added jpg encoding in array_to_data_url

dash_canvas/utils/io_utils.py

@@ -3,7 +3,7 @@
 import base64
 
 
-def array_to_data_url(img, dtype=None):
+def array_to_data_url(img, dtype=None, img_format='png'):
     """
     Converts numpy array to data string, using Pillow.
 
@@ -24,8 +24,13 @@ def array_to_data_url(img, dtype=None):
         img = img.astype(dtype)
     pil_img = Image.fromarray(img)
     buff = BytesIO()
-    pil_img.save(buff, format="png")
-    prefix = b'data:image/png;base64,'
+    pil_img.save(buff, format=img_format)
+    if img_format == 'png':
+        prefix = b'data:image/png;base64,'
+    elif img_format == 'jpeg':
+        prefix = b'data:image/jpeg;base64,'
+    else:
+        raise ValueError("accepted image formats are 'png' and 'jpeg' but %s was passed" %format)
     image_string = (prefix + base64.b64encode(buff.getvalue())).decode("utf-8")
     return image_string
 
@@ -34,4 +39,9 @@ def image_string_to_PILImage(image_string):
     """
     Converts image string to PIL image object.
     """
-    return Image.open(BytesIO(base64.b64decode(image_string[22:])))
+    if 'png' in image_string[:22]:
+        return Image.open(BytesIO(base64.b64decode(image_string[22:])))
+    elif 'jpeg' in image_string[:23]:
+        return Image.open(BytesIO(base64.b64decode(image_string[23:])))
+    else:
+        raise ValueError("image string format not recognized")