title: Perlin Noise and FBM generated image too grey
body: <p>I've been working on generating noise using Perlin Noise and FBM as I understand it and I've seem to come into a bit of a problem. </p>
  
  <p>The images I am generating seem to be too grey when they're meant to be greyscale but I see no variations of whites or blacks. </p>
  
  <p>An example of this image is (This is generated using 8 octaves)</p>
  
  <p><img src="https://i.stack.imgur.com/HsXNg.png" alt="Perlin Noise example"></p>
  
  <p>An image of what I am expecting to produce;</p>
  
  <p><img src="https://i.stack.imgur.com/2XVXD.png" alt="enter image description here"></p>
  
  <p>I am generating the noise as follows;</p>
  
  <pre><code>float result = 0.0f;
    float amp = 1.0f;
    float frequency = 2.0f;
  
    float maxAmplitude = 0.0f;
    int i = _octaves;
    while (i--){
    result += noise(x * frequency, y * frequency, z * frequency) * amp;
    frequency *= 2.0f;
    maxAmplitude += amp;
    amp *= 0.5f;
    }
    return result / maxAmplitude;
    }
  </code></pre>
  
  <p>where the noise function is Ken Perlin's Improved Noise function found here; <a href="http://mrl.nyu.edu/~perlin/noise/" rel="nofollow noreferrer">http://mrl.nyu.edu/~perlin/noise/</a> and I am using the default permutation table.</p>
  
  <p>Then as I generate the images, I do the following to get a greyscale image;</p>
  
  <pre><code>ppm_image.pixel_colour[kk] = 255.0f  * noise;
  </code></pre>
  
  <p>I was just wondering how I can generate the same heightmap with a wider variation in the colours (more whites and blacks rather than just narrow greys).</p>