using System;

 using System.Collections.Generic;

 using System.Text;

 using System.Drawing;

 using System.Runtime.InteropServices;

 using System.Drawing.Imaging;

 namespace Aga.Controls

 {

 	public static class BitmapHelper

 	{

 		[StructLayout(LayoutKind.Sequential)]

 		private struct PixelData

 		{

 			public byte B;

 			public byte G;

 			public byte R;

 			public byte A;

 		}

 		public static void SetAlphaChanelValue(Bitmap image, byte value)

 		{

 			if (image == null)

 				throw new ArgumentNullException("image");

 			if (image.PixelFormat != PixelFormat.Format32bppArgb)

 				throw new ArgumentException("Wrong PixelFormat");

 			BitmapData bitmapData = image.LockBits(new Rectangle(0, 0, image.Width, image.Height),

 									 ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);

 			unsafe

 			{

 				PixelData* pPixel = (PixelData*)bitmapData.Scan0;

 				for (int i = 0; i < bitmapData.Height; i++)

 				{

 					for (int j = 0; j < bitmapData.Width; j++)

 					{

 						pPixel->A = value;

 						pPixel++;

 					}

 					pPixel += bitmapData.Stride - (bitmapData.Width * 4);

 				}

 			}

 			image.UnlockBits(bitmapData);

 		}

 	}

 }