BitMiracle.LibTiff.Classic.TiffRgbaImage.makebwmap C# (CSharp) Method

        private bool makebwmap()
        {
            int nsamples = 8 / bitspersample;
            if (nsamples == 0)
                nsamples = 1;

            BWmap = new int[256][];
            for (int i = 0; i < 256; i++)
                BWmap[i] = new int[nsamples];

            for (int i = 0; i < 256; i++)
            {
                int j = 0;
                switch (bitspersample)
                {
                    case 1:
                        GREY(i >> 7, i, ref j);
                        GREY((i >> 6) & 1, i, ref j);
                        GREY((i >> 5) & 1, i, ref j);
                        GREY((i >> 4) & 1, i, ref j);
                        GREY((i >> 3) & 1, i, ref j);
                        GREY((i >> 2) & 1, i, ref j);
                        GREY((i >> 1) & 1, i, ref j);
                        GREY(i & 1, i, ref j);
                        break;
                    case 2:
                        GREY(i >> 6, i, ref j);
                        GREY((i >> 4) & 3, i, ref j);
                        GREY((i >> 2) & 3, i, ref j);
                        GREY(i & 3, i, ref j);
                        break;
                    case 4:
                        GREY(i >> 4, i, ref j);
                        GREY(i & 0xf, i, ref j);
                        break;
                    case 8:
                    case 16:
                        GREY(i, i, ref j);
                        break;
                }
            }

            return true;
        }