Q:

How to remove undesired lines in table

I want to remove the red marked line in the below picture, does anyone know how to do it? 
The Latex script I use is:
\begin{tabular}{|c|c||c|c|c|}\hline
\multicolumn{2}{|c||}{\backslashbox{Challenges~}{Input~~}}
& 2D & 3D & 2.5D \\\hline \hline
\multirow{4}{*}{Changes}
&viewpoint & 1 & 2 & 3\\\hline
&illumination & 1 & 2 & 3\\\hline
&scale & 1 & 2 & 3\\\hline
&deformation & 1 & 2 & 3\\\hline

\multirow{2}{*}{\specialcell{Content \\ Changes}}
&occlusion & 1 & 2 & 3\\\hline
&\specialcell{background \\ cluster} & 1 & 2 & 3\\\hline
\end{tabular}

A:

Tha table could be improved using hhline: it helps double lines intersect nicely with other (single or double) lines.  I also used the makecell package that is designed to allow linebreaks inside tabular cells (and also common formatting of cells contents):
\documentclass{scrartcl}
\usepackage[utf8]{inputenc}
\usepackage{multirow}
\usepackage{hhline}
\usepackage{colortbl}
\usepackage{diagbox} 
\usepackage{makecell} 
\setlength\doublerulesep{3pt}

\begin{document}

\begin{tabular}{|c|c||c|c|c|}
\hhline{--||---}
\multicolumn{2}{|c||}{\backslashbox{Challenges~}{Input~~}}
& 2D & 3D & 2.5D \\
\hhline{==::===}
\multirow{4}{*}{Changes}
&viewpoint & 1 & 2 & 3\\
\hhline{~-||---}
&illumination & 1 & 2 & 3\\
\hhline{~-||---}
&scale & 1 & 2 & 3\\
\hhline{~-||---}
&deformation & 1 & 2 & 3\\
\hhline{--||---}
\multirowcell{3}{Content \\ Changes}
&occlusion & 1 & 2 & 3\\
\hhline{~-||---}
&\makecell{background \\ cluster} & 1 & 2 & 3\\
\hhline{--||---}
\end{tabular}

\end{document} 

A:

Use \cline{2-5} instead of \hline.