Expand README.md

README.md

 1997.](http://www.pauldebevec.com/Research/HDR/debevec-siggraph97.pdf))
 
 
-There are several interfaces available.
+There are two interfaces available.
 
 ## Command Line Interface
 
 $ ./haader <image1.jpg> <image2.jpg> <image3.jpg> ...
 ```
 
+This will output several files if the reconstruction of the sensor response
+function was successful:
+
+* `expose_*.ppm`: Simulated exposures of the scene with different exposure
+  times
+* `log_image.ppm`: A logarithmic mapping of the HDR-image
+* `rf.csv`: The sensor response function as a simple table with two columns. The
+  first column contains the logarithmic luminance relative to the central
+  response (128). The second row contains the response value (0-255).
+* `irf.csv`: The inverse sensor response function as a simple table with two
+  columns.
+
 ## GTK Interface
 
 Needs GTK+3.0 and the corresponding development packages:
 $ cd gui_gtk
 $ make run
 ```
+
+Click `Select files` to open multiple images of the same scene and start the
+reconstruction. Alternatively, it is possible to specify the images and exposure
+times with a simple two-column CSV file:
+```csv
+</absolute/image/path1.png>,<exposure time in seconds>
+</absolute/image/path2.png>,<exposure time in seconds>
+...
+```