fix padding for rectangular inference (#1165)

Co-authored-by: swsong <swsong@stratosphere.mobi>

utils/datasets.py

@@ -731,7 +731,7 @@ def letterbox(img, new_shape=(640, 640), color=(114, 114, 114), auto=True, scale
     new_unpad = int(round(shape[1] * r)), int(round(shape[0] * r))
     dw, dh = new_shape[1] - new_unpad[0], new_shape[0] - new_unpad[1]  # wh padding
     if auto:  # minimum rectangle
-        dw, dh = np.mod(dw, 64), np.mod(dh, 64)  # wh padding
+        dw, dh = np.mod(dw, 32), np.mod(dh, 32)  # wh padding
     elif scaleFill:  # stretch
         dw, dh = 0.0, 0.0
         new_unpad = (new_shape[1], new_shape[0])