/// <summary>
/// 使用byte[]数据，生成256色灰度　BMP 位图
/// </summary>
/// <param name="originalImageData"></param>
/// <param name="originalWidth"></param>
/// <param name="originalHeight"></param>
/// <returns></returns>
        public static Bitmap CreateBitmap(byte[] originalImageData, int originalWidth, int originalHeight)
{
//指定8位格式。即256色
            Bitmap resultBitmap = new Bitmap(originalWidth, originalHeight, System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
//将该位图存入内存中
            MemoryStream curImageStream = new MemoryStream();
resultBitmap.Save(curImageStream, System.Drawing.Imaging.ImageFormat.Bmp);
curImageStream.Flush();
//由于位图数据须要DWORD对齐（4byte倍数），计算须要补位的个数
            int curPadNum = ((originalWidth * 8 + 31) / 32 * 4) - originalWidth;
//终于生成的位图数据大小
            int bitmapDataSize = ((originalWidth * 8 + 31) / 32 * 4) * originalHeight;
//数据部分相对文件開始偏移。详细能够參考位图文件格式
            int dataOffset = ReadData(curImageStream, 10, 4);
//改变调色板，由于默认的调色板是32位彩色的，须要改动为256色的调色板
            int paletteStart = 54;
int paletteEnd = dataOffset;
int color = 0;
for (int i = paletteStart; i < paletteEnd; i += 4)
{
byte[] tempColor = new byte[4];
tempColor[0] = (byte)color;
tempColor[1] = (byte)color;
tempColor[2] = (byte)color;
tempColor[3] = (byte)0;
color++;
curImageStream.Position = i;
curImageStream.Write(tempColor, 0, 4);
}
//终于生成的位图数据。以及大小，高度没有变，宽度须要调整
            byte[] destImageData = new byte[bitmapDataSize];
int destWidth = originalWidth + curPadNum;
//生成终于的位图数据，注意的是。位图数据 从左到右，从下到上。所以须要颠倒
            for (int originalRowIndex = originalHeight - 1; originalRowIndex >= 0; originalRowIndex--)
{
int destRowIndex = originalHeight - originalRowIndex - 1;
for (int dataIndex = 0; dataIndex < originalWidth; dataIndex++)
{
//同一时候还要注意，新的位图数据的宽度已经变化destWidth，否则会产生错位
                    destImageData[destRowIndex * destWidth + dataIndex] = originalImageData[originalRowIndex * originalWidth + dataIndex];
}
}
//将流的Position移到数据段   
            curImageStream.Position = dataOffset;
//将新位图数据写入内存中
            curImageStream.Write(destImageData, 0, bitmapDataSize);
curImageStream.Flush();
//将内存中的位图写入Bitmap对象
            resultBitmap = new Bitmap(curImageStream);
return resultBitmap;
}
/// <summary>
/// 从内存流中指定位置，读取数据
/// </summary>
/// <param name="curStream"></param>
/// <param name="startPosition"></param>
/// <param name="length"></param>
/// <returns></returns>
        public static int ReadData(MemoryStream curStream, int startPosition, int length)
{
int result = -1;
byte[] tempData = new byte[length];
curStream.Position = startPosition;
curStream.Read(tempData, 0, length);
result = BitConverter.ToInt32(tempData, 0);
return result;
}
/// <summary>
/// 向内存流中指定位置，写入数据
/// </summary>
/// <param name="curStream"></param>
/// <param name="startPosition"></param>
/// <param name="length"></param>
/// <param name="value"></param>
        public static void WriteData(MemoryStream curStream, int startPosition, int length, int value)
{
curStream.Position = startPosition;
curStream.Write(BitConverter.GetBytes(value), 0, length);
}

转自：http://tech.sina.com.cn/s/2008-06-24/1206706116.shtml