add option to save images to MuMapDataset main method

mu_map/data/datasets.py

@@ -200,11 +200,14 @@ if __name__ == "__main__":
         cv.imshow(wname, combine_images((recon, mu_map), (ir, im)))
         key = cv.waitKey(timeout)
 
+        running = 0
         while True:
             ir = (ir + 1) % recon.shape[0]
             im = (im + 1) % mu_map.shape[0]
 
-            cv.imshow(wname, combine_images((recon, mu_map), (ir, im)))
+            to_show = combine_images((recon, mu_map), (ir, im))
+            cv.imshow(wname, to_show)
+
 
             key = cv.waitKey(timeout)
 
@@ -219,3 +222,6 @@ if __name__ == "__main__":
             elif key == 81:  # left arrow key
                 ir = max(ir - 2, 0)
                 im = max(im - 2, 0)
+            elif key == ord("s"):
+                cv.imwrite(f"{running:03d}.png", to_show)
+                running += 1