app.py

import gradio as gr
import imageio

def dummy(img):
  imageio.imwrite("output_image.png", img["mask"])
  return img["image"], img["mask"]

with gr.Blocks() as demo:
  with gr.Row():
    img = gr.Image(tool="sketch", label="base image", width=512, height=512, show_label=True)
    img1 = gr.Image()
    img2 = gr.Image(label="mask image", show_label=True)
  btn = gr.Button()
  btn.click(dummy, img, [img1, img2])

demo.launch(debug=True)