javascript - The background of the PNG image loaded by exif.js is black?

This is the picture before uploading

This is the picture after uploading

Using exif.js to parse pictures, I don’t know why the uploaded png format has a black background

Post the code directly below

<code>/**
 * 上传多张图片
 * @method uploadImg
 * @params url:上传图片请求的服务器端的文件的地址,
 * @params container:图片上传之后渲染到哪个父盒子,
 * @params maxCount:最多可上传的数目,
 * @params maxMb:上传的大小MB
 * @params fileInput:上传图片的文件域
 * @params scale:图片的缩放比例  大小
 * @params name:参数名称
 * @params success:上传成功之后执行的回调函数
 * @params error:上传失败之后执行的回调函数
 * @params warn:不符合上传条件时执行的回调函数
 * @return 元素对象.uploadImg(Objext)
 */
(function($){     
    $.fn.extend({     
        uploadImg:function(opt){     
            var up=new UploadImg(opt,this);
        }     
    });
    function UploadImg(option,self){
       var _defaults={
          url:"",
          container:self,
          maxCount:3,
          maxMb:2,
          fileInput:$(self).find(".fileImg"),
          scale:0.8,
          name:"img",
          success:function(data,idx){
                
          },
          error:function(msg){
             alertBox(msg,1,"关 闭","",cancelAlert);
          },
          warn:function(msg){
             alertBox(msg,1,"关 闭","",cancelAlert);
          }
       };
       this.opt=$.extend({},_defaults,option);
       this.init(self);
    }

    UploadImg.prototype={
        init:function(self){
           var _this=this;
           var liIndex=0;
           // 给文件域绑定事件
           _this.opt.fileInput.on('change',function(){
               var files=this.files?this.files:null,
                   _tar=files[0],
                   maxSize=_this.opt.maxMb*1024*1024,
                   reg=/\.(jpg)|(jpeg)|(gif)|(png)$/i,
                   err="",
                   html="";

               if(!(reg.test(_tar.name))){
                  err="请上传jpg/jpeg/gif/png格式的图片";
               }else{
                    if(_tar.size>maxSize){
                      err="图片尺寸超出限制，请上传低于"+_this.opt.maxMb+"M的图片";
                   }
               }
               
               if(err){
                   _this.opt.warn && _this.opt.warn(err);
                   return;
               }
                
               liIndex++;
               
               html='<li class="upload-img upload-loading">'
                        +'<img  src="" alt="javascript - The background of the PNG image loaded by exif.js is black?" >'
                        +'<a href="javascript:void(0)" class="upload_delete" title="删除"></a>'
                   +'</li>';

               $(html).prependTo($(_this.opt.container));

               _this.getCount(liIndex);

               // 上传图片
               _this.zipImg({
                     files:files,
                     scale:_this.opt.scale,
                     callback:function(tar){
                     if(tar.constructor!='Array'){
                        tar=[tar];
                     }
                     _this.submit(tar,liIndex,self);
                     }
               })
           })
           // 关闭
           $(_this.opt.container).on('click','.upload_delete',function(){
                  liIndex-=1;
                  $(this).parents('li.upload-img').remove();
                  _this.getCount(liIndex);
           })
        },
        //压缩图片方法
        zipImg: function(cfg){
         /*
          * cfg.files      input对象触发onchange时候的files
          * cfg.scale      压缩比例
          * cfg.callback     压缩成功后的回调
          */
          var _this = this;
          var options = cfg;
         [].forEach.call(options.files, function(v, k){
           var fr = new FileReader();  
           fr.onload= function(e) {  
             var oExif = EXIF.readFromBinaryFile(new BinaryFile(e.target.result)) || {};

             var $img = document.createElement('img');                         
             $img.onload = function(){                 
               _this.fixDirect().fix($img, oExif, options.callback,options.scale);
             };  
             if(typeof(window.URL) != 'undefined'){
              $img.src = window.URL.createObjectURL(v);
             }else{
              $img.src = e.target.result;       
             }
           };  
           //fr.readAsDataURL(v);
           fr.readAsBinaryString(v);
         }); 
        },
        //调整图片方向
        fixDirect: function(){
         var r = {};
         r.fix = function(img, a, callback,scale) {
           var n = img.naturalHeight,
             i = img.naturalWidth,
             c = 1024,
             o = document.createElement("canvas"),
             s = o.getContext("2d");
           a = a || {};
           //o.width = o.height = c;
           //debugger;
           if(n > c || i > c){
             o.width = o.height = c;
           }else{
             o.width = i;
             o.height = n;
           }
           a.Orientation = a.Orientation || 1;
           r.detectSubSampling(img) && (i /= 2, n /= 2);
           var d, h;
           i > n ? (d = c, h = Math.ceil(n / i * c)) : (h = c, d = Math.ceil(i / n * c));
           // var g = c / 2,
           var g = Math.max(o.width,o.height)/2,
             l = document.createElement("canvas");
           if(n > c || i > c){
             l.width = g, l.height = g;
           }else{
             l.width = i;
             l.height = n;
             d = i;
             h =n;
           }
           //l.width = g, l.height = g;
           var m = l.getContext("2d"), u = r.detect(img, n) || 1;
           s.save();
           r.transformCoordinate(o, d, h, a.Orientation);
           var isUC = navigator.userAgent.match(/UCBrowser[\/]?([\d.]+)/i);
           if (isUC && $.os.android){
             s.drawImage(img, 0, 0, d, h);
           }else{
             for (var f = g * d / i, w = g * h / n / u, I = 0, b = 0; n > I; ) {
               for (var x = 0, C = 0; i > x; )
                 m.clearRect(0, 0, g, g), m.drawImage(img, -x, -I), s.drawImage(l, 0, 0, g, g, C, b, f, w), x += g, C += f;
               I += g, b += w
             }
           }
           s.restore();
           a.Orientation = 1;
           img = document.createElement("img");
           img.onload = function(){
             a.PixelXDimension = img.width;
             a.PixelYDimension = img.height;
             //e(img, a);
           };
           
           callback && callback(o.toDataURL("image/jpeg", scale).substring(22));//压缩图片
         };
         r.detect = function(img, a) {
           var e = document.createElement("canvas");
           e.width = 1;
           e.height = a;
           var r = e.getContext("2d");
           r.drawImage(img, 0, 0);
           for(var n = r.getImageData(0, 0, 1, a).data, i = 0, c = a, o = a; o > i; ) {
             var s = n[4 * (o - 1) + 3];
             0 === s ? c = o : i = o, o = c + i >> 1
           }
           var d = o / a;
           return 0 === d ? 1 : d
         };
         r.detectSubSampling = function(img) {
           var a = img.naturalWidth, e = img.naturalHeight;
           if (a * e > 1048576) {
             var r = document.createElement("canvas");
             r.width = r.height = 1;
             var n = r.getContext("2d");
             return n.drawImage(img, -a + 1, 0), 0 === n.getImageData(0, 0, 1, 1).data[3]
           }
           return !1;
         };
         r.transformCoordinate = function(img, a, e, r) {
           switch (r) {
             case 5:
             case 6:
             case 7:
             case 8:
               img.width = e, img.height = a;
               break;
             default:
               img.width = a, img.height = e
           }
           var n = img.getContext("2d");
           switch (r) {
             case 2:
               n.translate(a, 0), n.scale(-1, 1);
               break;
             case 3:
               n.translate(a, e), n.rotate(Math.PI);
               break;
             case 4:
               n.translate(0, e), n.scale(1, -1);
               break;
             case 5:
               n.rotate(.5 * Math.PI), n.scale(1, -1);
               break;
             case 6:
               n.rotate(.5 * Math.PI), n.translate(0, -e);
               break;
             case 7:
               n.rotate(.5 * Math.PI), n.translate(a, -e), n.scale(-1, 1);
               break;
             case 8:
               n.rotate(-.5 * Math.PI), n.translate(-a, 0)
           }
         };
         return r;
        },
        getCount:function(idx){
            var _this=this,
                size=$(_this.opt.container).find('li.upload-img').size(),
                $uploadLi=$(_this.opt.fileInput).parents("li");

            if(idx>=_this.opt.maxCount){
               $uploadLi.hide();
            }else{
               $uploadLi.show();
            }
        },
        submit:function(files,idx,t){
           var _this=this,
               files=files[0],
               param={},
               url=_this.opt.url;
           param[_this.opt.name]=files;
           $.ajax({
                 url:url,
                 type:"post",
                 data:param,
                 success:function(data){
                  data=JSON.parse(data);
                  _this.opt.success && _this.opt.success(data,idx);
                  $(t).find("li").eq(0).removeClass('upload-loading').find('img').attr('src',data.url);
                 },
                 error:function(data){
                 _this.opt.error && _this.opt.error(data.msg); 
                 }
           })
        }
    }
})(jQuery);</code>

EXIF used in compressing images is where the images are processed. I don’t know how to process the uploaded images in PNG format. The background is black. Please help me! ! !

You can also download and run it directly, mainly because the transparent png you encounter has a black background when you synthesize it! The purpose is to remove the black background! !

<code>git clone https://github.com/Shoestrong/uploadimg.git</code>

Additional point: I just discovered that there is a problem with the size when uploading png, please solve it by the way! !

Reply content:

This is the picture before uploading

This is the picture after uploading

Using exif.js to parse the picture, I don’t know why the uploaded png format has a black background

Post the code directly below

<code>/**
 * 上传多张图片
 * @method uploadImg
 * @params url:上传图片请求的服务器端的文件的地址,
 * @params container:图片上传之后渲染到哪个父盒子,
 * @params maxCount:最多可上传的数目,
 * @params maxMb:上传的大小MB
 * @params fileInput:上传图片的文件域
 * @params scale:图片的缩放比例  大小
 * @params name:参数名称
 * @params success:上传成功之后执行的回调函数
 * @params error:上传失败之后执行的回调函数
 * @params warn:不符合上传条件时执行的回调函数
 * @return 元素对象.uploadImg(Objext)
 */
(function($){     
    $.fn.extend({     
        uploadImg:function(opt){     
            var up=new UploadImg(opt,this);
        }     
    });
    function UploadImg(option,self){
       var _defaults={
          url:"",
          container:self,
          maxCount:3,
          maxMb:2,
          fileInput:$(self).find(".fileImg"),
          scale:0.8,
          name:"img",
          success:function(data,idx){
                
          },
          error:function(msg){
             alertBox(msg,1,"关 闭","",cancelAlert);
          },
          warn:function(msg){
             alertBox(msg,1,"关 闭","",cancelAlert);
          }
       };
       this.opt=$.extend({},_defaults,option);
       this.init(self);
    }

    UploadImg.prototype={
        init:function(self){
           var _this=this;
           var liIndex=0;
           // 给文件域绑定事件
           _this.opt.fileInput.on('change',function(){
               var files=this.files?this.files:null,
                   _tar=files[0],
                   maxSize=_this.opt.maxMb*1024*1024,
                   reg=/\.(jpg)|(jpeg)|(gif)|(png)$/i,
                   err="",
                   html="";

               if(!(reg.test(_tar.name))){
                  err="请上传jpg/jpeg/gif/png格式的图片";
               }else{
                    if(_tar.size>maxSize){
                      err="图片尺寸超出限制，请上传低于"+_this.opt.maxMb+"M的图片";
                   }
               }
               
               if(err){
                   _this.opt.warn && _this.opt.warn(err);
                   return;
               }
                
               liIndex++;
               
               html='<li class="upload-img upload-loading">'
                        +'<img  src="" alt="javascript - The background of the PNG image loaded by exif.js is black?" >'
                        +'<a href="javascript:void(0)" class="upload_delete" title="删除"></a>'
                   +'</li>';

               $(html).prependTo($(_this.opt.container));

               _this.getCount(liIndex);

               // 上传图片
               _this.zipImg({
                     files:files,
                     scale:_this.opt.scale,
                     callback:function(tar){
                     if(tar.constructor!='Array'){
                        tar=[tar];
                     }
                     _this.submit(tar,liIndex,self);
                     }
               })
           })
           // 关闭
           $(_this.opt.container).on('click','.upload_delete',function(){
                  liIndex-=1;
                  $(this).parents('li.upload-img').remove();
                  _this.getCount(liIndex);
           })
        },
        //压缩图片方法
        zipImg: function(cfg){
         /*
          * cfg.files      input对象触发onchange时候的files
          * cfg.scale      压缩比例
          * cfg.callback     压缩成功后的回调
          */
          var _this = this;
          var options = cfg;
         [].forEach.call(options.files, function(v, k){
           var fr = new FileReader();  
           fr.onload= function(e) {  
             var oExif = EXIF.readFromBinaryFile(new BinaryFile(e.target.result)) || {};

             var $img = document.createElement('img');                         
             $img.onload = function(){                 
               _this.fixDirect().fix($img, oExif, options.callback,options.scale);
             };  
             if(typeof(window.URL) != 'undefined'){
              $img.src = window.URL.createObjectURL(v);
             }else{
              $img.src = e.target.result;       
             }
           };  
           //fr.readAsDataURL(v);
           fr.readAsBinaryString(v);
         }); 
        },
        //调整图片方向
        fixDirect: function(){
         var r = {};
         r.fix = function(img, a, callback,scale) {
           var n = img.naturalHeight,
             i = img.naturalWidth,
             c = 1024,
             o = document.createElement("canvas"),
             s = o.getContext("2d");
           a = a || {};
           //o.width = o.height = c;
           //debugger;
           if(n > c || i > c){
             o.width = o.height = c;
           }else{
             o.width = i;
             o.height = n;
           }
           a.Orientation = a.Orientation || 1;
           r.detectSubSampling(img) && (i /= 2, n /= 2);
           var d, h;
           i > n ? (d = c, h = Math.ceil(n / i * c)) : (h = c, d = Math.ceil(i / n * c));
           // var g = c / 2,
           var g = Math.max(o.width,o.height)/2,
             l = document.createElement("canvas");
           if(n > c || i > c){
             l.width = g, l.height = g;
           }else{
             l.width = i;
             l.height = n;
             d = i;
             h =n;
           }
           //l.width = g, l.height = g;
           var m = l.getContext("2d"), u = r.detect(img, n) || 1;
           s.save();
           r.transformCoordinate(o, d, h, a.Orientation);
           var isUC = navigator.userAgent.match(/UCBrowser[\/]?([\d.]+)/i);
           if (isUC && $.os.android){
             s.drawImage(img, 0, 0, d, h);
           }else{
             for (var f = g * d / i, w = g * h / n / u, I = 0, b = 0; n > I; ) {
               for (var x = 0, C = 0; i > x; )
                 m.clearRect(0, 0, g, g), m.drawImage(img, -x, -I), s.drawImage(l, 0, 0, g, g, C, b, f, w), x += g, C += f;
               I += g, b += w
             }
           }
           s.restore();
           a.Orientation = 1;
           img = document.createElement("img");
           img.onload = function(){
             a.PixelXDimension = img.width;
             a.PixelYDimension = img.height;
             //e(img, a);
           };
           
           callback && callback(o.toDataURL("image/jpeg", scale).substring(22));//压缩图片
         };
         r.detect = function(img, a) {
           var e = document.createElement("canvas");
           e.width = 1;
           e.height = a;
           var r = e.getContext("2d");
           r.drawImage(img, 0, 0);
           for(var n = r.getImageData(0, 0, 1, a).data, i = 0, c = a, o = a; o > i; ) {
             var s = n[4 * (o - 1) + 3];
             0 === s ? c = o : i = o, o = c + i >> 1
           }
           var d = o / a;
           return 0 === d ? 1 : d
         };
         r.detectSubSampling = function(img) {
           var a = img.naturalWidth, e = img.naturalHeight;
           if (a * e > 1048576) {
             var r = document.createElement("canvas");
             r.width = r.height = 1;
             var n = r.getContext("2d");
             return n.drawImage(img, -a + 1, 0), 0 === n.getImageData(0, 0, 1, 1).data[3]
           }
           return !1;
         };
         r.transformCoordinate = function(img, a, e, r) {
           switch (r) {
             case 5:
             case 6:
             case 7:
             case 8:
               img.width = e, img.height = a;
               break;
             default:
               img.width = a, img.height = e
           }
           var n = img.getContext("2d");
           switch (r) {
             case 2:
               n.translate(a, 0), n.scale(-1, 1);
               break;
             case 3:
               n.translate(a, e), n.rotate(Math.PI);
               break;
             case 4:
               n.translate(0, e), n.scale(1, -1);
               break;
             case 5:
               n.rotate(.5 * Math.PI), n.scale(1, -1);
               break;
             case 6:
               n.rotate(.5 * Math.PI), n.translate(0, -e);
               break;
             case 7:
               n.rotate(.5 * Math.PI), n.translate(a, -e), n.scale(-1, 1);
               break;
             case 8:
               n.rotate(-.5 * Math.PI), n.translate(-a, 0)
           }
         };
         return r;
        },
        getCount:function(idx){
            var _this=this,
                size=$(_this.opt.container).find('li.upload-img').size(),
                $uploadLi=$(_this.opt.fileInput).parents("li");

            if(idx>=_this.opt.maxCount){
               $uploadLi.hide();
            }else{
               $uploadLi.show();
            }
        },
        submit:function(files,idx,t){
           var _this=this,
               files=files[0],
               param={},
               url=_this.opt.url;
           param[_this.opt.name]=files;
           $.ajax({
                 url:url,
                 type:"post",
                 data:param,
                 success:function(data){
                  data=JSON.parse(data);
                  _this.opt.success && _this.opt.success(data,idx);
                  $(t).find("li").eq(0).removeClass('upload-loading').find('img').attr('src',data.url);
                 },
                 error:function(data){
                 _this.opt.error && _this.opt.error(data.msg); 
                 }
           })
        }
    }
})(jQuery);</code>

EXIF used in compressing images is where the images are processed. I don’t know how to process the uploaded images in PNG format. The background is black. Please help me! ! !

You can also download and run it directly, mainly because the transparent png you encounter has a black background when you synthesize it! The purpose is to remove the black background! !

<code>git clone https://github.com/Shoestrong/uploadimg.git</code>

Additional point: I just discovered that there is a problem with the size when uploading png, please solve it by the way! !

First of all, I am not sure whether EXIF.readFromBinaryFile() will read the image into JPG format - I may need to talk about PNG and JPG first: their difference is still relatively big, but for this problem, the main thing is that PNG can Transparent, while JPG cannot be transparent. When a transparent image is processed into an opaque image, the transparent pixels will be replaced by the default color, which may be white, black, or other colors.

So, the first possible pitfall is EXIF.readFromBinaryFile()

Then you used canvas to process the image. I don’t know much about HTML canvas, but I think it can handle transparent pixels. But it cannot be ruled out that this is the second possible pit.

Finally, o.toDataURL("image/jpeg", ... This is definitely a pitfall, because even if the first two pitfalls do not exist, the image in the canvas is transparent, but if you output it in jpeg format, then It has also become opaque...

I don’t know exactly where the pitfalls are. The above ideas are for reference only.