Midpoint Algorithm - Strange Results

I am writing my own midpoint offset algorithm for training purposes, and I decided to implement it in my own way to find out if I was 1) able to understand the algorithm and 2) see if I could change it to my liking.

here is the code for generating the fractal:

 public void Generate(Double rg, int size)
    {
        Random rand = new Random();
        int min = -127;
        int max = 128;

        // Starting points of the rectangle
        MDP_Point s1 = new MDP_Point(0, 0, rand.Next(min, max));
        MDP_Point s2 = new MDP_Point(size, 0, rand.Next(min, max));
        MDP_Point s3 = new MDP_Point(size, size, rand.Next(min, max));
        MDP_Point s4 = new MDP_Point(0, size, rand.Next(min, max));

        // Lists containing the rectangles
        List<MDP_Rect> newRect = new List<MDP_Rect>();  // Newly created rectangles
        List<MDP_Rect> oldRect = new List<MDP_Rect>();  // Rectangles being divided


        // Starting rectangle is added to the list
        oldRect.Add(new MDP_Rect(s1, s2, s3, s4));

        // Distance between 2 points in a rectangle
        int h = size;

        while (h > 1)
        {
            foreach (MDP_Rect r in oldRect)
            {
                // Middle points of rectangle segments
                MDP_Point m1 = new MDP_Point();
                MDP_Point m2 = new MDP_Point();
                MDP_Point m3 = new MDP_Point();
                MDP_Point m4 = new MDP_Point();
                // Middle point of rectangle
                MDP_Point mm = new MDP_Point();

                m1.x = (r.C1.x + r.C2.x) / 2;
                m1.y = (r.C1.y + r.C2.y) / 2;
                m1.z = ((r.C1.z + r.C2.z) / 2) +(rand.Next(min, max) * rg);

                m2.x = (r.C2.x + r.C3.x) / 2;
                m2.y = (r.C2.y + r.C3.y) / 2;
                m2.z = ((r.C2.z + r.C3.z) / 2) +(rand.Next(min, max) * rg);

                m3.x = (r.C3.x + r.C4.x) / 2;
                m3.y = (r.C3.y + r.C4.y) / 2;
                m3.z = ((r.C3.z + r.C4.z) / 2) +(rand.Next(min, max) * rg);

                m4.x = (r.C1.x + r.C4.x) / 2;
                m4.y = (r.C1.y + r.C4.y) / 2;
                m4.z = ((r.C1.z + r.C4.z) / 2) + (rand.Next(min, max) * rg);

                mm.x = (r.C1.x + r.C2.x + r.C3.x + r.C4.x) / 4;
                mm.y = (r.C1.y + r.C2.y + r.C3.y + r.C4.y) / 4;
                mm.z = ((r.C1.z + r.C2.z + r.C3.z + r.C4.z) / 4) + (rand.Next(min, max) * rg);

                newRect.Add(new MDP_Rect(r.C1, m1, mm, m4));
                newRect.Add(new MDP_Rect(m1, r.C2, m2, mm));
                newRect.Add(new MDP_Rect(mm, m2, r.C3, m3));
                newRect.Add(new MDP_Rect(m4, mm, m3, r.C4));
            }


            oldRect.Clear();
            oldRect = new List<MDP_Rect>(newRect);
            newRect.Clear();
            h /= 2;
        }

        List<MDP_Rect> sorted = new List<MDP_Rect>();
        sorted = oldRect.OrderBy(y => y.C1.y).ThenBy(x => x.C1.x).ToList();

        List<MDP_Point> mapArray = new List<MDP_Point>();
        mapArray.AddRange(CreateArray(sorted));

        CreateImage(size, mapArray, rg);
    }

MDP_Point contains only x, y and z values ​​MDP_Rectangle contains 4 points, creating a rectangle

The CreateArray () method accepts only an ordered list of rectangles and displays a list of points in the correct order to create the image.

CreateArray ():

        private List<MDP_Point> CreateArray(List<MDP_Rect> lRect)
    {
        List<MDP_Point> p = new List<MDP_Point>();

        int size = (int)Math.Sqrt(lRect.Count);

        int i = 0;
        foreach (MDP_Rect r in lRect)
        {
            p.Add(new MDP_Point((int)r.C1.x, (int)r.C1.y, (int)r.C1.z));

            if (i > 0 && i % size == size - 1)
            {
                p.Add(new MDP_Point((int)r.C2.x, (int)r.C2.y, (int)r.C2.z));
            }

            i++;
        }

        for (int a = 0; a < size; a++)
        {
            p.Add(new MDP_Point((int)lRect[(size * size - size) + a].C4.x,
                (int)lRect[(size * size - size) + a].C4.y,
                (int)lRect[(size * size - size) + a].C4.z));

            if (a > 0 && a % size == size - 1)
            {
                p.Add(new MDP_Point((int)lRect[(size * size - size) + a].C3.x,
                    (int)lRect[(size * size - size) + a].C3.y,
                    (int)lRect[(size * size - size) + a].C3.z));
            }
        }

        return p;
    }

This is a way to create an image:

        private void CreateImage(int size, List<MDP_Point> arr, double roughness)
    {
        Bitmap map = new Bitmap(size, size);

        int ver = 0;
        for (int i = 0; i < map.Height; i++)
        {
            for (int n = 0; n < map.Width; n++ )
            {
                int h = (int)arr[ver].z + 127;
                if (h < 0)
                {
                    h = 0;
                }
                else if (h > 255)
                {
                    h = 255 ;
                }
                Color c = Color.FromArgb(h, h, h);

                //map.SetPixel(n, i, c);
                map.SetPixel(i, n, c);
                ver++;
            }
        }

        Bitmap m = new Bitmap(map);
        bool saved = true;
        int num = 0;

        while (saved)
        {
            if (File.Exists("map_S" + size + "_R" + roughness + "_" + num + ".png"))
            {
                num++;
            }
            else
            {
                m.Save("map_S" + size + "_R" + roughness + "_" + num + ".png", System.Drawing.Imaging.ImageFormat.Png);
                saved = false;
            }
        }

        map.Dispose();
        m.Dispose();
    }

The fact that any value below 0 is set to 0, and any value above 255 is set to 255 is probably a big problem ... not sure what to do with it.

, : : 1024 : 0,5

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