libtuning: Fix visualize_macbeth_chart()

The old function uses PIL to save the image, which is not in the
requirements file. As we are already requiring opencv, use that to save
images instead of an additional dependency

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

utils/tuning/libtuning/utils.py

@@ -5,6 +5,7 @@
 #
 # Utilities for libtuning
 
+import cv2
 import decimal
 import math
 import numpy as np
@@ -162,6 +163,6 @@ def visualise_macbeth_chart(macbeth_rgb, original_rgb, new_rgb, output_filename)
                 for g in range(100):
                     image[xlocation + i, ylocation + g] = new_rgb[colorindex]
 
-    img = Image.fromarray(image, 'RGB')
-    img.save(str(output_filename) + 'Generated Macbeth Chart.png')
+    im_bgr = cv2.cvtColor(image, cv2.COLOR_RGB2BGR)
+    cv2.imwrite(f'{output_filename} Generated Macbeth Chart.png', im_bgr)