Canvas 图片灰度

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胜东 2021-06-04 17:20:46 ©著作权

文章标签 Canvas教程 Canvas 文章分类 前端开发

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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>