var width = 50;
            var height = 50;

            var stream = new MemoryStream(File.ReadAllBytes("C:\\asd.png"));
            var bmp = BitmapFactory.New(1, 1).FromStream(stream);

            var x1 = bmp.PixelWidth / width;
            var y1 = bmp.PixelHeight / height;

            for (int x = 0; x < x1; x++)
            {
                for (int y = 0; y < y1; y++)
                {
                    var crop = bmp.Crop(x * width, y * height, width, height);

                    using (var file = File.Create("result\\" + x + "x" + y + ".png"))
                    {
                        var encoder = new PngBitmapEncoder();
                        encoder.Frames.Add(BitmapFrame.Create(crop));
                        encoder.Save(file);
                    }
                }
            }

            MessageBox.Show("OK");