determined by applying the matrix to the corresponding source pixel and its neighboring pixels.

For a 3 x 3 matrix convolution, the following formula is used for each independent color channel:


	dst (x, y) = ((src (x-1, y-1) * a0 + src(x, y-1) * a1....
	                  src(x, y+1) * a7 + src (x+1,y+1) * a8) / divisor) + bias
	

Certain filter specifications perform faster when run by a processor that offers SSE (Streaming SIMD Extensions). The following are criteria for faster convolution operations:

  • The filter must be a 3x3 filter.
  • All the filter terms must be integers between -127 and +127.
  • The sum of all the filter terms must not have an absolute value greater than 127.
  • If any filter term is negative, the divisor must be between 2.00001 and 256.
  • If all filter terms are positive, the divisor must be between 1.1 and 256.
  • The bias must be an integer.

Note: If you create a ConvolutionFilter instance using the constructor without parameters, the order you assign values to matrix properties affects the behavior of the filter. In the following case, the matrix array is assigned while the matrixX and matrixY properties are still set to 0 (the default value):

    public var myfilter:ConvolutionFilter = new ConvolutionFilter();
    myfilter.matrix = [0, 0, 0, 0, 1, 0, 0, 0, 0];
    myfilter.matrixX = 3;
    myfilter.matrixY = 3;
    

In the following case, the matrix array is assigned while the matrixX and matrixY properties are set to 3:

    public var myfilter:ConvolutionFilter = new ConvolutionFilter();
    myfilter.matrixX = 3;
    myfilter.matrixY = 3;
    myfilter.matrix = [0, 0, 0, 0, 1, 0, 0, 0, 0];
    



Implementation
    public function get matrix():Array
    public function set matrix(value:Array):void

Throws
TypeError — The Array is null when being set

matrixX

property 
matrixX:Number

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

The x dimension of the matrix (the number of columns in the matrix). The default value is 0.



Implementation
    public function get matrixX():Number
    public function set matrixX(value:Number):void

matrixY

property 
matrixY:Number

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

The y dimension of the matrix (the number of rows in the matrix). The default value is 0.



Implementation
    public function get matrixY():Number
    public function set matrixY(value:Number):void

preserveAlpha

property 
preserveAlpha:Boolean

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

Indicates if the alpha channel is preserved without the filter effect or if the convolution filter is applied to the alpha channel as well as the color channels. A value of false indicates that the convolution applies to all channels, including the alpha channel. A value of true indicates that the convolution applies only to the color channels. The default value is true.



Implementation
    public function get preserveAlpha():Boolean
    public function set preserveAlpha(value:Boolean):void
Constructor Detail

ConvolutionFilter

()Constructor
public function ConvolutionFilter(matrixX:Number = 0, matrixY:Number = 0, matrix:Array = null, divisor:Number = 1.0, bias:Number = 0.0, preserveAlpha:Boolean = true, clamp:Boolean = true, color:uint = 0, alpha:Number = 0.0)

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

Initializes a ConvolutionFilter instance with the specified parameters.

Parameters
matrixX:Number (default = 0) — The x dimension of the matrix (the number of columns in the matrix). The default value is 0.
 
matrixY:Number (default = 0) — The y dimension of the matrix (the number of rows in the matrix). The default value is 0.
 
matrix:Array (default = null) — The array of values used for matrix transformation. The number of items in the array must equal matrixX * matrixY.
 
divisor:Number (default = 1.0) — The divisor used during matrix transformation. The default value is 1. A divisor that is the sum of all the matrix values evens out the overall color intensity of the result. A value of 0 is ignored and the default is used instead.
 
bias:Number (default = 0.0) — The bias to add to the result of the matrix transformation. The default value is 0.
 
preserveAlpha:Boolean (default = true) — A value of false indicates that the alpha value is not preserved and that the convolution applies to all channels, including the alpha channel. A value of true indicates that the convolution applies only to the color channels. The default value is true.
 
clamp:Boolean (default = true) — For pixels that are off the source image, a value of true indicates that the input image is extended along each of its borders as necessary by duplicating the color values at the given edge of the input image. A value of false indicates that another color should be used, as specified in the color and alpha properties. The default is true.
 
color:uint (default = 0) — The hexadecimal color to substitute for pixels that are off the source image.
 
alpha:Number (default = 0.0) — The alpha of the substitute color.
Method Detail

clone

()method
override public function clone():BitmapFilter

Language Version: ActionScript 3.0
Runtime Versions: AIR 1.0 Flash Player 9

Returns a copy of this filter object.

Returns
BitmapFilter — BitmapFilter A new ConvolutionFilter instance with all the same properties as the original ConvolutionMatrixFilter instance.
ConvolutionFilterExample.as

The following example applies different convolution filters to an image file. The filter constructor calls buildChild() four times to load and display four instances of the image. Each call to buildChild() takes as an argument a function that applies no filter to the first instance and a different convolution filter to each subsequent instance.

The buildChild() function creates a new Loader object named loader. For each call to buildChild(), attach an event listener to the Loader object to listen for complete events, which are handled by the function passed to buildChild().

The applyBrightness(), applySharpness(), and applyOutline() functions use different values for the matrix array to achieve different ConvolutionFilter effects.

Note: For best results, use an image approximately 80 pixels in width. The name and location of the image file should match the value you pass to the url property. For example, the value passed to url in the example points to an image file named "Image.jpg" that is in the same directory as your SWF file.


package {
    import flash.display.DisplayObject;
    import flash.display.Loader;
    import flash.display.Sprite;
    import flash.events.*;
    import flash.filters.BitmapFilter;
    import flash.filters.ConvolutionFilter;
    import flash.net.URLRequest;
    import flash.text.TextField;
    import flash.text.TextFieldAutoSize;

    public class ConvolutionFilterExample extends Sprite {
        private var size:uint = 140;
        private var url:String = "Image.jpg";

        public function ConvolutionFilterExample() {
            buildChild(applyNothing);
            buildChild(applyBrightness);
            buildChild(applySharpness);
            buildChild(applyOutline);
        }

        private function buildChild(loadHandler:Function):void {
            var loader:Loader = new Loader();
            loader.x = numChildren * size;
            loader.y = size;
            loader.contentLoaderInfo.addEventListener(IOErrorEvent.IO_ERROR, ioErrorHandler);
            if(loadHandler != null) {
                loader.contentLoaderInfo.addEventListener(Event.COMPLETE, loadHandler);
            }

            var request:URLRequest = new URLRequest(url);
            loader.load(request);
            addChild(loader);
        }

        private function applyNothing(event:Event):void {
            var child:DisplayObject = DisplayObject(event.target.loader);
            applyLabel(child, "no filter");
        }

        private function applyBrightness(event:Event):void {
            var child:DisplayObject = DisplayObject(event.target.loader);
            var matrix:Array = [5, 5, 5,
                                5, 0, 5,
                                5, 5, 5];
            applyFilter(child, matrix);
            applyLabel(child, "brightness");
        }

        private function applySharpness(event:Event):void {
            var child:DisplayObject = DisplayObject(event.target.loader);
            var matrix:Array = [0, -1, 0,
                               -1, 20, -1,
                                0, -1, 0];
            applyFilter(child, matrix);
            applyLabel(child, "sharpness");
        }

        private function applyOutline(event:Event):void {
            var child:DisplayObject = DisplayObject(event.target.loader);
            var matrix:Array = [-30, 30, 0,
                                -30, 30, 0,
                                -30, 30, 0];
            applyFilter(child, matrix);
            applyLabel(child, "outline");
        }

        private function applyFilter(child:DisplayObject, matrix:Array):void {
            var matrixX:Number = 3;
            var matrixY:Number = 3;
            var divisor:Number = 9;
            var filter:BitmapFilter = new ConvolutionFilter(matrixX, matrixY, matrix, divisor);
            var filters:Array = new Array();
            filters.push(filter);
            child.filters = filters;
        }

        private function applyLabel(child:DisplayObject, label:String):void {
            var tf:TextField = new TextField();
            tf.x = child.x;
            tf.y = child.height;
            tf.autoSize = TextFieldAutoSize.LEFT;
            tf.text = label;
            addChild(tf);
        }

        private function ioErrorHandler(event:IOErrorEvent):void {
            trace("Unable to load image: " + url);
        }
    }
}