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

        private void InitWithCGImage(CGImage image)
        {
            int	width, height;
            CGBitmapContext bitmap = null;
            bool hasAlpha;
            CGImageAlphaInfo alphaInfo;
            CGColorSpace colorSpace;
            int bitsPerComponent, bytesPerRow;
            CGBitmapFlags bitmapInfo;
            bool premultiplied = false;
            int bitsPerPixel = 0;

            if (image == null) {
                throw new ArgumentException (" image is invalid! " );
            }

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

            imageSize.Width = (int)image.Width;
            imageSize.Height = (int)image.Height;

            width = (int)image.Width;
            height = (int)image.Height;

            // Not sure yet if we need to keep the original image information
            // before we change it internally.  TODO look at what windows does
            // and follow that.
            bitmapInfo = image.BitmapInfo;
            bitsPerComponent = (int)image.BitsPerComponent;
            bitsPerPixel = (int)image.BitsPerPixel;
            bytesPerRow = width * bitsPerPixel/bitsPerComponent;
            int size = bytesPerRow * height;

            colorSpace = image.ColorSpace;

            // Right now internally we represent the images all the same
            // I left the call here just in case we find that this is not
            // possible.  Read the comments for non alpha images.
            if(colorSpace != null) {
                if( hasAlpha ) {
                    premultiplied = true;
                    colorSpace = CGColorSpace.CreateDeviceRGB ();
                    bitsPerComponent = 8;
                    bitsPerPixel = 32;
                    bitmapInfo = CGBitmapFlags.PremultipliedLast;
                }
                else
                {
                    // even for images without alpha we will internally
                    // represent them as RGB with alpha.  There were problems
                    // if we do not do it this way and creating a bitmap context.
                    // The images were not drawing correctly and tearing.  Also
                    // creating a Graphics to draw on was a nightmare.  This
                    // should probably be looked into or maybe it is ok and we
                    // can continue representing internally with this representation
                    premultiplied = true;
                    colorSpace = CGColorSpace.CreateDeviceRGB ();
                    bitsPerComponent = 8;
                    bitsPerPixel = 32;
                    bitmapInfo = CGBitmapFlags.NoneSkipLast;
                }
            } else {
                premultiplied = true;
                colorSpace = CGColorSpace.CreateDeviceRGB ();
                bitsPerComponent = 8;
                bitsPerPixel = 32;
                bitmapInfo = CGBitmapFlags.NoneSkipLast;
            }

            bytesPerRow = width * bitsPerPixel/bitsPerComponent;
            size = bytesPerRow * height;

            bitmapBlock = Marshal.AllocHGlobal (size);
            bitmap = new CGBitmapContext (bitmapBlock,
                                          width, height,
                                          bitsPerComponent,
                                          bytesPerRow,
                                          colorSpace,
                                          bitmapInfo);

            bitmap.ClearRect (new CGRect (0,0,width,height));

            // We need to flip the Y axis to go from right handed to lefted handed coordinate system
            var transform = new CGAffineTransform(1, 0, 0, -1, 0, image.Height);
            bitmap.ConcatCTM(transform);

            bitmap.DrawImage (new CGRect (0, 0, image.Width, image.Height), image);

            var provider = new CGDataProvider (bitmapBlock, size, true);
            NativeCGImage = new CGImage (width, height, bitsPerComponent,
                                         bitsPerPixel, bytesPerRow,
                                         colorSpace,
                                         bitmapInfo,
                                         provider, null, true, image.RenderingIntent);

            colorSpace.Dispose();
            bitmap.Dispose();
        }