I'm making a small app where children can fill preset illustrations with colours. I've succesfully implemented an MS-paint style paint bucket using the flood fill argorithm. However, near the edges of image elements pixels are left unfilled, because the lines are anti-aliased. This is because the current condition on whether to fill is colourAtCurrentPixel == colourToReplace (the colours are RGB uints)

I'd like to add a smoothing/treshold option like in Photoshop and other sophisticated tools, but what's the algorithm to determine the equality/distance between two colours?

if (match(pixel(x,y), colourToReplace) setpixel(x,y,colourToReplaceWith)

How to fill in match()?

Here's my current full code:

            var b:BitmapData = settings.background;
            b.lock();

            var from:uint = b.getPixel(x,y);


            var q:Array = [];


            var xx:int;
            var yy:int;
            var w:int = b.width;
            var h:int = b.height;
            q.push(y*w + x);
            while (q.length != 0) {
                var xy:int = q.shift();
                xx = xy % w;
                yy = (xy - xx) / w;
                if (b.getPixel(xx,yy) == from) {
                    b.setPixel(xx,yy,to);
                    if (xx != 0) q.push(xy-1);
                    if (xx != w-1) q.push(xy+1);
                    if (yy != 0) q.push(xy-w);
                    if (yy != h-1) q.push(xy+w);
                }
            }
            b.unlock(null);