Add `allow_background_images=True` in split_dota.py (#15037)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/data/split_dota.py

@@ -144,7 +144,7 @@ def get_window_obj(anno, windows, iof_thr=0.7):
         return [np.zeros((0, 9), dtype=np.float32) for _ in range(len(windows))]  # window_anns
 
 
-def crop_and_save(anno, windows, window_objs, im_dir, lb_dir):
+def crop_and_save(anno, windows, window_objs, im_dir, lb_dir, allow_background_images=True):
     """
     Crop images and save new labels.
 
@@ -154,6 +154,7 @@ def crop_and_save(anno, windows, window_objs, im_dir, lb_dir):
         window_objs (list): A list of labels inside each window.
         im_dir (str): The output directory path of images.
         lb_dir (str): The output directory path of labels.
+        allow_background_images (bool): Whether to include background images without labels.
 
     Notes:
         The directory structure assumed for the DOTA dataset:
@@ -173,19 +174,19 @@ def crop_and_save(anno, windows, window_objs, im_dir, lb_dir):
         patch_im = im[y_start:y_stop, x_start:x_stop]
         ph, pw = patch_im.shape[:2]
 
-        cv2.imwrite(str(Path(im_dir) / f"{new_name}.jpg"), patch_im)
         label = window_objs[i]
-        if len(label) == 0:
-            continue
-        label[:, 1::2] -= x_start
-        label[:, 2::2] -= y_start
-        label[:, 1::2] /= pw
-        label[:, 2::2] /= ph
-
-        with open(Path(lb_dir) / f"{new_name}.txt", "w") as f:
-            for lb in label:
-                formatted_coords = ["{:.6g}".format(coord) for coord in lb[1:]]
-                f.write(f"{int(lb[0])} {' '.join(formatted_coords)}\n")
+        if len(label) or allow_background_images:
+            cv2.imwrite(str(Path(im_dir) / f"{new_name}.jpg"), patch_im)
+        if len(label):
+            label[:, 1::2] -= x_start
+            label[:, 2::2] -= y_start
+            label[:, 1::2] /= pw
+            label[:, 2::2] /= ph
+
+            with open(Path(lb_dir) / f"{new_name}.txt", "w") as f:
+                for lb in label:
+                    formatted_coords = ["{:.6g}".format(coord) for coord in lb[1:]]
+                    f.write(f"{int(lb[0])} {' '.join(formatted_coords)}\n")
 
 
 def split_images_and_labels(data_root, save_dir, split="train", crop_sizes=(1024,), gaps=(200,)):