C#

public static bool Brightness(Bitmap b, int nBrightness)
		{
			if (nBrightness < -255 || nBrightness > 255)
				return false;

			// GDI+ still lies to us - the return format is BGR, NOT RGB.
			BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

			int stride = bmData.Stride;
			System.IntPtr Scan0 = bmData.Scan0;

			int nVal = 0;

			unsafe
			{
				byte * p = (byte *)(void *)Scan0;

				int nOffset = stride - b.Width*3;
				int nWidth = b.Width * 3;

				for(int y=0;y<b.Height;++y)
				{
					for(int x=0; x < nWidth; ++x )
					{
						nVal = (int) (p[0] + nBrightness);
		
						if (nVal < 0) nVal = 0;
						if (nVal > 255) nVal = 255;

						p[0] = (byte)nVal;

						++p;
					}
					p += nOffset;
				}
			}

			b.UnlockBits(bmData);

			return true;
		}

		public static bool Contrast(Bitmap b, sbyte nContrast)
		{
			if (nContrast < -100) return false;
			if (nContrast >  100) return false;

			double pixel = 0, contrast = (100.0+nContrast)/100.0;

			contrast *= contrast;

			int red, green, blue;
			
			// GDI+ still lies to us - the return format is BGR, NOT RGB.
			BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

			int stride = bmData.Stride;
			System.IntPtr Scan0 = bmData.Scan0;

			unsafe
			{
				byte * p = (byte *)(void *)Scan0;

				int nOffset = stride - b.Width*3;

				for(int y=0;y<b.Height;++y)
				{
					for(int x=0; x < b.Width; ++x )
					{
						blue = p[0];
						green = p[1];
						red = p[2];
				
						pixel = red/255.0;
						pixel -= 0.5;
						pixel *= contrast;
						pixel += 0.5;
						pixel *= 255;
						if (pixel < 0) pixel = 0;
						if (pixel > 255) pixel = 255;
						p[2] = (byte) pixel;

						pixel = green/255.0;
						pixel -= 0.5;
						pixel *= contrast;
						pixel += 0.5;
						pixel *= 255;
						if (pixel < 0) pixel = 0;
						if (pixel > 255) pixel = 255;
						p[1] = (byte) pixel;

						pixel = blue/255.0;
						pixel -= 0.5;
						pixel *= contrast;
						pixel += 0.5;
						pixel *= 255;
						if (pixel < 0) pixel = 0;
						if (pixel > 255) pixel = 255;
						p[0] = (byte) pixel;					

						p += 3;
					}
					p += nOffset;
				}
			}

			b.UnlockBits(bmData);

			return true;
		}

foreach (FileInfo info in new DirectoryInfo(@"C:\test").GetFiles())
{
    Console.WriteLine(info.Length);
}

using System.Drawing;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        
        public Form1()
        {
            InitializeComponent();
        }
        protected override void OnPaint(PaintEventArgs e)
        {
            using (Pen pen = new Pen(Color.Black))
            {
                e.Graphics.DrawLine(pen, Point.Empty, new Point(ClientSize.Width, ClientSize.Height));
            }
            base.OnPaint(e);
        }
    }
}