update mask2segments and saving results (#9785)

* update mask2segments and saving results

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update general.py

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

* Update predict.py

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

utils/segment/general.py

@@ -126,9 +126,12 @@ def masks2segments(masks, strategy='largest'):
     segments = []
     for x in masks.int().cpu().numpy().astype('uint8'):
         c = cv2.findContours(x, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)[0]
-        if strategy == 'concat':  # concatenate all segments
-            c = np.concatenate([x.reshape(-1, 2) for x in c])
-        elif strategy == 'largest':  # select largest segment
-            c = np.array(c[np.array([len(x) for x in c]).argmax()]).reshape(-1, 2)
+        if c:
+            if strategy == 'concat':  # concatenate all segments
+                c = np.concatenate([x.reshape(-1, 2) for x in c])
+            elif strategy == 'largest':  # select largest segment
+                c = np.array(c[np.array([len(x) for x in c]).argmax()]).reshape(-1, 2)
+        else:
+            c = np.zeros((0, 2))  # no segments found
         segments.append(c.astype('float32'))
     return segments