图片的上传与压缩

[chenyinkai]

图片上传以及压缩

上传图片按钮

<input type="file" name="img" id="imgUpload" accept="image/jpeg, image/png, image/jpg, image/gif" onchange="uploadImg(this)">

图片上传

function uploadImg(imgUrl) {
    //判断是否支持FileReader
    if (window.FileReader) {
        var reader = new FileReader();
    } else {
        alert("您的设备不支持图片预览功能，如需该功能请升级您的设备！");
    }

    //获取文件
    var file = imgUrl.files[0];
    var picType = file.name.substring(file.name.lastIndexOf(".") + 1, file.name.length); //获取图片的后缀名
    var imageType = /^image\//;
    //是否是图片
    if (!imageType.test(file.type)) {
        alert("请选择图片！");
        return;
    }
    //读取完成
    reader.onload = function (e) {
        console.log(e.target.result)
    };
    reader.readAsDataURL(file);
}

图片压缩

var canvas = document.createElement("canvas");
var ctx = canvas.getContext('2d');
var tCanvas = document.createElement("canvas");
var tctx = tCanvas.getContext("2d");
var maxsize = 100 * 1024;

// 参数 img 为 <img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAE..."> 这种格式
function compress(img) {
    var initSize = img.src.length;
    var width = img.width;
    var height = img.height;
    // 如果图片大于四百万像素，计算压缩比并将大小压至400万以下
    var ratio;
    if ((ratio = width * height / 4000000) > 1) {
        ratio = Math.sqrt(ratio);
        width /= ratio;
        height /= ratio;
    } else {
        ratio = 1;
    }
    canvas.width = width;
    canvas.height = height;
    // 铺底色
    ctx.fillStyle = "#fff";
    ctx.fillRect(0, 0, canvas.width, canvas.height);
    // 如果图片像素大于100万则使用瓦片绘制
    var count;
    if ((count = width * height / 1000000) > 1) {
        count = ~~(Math.sqrt(count) + 1); // 计算要分成多少块瓦片
        // 计算每块瓦片的宽和高
        var nw = ~~(width / count);
        var nh = ~~(height / count);
        tCanvas.width = nw;
        tCanvas.height = nh;
        for (var i = 0; i < count; i++) {
            for (var j = 0; j < count; j++) {
                tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
                ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
            }
        }
    } else {
        ctx.drawImage(img, 0, 0, width, height);
    }
    // 进行最小压缩
    var ndata = canvas.toDataURL('image/jpeg', 0.1);
    tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
    return ndata; // 返回压缩后的数据 格式: data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAE...
}