How do I calculate average of multiple bitmap images in C#

public Bitmap GetAveragedBitmap()
    {

        int numberOfImages = _imageCollection.Count;
        Bitmap bmpresult = null;


        if (numberOfImages > 1)
        {
            Stopwatch clock = new Stopwatch();
            clock.Start();
            BitmapData[] bmpData = new BitmapData[numberOfImages];
            Bitmap[] bit = new Bitmap[numberOfImages];
            int width = 0;
            int height = 0;

            for (int index = 0; index < numberOfImages; index++)
            {
                bmpData[index] = _imageCollection[index].LockBits(new Rectangle(0, 0, _imageCollection[index].Width, _imageCollection[index].Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
                if (index > 0)
                {
                    if (bmpData[index].Width > width)
                    {
                        width = bmpData[index].Width;
                    }
                    if (bmpData[index].Height > height)
                    {
                        height = bmpData[index].Height;
                    }
                }
                else
                {
                    width = bmpData[0].Width;
                    height = bmpData[0].Height;
                }

                _imageCollection[index].UnlockBits(bmpData[index]);




            }//end of for loop
            for (int index = 0; index < numberOfImages; index++)
            {
                bit[index] = new Bitmap(_imageCollection[index], width, height);

            }

            bmpresult = new Bitmap(width, height);
            BitmapData[] data = new BitmapData[numberOfImages];
            for (int index = 0; index < numberOfImages; index++)
            {
                data[index] = bit[index].LockBits(new Rectangle(0, 0, bit[index].Width, bit[index].Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
            }
            data[1].Reserved = 1;
            BitmapData dataResult = bmpresult.LockBits(new Rectangle(0, 0, bmpresult.Width, bmpresult.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

            unsafe
            {
                int[] remain = new int[numberOfImages];
                byte*[] ptr = new byte*[numberOfImages];
                long totalIntensity = 0;

                for (int index = 0; index < numberOfImages; index++)
                {
                    ptr[index] = (byte*)data[index].Scan0;
                    remain[index] = data[index].Stride - data[index].Width * 3;
                }
                byte* ptrResult = (byte*)dataResult.Scan0;
                //for resultant image
                int remainResult = dataResult.Stride - dataResult.Width * 3;


                for (int i = 0; i < height; i++)
                    for (int j = 0; j < width * 3; j++)
                    {
                        for (int index = 0; index < numberOfImages; index++)
                        {
                            totalIntensity += (int)(ptr[index][0]);
                            ptr[index]++;
                        }
                    }

                int average = (int)totalIntensity / (numberOfImages * height * width);
                //reset the pointer
                for (int index = 0; index < numberOfImages; index++)
                {
                    ptr[index] = (byte*)data[index].Scan0;
                }

                for (int i = 0; i < height; i++)
                {
                    for (int j = 0; j < width * 3; j++)
                    {

                        int result = 1;
                        for (int k = 0; k < numberOfImages; k++)
                        {

                            result = (ptr[k][0] * result);

                        }

                       // result = ptr[0][0] + result * (2 - 1);

                        ptrResult[0] = (byte)(result / average);

                        for (int index = 0; index < numberOfImages; index++)
                        {
                            ptr[index]++;
                        }
                        ptrResult++;

                    }
                    for (int index = 0; index < numberOfImages; index++)
                    {
                        ptr[index] += remain[index];

                    }

                    ptrResult += remainResult;

                }

                //  }//end of for loop

            }//end of unsafe

            for (int index = 0; index < numberOfImages; index++)
            {
                bit[index].UnlockBits(data[index]);
            }
            bmpresult.UnlockBits(dataResult);
            clock.Stop();
            Debug.WriteLine("Time for average " + clock.ElapsedMilliseconds.ToString());

        }
        return bmpresult;



    }