bias (ConvolutionFilter.bias property)

import flash.filters.ConvolutionFilter;
import flash.display.BitmapData;
    
var bias:Number = 50;
var filter:ConvolutionFilter = new ConvolutionFilter(3, 3, [1, 1, 1, 1, 1, 1, 1, 1, 1], 9, bias);

var myBitmapData:BitmapData = new BitmapData(100, 80, false, 0x00FF0000);

var mc:MovieClip = this.createEmptyMovieClip("mc", this.getNextHighestDepth());
mc.attachBitmap(myBitmapData, this.getNextHighestDepth());
myBitmapData.noise(128);

mc.onPress = function() {
    myBitmapData.applyFilter(myBitmapData, myBitmapData.rectangle, new Point(0, 0), filter);
}