Canvas 图片灰度

我们可以通过下面几种方法，将其转换为灰度：

1.浮点算法：Gray=R*0.3+G*0.59+B*0.11

2.整数方法：Gray=(R*30+G*59+B*11)/100

3.移位方法：Gray =(R*76+G*151+B*28)>>8;

4.平均值法：Gray=（R+G+B）/3;

5.仅取绿色：Gray=G；

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title>gray</title>

</head>

<body>

    <canvas id='myCanvas' width='800' height='600'>

        your browser does not support canvas

    </canvas>

    <script type="text/javascript">

    var c = document.getElementById('myCanvas');

    var ctx = c.getContext('2d');

    var img = new Image();

    img.src = 'face.jpg';

    img.onload = function() {

        ctx.drawImage(img, 0, 0);

        var imgData = ctx.getImageData(0, 0, 250, 250);

        var pixels = imgData.data;

        for (var i = 0, n = pixels.length; i < n; i += 4) {

            var grayscale = pixels[i] * .3 + pixels[i + 1] * .59 + pixels[i + 2] * .11;

            pixels[i] = grayscale;

            pixels[i + 1] = grayscale;

            pixels[i + 2] = grayscale;

        }

        ctx.putImageData(imgData, 250, 0);

    };

    </script>

</body>

</html>

巴特西

Canvas 图片灰度

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