// our BITMAPINFOHEADER struct, as per gdi
// use LayoutKind to make sure data is marshalled as we've laid it out
[StructLayout(LayoutKind.Sequential)]
public struct BITMAPINFOHEADER
{
public uint biSize;
public int biWidth;
public int biHeight;
public ushort biPlanes;
public ushort biBitCount;
public uint biCompression;
public uint biSizeImage;
public int biXPelsPerMeter;
public int biYPelsPerMeter;
public uint biClrUsed;
public uint biClrImportant;
public void Init()
{
 biSize = (uint)Marshal.SizeOf(this);
}
}

public static Bitmap BitmapFromDIB(MemoryStream dib)
{
// get byte array of device independent bitmap
byte[] dibBytes = dib.ToArray();

// get the handle for the byte array and "pin" that memory (i.e. prevent garbage collector from
// gobbling it up right away)...
GCHandle hdl = GCHandle.Alloc(dibBytes, GCHandleType.Pinned);

// marshal our data into a BITMAPINFOHEADER struct per Win32 definition of BITMAPINFOHEADER
BITMAPINFOHEADER dibHdr = (BITMAPINFOHEADER)Marshal.PtrToStructure(hdl.AddrOfPinnedObject(), typeof(BITMAPINFOHEADER));

// go ahead and release the "pin" from our handle on that memory
hdl.Free();

// If the target device does not have one plane, or we're working with a bitmap other than a
// non-compressed (BI_RGB) bitmap, we're not gonna work woith it
if (dibHdr.biPlanes != 1 || dibHdr.biCompression != 0)
 return null;

// we need to know beforehand the pixel-depth of our bitmap
PixelFormat fmt = PixelFormat.Format24bppRgb;
switch (dibHdr.biBitCount)
{
 case 32:
  fmt = PixelFormat.Format32bppRgb;
  break;
 case 24:
  fmt = PixelFormat.Format24bppRgb;
  break;
 case 16:
  fmt = PixelFormat.Format16bppRgb555;
  break;
 default:
  return null;
}

// prepare for our output bitmap
Bitmap bmp = new Bitmap(dibHdr.biWidth, dibHdr.biHeight, fmt);

// load our "empty" bitmap into memory and lock it for writing in the format we specified
BitmapData bd = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.WriteOnly, fmt);

// marshal our device independent bitmap data over to our output bitmap
Marshal.Copy(dibBytes, Marshal.SizeOf(dibHdr), bd.Scan0, bd.Stride * bd.Height);

// we're done marshalling, so release our bitmapdata lock
bmp.UnlockBits(bd);

// DIB data is upside-down for some reason, so flip it
bmp.RotateFlip(RotateFlipType.RotateNoneFlipY);

// return our bitmap
return bmp;
}