added doxygen comments

Author: stfuchs

include/libfreenect2/frame_listener.hpp

@@ -54,9 +54,9 @@ class LIBFREENECT2_API Frame
   size_t height;          ///< Number of lines in the frame.
   size_t bytes_per_pixel; ///< Number of bytes in a pixel.
   unsigned char* data;    ///< Data of the frame (aligned).
-  float exposure;
-  float gain;
-  float gamma;
+  float exposure;         ///< Get the exposure time set by the color camera.
+  float gain;             ///< Get the gain set by the color camera.
+  float gamma;            ///< Get the gamma level set by the color camera.
 
   Frame(size_t width, size_t height, size_t bytes_per_pixel) :
     width(width),