发送单聊图片 失败

sendImg() {
                var that = this
                var imageBase64 = localStorage.getItem('screenshot')
                var bytes=window.atob(imageBase64.split(',')[1]);        //去掉url的头，并转换为byte 
                //处理异常,将ascii码小于0的转换为大于0  
                var ab = new ArrayBuffer(bytes.length);  
                var ia = new Uint8Array(ab);  
                for (var i = 0; i < bytes.length; i++) {  
                    ia[i] = bytes.charCodeAt(i);  
                }  
                var fd = new Blob( [ab] , {type :'image/png'});  
                console.log(fd);
                // return
                JIM.sendSinglePic({
                    'target_username' : this.target_name,
                    'image' : fd,
                    'extras' : {
                                    type: 'addPic',
                                    avatar: that.avatar,
                                }
                }).onSuccess((data, msg) =>{
                    console.log('》》》》》》》》》发送图片成功');
                    that.dealPic(msg)
                    that.setAche(msg)
                })
                .onFail((err)=>{
                    console.log('>>>>>>>>send img err:');
                    console.log(err)
                })
            },

JM版本：jmessage-sdk-web.2.6.0.min.js