title: Measure luminance of the light from a camera
body: <p>Can I detect the intensity or the amount of light in a picture ? </p>
  
  <p>For example, </p>
  
  <blockquote>
    <p>I have some pictures which are captured at morning ,afternoon and the
    time before the sunset and i want to know the amount of the light.</p>
  </blockquote>
  
  <p>I just need an idea of how to do it. Also I have an access to the camera gain, exposure and other parameters.
  The camera which I am using is the ZED Camera.
  I understand the formula which convert from RGB space to luminance space as stated <a href="https://en.wikipedia.org/wiki/Relative_luminance" rel="nofollow noreferrer">here</a>. But I'm not sure if it's an efficient solution or not.</p>