some fixes in the coordinate re-scaling and default multi-job data loading (using multi-threading as default now)

cvdatasets/utils/dataset.py

@@ -12,7 +12,7 @@ def _uuid_check(uuids):
 		"UUIDs are not unique!"
 
 def new_iterator(data, n_jobs, batch_size, repeat=True, shuffle=True, n_prefetch=2, *,
-	use_threads: bool = False):
+	use_threads: bool = True):
 	from chainer.iterators import SerialIterator, MultiprocessIterator, MultithreadIterator
 
 	it_kwargs = dict(batch_size=batch_size, repeat=repeat, shuffle=shuffle)

cvdatasets/utils/transforms.py

@@ -23,6 +23,9 @@ def dimensions(im):
 def rescale(im, coords, rescale_size, center_cropped=True, no_offset=False):
 	h, w, c = dimensions(im)
 
+	if np.all(coords == -1):
+		return coords
+
 	offset = 0
 	if center_cropped:
 		_min_val = min(w, h)