Add loadImage.replaceHead method.

Author: blueimp

README.md

@@ -37,6 +37,7 @@
   - [crossOrigin](#crossorigin)
   - [noRevoke](#norevoke)
 - [Meta data parsing](#meta-data-parsing)
+  - [Image head](#image-head)
   - [Exif parser](#exif-parser)
   - [IPTC parser](#iptc-parser)
 - [License](#license)
@@ -386,15 +387,43 @@ loadImage.parseMetaData(
 )
 ```
 
-**Note:**  
-Blob objects of resized images can be created via
-[canvas.toBlob()](https://github.com/blueimp/JavaScript-Canvas-to-Blob).
-
 The Meta data extension also adds additional options used for the
 `parseMetaData` method:
 
 - `maxMetaDataSize`: Maximum number of bytes of meta data to parse.
 - `disableImageHead`: Disable parsing the original image head.
+- `disableMetaDataParsers`: Disable parsing meta data (image head only)
+
+### Image head
+
+Resized JPEG images can be combined with their original image head via
+`loadImage.replaceHead`, which requires the resized image as `Blob` object as
+first argument and an `ArrayBuffer` image head as second argument. The third
+argument must be a `callback` function, which is called with the new `Blob`
+object:
+
+```js
+loadImage(
+  fileOrBlobOrUrl,
+  function (img, data) {
+    if (data.imageHead && data.exif) {
+      img.toBlob(function (blob) {
+        loadImage.replaceHead(blob, data.imageHead, function (newBlob) {
+          // do something with newBlob
+        })
+      }, 'image/jpeg')
+    }
+  },
+  { meta: true, canvas: true, maxWidth: 800 }
+)
+```
+
+**Note:**  
+Blob objects of resized images can be created via
+[canvas.toBlob](https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob).
+For browsers which don't have native support, a
+[canvas.toBlob polyfill](https://github.com/blueimp/JavaScript-Canvas-to-Blob)
+is available.
 
 ### Exif parser
 

js/load-image-meta.js

@@ -118,7 +118,7 @@
                   break
                 }
                 parsers = loadImage.metaDataParsers.jpeg[markerBytes]
-                if (parsers) {
+                if (parsers && !options.disableMetaDataParsers) {
                   for (i = 0; i < parsers.length; i += 1) {
                     parsers[i].call(
                       that,
@@ -162,6 +162,23 @@
     }
   }
 
+  // Replaces the image head of a JPEG blob with the given one.
+  // Calls the callback with the new Blob:
+  loadImage.replaceHead = function (blob, head, callback) {
+    loadImage.parseMetaData(
+      blob,
+      function (data) {
+        callback(
+          new Blob(
+            [head, loadImage.blobSlice.call(blob, data.imageHead.byteLength)],
+            { type: 'image/jpeg' }
+          )
+        )
+      },
+      { maxMetaDataSize: 256, disableMetaDataParsers: true }
+    )
+  }
+
   // Determines if meta data should be loaded automatically:
   loadImage.hasMetaOption = function (options) {
     return options && options.meta