Creating ridged perlin noise

Hi, I'm trying to figure out how I can create a ridged perlin noise function. If I unterstood correctly, you have to substract the abs value of perlin noise from 1 to create a ridged noise value. This is my code:

 int size = 1024;
 int mountainSeed = 0;
 float mountainScale = 42.7f;
 public float[,] createMountainMap(){
         float[,] data = new float[size, size];
         for(int x = 0;x < size;x++){
             for(int y = 0;y < size;y++){
                 float noise = 0.0f;
                 float gain = 1.0f;
                 for(int i = 0;i < mountainOctaves;i++){
                     noise += (1f - Mathf.Abs(Mathf.PerlinNoise(x * gain / mountainScale + mountainSeed, y * gain / mountainScale + mountainSeed)));
                     gain *= 2.0f;
                 }
                 data[x, y] = noise;
             }
         }
         return data;
     }

But the result isn't as expected:

I expected something like this image:

I don't know what I'm doing wrong or how to get the wanted result. How can I do it? Thankful for any help!