Update images.py

The `flatten` function has been updated with a conditional check to see if the image has an "RGBA" mode, meaning it contains an alpha channel for transparency. If that is the case, it flattens the image by creating a new solid background image with the specified background color and pasting the original image onto it, using the original image itself as the mask to retain its alpha transparency. Finally, the function returns the modified image converted to "RGB" mode with no transparency.

modules/images.py

@@ -783,11 +783,20 @@ def image_data(data):
 
 
 def flatten(img, bgcolor):
-    """replaces transparency with bgcolor (example: "#ffffff"), returning an RGB mode image with no transparency"""
-
-    if img.mode == "RGBA":
-        background = Image.new('RGBA', img.size, bgcolor)
-        background.paste(img, mask=img)
-        img = background
-
-    return img.convert('RGB')
+    if img.mode in ("RGB", "RGBA"):
+        with_alpha = "A" in img.getbands()
+
+        if with_alpha and isinstance(bgcolor, bytes):
+            alpha = img.split()[3]
+            bg = Image.new("RGB", img.size, bgcolor)
+            bg.paste(img, mask=alpha)
+            return bg
+        elif with_alpha and not isinstance(bgcolor, bytes):
+            background = Image.new('RGBA', img.size, bgcolor)
+            background.paste(img, mask=img)
+            img = background
+            return img.convert('RGB')
+        else:
+            return img
+
+    return img