Load tuning files in without using Picamera2

src/openflexure_microscope_server/things/camera/picamera_tuning_file_utils.py

@@ -6,34 +6,34 @@ the future.
 
 from typing import Any
 from copy import deepcopy
-
-from picamera2 import Picamera2
-import numpy as np
 import os
+import json
+
+import numpy as np
+
 
 THIS_DIR = os.path.dirname(os.path.abspath(__file__))
 
+
+class TuningFileError(RuntimeError):
+    """Raised if the tuning file cannot be loaded for any reason."""
+
+
 def load_default_tuning(sensor_model: str) -> dict:
     """Load the default tuning file for the camera.
 
     This will load the tuning file based on the specified sensor model.
     """
     fname = f"{sensor_model}.json"
-    custom_path = os.path.join(THIS_DIR, 'tuning_files', fname)
+    # Note the vc4 here. This locks us to Pi4. We will need to update this to support
+    # the Raspberry Pi 5.
+    tuning_path = os.path.join(THIS_DIR, "tuning_files", "vc4", fname)
 
-    # Attempt to load custom tuning file from OpenFlexure settings
-    if os.path.isfile(custom_path):
-        return Picamera2.load_tuning_file(fname, dir=os.path.join(THIS_DIR, 'tuning_files'))
     try:
-        return Picamera2.load_tuning_file(fname)
-    except RuntimeError:
-        tuning_dir = "/usr/share/libcamera/ipa/raspberrypi"
-        # from picamera2 v0.3.9
-        # The directory above has been removed from the search path seems
-        # odd - as that's where the files currently are on a default
-        # Raspbian image. This may need updating if the files have moved
-        # in future updates to the system libcamera package
-        return Picamera2.load_tuning_file(fname, dir=tuning_dir)
+        with open(tuning_path, "r") as fp:
+            return json.load(fp)
+    except (json.decoder.JSONDecodeError, IOError) as e:
+        raise TuningFileError(f"Could not load tuning from {tuning_path}.") from e
 
 
 def find_tuning_algo(tuning: dict[str, dict], name: str) -> dict[str, Any]: