Creating a custom bounding box editor in Gradio: How to display an image on a canvas?

Other Questions JavaScript
1

I’m trying to build a bounding box editor in Gradio using my own HTML and JavaScript. The goal is to let users move, resize, and create new bounding boxes. My main issue is figuring out how to show the uploaded image on a canvas element.

So far, I’ve managed to display the image using an img tag, but I can’t get it on the canvas. Here’s a simplified version of what I’ve done:

import gradio as gr
import base64
from PIL import Image
from io import BytesIO

def process_image(img):
    img_pil = Image.fromarray(img)
    buffered = BytesIO()
    img_pil.save(buffered, format='PNG')
    img_b64 = base64.b64encode(buffered.getvalue()).decode()
    
    html_content = f'''
    <img src="data:image/png;base64,{img_b64}" alt="Uploaded image">
    <canvas id="myCanvas"></canvas>
    '''
    
    return gr.HTML(html_content)

demo = gr.Interface(
    fn=process_image,
    inputs=gr.Image(type='numpy'),
    outputs=gr.HTML()
)

demo.launch()

I’m stuck on the JavaScript part. How can I draw the uploaded image onto the canvas? Any tips or examples would be super helpful. Also, if there are other ways to create a bounding box editor in Gradio, I’d love to hear about them!

2

I’ve worked on similar projects, and drawing images on canvas can be tricky. Here’s a solution that might work for you:

In your Python code, pass the base64 image data to a JavaScript function. Then, in your HTML, add this script:

const canvas = document.getElementById(‘myCanvas’);
const ctx = canvas.getContext(‘2d’);
const img = new Image();
img.onload = function() {
canvas.width = img.width;
canvas.height = img.height;
ctx.drawImage(img, 0, 0);
};
img.src = ‘data:image/png;base64,’ + imageData;

This will draw your image on the canvas. For bounding boxes, you’ll need to add event listeners for mouse actions. Consider using a library like Fabric.js to simplify the process.

Remember to send the bounding box data back to your Gradio backend for processing. Good luck with your project!

3

As someone who’s worked extensively with image processing in web applications, I can share some insights on your Gradio bounding box editor project.

Your approach of using a canvas to display and interact with the image is spot-on. The JavaScript code you’re looking for to draw the image onto the canvas would look something like this:

function drawImage(base64Image) {
    const canvas = document.getElementById('myCanvas');
    const ctx = canvas.getContext('2d');
    const img = new Image();
    img.onload = function() {
        canvas.width = img.width;
        canvas.height = img.height;
        ctx.drawImage(img, 0, 0);
    };
    img.src = 'data:image/png;base64,' + base64Image;
}

You’d need to call this function with the base64-encoded image data from your Python backend.

For the bounding box functionality, you’ll want to add event listeners for mouse actions on the canvas. These will handle drawing, moving, and resizing boxes. It’s a bit complex to implement from scratch, so you might want to consider using a library like Fabric.js or Paper.js to simplify the process.

Remember to periodically save the bounding box data back to your Gradio backend for processing. Good luck with your project!

4

hey, i’ve messed around with canvas stuff before. for your problem, you might wanna try something like this in your js:

const canvas = document.getElementById(‘myCanvas’);
const ctx = canvas.getContext(‘2d’);
const img = new Image();
img.onload = () => {
canvas.width = img.width;
canvas.height = img.height;
ctx.drawImage(img, 0, 0);
};
img.src = ‘data:image/png;base64,’ + yourBase64String;

hope that helps! lmk if u need anything else