Threshold and mask

Hi everyone.

I need to remove only dark red in a bitmapdata.

I wrote below code where I create gradient fill of red-black, red-white, blue-black and blue-white for test purposes.

Draw that to bitmapdata and then try to use threshold method to do it.

Whatever I set mask an copysource parameters of that method I can't succeed.

I thought that mask parameter is for setting a channel, so if I set it to 0xFFFF0000 I set red channel with full alpha as a target of operation. But that doesn't happen.

Instead all dark colors are replaced and also some blue-light.

Please help me out.

CODE:

var rec:Rectangle = new Rectangle(0,0,50,200);

var m:Matrix = new Matrix;

m.createGradientBox(rec.width,rec.height, Math.PI / 2);

var r:Shape = new Shape;

//RED

r.graphics.beginGradientFill(GradientType.LINEAR, new Array(0xFF0000,0x000000),new Array(1,1),new Array(0,255), m);

r.graphics.drawRect(0,0,rec.width,rec.height);

addChild(r);

m.createGradientBox(rec.width,rec.height, Math.PI / 2, 50);

r.graphics.beginGradientFill(GradientType.LINEAR, new Array(0xFF0000,0xFFFFFF),new Array(1,1),new Array(0,255), m);

r.graphics.drawRect(50,0,rec.width,rec.height);

//BLUE

m.createGradientBox(rec.width,rec.height, Math.PI / 2, 100);

r.graphics.beginGradientFill(GradientType.LINEAR, new Array(0x0000FF,0x000000),new Array(1,1),new Array(0,255), m);

r.graphics.drawRect(100,0,rec.width,rec.height);

m.createGradientBox(rec.width,rec.height, Math.PI / 2, 150);

r.graphics.beginGradientFill(GradientType.LINEAR, new Array(0x0000FF,0xFFFFFF),new Array(1,1),new Array(0,255), m);

r.graphics.drawRect(150,0,rec.width,rec.height);

//BITMAPDATA

var bd:BitmapData = new BitmapData(200,200,true,0);

bd.draw(r);

bd.threshold(bd,bd.rect,new Point,'<', 0xFFAA0000, 0xFF, 0xFFFF0000, false);

var b:Bitmap = new Bitmap(bd);

addChild(b);

b.y = 200;

Four top strips is before threshold.

Four bottom is after use of threshold.