Speed Up Help

I found a class to help me build gif animation. However, some of the code takes a long time to exicute large images. In the code is suggest a "non-safe" method should be implimented to make it faster. I'm a VB coder and no nothing about c#.
Can anyone help me make this faster.

C# Code:

/**
         * Extracts image pixels into byte array "pixels"
         */
        protected void GetImagePixels() 
        {
            int w = image.Width;
            int h = image.Height;
            //      int type = image.GetType().;
            if ((w != width)
                || (h != height)
                ) 
            {
                // create new image with right size/format
                Image temp =
                    new Bitmap(width, height );
                Graphics g = Graphics.FromImage( temp );
                g.DrawImage(image, 0, 0);
                image = temp;
                g.Dispose();
            }
            /*
                ToDo:
                improve performance: use unsafe code 
            */
            pixels = GetPixels(image);
            return
            pixels = new Byte [ 3 * image.Width * image.Height ];
            int count = 0;
            Bitmap tempBitmap = new Bitmap( image );
            for (int th = 0; th < image.Height; th++)
            {
                for (int tw = 0; tw < image.Width; tw++)
                {
                    Color color = tempBitmap.GetPixel(tw, th);
                    pixels[count] = color.R;
                    count++;
                    pixels[count] = color.G;
                    count++;
                    pixels[count] = color.B;
                    count++;
                }
            }