PNG 9800*9800 you can not save picture, maybe out of memory?
PNG 8800*8800 will save, but either something gets wrong with format or simple program like paint can't handle bitmaps of that size because refuse to open claim format invalid.
PNG 6800*6800 works fine both save and open.
CODE BELOW
<!DOCTYPE html>
<html>
<body onload="createCanvasContext()">
<button id="pushit">Try it</button><br>
<canvas id="myCanvas" width="6800" height="6800" style="border:1px solid #000000;">
Your browser does not support the HTML5 canvas tag.
</canvas>
<script>
document.getElementById("pushit").addEventListener("click", savepng);
function createCanvasContext()
{
canvas = document.getElementById("myCanvas");
ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.arc(200,200,100,0,2*Math.PI);
ctx.fillStyle="#FF0000";
ctx.fill();
ctx.stroke();
}
function savepng() {
var mypic = canvas.toDataURL('png');
var anobject = document.createElement('a');
anobject.href = mypic;
anobject.download = 'image.png';
anobject.click()
}
</script>