SOURCE

// canvas转dataURL：canvas对象、转换格式、图像品质
// -------------------------
function canvasToDataURL(canvas, format, quality) {
  return canvas.toDataURL(format || 'image/jpeg', quality || 1.0);
}
// DataURL转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转canvas：图片地址
// -------------------------
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转image
// -------------------------
function canvasToImage(canvas) {
  var img = new Image();
  img.src = canvas.toDataURL('image/jpeg', 1.0);
  return img;
}
// File/Blob对象转DataURL
// -------------------------
function fileOrBlobToDataURL(obj, cb) {
  var a = new FileReader();
  a.readAsDataURL(obj);
  a.onload = function(e) {
    cb(e.target.result);
  };
}
// DataURL转Blob对象
// -------------------------
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转image
// -------------------------
function blobToImage(blob, cb) {
  fileOrBlobToDataURL(blob, function(dataurl) {
    var img = new Image();
    img.src = dataurl;
    cb(img);
  });
}
// image转Blob
// -------------------------
function imageToBlob(src, cb) {
  imageToCanvas(src, function(canvas) {
    cb(dataURLToBlob(canvasToDataURL(canvas)));
  });
}
// Blob转canvas
// -------------------------
function BlobToCanvas(blob, cb) {
  fileOrBlobToDataURL(blob, function(dataurl) {
    dataURLToCanvas(dataurl, cb);
  });
}
// canvas转Blob
// -------------------------
function canvasToBlob(canvas, cb) {
  cb(dataURLToBlob(canvasToDataURL(canvas)));
}
// image转dataURL
// -------------------------
function imageToDataURL(src, cb) {
  imageToCanvas(src, function(canvas) {
    cb(canvasToDataURL(canvas));
  });
}
// dataURL转image，这个不需要转，直接给了src就能用
// -------------------------
function dataURLToImage(dataurl) {
  var img = new Image();
  img.src = d;
  return img;
}