W3School TIY Editor
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<!DOCTYPE html> <html> <body> <canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;"> Your browser does not support the HTML5 canvas tag. </canvas> <script> var c=document.getElementById("myCanvas"); var ctx=c.getContext("2d"); ctx.fillStyle="green"; 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>