ITS: Use TEST_IMG_DIR

bug: 179302527
Change-Id: Iffead2ffb0b72d373be78bc9b51cddf39853ab73
diff --git a/apps/CameraITS/utils/opencv_processing_utils.py b/apps/CameraITS/utils/opencv_processing_utils.py
index 137e0a3..d427abc 100644
--- a/apps/CameraITS/utils/opencv_processing_utils.py
+++ b/apps/CameraITS/utils/opencv_processing_utils.py
@@ -30,8 +30,8 @@
 ANGLE_NUM_MIN = 10  # Minimum number of angles for find_angle() to be valid
 
 
-CHART_FILE = os.path.join(os.environ['CAMERA_ITS_TOP'], 'test_images',
-                          'ISO12233.png')
+TEST_IMG_DIR = os.path.join(os.environ['CAMERA_ITS_TOP'], 'test_images')
+CHART_FILE = os.path.join(TEST_IMG_DIR, 'ISO12233.png')
 CHART_HEIGHT = 13.5  # cm
 CHART_DISTANCE_RFOV = 31.0  # cm
 CHART_DISTANCE_WFOV = 22.0  # cm
@@ -63,8 +63,6 @@
 SQUARE_AREA_MIN_REL = 0.05  # Minimum size for square relative to image area
 SQUARE_TOL = 0.1  # Square W vs H mismatch RTOL
 
-TEST_IMG_DIR = os.path.join(os.environ['CAMERA_ITS_TOP'], 'test_images')
-
 VGA_HEIGHT = 480
 VGA_WIDTH = 640