<html>
<body>
<canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">
您的浏览器不支持 HTML5 canvas 标签。</canvas>
<script>
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.fillStyle="red";
ctx.fillRect(10,10,50,50);
var imgData=ctx.getImageData(30,30,50,50);
red=imgData.data[0];
green=imgData.data[1];
blue=imgData.data[2];
alpha=imgData.data[3];
alert(red + " " + green + " " + blue + " " + alpha);
</script>
</body>
</html>