read tiff to bmp in c# got only white image

i want to convert a tif image to bmp i was following tutorial in https://trac.osgeo.org/gdal/wiki/GdalOgrCsharpRaster but i dont get an image i want to see

the code is :

// Creating a Bitmap to store the GDAL image in
            Bitmap bitmap = new Bitmap(xsize, ysize, PixelFormat.Format32bppRgb);
            // Creating a C# array to hold the image data
            byte[] r = new byte[xsize * ysize];
            bands[0].ReadRaster(0, 0, xsize, ysize, r, xsize, ysize, 0, 0);
            // Copying the pixels into the C# bitmap

            for (int i = 0; i < xsize; i++)
            {
                for (int j = 0; j < ysize; j++)
                {
                    Color newColor = Color.FromArgb(Convert.ToInt32(r[i + j * xsize]), Convert.ToInt32(r[i + j * xsize]), Convert.ToInt32(r[i + j * xsize]));
                    bitmap.SetPixel(i, j, newColor);
                }
            }

            bitmap.Save("F:\dijajal.jpeg", ImageFormat.Jpeg);

Original image

Output Image