\section{Color calibration}

All our detection algorithms require color calibration, and when the lighting
conditions on the field change, colors might have to be newly calibrated. For
us this meant that a tool was necessary, that could simplify this process as
far as possible. For this reason, we implemented a small OpenCV-based program,
that we called \verb|Colorpicker|. This program can access various video
sources, as well as use still images for calibration. The main interface
contains the sliders for adjusting the HSV interval, as well as the video area,
demonstrating the resulting binary mask. The colors can be calibrated for three
targets: ball, goal and field; and the quality of detection, depending on the
chosen target is demonstrated. When the program is closed, the calibration
values are automatically saved to the settings file \verb|nao_defaults.json|.
The interface of the Colorpicker is demonstrated in the figure \ref{p figure
  colorpicker}.

\begin{figure}[ht]
  \includegraphics[width=\textwidth]{\fig colorpicker}
  \caption{Interface of the Colorpicker}
  \label{p figure colorpicker}
\end{figure}
