better data clipping check and background subtraction

lib/imaging.py

@@ -168,9 +168,14 @@ class FluorescenceData(ImagingData):
         for label, array in self.arrays.items():
             if label == "background":
                 continue
+            if array.max() == np.iinfo(array.dtype).max:
+                print("[imaging] WARNING: image may contain clipping")
             N = compute_mot_number(
                 array if "background" not in self.arrays.keys() \
-                        else array - self.arrays["background"],
+                        else (
+                            array.astype(np.float64)
+                            - self.arrays["background"].astype(np.float64)
+                        ),
                 0.40,
                 self.config["gain"], # dB
                 self.config["exposure_time"] * 1e-6, # s
@@ -191,8 +196,6 @@ class FluorescenceData(ImagingData):
 
 def compute_mot_number(image, QE, gain, exposure_time, solid_angle,
         detuning, intensity_parameter):
-    if image.max() >= np.iinfo(image.dtype).max:
-        print("[imaging] WARNING: image may contain clipping")
     H, W = image.shape
     im = image[H//3:2*H//3, W//3:2*W//3]
     pd.Plotter().imshow(im).savefig("img.png").close()