Graphic output: "eps"

Most of the scientific journals asks for figures in "eps" (encapsuled postscript) to publish a paper. The option in gnuplot is:

set term postscript eps enhanced options

where options can be color, solid and/or dashed (only in the newest versions). The font and size used in all labels can be controlled here using: font "FONT, size" .

Using ampersand (&) in labels

To use the ampersand symbol (&) in labels, write \&.

Labels in two lines

If the axis label is too long and you need to split it in two lines, you should write \n in the breaking point.

References in Latex: entry types

When creating the bibliography file of your Latex document (whatever.bib), you can reference several kinds of document. Here you will find a description of them.

Colours and formats

It is a difficult task to control colours in GNUPLOT. Each type of output file (png, ps, eps, etc.) has its own colour definition. In order to know which colour belongs to each line style, an easy method is to type test after selecting the output format.

Example:

• set term png
• set output 'test_colour.png'
• test

Then, the file test_colour.png will look like:

This can be done for all output formats (png, ps, eps...).

Palettes

There are several methods for defining a colour palette in GNUPLOT. Here one of them is presented and explained in a simple way. If you want to go deep into this topic, you will have to look for more extensive references (some of them listed as useful links).

First of all, we need to define the number of colours that our palette will contain using this command:

• set palette maxcolors <number>

Then, what we have to do is to specify the colour of each part of the palette using the following command:

• set palette defined (<position1> "<colour1>", <position2> "<colour2>", ...)

Example (A):

• set palette maxcolors 100
• set palette defined (0 "red", 99 "blue")

These lines will create a palette of 100 colours from red (position 0) to blue (position 99). Between both positions, GNUPLOT will perform a gradation.

We can specify as much colours as we want, for example (B):

• set palette maxcolors 1000
• set palette defined (\
• 0 "red", \
• 249 "yellow", \
• 749 "green", \ 
• 999 "blue")

As a final example, if we want to ascribe a specific colour to the middle value of the palette (in order, for instance, to separate positive and negative values), we will have to write something like this (C):

• set palette maxcolors 4001
• set palette defined (\
• 0 "red", \
• 1000 "orange", \
• 1600 "dark-yellow", \
• 1999 "yellow", \
• 2000 "grey", \
• 2001 "green", \
• 2400 "dark-green", \
• 3000 "cyan", \
• 4000 "blue")

Note that only the value in the middle corresponds to gray. The previous and the following values (with a precision that depends on the number of colours selected) will correspond to yellow and green respectively.

Caution: The palettes presented here work in eps output files. If you work with other types of file, you may have some troubles with the colours.

Converting eps to png

Although this post is not dedicated to GNUPLOT, it can be useful for those working with image files. If you have tried to use the Linux command convert with eps files, you will have found that it usually ends in a dramatic reduction in the resolution of your figures, i.e. the next command does not work properly:

• convert whatever.eps whatever.png

This is because the eps files, as they are vectorial, do not have a concrete resolution and the one used by default in the conversion is very rude. Nevertheless, adding the option density you can specify the "density" of the resulting png image in points per inch (I do not really understand what represents; if you do, please leave a comment). The syntaxis is, then:

• convert -density <density> whatever.eps whatever.png

Example:

• convert -density 200 whatever.eps whatever.png