使用canvas实现图片预览、缩放（压缩）以及生成文件下载

参考

https://www.runoob.com/html/html5-canvas.html
https://www.cnblogs.com/yuanzhiguo/p/8288822.html
https://www.cnblogs.com/goloving/p/8260206.html

 

工作中遇到的一个问题，手机端上传图片出现卡顿，经排查发现是图片过大引起的。参考网上资料，整理出一个图片压缩（缩放）的demo页面。

demo包含图片预览，缩放以及生成文件下载三个功能，放在这里备忘，有需要的朋友可以拿去参考。

 

canvas-preview-and-zoom.html

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>canvas 预览和缩放</title>
        <style type="text/css">
            .button {
                display: inline-block;
                padding: 0px;
                width: 45px;
                height: 25px;
                line-height: 25px;
                text-align: center;
                font-size: 16px;
                border: solid 1px;
                background: #e3e3e3;
            }
        </style>
    </head>
    <body>
        <div>
            <img style="width: 600px; height: 600px;" id="preview">
            <img style="width: 300px; height: 300px;" id="target">
        </div>
        <div>
            <input type="file" id="select" style="display: none;">
            <label for="select" class="button">选择</label>
            <label type="button" id="zoom" class="button">缩放</label>
            <label type="button" id="download" class="button">下载</label>
        </div>
        <script type="text/javascript">
            var image = document.querySelector('#preview');
            var reader = new FileReader();
            // 预览
            reader.onload = function(e) {
                image.src = e.target.result;
            }
            // 预览
            document.querySelector('#select').addEventListener('change', function(event) {
                if (event.target.files.length == 0) {
                    return;
                }
                file = event.target.files[0];
                if (/^image\//.test(file.type)) {
                    reader.readAsDataURL(file);
                } else {
                    alert('请选择图片');
                }
            });
            // 缩放
            function zoomImage(img, width, height, quality) {        
                var canvas = document.createElement('canvas');        
                canvas.width = width;
                canvas.height = height;
                var context = canvas.getContext('2d');        
                context.drawImage(img, 0, 0, width, height);
                return canvas.toDataURL('image/jpeg', quality);
            }
            // 缩放
            document.querySelector('#zoom').onclick = function() {
                var img64 = zoomImage(image, 300, 300, 1);
                document.querySelector('#target').src = img64;
            };
            // 下载
            document.querySelector('#download').onclick = function() {
                var a = document.createElement('a');
                a.href = document.querySelector('#target').src;
                a.download = 'zoom.jpg';
                a.click();
                a.remove();
            }
        </script>
    </body>
</html>
View Code

 

posted @ 2019-11-08 17:02  lichmama  阅读(878)  评论(0)  编辑  收藏  举报