Jcrop插件本身并不含有图片截取功能，它仅仅是在前端层面构建一套截取动画效果并产生4个坐标点，插件使用者将这4个坐标点传回至服务器接口上进行截取操作。其优点是具有较高的通用性、浏览器兼容性（IE6+）及稳定性高，缺点是无法适用于手机H5开发（无图片缩放、拖拽效果）。
最新版的Jcrop已更新到v3.0+了，本文基于 v0.9.12，由于这版本之间API及使用方式差异非常大，故本文不具备 Jcrop v3.0+ 的使用参考价值，请读者悉知。
Jcrop V0.9+ 下载地址：http://deepliquid.com/content/Jcrop.html
Jcrop V0.9+ API中文说明：https://blog.csdn.net/xht555/article/details/43407141?utm_source=blogxgwz6
Jcrop V3.0+ 下载地址： https://github.com/tapmodo/Jcrop
html代码，这里没放出Jcrop.js、jcrop.css的引用，请读者不要漏了这关键的两步。
<div class="item"> <h3> 5、上传头像实例（预览\截取） h3> <form id="form_upload" enctype="multipart/form-data" action="./UploadPhoto" method="post"> <input id="File5" name="UserPhoto" type="file" value="" /> <input id="btnUpload5" type="submit" value="提交上传" /> form> <div id="photoWrap"> <div id="crop_area"> <img id="crop_img" alt="头像" style="display: none"/> div> <div id="preview_area"> <div id="preview_title">当前头像div> <div id="preview_small_txt">48px × 48pxdiv> <div id="preview_small_wrap"> <img id="preview_small_img" alt="小预览图" src="~/Content/default_48.png"/> div> <div id="preview_large_txt">180px × 180pxdiv> <div id="preview_large_wrap"> <img id="preview_large_img" alt="大预览图" src="~/Content/default_180.png"/> div> div> div> <div id="crop_operation"> <form id="form_crop" action="./CropPhoto" method="post"> <input id="url" type="hidden" name="url" /> <input id="x" type="hidden" name="x" /> <input id="y" type="hidden" name="y" /> <input id="w" type="hidden" name="w" /> <input id="h" type="hidden" name="h" /> <input id="btn_crop" type="submit" value="裁剪并保存" /> form> div> div>
JS代码，所需参数
//jcrop 所需参数 var jcrop_api; var boundx; var boundy; //上方是必选参数 //下方是用于截取预览图的参数，可选的 //我这里设置了48*48 180*180 两种规格的预览效果 var $pimg_small; var $pimg_large; var xsize_small = 48; var ysize_small = 48; var xsize_large = 180; var ysize_large = 180; $(function() { $pimg_small = $('#preview_small_img'); $pimg_large = $('#preview_large_img'); });
JS代码，主体逻辑
//上传图片 $('#form_upload').ajaxForm({ dataType: "json", data:$('#form_upload').serialize(), success: function (data, textStatus, jqXHR) { if (data.Status == 'success') { //上传成功后，为主截取区、截取预览区的img赋值 $("#crop_img,#preview_small_img,#preview_large_img").attr('src', data.ImgUrl); //用input hidden保存返回值，以便截取时使用 $("#url").val(data.ImgUrl); //if (jcrop_api != null) { // jcrop_api.setImage(data.ImgUrl, function () { // var bounds = jcrop_api.getBounds(); // boundx = bounds[0]; // boundy = bounds[1]; // var size = Math.min(boundx, boundy); // jcrop_api.setSelect([0,0,size,size]); // }); //} return; } if (data.Status == 'error') { showMessage(data.Msg); } }, error: function (jqXHR, textStatus, errorThrown) { showMessage('上传失败'); console.error(textStatus); } }); //当图片加载完毕时，调用Jcrop初始化函数 //因为存在多次上传图片的情况，所以此处用标签的load事件，每加载完毕一次就初始化一次 $("#crop_img").load(function () {
if (jcrop_api != null) {
jcrop_api.destroy();
}
$("#crop_img").Jcrop({ onChange: updatePreview,//截取框变化事件，主要用于实时更新预览图 onSelect: updateCropData,//截取框选定事件，主要用于获得截取框的4个坐标点 aspectRatio: 1 //截取框的比例，1则是正方形 }, function () { //$().Jcrop()初始化后的回调函数； //这里为提高用户体验而设置了一个可选范围内最大的截取框，以告诉用户“你可以进行截取了”。 jcrop_api = this; var bounds = this.getBounds();//获取图片实际尺寸，格式为：[w,h] boundx = bounds[0]; boundy = bounds[1]; var size = Math.min(boundx, boundy); jcrop_api.setSelect([0, 0, size, size]);//4个坐标点设定一个截取框 }); }); //更新预览图，这函数是官方demo给出的代码，各位可以直接copy不必深究 function updatePreview(c) { if (parseInt(c.w) > 0) { var rx_large = xsize_large / c.w; var ry_large = ysize_large / c.h; $pimg_large.css({ width: Math.round(rx_large * boundx) + 'px', height: Math.round(ry_large * boundy) + 'px', marginLeft: '-' + Math.round(rx_large * c.x) + 'px', marginTop: '-' + Math.round(ry_large * c.y) + 'px' }); var rx_small = xsize_small / c.w; var ry_small = ysize_small / c.h; $pimg_small.css({ width: Math.round(rx_small * boundx) + 'px', height: Math.round(ry_small * boundy) + 'px', marginLeft: '-' + Math.round(rx_small * c.x) + 'px', marginTop: '-' + Math.round(ry_small * c.y) + 'px' }); } }; //截取框选定事件的处理函数，用于获取最左上角的坐标点（x、y），截取框的宽高（w、h） function updateCropData(c) { jQuery("#x").val(c.x); jQuery("#y").val(c.y); jQuery("#w").val(c.w); jQuery("#h").val(c.h) console.group('updateCropData'); console.info(c.x) console.info(c.y) console.info(c.w) console.info(c.h) console.groupEnd('updateCropData'); } //请求后台接口，进行真正的图片截取 //因为4个坐标点是由updateCropData()函数实时更新至的隐藏域里的， //所以这里只要提交表单即可，这里是使用了jquery.form.js插件，我上一篇文章中有提到jquery.form.js的使用 $('#form_crop').ajaxForm({ dataType: "json", success: function (data, textStatus, jqXHR) { if (data.Status == 'success') { showMessage('保存成功'); jcrop_api.destroy();//上传成功后释放jcrop return; } if (data.Status == 'error') { showMessage(data.Msg); } }, error: function (jqXHR, textStatus, errorThrown) { showMessage('请求错误'); console.error(textStatus); } });
后台代码。
[HttpPost] public ActionResult UploadPhoto() { HttpPostedFileBase file = Request.Files["UserPhoto"]; string contentType = file.ContentType; string extension = Path.GetExtension(file.FileName); //检查图片格式 if (!IsAllowImg(contentType, extension)) { return Json(new { Status = "error", Msg = "上传文件格式不符合要求。" }); } //保存形成保存路径 TimeSpan ts = DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, 0); string newFileName = Convert.ToInt64(ts.TotalMilliseconds).ToString(CultureInfo.InvariantCulture) + new Random().Next(100, 999); string path = Server.MapPath("~/Upload/") + newFileName + ".jpeg"; //压缩图片、转换格式（jpeg） Image ResourceImage = Image.FromStream(file.InputStream); if(ResourceImage.Width>300) { int dWidth = 300; int dHeight = 300 * ResourceImage.Height / ResourceImage.Width; CompressPicture(file.InputStream, path, dWidth, dHeight,100); } else { CompressPicture(file.InputStream, path, ResourceImage.Width, ResourceImage.Height, 100); } file.InputStream.Close(); string url = Request.ApplicationPath + "Upload/" + newFileName + ".jpeg"; return Json(new { Status = "success", Msg = "上传成功",ImgUrl= url }); } #region 压缩图像 ////// 无损压缩图片 /// /// 原图片 /// 压缩后保存位置 /// 宽度 /// 高度 /// 压缩质量 1-100 /// public bool CompressPicture(Stream inputStream, string dFile, int dWidth, int dHeight, int flag) { System.Drawing.Image iSource = System.Drawing.Image.FromStream(inputStream); ImageFormat tFormat = iSource.RawFormat; int sW = 0, sH = 0; //按比例缩放 Size tem_size = new Size(iSource.Width, iSource.Height); if (tem_size.Width > dWidth || tem_size.Height > dHeight) { if ((tem_size.Width * dHeight) > (tem_size.Height * 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); Graphics g = Graphics.FromImage(ob); g.Clear(Color.WhiteSmoke); g.CompositingQuality = CompositingQuality.HighQuality; g.SmoothingMode = SmoothingMode.HighQuality; g.InterpolationMode = 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 } else { ob.Save(dFile, tFormat); } return true; } catch { return false; } finally { iSource.Dispose(); ob.Dispose(); } } /// /// 无损压缩图片 /// /// 原图片 /// 压缩后保存位置 /// 宽度 /// 高度 /// 压缩质量 1-100 /// public bool CompressPicture(string sFile, string dFile, int dWidth, int dHeight, int flag) { System.Drawing.Image iSource = System.Drawing.Image.FromFile(sFile); ImageFormat tFormat = iSource.RawFormat; int sW = 0, sH = 0; //按比例缩放 Size tem_size = new Size(iSource.Width, iSource.Height); if (tem_size.Width > dWidth || tem_size.Height > dHeight) { if ((tem_size.Width * dHeight) > (tem_size.Height * 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); Graphics g = Graphics.FromImage(ob); g.Clear(Color.WhiteSmoke); g.CompositingQuality = CompositingQuality.HighQuality; g.SmoothingMode = SmoothingMode.HighQuality; g.InterpolationMode = 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 } else { ob.Save(dFile, tFormat); } return true; } catch { return false; } finally { iSource.Dispose(); ob.Dispose(); } } /// /// 按指定规格裁剪图片 /// /// 源文件路径 /// 输出文件路径 /// 裁剪区域的起点 /// 裁剪区域的大小 /// 生成的规格 /// 压缩质量 1-100 /// public bool CropPicture(string sFile, string dFile, Point originPoint , Size sSize, Size dSize, int flag) { System.Drawing.Image iSource = System.Drawing.Image.FromFile(sFile); ImageFormat tFormat = iSource.RawFormat; Bitmap ob = new Bitmap(dSize.Width, dSize.Height); Graphics g = Graphics.FromImage(ob); g.Clear(Color.WhiteSmoke); g.CompositingQuality = CompositingQuality.HighQuality; g.SmoothingMode = SmoothingMode.HighQuality; g.InterpolationMode = InterpolationMode.HighQualityBicubic; g.DrawImage(iSource, new Rectangle(0, 0, dSize.Width, dSize.Height), originPoint.X, originPoint.Y, sSize.Width, sSize.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 i = 0; i < arrayICI.Length; i++) { if (arrayICI[i].FormatDescription.Equals("JPEG")) { jpegICIinfo = arrayICI[i]; break; } } if(string.IsNullOrEmpty(dFile)) { string[] temp = sFile.Split(new char[] { '\\' }, StringSplitOptions.RemoveEmptyEntries); string fileName = temp[temp.Length - 1]; fileName = fileName.Insert(fileName.IndexOf('.'), '_'+ dSize.Width.ToString() + '_' + dSize.Height.ToString()); temp[temp.Length - 1] = fileName; dFile = string.Empty; foreach(string item in temp) { dFile += item + "\\"; } dFile=dFile.TrimEnd('\\'); } if (jpegICIinfo != null) { ob.Save(dFile, jpegICIinfo, ep); } else { ob.Save(dFile, tFormat); } return true; } catch { return false; } finally { iSource.Dispose(); ob.Dispose(); } } #endregion #region 判断图片格式 public bool IsAllowImg(string contentType, string fileExtension) { contentType = contentType.ToLower(); if(!contentType.Contains("image")) { return false; } fileExtension = fileExtension.ToLower(); string[] allowExtension = { ".bmp", ".gif", ".jpeg", ".jpg", ".png" }; foreach (string item in allowExtension) { if (fileExtension == item) { return true; } } return false; } public static bool IsAllowedExtension(HttpPostedFileBase file) { System.IO.Stream stream = file.InputStream; System.IO.BinaryReader reader = new System.IO.BinaryReader(stream); string fileclass = ""; //这里的位长要具体判断. byte buffer; try { //buffer = r.ReadByte(); //fileclass = buffer.ToString(); //buffer = r.ReadByte(); //fileclass += buffer.ToString(); for (int i = 0; i < 2; i++) { fileclass += reader.ReadByte().ToString(); } } catch { } reader.Close(); stream.Close(); if (fileclass == "255216" || fileclass == "7173")//说明255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar { return true; } else { return false; } } #endregion [HttpPost] public JsonResult CropPhoto(string url,int x,int y,int w,int h) { if (string.IsNullOrEmpty(url) || w == 0 || h == 0) { return Json(new { Status = "error", Msg = "参数错误" }); } Point origin = new Point(x, y); Size source = new Size(w, h); Size destSmall = new Size(48, 48); Size destLarge = new Size(180, 180); bool result1 =CropPicture(Server.MapPath(url), null, origin, source, destSmall, 100); bool result2 =CropPicture(Server.MapPath(url), null, origin, source, destLarge, 100); var jsonResult = result1 && result2 ? new { Status = "success", Msg = "操作成功" } : new { Status = "error", Msg = "裁剪图片出现错误" }; return Json(jsonResult); } }
在上传图片时，我对宽度大于300px的图片进行了等比压缩，目的是控制图片在浏览器截取区内显示的比较友好。
这里也可以直接返回源图，在 标签内使用 width属性控制图片宽度，再计算出缩放比例并将此数值存储于