canvas轉img，blob相互轉換

// canvas轉dataURL：canvas對象、轉換格式、圖像品質
function canvasToDataURL(canvas, format, quality){
    return canvas.toDataURL(format||'image/jpeg', quality||1.0);
}
// DataURL轉canvas
function dataURLToCanvas(dataurl, cb){
    var canvas = document.createElement('CANVAS');
    var ctx = canvas.getContext('2d');
    var img = new Image();
    img.onload = function(){
        canvas.width = img.width;
        canvas.height = img.height;
        ctx.drawImage(img, 0, 0);
        cb(canvas);
    };
    img.src = dataurl;
}
/*-----------------------------------------------------------------------*/
// image轉canvas：圖片地址
function imageToCanvas(src, cb){
    var canvas = document.createElement('CANVAS');
    var ctx = canvas.getContext('2d');
    var img = new Image();
    img.src = src;
    img.onload = function (){
        canvas.width = img.width;
        canvas.height = img.height;
        ctx.drawImage(img, 0, 0);
        cb(canvas);
    };
}
// canvas轉image
function canvasToImage(canvas){
    var img = new Image();
    img.src = canvas.toDataURL('image/jpeg', 1.0);
    return img;
}
/*-----------------------------------------------------------------------*/
// File/Blob對象轉DataURL
function fileOrBlobToDataURL(obj, cb){
    var a = new FileReader();
    a.readAsDataURL(obj);
    a.onload = function (e){
        cb(e.target.result);
    };
}
// DataURL轉Blob對象
function dataURLToBlob(dataurl){
    var arr = dataurl.split(',');
    var mime = arr[0].match(/:(.*?);/)[1];
    var bstr = atob(arr[1]);
    var n = bstr.length;
    var u8arr = new Uint8Array(n);
    while(n--){
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new Blob([u8arr], {type:mime});
}
/*-----------------------------------------------------------------------*/
// Blob轉image
function blobToImage(blob, cb){
    fileOrBlobToDataURL(blob, function (dataurl){
        var img = new Image();
        img.src = dataurl;
        cb(img);
    });
}
// image轉Blob
function imageToBlob(src, cb){
    imageToCanvas(src, function (canvas){
        cb(dataURLToBlob(canvasToDataURL(canvas)));
    });
}
/*-----------------------------------------------------------------------*/
// Blob轉canvas
function BlobToCanvas(blob, cb){
    fileOrBlobToDataURL(blob, function (dataurl){
        dataURLToCanvas(dataurl, cb);
    });
}
// canvas轉Blob
function canvasToBlob(canvas, cb){
    cb(dataURLToBlob(canvasToDataURL(canvas)));
}
/*-----------------------------------------------------------------------*/
// image轉dataURL
function imageToDataURL(src, cb){
    imageToCanvas(src, function (canvas){
        cb(canvasToDataURL(canvas));
    });
}
// dataURL轉image，這個不需要轉，直接給了src就能用
function dataURLToImage(dataurl){
    var img = new Image();
    img.src = d;
    return img;
}