anchor.diff:  , enableJPEG ? true, libjpeg
   , enablePNG ? true, libpng
   , enableTIFF ? true, libtiff
  -, enableEXR ? true, openexr, ilmbase
  +, enableEXR ? (!stdenv.isDarwin), openexr, ilmbase
   , enableJPEG2K ? true, jasper
   , enableFfmpeg ? false, ffmpeg
   , enableGStreamer ? false, gst_all
   , enableEigen ? false, eigen
  +, darwin
   }:
   
   let
  
positive.code: 
    passthru = lib.optionalAttrs enablePython { pythonPath = []; };
  
    meta = {
      description = "Open Computer Vision Library with more than 500 algorithms";
      homepage = http://opencv.org/;
      license = stdenv.lib.licenses.bsd3;
      maintainers = with stdenv.lib.maintainers; [viric flosse];
      platforms = with stdenv.lib.platforms; linux;
    };
  }
  
negative.code:     ++ lib.optional enableFfmpeg ffmpeg
      ++ lib.optionals enableGStreamer (with gst_all; [ gstreamer gst-plugins-base ])
      ++ lib.optional enableEigen eigen
      ++ lib.optionals stdenv.isDarwin (with darwin.apple_sdk.frameworks; [ Cocoa QTKit ])
      ;
  
    propagatedBuildInputs = lib.optional enablePython pythonPackages.numpy;
  