C#/JS 压缩到指定大小的图片

//因为浏览器安全问题，无法获取上传图片地址，需要先存一遍然后再获取地址作参数上传
var des = CompressImage(@"C:\Users\PC\Pictures\测试\1652344981(1).jpg", @"C:\Users\PC\Pictures\测试\ok.jpg");
Console.WriteLine(des);
Console.ReadLine();





/// <summary>
/// 无损压缩图片
/// </summary>
/// <param name="sFile">原图片地址</param>
/// <param name="dFile">压缩后保存图片地址</param>
/// <param name="flag">压缩质量（数字越小压缩率越高）1-100</param>
/// <param name="size">压缩后图片的最大大小</param>
/// <param name="sfsc">是否是第一次调用</param>
/// <returns></returns>
bool CompressImage(string sFile, string dFile, int flag = 90, int size = 200, bool sfsc = true)
{
    //如果是第一次调用，原始图像的大小小于要压缩的大小，则直接复制文件，并且返回true
    FileInfo firstFileInfo = new FileInfo(sFile);
    if (sfsc == true && firstFileInfo.Length < size * 1024)
    {
        firstFileInfo.CopyTo(dFile); return true;
    }
    Image iSource = Image.FromFile(sFile);
    ImageFormat tFormat = iSource.RawFormat;
    int dHeight = iSource.Height / 2;
    int dWidth = iSource.Width / 2;
    int sW = 0, sH = 0;
    //按比例缩放
    Size tem_size = new Size(iSource.Width, iSource.Height);
    if (tem_size.Width > dHeight || tem_size.Width > dWidth)
    {
        if ((tem_size.Width * dHeight) > (tem_size.Width * dWidth))
        {
            sW = dWidth; sH = (dWidth * tem_size.Height) / tem_size.Width;
        }
        else
        {
            sH = dHeight;
            sW = (tem_size.Width * dHeight) / tem_size.Height;
        }
    }
    else
    {
        sW = tem_size.Width;
        sH = tem_size.Height;
    }
    Bitmap ob = new Bitmap(dWidth, dHeight);
    using (Graphics g = Graphics.FromImage(ob))        //原代码再服务器上经常爆内存不足
        {
            g.Clear(Color.WhiteSmoke);
            g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
            g.DrawImage(iSource, new Rectangle((dWidth - sW) / 2, (dHeight - sH) / 2, sW, sH), 0, 0, iSource.Width, iSource.Height, GraphicsUnit.Pixel);
            g.Dispose();
        }
    //以下代码为保存图片时，设置压缩质量
    EncoderParameters ep = new EncoderParameters();
    long[] qy = new long[1];
    qy[0] = flag; //设置压缩的比例1-100
    EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
    ep.Param[0] = eParam;
    try
    {
        ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
        ImageCodecInfo jpegICIinfo = null;
        for (int x = 0; x < arrayICI.Length; x++)
        {
            if (arrayICI[x].FormatDescription.Equals("JPEG"))
            {
                jpegICIinfo = arrayICI[x]; break;
            }
        }
        if (jpegICIinfo != null)
        {
            ob.Save(dFile, jpegICIinfo, ep);//dFile是压缩后的新路径
            FileInfo fi = new FileInfo(dFile);
            if (fi.Length > 1024 * size)
            {
                flag = flag - 10;
                CompressImage(sFile, dFile, flag, size, false);
            }
        }
        else
        {
            ob.Save(dFile, tFormat);
        }
        return true;
    }
    catch { return false; }
    finally { iSource.Dispose(); ob.Dispose(); }
}

//JS版本

<input class="upload-input" name="uploadify1" type="file" id="uploadify1" value="上传" onchange="imgUp()" />

//人脸压缩上传
function imgUp() {
    var f = $('#uploadify1')[0].files[0];
    var formData = new FormData();
    var maxSize = 0.2 * 1024 * 1024; // 200K        定义好图片大小区间，JS插件已经做好大小压缩
    var minSize = 0.02 * 1024 * 1024; // 20K
    var photoCompress = new PhotoCompress(minSize, maxSize);
    photoCompress.compress(f, function (file) {
        var r = new FileReader()
        r.readAsDataURL(file)
        r.onload = function (e) {
            var reader = new FileReader();
            reader.readAsDataURL(file);
            reader.onload = function (e) {
                var imgBase64Data = e.target.result;
                var fileObj = base64ImgtoFile(imgBase64Data, "file");
                console.log("压缩后大小：" + (fileObj.size / 1024)+"K");
                formData.append('imgFile', fileObj);
                formData.append('dir', "image");
                $.ajax({
                    url: '/ajax/cUserHandler.aspx?action=cUserUploadImage',
                    type: "post",
                    dataType: "json",
                    data: formData,
                    cache: false,
                    contentType: false,
                    processData: false,
                    success: function (data) {
                        if (data.error === 0) {
                            var url = data.url;
                            //多图
                            //$("#file2").append("<li style=\"text-align:center;\"><img src=\"" + url + "\" style=\"width:80px;height:80px;\"><br><span><a onclick=\"del(this)\"></a></span></li>");
                            //$("#img_url1").val($("#img_url1").val() + url + "|");
                        
                            //单图
                            $("#file2").html("<li style=\"text-align:center;\"><img src=\"" + url + "\" style=\"width:80px;height:80px;\"><br><span><a onclick=\"del(this)\"></a></span></li>");
                            $("#img_url1").val(url);
                        } else { alert(data.message); }
                    }
                });
            }
        }
    });
}

// dataurl 为传进来的base64格式的图片地址， return 返回的为file格式
function base64ImgtoFile(dataurl, filename) {
    let arr = dataurl.split(',')
    let mime = arr[0].match(/:(.*?);/)[1]
    let suffix = mime.split('/')[1]
    let bstr = atob(arr[1])
    let n = bstr.length
    let u8arr = new Uint8Array(n)
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n)
    }
    return new File([u8arr], `${filename}.${suffix}`, {
        type: mime
    })
}


//compressUtil.js 引用
/**
 * 图片压缩类
 * @param minSize
 * @param maxSize
 * @constructor
 */
var PhotoCompress = function (minSize, maxSize) {
    var nextQ = 0.5; // 压缩比例
    var maxQ = 1;
    var minQ = 0;

    /**
     * 将base64转换为文件
     * @param base64Codes base64编码
     * @param fileName 文件名称
     * @returns {*}
     */
    PhotoCompress.prototype.dataUrlToFile = function (base64Codes, fileName) {
        var arr = base64Codes.split(','),
            mime = arr[0].match(/:(.*?);/)[1],
            bStr = atob(arr[1]),
            n = bStr.length,
            u8arr = new Uint8Array(n);
        while (n--) {
            u8arr[n] = bStr.charCodeAt(n);
        }
        return new File([u8arr], fileName, { type: mime });
    }

    /**
     * 图片压缩
     * @param file 文件
     * @param callback 回调函数
     */
    PhotoCompress.prototype.compress = function (file, callback) {
        var self = this;
        self.imgBase64(file, function (image, canvas) {
            var base64Codes = canvas.toDataURL(file.type, nextQ); // y压缩
            var compressFile = self.dataUrlToFile(base64Codes, file.name.split('.')[0]); // 转成file文件
            var compressFileSize = compressFile.size; // 压缩后文件大小 k
            console.log("图片质量：" + nextQ);
            console.log("压缩后文件大小：" + compressFileSize / 1024);
            if (compressFileSize > maxSize) { // 压缩后文件大于最大值
                maxQ = nextQ;
                nextQ = (nextQ + minQ) / 2; // 质量降低
                self.compress(file, callback);
            } else if (compressFileSize < minSize) { // 压缩以后文件小于最小值
                minQ = nextQ;
                nextQ = (nextQ + maxQ) / 2; // 质量提高
                self.compress(file, callback);
            } else {
                callback(compressFile);
            }
        });
    }

    /**
     * 将图片转化为base64
     * @param file 文件
     * @param callback 回调函数
     */
    PhotoCompress.prototype.imgBase64 = function (file, callback) {
        // 看支持不支持FileReader
        if (!file || !window.FileReader) return;
        var image = new Image();
        // 绑定 load 事件处理器，加载完成后执行
        image.onload = function () {
            var canvas = document.createElement('canvas')
            var ctx = canvas.getContext('2d')
            ctx.clearRect(0, 0, canvas.width, canvas.height);
            canvas.width = image.width * nextQ;
            canvas.height = image.height * nextQ;
            ctx.drawImage(image, 0, 0, canvas.width, canvas.height);
            callback(image, canvas);
        };
        if (/^image/.test(file.type)) {
            // 创建一个reader
            var reader = new FileReader();
            // 将图片将转成 base64 格式
            reader.readAsDataURL(file);
            // 读取成功后的回调
            reader.onload = function () {
                // self.imgUrls.push(this.result);
                // 设置src属性，浏览器会自动加载。
                // 记住必须先绑定事件，才能设置src属性，否则会出同步问题。
                image.src = this.result;
            }
        }
    }
};