DocuLens: A Document Scanner

A simple document scanning pipeline implemented in C++ with OpenCV. The program detects the largest 4-point contour in each frame of a video or webcam feed, applies a perspective transform, and shows a flattened, top-down “scan” of the document.

Steps

• Preprocessing (grayscale -> blur -> Canny -> dilate -> erode)
• Contour detection and 4-point polygon approximation
• Automatic ordering of detected points
• Perspective warp to get a top-down scan
• 2×2 stacked debug view (original, threshold, contour view, warped result)
• Live processing from video file or webcam

Requirements

• C++17
• OpenCV 4.x
• CMake >= 3.10

Install OpenCV (on Linux):

sudo apt install libopencv-dev

Build

Run build.sh to build the project.

Run

./build/document_scanner ./assets/testvideo.mp4

Output Windows

The program displays two windows:

1. Work Flow (2×2 grid)

• Original frame
• Thresholded frame
• Contours
• Warped (scanned) document

2. Result

• Clean final warp of the detected document

Press q to quit.

Note

No ML, just pure classical OpenCV contour detection. Hence, works best with well-lit videos where the document edge is clear.