C#

Image img=new Bitmap("filepath.jpg");
Bitmap bmp=null;
for(int i=0;i<img.Width;i++)
{
  for(int j=0;j<img.Height;j++)
  {
	Color col=img.GetPixel(i,j);
	int avg=((col.R+col.G+col.B)/3);
	img.SetPixel(i,j,Color.FromArgb(avg,avg,avg));	
  }
}
MemoryStream mem=new MemoryStream();
img.Save(mem,ImageFormat.Gif);
bmp=new Bitmap(mem);
this.pictureBox1.Image=bmp;

/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
    if (disposing && (components != null))
    {
        components.Dispose();

        if (m_Session != null)
        {
            while (true)
            {
                if (Marshal.ReleaseComObject(m_Session) <= 0)
                {
                    m_Session = null;
                    break;
                }
            }
        }
        if (m_System != null)
        {
            while (true)
            {
                if (Marshal.ReleaseComObject(m_System) <= 0)
                {
                    m_System = null;
                    break;
                }
            }
        }

    }
    base.Dispose(disposing);
}