C#で作成したが、Combobox等が実装されない

画像を取りこみ、その画像に処理をかけるプログラムをVisual Studio 2019で作成しました。
配られたお手本のソースコードに描いてある通りに作成したはずなんですが、
comboBox1
openFileDialog1
pictureBox1
saveFileDialog1
pictureBox2
textBox1
の部分にエラーメッセージ（CS0103）が表示され、現在のコンテキストに存在しないと出ます。

一体何がいけないのでしょうか？

エラーメッセージ

重大度レベル	コード	説明	プロジェクト	ファイル	行	抑制状態
エラー	CS0103	現在のコンテキストに 'comboBox1' という名前は存在しません。	WindowsFormsApp4	C:\Users\me\source\repos\WindowsFormsApp4\WindowsFormsApp4\Form1.cs	25	アクティブ

該当のソースコード

C#
1using System;
2using System.Collections.Generic;
3using System.ComponentModel;    
4using System.Data;            
5using System.Drawing;          
6using System.Linq;
7using System.Text;
8using System.Threading.Tasks;            
9using System.Windows.Forms;
10//追加のライブラリ
11           
12using System.IO;
13
14namespace WindowsFormsApp4
15{
16    public partial class Form1 : Form
17    {
18        public Form1()
19        {
20            InitializeComponent();
21        }
22        private void Form1_Load(object sender, EventArgs e)
23        {
24                //初期化
25                comboBox1.Items.Clear();
26
27                //項目の追加
28                comboBox1.Items.Add("処理なし");
29                comboBox1.Items.Add("平滑化");
30                comboBox1.Items.Add("鮮鋭化");
31                comboBox1.Items.Add("エッジ検出");
32                comboBox1.Items.Add("二値化");
33
34                //初期選択を"処理なし"に設定
35                comboBox1.SelectedIndex = 0;
36            }
37
38            //読み込み処理
39            private void button1_Click(object sender, EventArgs e)
40            {
41                if (openFileDialog1.ShowDialog() == DialogResult.OK)
42                {
43                    Bitmap bmp = new Bitmap(openFileDialog1.FileName);
44                    pictureBox1.Image = bmp;
45
46                }
47            }
48
49            //保存
50            private void button2_Click(object sender, EventArgs e)
51            {
52                if (saveFileDialog1.ShowDialog() == DialogResult.OK)
53                {
54                    pictureBox1.Image.Save(saveFileDialog1.FileName);
55                }
56            }
57
58            //処理開始
59            private void button3_Click(object sender, EventArgs e)
60            {
61                Bitmap origin = new Bitmap(pictureBox1.Image);
62
63                //画像サイズの取得
64                int nx = origin.Width;
65                int ny = origin.Height;
66
67                double[,] data = new double[origin.Width, origin.Height];
68                double[,] Result = new double[origin.Width, origin.Height];
69                Bitmap dst = new Bitmap(nx, ny);
70
71                //ピクセルデータの取得
72                for (int i = 0; i < nx; i++)
73                {
74                    for (int j = 0; j < ny; j++)
75                    {
76                        data[i, j] = (double)((origin.GetPixel(i, j).R + origin.GetPixel(i, j).G + origin.GetPixel(i, j).B) / 3);
77                    }
78                }
79
80                switch (comboBox1.SelectedItem.ToString())
81                {
82                    case "処理なし":
83                        pictureBox2.Image = pictureBox1.Image;
84                        break;
85
86                    case "平滑化":
87                        Result = smoothing(data);
88                        dst = gray_level_transformation(Result, nx, ny);
89                        pictureBox2.Image = dst;
90                        break;
91
92                    case "鮮鋭化":
93                        Result = sharpening(data);
94                        dst = gray_level_transformation(Result, nx, ny);
95                        pictureBox2.Image = dst;
96                        break;
97
98                    case "エッジ検出":
99                        Result = edge_detectioning(data);
100                        dst = gray_level_transformation(Result, nx, ny);
101                        pictureBox2.Image = dst;
102                        break;
103
104                    case "二値化":
105                        //閾値
106                        int n = int.Parse(textBox1.Text);
107                        Result = thresholding(data, n);
108                        dst = gray_level_transformation(Result, nx, ny);
109                        pictureBox2.Image = dst;
110                        break;
111                }
112
113            }
114
115            //処理結果保存
116            private void button4_Click(object sender, EventArgs e)
117            {
118                if (saveFileDialog1.ShowDialog() == DialogResult.OK)
119                {
120                    string extension = Path.GetExtension(saveFileDialog1.FileName);
121
122                    pictureBox2.Image.Save(saveFileDialog1.FileName);
123                }
124            }
125
126            //平滑化処理
127            private double[,] smoothing(double[,] data)
128            {
129                int xsize, ysize;
130                double[,] c = {
131                           { 1.0 / 9.0, 1.0 / 9.0, 1.0 / 9.0},
132                           { 1.0 / 9.0, 1.0 / 9.0, 1.0 / 9.0},
133                           { 1.0 / 9.0, 1.0 / 9.0, 1.0 / 9.0}
134                         };
135
136                xsize = data.GetLength(0);
137                ysize = data.GetLength(1);
138
139                double[,] Result = new double[xsize, ysize];
140
141                for (int j = 0; j < ysize; j++)
142                    for (int i = 0; i < xsize; i++)
143                        Result[i, j] = 0.0;
144                for (int j = 1; j < ysize - 1; j++)
145                    for (int i = 1; i < xsize - 1; i++)
146                    {
147                        for (int k = 0; k < 3; k++)
148                            for (int l = 0; l < 3; l++)
149                                Result[i, j] += (double)data[i + l - 1, j + k - 1] * c[l, k];
150                    }
151
152                return Result;
153            }
154
155            //鮮鋭化処理
156            private double[,] sharpening(double[,] data)
157            {
158                int xsize, ysize;
159                double[,] c = {
160                           {  0.0,  -1.0,  0.0},
161                           { -1.0,   5.0, -1.0},
162                           {  0.0,  -1.0,  0.0}
163                         };
164
165                xsize = data.GetLength(0);
166                ysize = data.GetLength(1);
167
168                double[,] Result = new double[xsize, ysize];
169
170                for (int j = 0; j < ysize; j++)
171                    for (int i = 0; i < xsize; i++)
172                        Result[i, j] = 0.0;
173                for (int j = 1; j < ysize - 1; j++)
174                    for (int i = 1; i < xsize - 1; i++)
175                    {
176                        for (int k = 0; k < 3; k++)
177                            for (int l = 0; l < 3; l++)
178                                Result[i, j] += (double)data[i + l - 1, j + k - 1] * c[l, k];
179                    }
180
181                return Result;
182            }
183
184            //エッジの検出
185            private double[,] edge_detectioning(double[,] data)
186            {
187                int xsize, ysize;
188                double[,] c = {
189                           {  0.0,   1.0,  0.0},
190                           {  1.0,  -4.0,  1.0},
191                           {  0.0,   1.0,  0.0}
192                         };
193
194                xsize = data.GetLength(0);
195                ysize = data.GetLength(1);
196
197                double[,] Result = new double[xsize, ysize];
198
199                for (int j = 0; j < ysize; j++)
200                    for (int i = 0; i < xsize; i++)
201                        Result[i, j] = 0.0;
202                for (int j = 1; j < ysize - 1; j++)
203                    for (int i = 1; i < xsize - 1; i++)
204                    {
205                        for (int k = 0; k < 3; k++)
206                            for (int l = 0; l < 3; l++)
207                                Result[i, j] += (double)data[i + l - 1, j + k - 1] * c[l, k];
208                    }
209
210                return Result;
211            }
212
213            //2値化処理
214            private double[,] thresholding(double[,] data, int th)
215            {
216
217                int xsize, ysize;
218
219                xsize = data.GetLength(0);
220                ysize = data.GetLength(1);
221
222
223                double[,] Result = new double[xsize, ysize];
224
225                for (int j = 0; j < ysize; j++)
226                    for (int i = 0; i < xsize; i++)
227                        Result[i, j] = 0.0;
228
229                for (int j = 0; j < ysize; j++)
230                    for (int i = 0; i < xsize; i++)
231                    {
232
233                        if (data[i, j] > th)
234                        {
235                            Result[i, j] = 255;
236
237                        }
238                        else
239                        {
240                            Result[i, j] = 0;
241                        }
242                    }
243                return Result;
244
245            }
246
247            //
248            private Bitmap gray_level_transformation(double[,] Result, int nx, int ny)
249            {
250                double max = double.MinValue;
251                double min = double.MaxValue;
252                byte[,] img = new byte[nx, ny];
253
254                for (int i = 0; i < nx; i++)
255                    for (int j = 0; j < ny; j++)
256                    {
257                        if (max < Result[i, j])
258                            max = Result[i, j];
259
260                        if (min > Result[i, j])
261                            min = Result[i, j];
262                    }
263                Bitmap bmp = new Bitmap(nx, ny);
264                Color c_c;
265                for (int i = 0; i < nx; i++)
266                    for (int j = 0; j < ny; j++)
267                    {
268                        img[i, j] = (byte)(255 * (Result[i, j] - min) / (max - min));
269                        c_c = Color.FromArgb(img[i, j], img[i, j], img[i, j]);
270                        bmp.SetPixel(i, j, c_c);
271                    }
272                return bmp;
273            }
274        }
275    }
276