Fix #52 Comparisons with empty masks

src/compare.py

@@ -72,6 +72,8 @@ def compare_l2_norm_masked(source, capture, mask) -> float:
     # The L2 Error is summed across all pixels, so this normalizes
     max_error = (3 * np.count_nonzero(mask) * 255 * 255) ** 0.5
 
+    if not max_error:
+        return 0
     return 1 - (error / max_error)
 
 def compare_template(source, capture) -> float:
@@ -155,10 +157,20 @@ def compare_phash_masked(source, capture, mask):
     source_hash = imagehash.phash(source)
     capture_hash = imagehash.phash(capture)
 
+    if not source_hash + capture_hash:
+        return 0
     return 1 - ((source_hash - capture_hash) / 64.0)
 
 
 def checkIfImageHasTransparency(image):
-    # TODO check for first transparent pixel, no need to iterate through the whole image
     # Check if there's a transparency channel (4th channel) and if at least one pixel is transparent (< 255)
-    return image.shape[2] == 4 and np.mean(image[:, :, 3]) != 255
+    if image.shape[2] != 4:
+        return False
+    mean = np.mean(image[:, :, 3])
+    if mean != 0:
+        # Non-transparent images code path is usually faster and simpler, so let's return that
+        return False
+        # TODO error message if all pixels are transparent
+        # (the image appears as all black in windows, so it's not obvious for the user what they did wrong)
+
+    return mean != 255