C# IMAPRO GetHistogram Values

public long[] GetHistogram(Bitmap picture)
        {
            long[] myHistogram = new long[256];

            for (int i = 0; i < picture.Size.Width; i++)
            {
                for (int j = 0; j < picture.Size.Height; j++)
                {
                    Color c = picture.GetPixel(i, j);

                    long Temp = 0;
                    Temp += c.R;
                    Temp += c.G;
                    Temp += c.B;

                    Temp = (int)Temp / 3;
                    myHistogram[Temp]++;
                }
            }
            return myHistogram;
        }