How can I fix the caption position in figures? [duplicate]

Question

Running the following code in Kile, I obtain a caption position of the first image that is different from the second one since the text inserted in the second picture is less than the first one. This is unaesthetic.

\begin{figure}[!ht]
\includegraphics[scale=0.80]{examplesignalchangesfrequency.png}
\caption{Example of time domain oscillating signal which contains four frequencies at four different times.}
\label{exampletimedomainsignal}
\end{figure}

Fig. \ref{exampleFFTtimedomainsignal} is the corresponding frequency spectrum.
\begin{figure}[!ht]
\includegraphics[scale=0.80]{exampleFFTsignalchangesfrequency.png}
\caption{Example of FFT applied to the signal in figure \ref{exampletimedomainsignal}.}
\label{exampleFFTtimedomainsignal}
\end{figure}

This is what I mean:

How can I fix this problem in a way that, for example, captions are all in the same position that is, in this case, the position of the first image ? So they are all starting on the "extreme left position" whatever is the length of text to be inserted in ?

Answer 1

By loading the package caption it is possible to configure the format of all document captions. For example

\documentclass[12pt,a4paper]{article}
\usepackage{graphicx}

\usepackage{caption} % added <<<<<<<    
\captionsetup[figure]{hangindent=0pt, singlelinecheck=false}% added <<<<<<<

\begin{document}
    
\begin{figure}[!ht]
    \includegraphics[scale=0.80]{example-image-a}
    \caption{Example of time domain oscillating signal which contains four frequencies at four different times.}
    \label{exampletimedomainsignal}
\end{figure}

Fig. \ref{exampleFFTtimedomainsignal} is the corresponding frequency spectrum.
\begin{figure}[!ht]
    \includegraphics[scale=0.80]{example-image-b}
    \caption{Example of FFT applied to the signal in figure~\ref{exampletimedomainsignal}.}
    \label{exampleFFTtimedomainsignal}
\end{figure}    
    
\end{document}

The standard LATEX document classes (article, report, and book) automatically center a caption if it fits in one single line.

singlelinecheck=false switches this extra centering off.

Answer 2

This uses a minipage to match both the left and right edges of the caption to the image.

\documentclass{article}
\usepackage{pgfplots}
\usepackage{showframe}% alignment tool

\begin{document}

\begin{figure}[!ht]
\sbox0{\includegraphics[scale=0.80]{example-image}}% measure width
\centering
\begin{minipage}{\wd0}
\usebox0
\caption{Example of time domain oscillating signal which contains four frequencies at four different times.}
\label{exampletimedomainsignal}
\end{minipage}
\end{figure}

\end{document}