diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 07a1381..8378c00 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -164,8 +164,8 @@ jobs:
               print('  pytesseract not available — skipping')
               sys.exit(0)
 
-          # Create test image
-          img = np.full((50, 200), 255, dtype=np.uint8)
+          # Create test image (3-channel for invert)
+          img = np.full((50, 200, 3), 255, dtype=np.uint8)
           cv2.putText(img, '123', (80, 35),
               cv2.FONT_HERSHEY_SIMPLEX, 1.0, (0, 0, 0), 2)