Windows Forms C# Графический векторный редактор

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

namespace MyGraphicEditor
{
    public partial class Form1 : Form
    {
        Bitmap map = new Bitmap(100,100);
        Pen pen = new Pen(Color.Black,3f);
        Graphics graphics;
        int cnt = 0;
        Point[][] p;
        bool mdown;
        String mode;
        bool point_focused;
        int catch_line_lindex;
        int catch_point_lindex;


        public Form1()
        {
            mode = "Рисуем линию";
            catch_line_lindex = -1;
            catch_point_lindex = -1;
            point_focused = false;
            mdown = false;
            InitializeComponent();
            setSize();
            p = new Point[100][];
            for (int i = 0; i < 100; i++)
                p[i] = new Point[2];
        }

        private void setSize()
        {
            Rectangle rectangle = Screen.PrimaryScreen.Bounds;
            map = new Bitmap(rectangle.Width, rectangle.Height);
            graphics = Graphics.FromImage(map);
            pen.StartCap = System.Drawing.Drawing2D.LineCap.Round;
            pen.EndCap = System.Drawing.Drawing2D.LineCap.Round;
           
        }
     
        private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
        {
            mdown = false;
            if (mode == "Рисуем линию")
            {
                p[cnt][1].X = e.X;
                p[cnt][1].Y = e.Y;
                cnt++;
            }
            if (mode == "Изменяем линию")
            {
                p[catch_line_lindex][catch_point_lindex].X = e.X;
                p[catch_line_lindex][catch_point_lindex].Y = e.Y;
            }
           
            pictureBox1.Invalidate();
            mode = "Рисуем линию";
        }
        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            mdown = true;
            if(mode == "Рисуем линию")
            {
                p[cnt][0].X = e.X;
                p[cnt][0].Y = e.Y;
            }
            if (mode == "Изменяем линию")
            {
                p[catch_line_lindex][catch_point_lindex].X = e.X;
                p[catch_line_lindex][catch_point_lindex].Y = e.Y;
            }


        }
        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (mdown)
            {
                if (mode == "Рисуем линию")
                {
                    p[cnt][1].X = e.X;
                    p[cnt][1].Y = e.Y;
                }
                if (mode == "Изменяем линию")
                {
                    p[catch_line_lindex][catch_point_lindex].X = e.X;
                    p[catch_line_lindex][catch_point_lindex].Y = e.Y;
                }
            }
            else
            {
                mode = "Рисуем линию";
                point_focused = false;
                catch_point_lindex = -1;
                catch_line_lindex = -1;
                for (int i = 0; i < cnt; i++)
                {
                    if(Math.Abs(p[i][0].X-e.X)<5 && Math.Abs(p[i][0].Y - e.Y) < 5)
                    {
                        point_focused = true;
                        catch_point_lindex = 0;
                        catch_line_lindex = i;
                        mode = "Изменяем линию";
                    }
                    if (Math.Abs(p[i][1].X - e.X) < 5 && Math.Abs(p[i][1].Y - e.Y) < 5)
                    {
                        point_focused = true;
                        catch_point_lindex = 1;
                        catch_line_lindex = i;
                        mode = "Изменяем линию";
                    }
                }
            }
            pictureBox1.Invalidate();
        }
        private void pictureBox1_Paint(object sender,PaintEventArgs e)
        {
            graphics = e.Graphics;

            if (point_focused)
            {
                graphics.DrawRectangle(new Pen(Color.Red), p[catch_line_lindex][catch_point_lindex].X - 5, p[catch_line_lindex][catch_point_lindex].Y - 5, 10,10);
            }
            
            for(int i = 0; i < cnt; i++)
            {
                graphics.DrawLine(pen, p[i][0].X, p[i][0].Y, p[i][1].X, p[i][1].Y);
            }
            if (mdown)
            {
                graphics.DrawLine(pen, p[cnt][0].X, p[cnt][0].Y, p[cnt][1].X, p[cnt][1].Y);
            }
        }

     
        private void button2_Click(object sender, EventArgs e)
        {
            graphics.Clear(pictureBox1.BackColor);
            pictureBox1.Image = map;
    
            
        }

        private void trackBar1_ValueChanged(object sender, EventArgs e)
        {
            pen.Width = trackBar1.Value;
        }

        private void button3_Click(object sender, EventArgs e)
        {  
            pen.Color = ((Button)sender).BackColor;
        }

        private void button5_Click(object sender, EventArgs e)
        {
            pen.Color = ((Button)sender).BackColor;
        }

        private void button4_Click(object sender, EventArgs e)
        {
            if (colorDialog1.ShowDialog() == DialogResult.OK)
            {
                pen.Color = colorDialog1.Color;
                ((Button)sender).BackColor = colorDialog1.Color;
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            saveFileDialog1.Filter = "JPG(*.JPG)|*.jpg";
            if (saveFileDialog1.ShowDialog() == DialogResult.OK)
            {
                if (pictureBox1.Image != null)
                {
                    pictureBox1.Image.Save(saveFileDialog1.FileName);
                }
            }
        }
    }
}

Только начал работать с windows forms в c#. У меня возникает ошибка в строке graphics.Clear(pictureBox1.BackColor); Пишет System.ArgumentException: "Parameter is not valid." Плюс у меня не сохраняется изображение в файл.