diff --git a/tests/unit/test_io.py b/tests/unit/test_io.py
index 3ba94a0d..2af81385 100644
--- a/tests/unit/test_io.py
+++ b/tests/unit/test_io.py
@@ -28,16 +28,23 @@ def test_imread_from_numpy():
     path.unlink()
 
 
-@pytest.mark.parametrize("shape", [(10, 20, 3), (10, 20)])
+@pytest.mark.parametrize("shape", [(10, 20, 3), (10, 20, 1), (10, 20)])
 def test_imread_from_bytes(shape):
     """Test imread for bytes images, for RGB and grayscale type images."""
 
-    # Generate array equivalent with 255 values
-    array = 255 * np.ones(shape, dtype=np.uint8)
+    # Generate array equivalent with random values
+    pre_array = (np.random.rand(*shape) * 255).astype(np.uint8)
 
-    # Save array as jpg using cv2
-    path = Path("random_distribution.jpg")
-    cv2.imwrite(str(path), array)
+    # Convert array to BGR format
+    if len(shape) == 3 and shape[2] == 3:
+        array = cv2.cvtColor(pre_array, cv2.COLOR_RGB2BGR)
+    else:
+        array = pre_array.copy()
+
+    # Save array lossfree using cv2
+    path = Path("random_distribution.png")
+    cv2.imwrite(str(path), array, [cv2.IMWRITE_PNG_COMPRESSION, 0])
+    print(Path(".").resolve())
 
     # Read numpy image
     with open(path, "rb") as file:
@@ -46,7 +53,7 @@ def test_imread_from_bytes(shape):
         bytes_image = darsia.imread_from_bytes(byte_str, dim=2, width=2, height=1)
 
     # Compare arrays.
-    assert np.allclose(bytes_image.img, array)
+    assert np.allclose(bytes_image.img.reshape(pre_array.shape), pre_array)
 
     # Clean up
     path.unlink()