title: Get luminance from iOS camera
body: <p>I want get luminance from camera, I've checked solution (count average luminance)
  <a href="http://b2cloud.com.au/tutorial/obtaining-luminosity-from-an-ios-camera" rel="nofollow">obtaining-luminosity-from-an-ios-camera</a></p>
  
  <p>but camera automatically set exposure, so if it turn camera to the source of light (e.g. bulb) then in first time luminance is very high, but after a while this value is lowe, because exposure settings was changed. I've tested with locking exposure but this is not good solution, because if exposure was locked when image from camera is dark, then little source of light is counted as very high value. Is any way to get absolute value of luminance ?
  I've checked application Light detector and this application works well, exposure is changed, but value of luminance is stable.</p>
  
  <p>Regards Adam</p>