HTML canvas getImageData() Method get first pixel color value

Introduction

The code for getting color/alpha information of the first pixel in the returned ImageData object:

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<!DOCTYPE html>
<html>
<body>

<canvas id="myCanvas" width="300" height="180" 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 = "red";
ctx.fillRect(10, 10, 50, 50);//w w w .  ja  va2 s . c  om

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>

You can use the getImageData() method to invert the color of every pixels of an image on the canvas. 

context.getImageData(x, y, width, height);

Parameter Values

Parameter Description
x The x coordinate of the upper-left corner to start copy from
y The y coordinate of the upper-left corner to start copy from
width The width of the rectangular area you will copy
heightThe height of the rectangular area you will copy



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