diff --git a/deploy/python/infer.py b/deploy/python/infer.py
index 7664b4f36279569eed79a91378f557f96816b859..01f044e0124da9e4dce24f0df320551cc2c11e52 100644
--- a/deploy/python/infer.py
+++ b/deploy/python/infer.py
@@ -115,9 +115,10 @@ class ImageReader:
     # image processing thread worker
     def process_worker(self, imgs, idx, use_pr=False):
         image_path = imgs[idx]
-        im = cv2.imread(image_path, -1)
-        if len(im.shape) == 2:
-            im = cv2.cvtColor(im, cv2.COLOR_GRAY2BGR)
+        cv2_imread_flag = cv2.IMREAD_COLOR
+        if self.config.channels == 4:
+            cv2_imread_flag = cv2.IMREAD_UNCHANGED
+        im = cv2.imread(image_path, cv2_imread_flag)
         channels = im.shape[2]
         if channels != 3 and channels != 4:
             print("Only support rgb(gray) or rgba image.")
@@ -133,8 +134,10 @@ class ImageReader:
 
         # if use models with no pre-processing/post-processing op optimizations
         if not use_pr:
-            im_mean = np.array(self.config.mean).reshape((3, 1, 1))
-            im_std = np.array(self.config.std).reshape((3, 1, 1))
+            im_mean = np.array(self.config.mean).reshape((self.config.channels,
+                                                          1, 1))
+            im_std = np.array(self.config.std).reshape((self.config.channels, 1,
+                                                        1))
             # HWC -> CHW, don't use transpose((2, 0, 1))
             im = im.swapaxes(1, 2)
             im = im.swapaxes(0, 1)