get back scanline

private void button4_Click(object sender, EventArgs e)
        {
            // GDI+ still lies to us - the return format is BGR, NOT RGB.
            BitmapData bmData = RImage.LockBits(new Rectangle(0, 0, RImage.Width, RImage.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

            int stride = bmData.Stride;
            System.IntPtr Scan0 = bmData.Scan0;

            unsafe
            {
                byte* p = (byte*)(void*)Scan0;

                int nOffset = stride - RImage.Width * 3;

                for (int y = 0; y < RImage.Height; ++y)
                {                   
                    for (int x = 0; x < RImage.Width; ++x)
                    {
                       
                        //supaya setiap y baru seed juga baru
                        if ((x == 0) || (seedR == 0))
                        {                            
                            //mengambil value seed
                            seedR = p[x];
                            seedG = p[x+1];
                            seedB = p[x+2];
                        }
                        else
                        {
                            if ((seedR - p[x] >= tred) || (p[x] - seedR >= tred))
                            {
                                for (int i = 0; i < 2; ++i)
                                {
                                    p[x] = p[x + 1] = p[x + 2] = 255;
                                    ++x;
                                }
                                                                    
                                seedR = 0;
                                seedG = 0;
                                seedB = 0;
                            }
                        }                        
                        
                        
                        p += 3;
                    }
                    p += nOffset;
                }
            }

            RImage.UnlockBits(bmData);
        }