C# getpixel() don't return correct value.

public partial class formMain : Form
{

    Bitmap b = new Bitmap(@"F:\Hrit1\MSG1MostO.bmp");

    private void mapMain_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
    {

        Coordinate c= mapMain.PixelToProj(new System.Drawing.Point(e.X , e.Y ));

        int pixel = Convert.ToInt32(c.X);
        int line = Convert.ToInt32(c.Y);
        if (line < 0 || pixel < 0 || line > 850 || pixel > 1145)
        {
            line = 0;
            pixel = 0;
        }

        Color col = b.GetPixel(pixel, line);

        textBox1.Text = col.ToString();

}
  }