html读取图片

//实现图片预览
function change_photo(){
    PreviewImage($("input[name='picture']")[0], 'img', 'imgtd');
}

function PreviewImage(fileObj,imgPreviewId,divPreviewId){  
    var allowExtention=".jpg,.bmp,.gif,.png";              //允许上传文件的后缀名document.getElementById("hfAllowPicSuffix").value;  
    var extention=fileObj.value.substring(fileObj.value.lastIndexOf(".")+1).toLowerCase();              
    var browserVersion= window.navigator.userAgent.toUpperCase();  
    if(allowExtention.indexOf(extention)>-1){   
        if(fileObj.files){                                 //HTML5实现预览，兼容chrome、火狐7+等  
            if(window.FileReader){  
                var reader = new FileReader();   
                reader.onload = function(e){  
                    document.getElementById(imgPreviewId).setAttribute("src",e.target.result);  
                }    
                reader.readAsDataURL(fileObj.files[0]);  
            }else if(browserVersion.indexOf("SAFARI")>-1){  
                alert("不支持Safari6.0以下浏览器的图片预览!");  
            }  
        }else if (browserVersion.indexOf("MSIE")>-1){  
            if(browserVersion.indexOf("MSIE 6")>-1){//ie6  
                document.getElementById(imgPreviewId).setAttribute("src",fileObj.value);  
            }else{//ie[7-9]  
                fileObj.select();  
                if(browserVersion.indexOf("MSIE 9")>-1)  
                    fileObj.blur();//不加上document.selection.createRange().text在ie9会拒绝访问  
                var newPreview =document.getElementById(divPreviewId+"New");  
                if(newPreview==null){  
                    newPreview =document.createElement("div");  
                    newPreview.setAttribute("id",divPreviewId+"New");  
                    newPreview.style.width = document.getElementById(imgPreviewId).width+"px";  
                    newPreview.style.height = document.getElementById(imgPreviewId).height+"px";  
                    newPreview.style.border="solid 1px #d2e2e2";  
                }  
                newPreview.style.filter="progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='scale',src='" + document.selection.createRange().text + "')";                              
                var tempDivPreview=document.getElementById(divPreviewId);  
                tempDivPreview.parentNode.insertBefore(newPreview,tempDivPreview);  
                tempDivPreview.style.display="none";                      
            }  
        }else if(browserVersion.indexOf("FIREFOX")>-1){//firefox  
            var firefoxVersion= parseFloat(browserVersion.toLowerCase().match(/firefox/([d.]+)/)[1]);  
            if(firefoxVersion<7){//firefox7以下版本  
                document.getElementById(imgPreviewId).setAttribute("src",fileObj.files[0].getAsDataURL());  
            }else{//firefox7.0+                      
                document.getElementById(imgPreviewId).setAttribute("src",window.URL.createObjectURL(fileObj.files[0]));  
            }  
        }else{  
            document.getElementById(imgPreviewId).setAttribute("src",fileObj.value);  
        }           
    }else{  
        alert("仅支持"+allowExtention+"为后缀名的文件!");  
        fileObj.value="";//清空选中文件  
        if(browserVersion.indexOf("MSIE")>-1){                          
            fileObj.select();  
            document.selection.clear();  
        }                  
        fileObj.outerHTML=fileObj.outerHTML;  
    }  
}

//图片转base64
function getBase64Image(img) {
  var canvas = document.createElement("canvas");
  canvas.width = img.width;
  canvas.height = img.height;

  var ctx = canvas.getContext("2d");
  ctx.drawImage(img, 0, 0, img.width, img.height);

  var dataURL = canvas.toDataURL("image/png");
  return dataURL

  // return dataURL.replace("data:image/png;base64,", "");
}