add docstring

heinsight.py

@@ -277,8 +277,18 @@ class HeinSight:
         ax3.set_xticks([self.x_time[0], self.x_time[-1]], realtime_tick_label)
 
 
-    def image_demo(self, pil_image, cap_ratio=0):
+    def image_demo(self, pil_image:Image.Image, cap_ratio=0):
+        """
+        analyze a vial image using heinsight. detect vial and dectet chemical content inside the vial.
+
+        Args:
+            pil_image (Image.Image): The input text to search through
+            cap_ratio (float): The ratio of the vial cap to the vial height
 
+        Returns:
+            output_image: output image with bounding boxes and detected chemical content
+            output_dict: output dict with turbidity, volume and color values
+        """
         self.clear_cache()
         frame = cv2.cvtColor(np.array(pil_image), cv2.COLOR_RGB2BGR)  # PIL → OpenCV
         phase_data = {}