Faster HSV augmentation (#3462)

remove datatype conversion process that can be skipped

utils/datasets.py

@@ -655,12 +655,12 @@ def augment_hsv(img, hgain=0.5, sgain=0.5, vgain=0.5):
     hue, sat, val = cv2.split(cv2.cvtColor(img, cv2.COLOR_BGR2HSV))
     dtype = img.dtype  # uint8
 
-    x = np.arange(0, 256, dtype=np.int16)
+    x = np.arange(0, 256, dtype=r.dtype)
     lut_hue = ((x * r[0]) % 180).astype(dtype)
     lut_sat = np.clip(x * r[1], 0, 255).astype(dtype)
     lut_val = np.clip(x * r[2], 0, 255).astype(dtype)
 
-    img_hsv = cv2.merge((cv2.LUT(hue, lut_hue), cv2.LUT(sat, lut_sat), cv2.LUT(val, lut_val))).astype(dtype)
+    img_hsv = cv2.merge((cv2.LUT(hue, lut_hue), cv2.LUT(sat, lut_sat), cv2.LUT(val, lut_val)))
     cv2.cvtColor(img_hsv, cv2.COLOR_HSV2BGR, dst=img)  # no return needed