If you’re using ConTeXt for complex layout tasks, you need to calculate with image sizes. Often it makes sense to use Lua functions.
'''Beware''', TeX calculates internally in "scaled points" (sp), 1 sp = 1/65536 pt.
== Measures in pure ConTeXt ==
Beware, You can get at a picture’s dimensions with one line of TeX calculates internally in "scaled points" (sp), 1 sp = 1/65536 pt.code:
<texcode>
\setupexternalfigures[location=default]% necessary to find pictures in tree
\getfiguredimensions[hacker.jpg]
% defines a bunch of variables, e.g.:
\figurefullname
\figurefilepath
\figurefilename
\figurefiletype
</texcode>
This defines a bunch of variables:
<context>
\setupexternalfigures[location=default]
\NC \string\figurecolordepth \NC \figurecolordepth \NC\NR
\NC \string\figuredepth \NC \figuredepth \NC\NR
\TB
\NC \string\figurefullname \NC \figurefullname \NC\NR
\NC \string\noffigurepages \NC \noffigurepages ~pages \NC\NR
\TB
\NC \string\figurefullname \NC \tfxx\figurefullname \NC\NR\NC \string\figurefilepath \NC \tfxx\figurefilepath \NC\NR
\NC \string\figurefilename \NC \figurefilename \NC\NR
\NC \string\figurefiletype \NC \figurefiletype \NC\NR
\stoptabulate
</context>