relative luminance

var Contrast_Ratio = function(){	this.array_values = function(array)	{		var t = new Array();		array.each(function(a) {			t[t.length] = a;		})		return t;	}		this.is_int = function(x)	{		var y=parseInt(x);		if (isNaN(y))		{			return false;		}		return x==y && x.toString()==y.toString();	}	this.calculate = function(foreground, background)	{		if (foreground.length == 3 && background.length == 3)		{			foreground = this.array_values(foreground);			background = this.array_values(background);			var l1 = this.relative_luminance(foreground[0], foreground[1], foreground[2]);			var l2 = this.relative_luminance(background[0], background[1], background[2]);			if (l2 > l1)			{				l3 = l1;				l1 = l2;				l2 = l3;			}			return (l1 + 0.05) / (l2 + 0.05);		}		else		{			window.alert('Contrast_Ratio.calculate() expects parameters to be arrays with three values each');		}	}		this.relative_luminance = function(r, g, b)	{		r = this.calculate_RGB_for_relative_luminance(r);		g = this.calculate_RGB_for_relative_luminance(g);		b = this.calculate_RGB_for_relative_luminance(b);		return 0.2126 * r + 0.7152 * g + 0.0722 * b;	}		this.calculate_RGB_for_relative_luminance = function(colour)	{		if (this.is_int(colour))		{			colour = colour / 255;		}		else		{			colour = parseFloat(colour);		}				if (colour <= 0.03928)		{			return colour / 12.92;		}		elseif (colour <= 1.0)		{			return Math.pow((colour + 0.055) / 1.055, 2.4);		}		else		{			window.alert('RGB value must be between 0 and 1');		}	}}