This trick add the legend to a map in a specific positon

composite -gravity southeast -geometry +10+10 leyenda.png mapa_sin.png mapa_con.png

Adding margins for a A4 pdf

convert montado000.jpg -bordercolor white -border 70 -page A4 salida.pdf

Take into account that the order of the parameters is important and -bordercolor should appear before of -border or everything will be grey.

Convert can be used to crop images

#!/bin/bash

mkdir cropped;
for i in `ls *.png`;
do convert -verbose -crop 1176x880+502+144 $i ./cropped/$i;
done;
echo FIN;

1176x880

is the final size of the image

+502+144

is the upper left corner where the cropping starts

You can get an histogram of the colours used in an image

convert RASTER2.jpg -format %c histogram:info:-

format

will return caracteristic information

%c

will return also the comments from the command

histogram

for getting the histogram

info

for getting additional info

-

the output will be via cli, it ...

You can use identify to get information from an image

$ identify imagename.ext

For images resizing

#!/bin/bash

mkdir 640x480;
for i in `ls *.png`;
do convert -verbose -quality 65 -strip -resize 640x480 $i ./640x480/$i;
done;
echo FIN;

65

is the final quality (%)

640x480

is the final size. The image will be resized to meet one of the two dimensions but respecting ...

A trick for splitting an A3 in 4 A4

pdftk mapA3.pdf burst output pgmapa3%d.pdf
convert -density 600x600 -limit memory 32 pgmapa31.pdf pgmapa31.jpg
convert -verbose -crop 3508x4960 pgmapa31.jpg pgmapa31_%02d.jpg
convert -page A4 -resize '2480x3508^>' -extent 2620x3706 pgmapa31_0* pgmapa4.pdf
gs -sDEVICE=pdfwrite -dNOPAUSE ...

You can transform several JPG into one PDF

convert * .jpg journal.pdf

You can conver a GIF into a series of PNGs

convert * .gif -transparent white name-%d.png

• it will convert all the gifs
• asigns white as the transparency color
• the output files will be named like name-01.png ...