No 63・ネガ効果で画像を表示

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace Ex13_07
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            // 
            OpenFileDialog openFileDialog = new OpenFileDialog();
            openFileDialog.Filter = " (JPeg, Gif, Bmp, etc.)|*.jpg;*.jpeg;*.gif;*.bmp;*.tif; *.tiff; *.png| JPeg  (*.jpg;*.jpeg)|*.jpg;*.jpeg |GIF  (*.gif)|*.gif |BMP (*.bmp)|*.bmp|Tiff (*.tif;*.tiff)|*.tif;*.tiff|Png (*.png)| *.png | (*.*)|*.*";
            if (openFileDialog.ShowDialog() == DialogResult.OK)
            {
                Bitmap MyBitmap = new Bitmap(openFileDialog.FileName);
                this.pictureBox1.Image = MyBitmap;
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            // 
            try
            {
                int Height = this.pictureBox1.Image.Height;
                int Width = this.pictureBox1.Image.Width;
                Bitmap newbitmap = new Bitmap(Width, Height);
                Bitmap oldbitmap = (Bitmap)this.pictureBox1.Image;
                Color pixel;
                for (int x = 1; x < Width; x++)
                {
                    for (int y = 1; y < Height; y++)
                    {
                        int r, g, b;
                        pixel = oldbitmap.GetPixel(x, y);
                        r = 255 - pixel.R;
                        g = 255 - pixel.G;
                        b = 255 - pixel.B;
                        newbitmap.SetPixel(x, y, Color.FromArgb(r, g, b));
                    }
                }
                this.pictureBox1.Image = newbitmap;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, " ", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
        }
    }
}