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:
    gr.Markdown(
        """
        # Image mask creator
        This is a demo of a simple image mask creator. You can draw on the image and the mask will be created.
        """
    )

    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)