+A histogram is almost always applied before motion tracking to clamp out noise in the darker pixels. Either save the motion vectors in a tracking pass and disable the histogram for the action pass or apply the histogram just to the master layer. Finally, you can use the histogram to increase contrast.
+
+\subsubsection*{Possible sources of errors}
+\label{ssub:possible_sources_errors}
+
+\begin{description}
+ \item[Search radius too small:] the traced object moves too fast with respect to the size of the search box set.
+ \item[Search radius too large:] The search box is so large that it also collects other similar items in the frame.
+ \item[Occlusions:] the traced object is temporarily hidden by some other element. \textit{Offset tracking} or splitting of the video into several homogeneous clips is required.
+ \item[Focus change:] you may get errors if the object changes its focus. The video must be divided into several homogeneous clips.
+ \item[Motion Blur:] blurs the object making the calculation of the motion vector less precise. Very little can be done.
+ \item[Shape change:] you can use \textit{Track previous frame} or the subdivision of the video in more homogeneous clips.
+ \item[Lighting change:] Contrast change can produce errors. \textit{Track previous frame} or color correction can be used to return to the initial illumination.
+\end{description}