Very simple conversion of bitmap to indexed bitmap

private static unsafe Bitmap ToIndexed(Bitmap source, PixelFormat format)
        {
            Rectangle rectangle = new Rectangle(0, 0, source.Width, source.Height);
            Bitmap result = new Bitmap(source.Width, source.Height, format);

            BitmapData sourceData = source.LockBits(rectangle, 
                ImageLockMode.ReadOnly, source.PixelFormat),
                resultData = result.LockBits(rectangle, 
                ImageLockMode.WriteOnly, format);

            int sourceFlags = sourceData.Stride * sourceData.Height,
                resultFlags = resultData.Stride * resultData.Height;

            byte* sourceBuffer = (byte*)sourceData.Scan0.ToPointer(), 
                resultBuffer = (byte*)resultData.Scan0.ToPointer();

            int offset = sourceFlags / resultFlags;
            for (int i = 0; i < sourceFlags; i++)
            {
                resultBuffer[i / offset] = sourceBuffer[i];
            }

            result.UnlockBits(resultData);
            source.UnlockBits(sourceData);
            return result;
        }