How to format table with images?

How to format this table? I do not know how to handle the images...

\begin{table}[h]
\centering
\begin{tabular}{llll}
\hline
\multicolumn{1}{l}{Name} & \multicolumn{1}{l}{Function} & \multicolumn{1}{l}{Derivative} & \multicolumn{1}{l}{Figure} \\ \hline
Sigmoid & $\sigma(x)=\frac{1}{1+e^{-x}}$ & $f'(x)=f(x)(1-f(x))^2$  &  \includegraphics[width=0.2\textwidth]{sigmoid}\\
tanh & $\sigma(x)=\frac{e^x-e^{-x}}{e^z+e^{-z}}$ & $f'(x)=1-f(x)^2$   &  \includegraphics[width=0.2\textwidth]{tanh} \\
ReLU & $f(x) \left\{\begin{matrix} 0 & if \; x<0 \\ x & if \;x \geq 0. \end{matrix}\right.$ & $f(x) \left\{\begin{matrix} 0 & if \; x<0 \\ x & if \;x \geq 0. \end{matrix}\right.$ & \includegraphics[width=0.2\textwidth]{relu} \\
Softmax & $f(x)=\frac{e^x}{\sum_i e^x}$ & $f'(x)=\frac{e^x}{\sum_i e^x} - \frac{(e^x)^2}{(\sum_i e^x)^2}$ &
\end{tabular}
\caption{Non-linear activation functions.}
\label{tab:activationfct}
\end{table}


The current output looks like this: These are the images in the table:

[ • there i tons of similar questions ... you need to move image baseline to the center of images. see tex.stackexchange.com/questions/19080/…, or tex.stackexchange.com/questions/430760/… – Zarko May 11 '18 at 21:23
• Welcome to TeX.SX! Can you please expand the code snippet that you have posted to a full minimal working example. It is much easier to help you if we can start with some compilable code that illustrates your problem. A MWE should start with a \documentclass command, include any necessary packages and be as small as possible to demonstrate your problem. At the moment we cannot reproduce your problem from the code that you have given us which makes it harder to help you. – Andrew May 11 '18 at 21:28

\documentclass{scrreprt}
\usepackage[export, demo]{adjustbox}    % in real document delete option "demo"
% for manipulating boxes, among them here is used "valign"
\usepackage{cellspace,                  % for adding vertical space around cells' contents
tabularx}
\setlength\cellspacetoplimit{4pt}
\setlength\cellspacebottomlimit{4pt}
\usepackage{ragged2e}

\begin{document}

\begin{table}[htb]
\centering
\setkeys{Gin}{width=0.2\textwidth}   % with real images should be sufficient defined only image width
\begin{tabular}{l *{2}{>{$\displaystyle}Sl<{$}} Sl} % changed
\hline
{Name}      & {Function}
& {Derivative}
& {Figure}                      \\
\hline
Sigmoid & \sigma(x)=\frac{1}{1+e^{-x}}
& f'(x)=f(x)(1-f(x))^2
&  \includegraphics[valign=c]{sigmoid}        \\
tanh    & \sigma(x)=\frac{e^x-e^{-x}}{e^z+e^{-z}}
& f'(x)=1-f(x)^2
&  \includegraphics[valign=c]{tanh}           \\
ReLU    & f(x) \begin{cases} % changed and corrected
0 & if \; x<0 \\
x &  if \;x \geq 0.
\end{cases}
& f(x) \begin{cases} % changed and corrected
0 & if \; x<0 \\
x &  if \;x \geq 0.
\end{cases}
& \includegraphics[valign=c]{relu}            \\
Softmax & f(x)=\frac{e^x}{\sum_i e^x}
& f'(x)=\frac{e^x}{\sum_i e^x} - \frac{(e^x)^2}{(\sum_i e^x)^2}
&                                   \\
\hline
\end{tabular}
\caption{Non-linear activation functions.}
\label{tab:activationfct}
\end{table}
\end{document} I'd like to argue that it is more fun to draw these functions with TikZ. You'll then have full control over the vertical placement with baseline, as I illustrate below, and if you decide to add axis labels etc. they'll have the same fonts and appearance. And I used the opportunity to fix a few typos and to use cases where appropriate. Note also that you can use scale to make the plots larger. \documentclass{article}
\usepackage{tikz}
\usepackage{amsmath}
\begin{document}
\begin{table}[h]
\centering
\begin{tabular}{llll}
\hline
\multicolumn{1}{l}{Name} & \multicolumn{1}{l}{Function} & \multicolumn{1}{l}{Derivative} & \multicolumn{1}{l}{Figure} \\
\hline
Sigmoid & $\sigma(x)=\frac{1}{1+e^{-x}}$ & $f'(x)=f(x)(1-f(x))^2$  &
\begin{tikzpicture}[baseline={(0,0.2)}]
\draw (-1,0) -- (1,0);
\draw (0,0) -- (0,1);
\draw plot[domain=-1:1,variable=\x] ({\x},{1/(1+exp(-4*\x))});
\end{tikzpicture}\\
\\
tanh & $\sigma(x)=\frac{e^x-e^{-x}}{e^z+e^{-z}}$ & $f'(x)=1-f(x)^2$
&  \begin{tikzpicture}[baseline={(0,0)}]
\draw (-1,0) -- (1,0);
\draw (0,-1) -- (0,1);
\draw plot[domain=-1:1,variable=\x] ({\x},{tanh(4*\x)});
\end{tikzpicture} \\
ReLU & $f(x) =\begin{cases} 0 & ~\text{if}~ x<0 \\ x & ~\text{if}~x \geq 0. \end{cases}$ & $f'(x)=\begin{cases} 0 & ~\text{if}~ x<0 \\ x & ~\text{if}~1 \geq 0. \end{cases}$ &
\begin{tikzpicture}[baseline={(0,0.5)}]
\draw (-1,0) -- (1,0);
\draw (0,0) -- (0,1);
\draw plot[domain=-1:1,variable=\x] ({\x},{ifthenelse(\x<0,0,\x)});
\end{tikzpicture}\\
Softmax & $f(x)=\frac{e^x}{\sum_i e^x}$ & $f'(x)=\frac{e^x}{\sum_i e^x} - \frac{(e^x)^2}{(\sum_i e^x)^2}$ &
\end{tabular}
\caption{Non-linear activation functions.}
\label{tab:activationfct}
\end{table}
\end{document}