SOURCE

(function(){
	var canvas = {},
		image = {};
	//获取canvas元素
	canvas.obj = document.getElementById('myCanvas');

	if(canvas.obj.getContext) {

		//获取渲染上下文
		canvas.ctx = canvas.obj.getContext('2d');

		//设置画布大小为屏幕宽高
		canvas.w = canvas.obj.width = document.body.clientWidth;
		canvas.h = canvas.obj.height = document.body.clientHeight;

		//新建一个image对象
		var img = new Image();

		//图像加载完后
		img.onload = function() {
			//把图像信息保存在image里面
			image.obj = img;
			image.w = img.width;
			image.h = img.height;
			image.x = parseInt(canvas.w/2 - image.w/2);
			image.y = parseInt(canvas.h/2 - image.h/2);

			//把图像绘制到画布坐标为(100,100)的地方
      //drawImage (image, dx, dy)
      //drawImage (image, dx, dy, dw, dy)
      //drawImage (image, sx, sy, sw, sh, dx, dy, dw, dh)
      //    s == source  d == draw
			canvas.ctx.drawImage(image.obj,image.x,image.y,image.w,image.h);
		};

		//设置image的source
		img.src = 'http://img06.mifile.cn/v1/MI_55950AFBBEDCB/T1_WK_ByVT1R4cSCrK.png';
	}
}())

<canvas id="myCanvas">您的浏览器不支持Canvas。</canvas>

		body{background-color: #0c1328;position: absolute;left: 0;top: 0;right: 0;bottom: 0;}
canvas{border: 1px dotted #fff}