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copied!<p>GDI+ has a number of problems related to alpha blending when doing interop with GDI (and Win32). In this case, the call to bmp.GetHbitmap() will blend your image with a black background. An <a href="http://www.codeproject.com/KB/miscctrl/AlphaImageImagelist.aspx" rel="noreferrer">article on CodeProject</a> gives more detail on the problem, and a solution that was used for adding images to an image list.</p> <p>You should be able to use similar code to get the HBITMAP to use for the mask:</p> <pre><code>[DllImport("kernel32.dll")] public static extern bool RtlMoveMemory(IntPtr dest, IntPtr source, int dwcount); [DllImport("gdi32.dll")] public static extern IntPtr CreateDIBSection(IntPtr hdc, [In, MarshalAs(UnmanagedType.LPStruct)]BITMAPINFO pbmi, uint iUsage, out IntPtr ppvBits, IntPtr hSection, uint dwOffset); public static IntPtr GetBlendedHBitmap(Bitmap bitmap) { BITMAPINFO bitmapInfo = new BITMAPINFO(); bitmapInfo.biSize = 40; bitmapInfo.biBitCount = 32; bitmapInfo.biPlanes = 1; bitmapInfo.biWidth = bitmap.Width; bitmapInfo.biHeight = -bitmap.Height; IntPtr pixelData; IntPtr hBitmap = CreateDIBSection( IntPtr.Zero, bitmapInfo, 0, out pixelData, IntPtr.Zero, 0); Rectangle bounds = new Rectangle(0, 0, bitmap.Width, bitmap.Height); BitmapData bitmapData = bitmap.LockBits( bounds, ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb ); RtlMoveMemory( pixelData, bitmapData.Scan0, bitmap.Height * bitmapData.Stride); bitmap.UnlockBits(bitmapData); return hBitmap; } </code></pre>

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