app.py

#######################################################################################
#
# MIT License
#
# Copyright (c) [2025] [leonelhs@gmail.com]
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
#
#######################################################################################
#
#
# Source code is based on or inspired by several projects.
# For more details and proper attribution, please refer to the following resources:
#
# - [stackoverflow] - [https://stackoverflow.com/questions/22656698/perspective-correction-in-opencv-using-python]
# - [rembg] [https://huggingface.co/spaces/leonelhs/rembg]
# - [rembg] [https://github.com/danielgatis/rembg]
# - [Chatgpt] [https://chatgpt.com/]
#
# The image is first processed by an AI service.
# This step provides a cleaner, bounded version of the image,
# because OpenCV’s edge detection is not always reliable on raw inputs.
# With the improved intermediate image, OpenCV can detect borders more consistently
# and the perspective unwrap produces better results.


import cv2
import numpy as np
import gradio as gr
from gradio_client import Client, handle_file

client = Client("leonelhs/rembg")

def unwrap(image, mask):
    img = cv2.cvtColor(image, cv2.COLOR_RGB2BGR)
    gray = cv2.cvtColor(mask, cv2.COLOR_BGR2GRAY)

    _, thresh = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)
    contours, _ = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
    contours = sorted(contours, key=cv2.contourArea, reverse=True)

    if len(contours) > 0:
        cnt = contours[0]
        peri = cv2.arcLength(cnt, True)
        approx = cv2.approxPolyDP(cnt, 0.02 * peri, True)

        if len(approx) == 4:
            corners = approx.reshape(4, 2).astype(np.float32)

            # Order points: top-left, top-right, bottom-right, bottom-left
            rect = np.zeros((4, 2), dtype="float32")
            s = corners.sum(axis=1)
            rect[0] = corners[np.argmin(s)]
            rect[2] = corners[np.argmax(s)]

            diff = np.diff(corners, axis=1)
            rect[1] = corners[np.argmin(diff)]
            rect[3] = corners[np.argmax(diff)]

            (tl, tr, br, bl) = rect

            # Compute width & height
            widthA = np.linalg.norm(br - bl)
            widthB = np.linalg.norm(tr - tl)
            maxWidth = int(max(widthA, widthB))

            heightA = np.linalg.norm(tr - br)
            heightB = np.linalg.norm(tl - bl)
            maxHeight = int(max(heightA, heightB))

            dst = np.array([
                [0, 0],
                [maxWidth - 1, 0],
                [maxWidth - 1, maxHeight - 1],
                [0, maxHeight - 1]
            ], dtype="float32")

            # Perspective transform
            M = cv2.getPerspectiveTransform(rect, dst)
            warped = cv2.warpPerspective(img, M, (maxWidth, maxHeight))

            return cv2.cvtColor(warped, cv2.COLOR_BGR2RGB), mask, corners

    # fallback: return original if no rectangle
    return image, mask, contours

def predict(img):
    """
        Unwrap an image using AI-assisted preprocessing and OpenCV.

        The algorithm first leverages an AI service to generate a cleaner,
        well-bounded intermediate image. This helps OpenCV detect borders
        more reliably before performing the perspective unwrap.

        Parameters:
            img (string): File path to the input image to be unwrapped.

        Returns:
            path (string): File path to the generated, unwrapped image.
    """

    # Step 1: Use an AI service to preprocess the image.
    #   - OpenCV can detect edges, but results are inconsistent depending on noise/lighting.
    #   - The AI model generates a cleaner, well-bounded intermediate image.
    crop, mask = client.predict(image=handle_file(img), session="U2NET", smoot=True, api_name="/predict")

    # Step 2: Apply OpenCV on this intermediate image for more accurate border detection
    #         before performing the perspective unwrap.
    crop = cv2.imread(crop)
    mask = cv2.imread(mask)
    return unwrap(crop, mask)


with gr.Blocks() as app:
    gr.Markdown("## 🖼️ Rectangle Detection & Perspective Unwrap")
    with gr.Row():
        with gr.Column(scale=1):
            inp = gr.Image(type="filepath", label="Upload Image")
            btn_unwrap = gr.Button("📐 Perspective Unwrap")
        with gr.Column(scale=2):
            with gr.Row():
                with gr.Column(scale=1):
                    out_unwrap = gr.Image(type="numpy", label="Unwrapped Rectangle")
                    with gr.Accordion("See intermediates", open=False):
                        out_mask = gr.Image(type="numpy", label="Detected Corners")
                        out_corners = gr.JSON(label="Corners (x,y)")

    btn_unwrap.click(predict, inputs=inp, outputs=[out_unwrap, out_mask, out_corners])

app.launch(share=False, debug=True, show_error=True, mcp_server=True)
app.queue()