ColorMatrixFilter.prototype.greyscale = function(scale, multiply)
{
    var matrix = [
        scale, scale, scale, 0, 0,
        scale, scale, scale, 0, 0,
        scale, scale, scale, 0, 0,
        0,0,0,1,0,
        0,0,0,0,1
    ];

    this._loadMatrix(matrix, multiply);
};