Stitching images by using the concept of image substraction

public Bitmap Substraction(Bitmap bmpA, Bitmap bmpB)
 {

     BitmapData bmpData_A = bmpA.LockBits(new Rectangle(0, 0, bmpA.Width, bmpA.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
     BitmapData bmpData_B = bmpB.LockBits(new Rectangle(0, 0, bmpB.Width, bmpB.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

     int width_A = bmpData_A.Width;
     int width_B = bmpData_B.Width;

     int height_A = bmpData_A.Height;
     int height_B = bmpData_B.Height;

     bmpA.UnlockBits(bmpData_A);
     bmpB.UnlockBits(bmpData_B);


     Bitmap input_img1 = new Bitmap(bmpA, width_A, height_A);
     Bitmap input_img2 = new Bitmap(bmpB, width_B, height_B);

     int width_output = width_A + width_B;
     int height_output = height_A + width_B;

     Bitmap output_image = new Bitmap(width_A, height_B);

     BitmapData bmpdata1 = input_img1.LockBits(new Rectangle(0, 0, input_img1.Width, input_img1.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
     BitmapData bmpdata2 = input_img2.LockBits(new Rectangle(0, 0, input_img2.Width, input_img2.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
     BitmapData bmpoutput = output_image.LockBits(new Rectangle(0, 0, output_image.Width, output_image.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);


     unsafe
     {
         int ptr1 = bmpdata1.Stride - bmpdata1.Width * 3;
         int ptr2 = bmpdata2.Stride - bmpdata2.Width * 3;
         int ptr3 = bmpoutput.Stride - bmpoutput.Width * 3;

         //Pointing towards the 1st byte in Array
         byte* p1 = (byte*)bmpdata1.Scan0;
         byte* p2 = (byte*)bmpdata2.Scan0;
         byte* p3 = (byte*)bmpoutput.Scan0;


         for (int y = 0; y < height_A; y++)
         {
             for (int x = 0; x < width_A * 3; x++)
             {

                     p3[0] = (byte)(Math.Abs(p2[0] - p1[0]));

                     p1++;
                     p2++;
                     p3++;


             }

             p1 += ptr1;
             p2 += ptr2;
             p3 += ptr3;

         }

     }

     input_img1.UnlockBits(bmpdata1);
     input_img2.UnlockBits(bmpdata2);
     output_image.UnlockBits(bmpoutput);

     return output_image;

 }