C#のWinFormsで画像加工アプリ3「2値化」

    // 2値化(Form1のメンバーとして追加)
    readonly ToolStripMenuItem thresholdMenuItem = new()
    {
        Text = "2値化",
    };

        // 2値化(Form1のコンストラクタに追加)
        filterMenuItem.DropDownItems.Add(thresholdMenuItem);
        thresholdMenuItem.Click += async (s, e) =>
        {
            if (_buffBmp is null) return;
            Bitmap? bmp = await ThresholdDialog(_buffBmp);
            if (bmp is not null)
            {
                this.Bmp = bmp;
                mainPicbox.Image = this.Bmp;
            }
        };

using OpenCvSharp;
using OpenCvSharp.Extensions;

namespace GazouKakou01;
public partial class Form1 : Form
{
    public static async Task<Bitmap?> ThresholdDialog(Bitmap src)
    {
        const string filterName = "2値化";

        Form frm = new Form
        {
            FormBorderStyle = FormBorderStyle.FixedDialog,
            ClientSize = new System.Drawing.Size(640, 480),
            Text = filterName,
        };
        Label lbl = new Label
        {
            Size = new System.Drawing.Size(600, 60),
            Location = new System.Drawing.Point(10, 10),
            Text = filterName,
        };
        lbl.Parent = frm;
        PictureBox picbox = new()
        {
            Size = new System.Drawing.Size(600, 320),
            Location = new System.Drawing.Point(10, 70),
            Parent = frm,
        };
        Button okBtn = new Button
        {
            Size = new System.Drawing.Size(80,40),
            Location = new System.Drawing.Point(10, 410),
            Text = "OK",
            DialogResult = DialogResult.OK,
            Visible = false,
        };
        okBtn.Parent = frm;
        Button cancelBtn = new Button
        {
            Size = new System.Drawing.Size(80,40),
            Location = new System.Drawing.Point(100, 410),
            Text = "Cancel",
            DialogResult = DialogResult.Cancel,
            Visible = false,
        };
        cancelBtn.Parent = frm;

        frm.AcceptButton = okBtn;
        frm.CancelButton = cancelBtn;

        Label label1 = new()
        {
            Text = "閾値:0",
            Size = new System.Drawing.Size(120,40),
            Location = new System.Drawing.Point(190, 410),
            Parent = frm,
        };
        TrackBar track1 = new()
        {
            Minimum = 0,
            Maximum = 255,
            Value = 0,
            Size = new System.Drawing.Size(256,40),
            Location = new System.Drawing.Point(320, 410),
            Parent = frm,
        };
        Mat srcMat = await Task.Run(()=>
        {
            // mat変換
            var mat = BitmapConverter.ToMat(src);
            if (mat.Channels() >= 3)
            {
                // グレイスケール
                Cv2.CvtColor(mat, mat, ColorConversionCodes.RGB2GRAY);
            }
            return mat;
        });
        double th = 127.0d;
        Func<Task> filter = new(async ()=>
        {
            okBtn.Visible = false;
            cancelBtn.Visible = false;

            var dst = await Task.Run(()=>
            {
                var mat = new Mat();
                picbox?.Invoke(()=>{th = (double)track1.Value;});
                // 2値化
                Cv2.Threshold(srcMat, mat, th, 255.0d, ThresholdTypes.Binary);
                // bmp変換
                return BitmapConverter.ToBitmap(mat);
            });
            picbox.Image?.Dispose();
            picbox.Image = dst;
            okBtn.Visible = true;
            cancelBtn.Visible = true;
            label1.Text = String.Format("閾値:{0}", th);
        });
        track1.ValueChanged += async (s, e) => await filter();
        frm.Load += (s, e) =>
        {
            track1.Value = 127;
        };

        if (frm.ShowDialog() == DialogResult.Cancel)
        {
            return null;
        }
        return (Bitmap)picbox.Image;
    }
}