C / C++ / MFC

// width & height are size of bitmap in char array, source [] is char array BGRA ( most likely format )
	Bitmap bitmap(width, height, PixelFormat32bppARGB); // Default pixel format value

	BitmapData data;
	bitmap->LockBits(Rect(0, 0, width, height),
		ImageLockModeWrite | ImageLockModeRead, PixelFormat32bppARGB, &data);

	unsigned char * bits = (unsigned char*)data.Scan0;

	for (unsigned int y = 0; y < data.Height; y++)
	{
		for (unsigned int x = 0; x < data.Width * 3; x+=3)
		{
			memset(bits[0], 0, 4); // Probably not needed, bitmap should be black anyhow

			if (we want the red mask)
				bits[1] = source[2];
			if(we want the green mask)
				bits[2] = source[1];
			if (we want the blue mask)
				bits[3] = source[0];
			if (we want the greyscale alpha mask)
				bits[0] = source[3];
				
			bits += 4;
			source += 4;
		}
		bits += data.Stride - data.Width*4;  // jump stride value
	}

	bitmap->UnlockBits(&data);

	// The bitmap now has the mask drawn onto it, we can select a DC containing a HBITMAP
	// and draw onto it.  We can also use the GetHBITMAP method, but if we want to return it
	// we should probably change the code to use a Bitmap*, so that the HBITMAP is not
	// destroyed when the Bitmap goes out of scope.

	// Sorry that this is untested and not complete, but I wanted to get you *something*
	// after promising I would and I ended up teached C++ 101 to a friends son last
	// night after an imprompu dinner invitation.