How to make ImageMagick to work with large files

Edit file /etc/ImageMagick-6/policy.xml and change lines

<policy domain="resource" name="area" value="256KP"/>
<policy domain="resource" name="disk" value="1GiB"/>

to read

<policy domain="resource" name="area" value="1GiB"/>
<policy domain="resource" name="disk" value="8GiB"/>