像素（px）与毫米（mm）间的转换

//获取DPI，图像每英寸长度内的像素点数
function getDPI() {
	var arrDPI = new Array;
	if (window.screen.deviceXDPI) {
		arrDPI[0] = window.screen.deviceXDPI;
		arrDPI[1] = window.screen.deviceYDPI;
	} else {
		var tmpNode = document.createElement("DIV");
		tmpNode.style.cssText = "width:1in;height:1in;position:absolute;left:0px;top:0px;z-index:99;visibility:hidden";
		document.body.appendChild(tmpNode);
		arrDPI[0] = parseInt(tmpNode.offsetWidth);
		arrDPI[1] = parseInt(tmpNode.offsetHeight);
		tmpNode.parentNode.removeChild(tmpNode);
	}
	return arrDPI;
}
//px转毫米
function pxToMm(value) {
	var inch = value / getDPI()[0];
	var c_value = inch * 25.4;
	return c_value;
};
//毫米转px
function mmToPx(value) {
	var inch = value / 25.4;
	var c_value = inch * getDPI()[0];
	return c_value;
}