canvas转img，blob相互转换

 1 // canvas转dataURL：canvas对象、转换格式、图像品质
 2 function canvasToDataURL(canvas, format, quality){
 3     return canvas.toDataURL(format||'image/jpeg', quality||1.0);
 4 }
 5 // DataURL转canvas
 6 function dataURLToCanvas(dataurl, cb){
 7     var canvas = document.createElement('CANVAS');
 8     var ctx = canvas.getContext('2d');
 9     var img = new Image();
10     img.onload = function(){
11         canvas.width = img.width;
12         canvas.height = img.height;
13         ctx.drawImage(img, 0, 0);
14         cb(canvas);
15     };
16     img.src = dataurl;
17 }
18 /*-----------------------------------------------------------------------*/
19 // image转canvas：图片地址
20 function imageToCanvas(src, cb){
21     var canvas = document.createElement('CANVAS');
22     var ctx = canvas.getContext('2d');
23     var img = new Image();
24     img.src = src;
25     img.onload = function (){
26         canvas.width = img.width;
27         canvas.height = img.height;
28         ctx.drawImage(img, 0, 0);
29         cb(canvas);
30     };
31 }
32 // canvas转image
33 function canvasToImage(canvas){
34     var img = new Image();
35     img.src = canvas.toDataURL('image/jpeg', 1.0);
36     return img;
37 }
38 /*-----------------------------------------------------------------------*/
39 // File/Blob对象转DataURL
40 function fileOrBlobToDataURL(obj, cb){
41     var a = new FileReader();
42     a.readAsDataURL(obj);
43     a.onload = function (e){
44         cb(e.target.result);
45     };
46 }
47 // DataURL转Blob对象
48 function dataURLToBlob(dataurl){
49     var arr = dataurl.split(',');
50     var mime = arr[0].match(/:(.*?);/)[1];
51     var bstr = atob(arr[1]);
52     var n = bstr.length;
53     var u8arr = new Uint8Array(n);
54     while(n--){
55         u8arr[n] = bstr.charCodeAt(n);
56     }
57     return new Blob([u8arr], {type:mime});
58 }
59 /*-----------------------------------------------------------------------*/
60 // Blob转image
61 function blobToImage(blob, cb){
62     fileOrBlobToDataURL(blob, function (dataurl){
63         var img = new Image();
64         img.src = dataurl;
65         cb(img);
66     });
67 }
68 // image转Blob
69 function imageToBlob(src, cb){
70     imageToCanvas(src, function (canvas){
71         cb(dataURLToBlob(canvasToDataURL(canvas)));
72     });
73 }
74 /*-----------------------------------------------------------------------*/
75 // Blob转canvas
76 function BlobToCanvas(blob, cb){
77     fileOrBlobToDataURL(blob, function (dataurl){
78         dataURLToCanvas(dataurl, cb);
79     });
80 }
81 // canvas转Blob
82 function canvasToBlob(canvas, cb){
83     cb(dataURLToBlob(canvasToDataURL(canvas)));
84 }
85 /*-----------------------------------------------------------------------*/
86 // image转dataURL
87 function imageToDataURL(src, cb){
88     imageToCanvas(src, function (canvas){
89         cb(canvasToDataURL(canvas));
90     });
91 }
92 // dataURL转image，这个不需要转，直接给了src就能用
93 function dataURLToImage(dataurl){
94     var img = new Image();
95     img.src = d;
96     return img;
97 }