Update app.py

app.py

@@ -260,7 +260,7 @@ with gr.Blocks() as app:
                     label="base image",
                     show_label=True
                 )
-                img2 = gr.Image(label="mask image", show_label=True)
+                img2 = gr.Image(label="mask image", show_label=True, format="png")
 
             btn = gr.Button("Generate Mask")
             btn.click(dummy, inputs=img, outputs=img2)