Question

I am trying to write something in my Flex 3 application with actionscript that will take an image and when a user clicks a button, it will strip out all the white(ish) pixels and convert them to transparent, I say white(ish) because I have tried exactly white, but I get a lot of artifacts around the edges. I have gotten somewhat close using the following code:

targetBitmapData.threshold(sourceBitmapData, sourceBitmapData.rect, new Point(0,0), '>=', 0xFFf7f0f2, 0x00FFFFFF, 0xFFFFFFFF, true); 

However, it also makes red or yellows disappear. Why is it doing this? I’m not exactly sure how to make this work. Is there another function that is better suited for my needs?

Answer 1

A friend and I were trying to do this a while back for a project, and found writing an inline method that does this in ActionScript to be incredibly slow. You have to scan each pixel and do a computation against it, but doing it with PixelBender proved to be lightning fast (if you can use Flash 10, otherwise your stuck with slow AS).

The pixel bender code looks like:

input image4 src; output float4 dst;  // How close of a match you want parameter float threshold <   minValue:     0.0;   maxValue:     1.0;   defaultValue: 0.4; >;  // Color you are matching against. parameter float3 color <   defaultValue: float3(1.0, 1.0, 1.0); >;  void evaluatePixel() {   float4 current = sampleNearest(src, outCoord());   dst = float4((distance(current.rgb, color) < threshold) ? 0.0 : current); } 

If you need to do it in AS you can use something like:

function threshold(source:BitmapData, dest:BitmapData, color:uint, threshold:Number) {   dest.lock();    var x:uint, y:uint;   for (y = 0; y < source.height; y++) {     for (x = 0; x < source.width; x++) {       var c1:uint = source.getPixel(x, y);       var c2:uint = color;       var rx:uint = Math.abs(((c1 & 0xff0000) >> 16) - ((c2 & 0xff0000) >> 16));       var gx:uint = Math.abs(((c1 & 0xff00) >> 8) - ((c2 & 0xff00) >> 8));       var bx:uint = Math.abs((c1 & 0xff) - (c2 & 0xff));        var dist = Math.sqrt(rx*rx + gx*gx + bx*bx);        if (dist <= threshold)         dest.setPixel(x, y, 0x00ffffff);       else         dest.setPixel(x, y, c1);     }   }   dest.unlock(); }