Extreme vertical spacing between lines

Question

How can I fine tune and reduce the vertical spacing of lines so characters from lines above and below are almost pixel-touching each other?

Example:

Answer 1

While \offinterlineskip\lineskip1pt might seem to give the desired result, lines will be irregularly spaced, because the distance between base lines will depend on the presence of ascenders (letters like "d") or descenders (letters like "y"). Moreover not all descenders and ascenders are equal.

Tight typesetting can be obtained by calling, say, \fontsize{10}{10} for ten point size. One can get cheaply such a setting by modifying the internal function \set@fontsize:

\documentclass[a4paper]{article}
\usepackage{etoolbox,lipsum}
\makeatletter
\patchcmd\set@fontsize{#3}{#2}{}{}
\makeatother

\begin{document}
\lipsum[1]
\large\lipsum[2]
\end{document}

Only etoolbox is required, of course. The patch will substitute the call of the third argument to \set@fontsize with the second; the third parameter is indeed the baselineskip and the second is the font size.

Note that this will affect all text at all sizes.

If only some paragraphs are to be "tightly typeset", then the environment tight defined as follows will do the job. The \addvspace commands have been used on the assumption that the code is used for examples. Variations on the theme are possible.

\makeatletter
\let\tightset@fontsize\set@fontsize
\patchcmd\tightset@fontsize{#3}{#2}{}{}
\newenvironment{tight}
  {\par\addvspace\topsep
   \let\set@fontsize\tightset@fontsize
   \fontsize{\f@size}{\f@baselineskip}\selectfont}
  {\par\addvspace\topsep}
\makeatother

If tight typesetting is needed for captions, it's simpler. With the caption package define the font used by saying something like

\DeclareCaptionFont{tight}{\fontsize{9}{9}\selectfont}
\captionsetup{font=tight,labelfont=bf}

Answer 2

\offinterlineskip is what you want.

\documentclass{article}
\usepackage{lipsum}

\begin{document}
\lipsum[1]
{% Use it LOCALLY
  \offinterlineskip
  \lipsum[2]
}
\lipsum[3]
\end{document}

You can add \lineskip=1pt after \offinterlineskip, if the lines are too close.

---

There're mainly three parameters about line spacing: \baselineskip, \lineskip and \lineskiplimit.

A good explanation of parameters about line spacing, is Chapter 12 (Glue) in TeXbook. Or you can see Chapter 15 (Baseline Distances) in TeX by Topic, it said:

• \baselineskip: The ‘ideal’ baseline distance between neighbouring boxes on a vertical list. Plain TeX default: 12pt.
• \lineskiplimit: Distance to be maintained between the bottom and top of neighbouring boxes on a vertical list. Plain TeX default: 0pt.
• \lineskip: Glue added if the distance between bottom and top of neighbouring boxes is less than \lineskiplimit. Plain TeX default: 1pt.

In LaTeX, we usually only change \baselineskip through \fontsize and \linespread, \lineskiplimit and \lineskip are not often used.

If you want to pry, in LaTeX kernel, \offinterlineskip is defined as:

\def\offinterlineskip{\baselineskip-\@m\p@
  \lineskip\z@ \lineskiplimit\maxdimen}

Answer 3

For stretching (or increasing) the line spacing, you can use the setspace package, or use \linespread{<factor>}. Using the latter, the following minimal example showcases some of the effects of changing the \linespread:

\documentclass{minimal}
\usepackage{lipsum}
\begin{document}
\lipsum[1]
\linespread{0.5}\selectfont
\lipsum[1]
\linespread{2}\selectfont
\lipsum[1]
\end{document}

The output looks like this:

Here is also a short discussion on this topic on the UK TeX FAQ.