C#

[DllImport("user32.dll", CharSet=CharSet.Auto)]
private extern static int SendMessage(IntPtr hwnd, int msg, int wParam, ref COPYDATASTRUCT lParam);
 
[StructLayout(LayoutKind.Sequential)]
struct COPYDATASTRUCT {  // cds 
    int dwData; 
    int cbData; 
    IntPtr lpData; 
}
 
//------Managed Way--------
 
//assume that the variable "data" holds the data
 
COPYDATASTRUCT cds=new COPYDATASTRUCT;
 
cds.cbData=Marshall.SizeOf(data);
IntPtr mem=Marshall.AllocHGlobal(cds.cbData);
cds.lpData=Marshall.StructureToPtr(data,mem,true);
cds.lpData=mem;
//now do the SendMessage call, then do cleanup of resources
 
//-----UnManaged Way------
 
[DllImport("user32.dll", CharSet=CharSet.Auto)]
private extern static int SendMessage(IntPtr hwnd, int msg, int wParam, void* lParam);
 
COPYDATASTRUCT cds=new COPYDATASTRUCT;
SendMessage(handle,WM_COPYDATA,wParam,(void*)&cds);
 

cds.lpData=Marshall.StructureToPtr(data,mem,true);

Marshall.StructureToPtr(data,mem,true);

//assume the original bitmap is named bmp, and the
//new pixel format flag is in a variable named format.
 
Bitmap newbmp=new Bitmap(format,bmp.Width,bm.Height);
Graphics newbmpgr=Graphics.FromImage((Image)newbmp);
 
newbmpgr.DrawImageUnscaled((Image)bmp,0,0);
newbmpgr.Dispose();
 
//newbmp now contains old bitmap's data, 
//but in the new format.