System.Drawing.Bitmap.MakeSureWeHaveAnAlphaChannel C# (CSharp) Method

        private void MakeSureWeHaveAnAlphaChannel()
        {
            // Initialize our prmultiplied tables.
            if (!ConversionHelpers.sTablesInitialized)
                ConversionHelpers.CalculateTables ();

            var alphaInfo = NativeCGImage.AlphaInfo;
            var hasAlpha = ((alphaInfo == CGImageAlphaInfo.PremultipliedLast)
                            || (alphaInfo == CGImageAlphaInfo.PremultipliedFirst)
                            || (alphaInfo == CGImageAlphaInfo.Last)
                            || (alphaInfo == CGImageAlphaInfo.First) ? true : false);

            if (cachedContext != null && cachedContext.Handle != IntPtr.Zero)
            {
                return;
            }

            // set our pixel format
            pixelFormat = PixelFormat.Format32bppArgb;
            // and mark the rawformat as from memory
            rawFormat = ImageFormat.MemoryBmp;

            //format = GetBestSupportedFormat (pixelFormat);
            cachedContext = CreateCompatibleBitmapContext ((int)NativeCGImage.Width, (int)NativeCGImage.Height, pixelFormat);

            // Fill our pixel data with the actual image information
            cachedContext.DrawImage (new CGRect (0, 0, (int)NativeCGImage.Width, (int)NativeCGImage.Height), NativeCGImage);

            // Dispose of the prevous image that is allocated.
            NativeCGImage.Dispose ();

            // Get a reference to the pixel data
            bitmapBlock = cachedContext.Data;
            int size = (int)(cachedContext.BytesPerRow * cachedContext.Height);
            var provider = new CGDataProvider (cachedContext.Data, size, true);

            // Get the image from the bitmap context.
            //NativeCGImage = bitmapContext.ToImage ();
            CGColorSpace colorSpace = CGColorSpace.CreateDeviceRGB();
            NativeCGImage = new CGImage ((int)cachedContext.Width, (int)cachedContext.Height, (int)cachedContext.BitsPerComponent,
                                         (int)cachedContext.BitsPerPixel, (int)cachedContext.BytesPerRow,
                                         colorSpace,
                                         cachedContext.AlphaInfo,
                                         provider, null, true, CGColorRenderingIntent.Default);
            colorSpace.Dispose ();
        }