用opencvsharp写一个文档扫描器的代码

没问题，我可以帮你回答关于OpenCVSharp文档扫描器的问题。你可以参考以下代码：

using System;
using System.Drawing;
using System.Windows.Forms;
using OpenCvSharp;

namespace DocumentScanner
{
    public partial class MainForm : Form
    {
        private Mat image;

        public MainForm()
        {
            InitializeComponent();
        }

        private void OpenButton_Click(object sender, EventArgs e)
        {
            using (var openFileDialog = new OpenFileDialog())
            {
                if (openFileDialog.ShowDialog() == DialogResult.OK)
                {
                    image = Cv2.ImRead(openFileDialog.FileName);
                    ImageBox.Image = BitmapConverter.ToBitmap(image);
                }
            }
        }

        private void ScanButton_Click(object sender, EventArgs e)
        {
            if (image == null)
            {
                MessageBox.Show("Please open an image first", "Error", MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
                return;
            }

            var gray = new Mat();
            Cv2.CvtColor(image, gray, ColorConversionCodes.BGR2GRAY);

            var blur = new Mat();
            Cv2.GaussianBlur(gray, blur, new Size(3, 3), 0);

            var edges = new Mat();
            Cv2.Canny(blur, edges, 100, 200);

            var contours = new Point[][] { };
            var hierarchy = new HierarchyIndex[] { };
            Cv2.FindContours(edges, out contours, out hierarchy, RetrievalModes.Tree,
                ContourApproximationModes.ApproxSimple);

            if (contours.Length == 0)
            {
                MessageBox.Show("No document found", "Error", MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
                return;
            }

            var contourAreaArray = new double[contours.Length];
            for (var i = 0; i < contours.Length; i++)
            {
                contourAreaArray[i] = Cv2.ContourArea(contours[i]);
            }

            var documentContourIndex = Array.IndexOf(contourAreaArray,
                Array.Find(contourAreaArray, area => area == contourAreaArray.Max()));

            var documentContour = contours[documentContourIndex];

            var perimeter = Cv2.ArcLength(documentContour, true);

            var approx = new MatOfPoint2f();
            Cv2.ApproxPolyDP(documentContour, approx, 0.02 * perimeter, true);

            var points = approx.ToArray();
            var rectangle = Cv2.BoundingRect(points);

            var croppedImage = new Mat(image, rectangle);

            ImageBox.Image = BitmapConverter.ToBitmap(croppedImage);
        }
    }
}

需要注意的是，使用 OpenCVSharp 开发扫描器需要同时安装 OpenCV 原生库，才能正常运行。