Cfrgtkky

Consider this example:

documentclass{report}

usepackage{subfig}

usepackage{graphicx}

usepackage{lipsum}

begin{document}

begin{figure}[htp]

  centering

  deftwidth{0.45}

  subfloat[{lipsum[1]}]{

    includegraphics[width=twidthtextwidth]{example-image-a}

  }

  subfloat[{lipsum[2]}]{

    includegraphics[width=twidthtextwidth]{example-image-b}

  }

end{figure}

end{document}

In the output:

the spacing between the subcaptions blurs. I could manually fix by inserting hspace{0.2cm} after the first subfloat.

Is there a better, automatic way of inserting a spacing between the subfloats?

There are two problems with your code.

Each image has a normal interword space on either side, generated by the endlines inside subfloat and you should watch out for them.

Second, the working of subfloat ends with ignorespaces, so the endline after the closing brace of the first subfloat doesn't generate space between the two parts.

You can insert instead hfill so the two images will be pushed to the margins leaving 0.1textwidth space in the middle. Or you can use hfil and you will have three equal spaces, left, center and right.

With the help of showframe we can see the boundaries of the text block. Choose a style and stick to it.

documentclass{report}

usepackage{subfig}

usepackage{graphicx,showframe}

usepackage{lipsum}

begin{document}



begin{figure}[htp]

  centering

  deftwidth{0.45}

  subfloat[{lipsum[1][1-3]}]{%

    includegraphics[width=twidthtextwidth]{example-image-a}%

  }hfil

  subfloat[{lipsum[2][1-3]}]{%

    includegraphics[width=twidthtextwidth]{example-image-b}%

  }

end{figure}



begin{figure}[htp]

  centering

  deftwidth{0.45}

  subfloat[{lipsum[1][1-3]}]{%

    includegraphics[width=twidthtextwidth]{example-image-a}%

  }hfill

  subfloat[{lipsum[2][1-3]}]{%

    includegraphics[width=twidthtextwidth]{example-image-b}%

  }

end{figure}



end{document}

Don't forget the % bits in the places I added them.

There is a third possibility: setting some margin for the subcaptions.

documentclass{report}

usepackage{subfig}

usepackage{graphicx,showframe}

usepackage{lipsum}



captionsetup[subfloat]{margin=1em}



begin{document}



begin{figure}[htp]

  centering

  deftwidth{0.45}

  subfloat[{lipsum[1][1-3]}]{%

    includegraphics[width=twidthtextwidth]{example-image-a}%

  }

  subfloat[{lipsum[2][1-3]}]{%

    includegraphics[width=twidthtextwidth]{example-image-b}%

  }

end{figure}



end{document}

A solution with floatrow:

documentclass{report}

usepackage[showframe]{geometry}

usepackage{subfig}

usepackage{floatrow}

usepackage{graphicx}

usepackage{lipsum}



DeclareFloatSeparators{Fil}{hspace*{0.1textwidth}}



begin{document}



begin{figure}[htp]

floatsetup[figure]{floatrowsep=Fil, objectset=centering, margins=centering}%

  centering

begin{subfloatrow}

ffigbox[FBwidth]{includegraphics[width=0.45textwidth]{example-image-a}}{caption{lipsum[1]}}

ffigbox[FBwidth]{includegraphics[width=0.45textwidth]{example-image-b}}{caption{lipsum[2]}}

end{subfloatrow}

end{figure}



end{document}

With the method you used, the caption text will be misaligned with the figure. For your particular case, it is not noticeable, but for other cases, it could be.

You can use hfill which will 'horizontally' fill a space between the two figures in such a way that each one will be on one end of the text width

A more advanced way can be useful if you have multiple figures. Use hspace{stretch{<factor>}} to specify a share for each given spacing. For instance, if you use hspace{stretch{2}} and hspace{stretch{5}}, then the second spacing will be 5/2 = 2.5 times larger than the first one like this

documentclass{report}

usepackage{subfig}

usepackage{graphicx}

usepackage{float}

usepackage{lipsum}

usepackage[showframe=true]{geometry}







begin{document}



begin{figure}[htp]



    centering



    deftwidth{0.45}

    subfloat[{lipsum[1]}]{

    includegraphics[width=twidthtextwidth]{example-image-a}

                        }

    %

    hfill

    subfloat[{lipsum[2]}]{

        includegraphics[width=twidthtextwidth]{example-image-b}

                        }

end{figure}



begin{figure}



    centering



    subfloat[{lipsum[1]}]{

        includegraphics[width=0.25textwidth]{example-image-a}

                        }

    %

    hspace{stretch{2}}

    subfloat[{lipsum[2]}]{

        includegraphics[width=0.25textwidth]{example-image-b}

                              }

    %

    hspace{stretch{5}}

    subfloat[{lipsum[2]}]{

        includegraphics[width=0.25textwidth]{example-image-c}

                        }

end{figure}



end{document}