title: Sigma Formula for image C++
body: <p>I'm trying to make a certain tone curve which is known as Sigma. </p>
  
  <p>Unfortunately, I do not know the formula for Sigma, i somehow cant find the formula for it.
  Can anyone help me? Thanks  </p>
  
  <p>Based on a graph x and y axis and this website : 3rd link:   <a href="http://www.mediachance.com/pseam/help/curves.html" rel="nofollow">http://www.mediachance.com/pseam/help/curves.html</a></p>
  
  <p>Using Windows Visual Studio 2010  </p>
  
  <pre><code>for(int y=0; y&lt;bih.biHeight; y++)
              {                       
                  for(int x=0; x&lt;bih.biWidth; x++)
                  {   
                  SetPixel(hdc, ((double)x/(double)(x+20))*bih.biWidth, bih.biHeight-x, red);
                  }
  </code></pre>