run.py

import gradio as gr
import numpy as np

def percent_of_pixels_selected(image):
    mask = image["layers"][0]
    mask_bool = mask[:,:,3] > 0
    return f"{round(np.sum(mask_bool) / mask_bool.size * 100, 2)}%"

image_editor = gr.Sketchpad(
    type="numpy",
)
output_image = gr.Label(
    label="Percent of Pixels Selected"
)

demo = gr.Interface(
    fn=percent_of_pixels_selected,
    inputs=image_editor,
    outputs=output_image,
    live=True
)

if __name__ == "__main__":
    demo.launch()