The module gr.Sketchpad，ImageMask cannot obtain the binary image normally.

[JunchuanYu]

Describe the bug

I want to obtain a binarized mask file through handwriting (with background as 0 and foreground as 1). However, when using gr.Sketchpador gr.ImageMask , if the image mode is set to "L", the output is an array of all zeros.
when i change the color of the pencil to white, the output is correct, but i can't see what is draw.
I found that this is because the program defaults to a background of all zeros and the pen default value is also zero, so the handwritten content cannot be seen. This is different from the old version of sketchpad.

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• I have searched and found no existing issues

Reproduction

import gradio as gr
import numpy as np

def sleep(im):
    a=im["composite"]
    b=a.shape
    c=np.max(a)
    return a, f'the image size is {b},\n the max value is {c}'

with gr.Blocks() as demo:
    with gr.Group():
        with gr.Row():
            out=gr.Textbox() 
        with gr.Row():
            im = gr.Sketchpad(type="numpy",image_mode="L")
            im_out_1 = gr.Image(type="pil")
    im.change(sleep, outputs=[im_out_1, out], inputs=im)
    demo.launch()

Screenshot

Logs

No response

System Info

gradio==4.24.0
windows

Severity

I can work around it

[JunchuanYu]

gradio==4.27.0
windows