fix: send the image index along with time and metadata when saving image

Author: WeisLeDocto

src/crappy/blocks/camera.py

@@ -28,9 +28,10 @@ class Camera(Block):
   can accept input Links is when an ``image_generator`` is defined, or when
   defining a ``software_trig_label``. If ``save_images`` is set to :obj:`True`,
   and if an output Link is present, a message is sent to downstream Blocks at
-  each saved image, containing the timestamp and the metadata of the image.
-  They are respectively carried by the `'t(s)'` and `'meta'` labels. This is
-  useful for performing an action conditionally at each new saved image.
+  each saved image, containing the timestamp, the index, and the metadata of
+  the image. They are respectively carried by the `'t(s)'`, `'img_index'` and
+  `'meta'` labels. This is useful for performing an action conditionally at
+  each new saved image.
 
   Most of the time, this Block is used for recording to the desired location
   the images it acquires. Optionally, the images can also be displayed in a

src/crappy/blocks/camera_processes/record.py

@@ -71,8 +71,8 @@ def __init__(self,
         backend ``'npy'``, that saves the images as raw numpy arrays.
       send_msg: In case no processing is performed, and if output Links are
         present, this argument is set to :obj:`True`. In that case, a message
-        containing the timestamp and the metadata of the image is sent to
-        downstream Blocks each time an image is saved.
+        containing the timestamp, the index, and the metadata of the image is
+        sent to downstream Blocks each time an image is saved.
 
         .. versionadded:: 2.0.5
     """
@@ -241,4 +241,6 @@ def loop(self) -> None:
 
     # Sending the results to the downstream Blocks
     if self._send_msg:
-      self.send({'t(s)': self.metadata['t(s)'], 'meta': self.metadata})
+      self.send({'t(s)': self.metadata['t(s)'],
+                 'img_index': self.metadata['ImageUniqueID'],
+                 'meta': self.metadata})