Thank you Henning and Marco,

but both scripts trow the same error on windows and linux-armhf:

grph-downsample.lua:32: bad argument #2 to 'format' (number has no integer representation)

Hans' luacode seem not to change the resolution of the pictures at all.
It works, the size of the pictures get smaller but the resolution remains the same.

Greetings Lutz

Am 15. Februar 2019 08:25:35 MEZ schrieb Marco Patzer <lists@homerow.info>:
On Fri, 15 Feb 2019 07:56:31 +0100
Lutz Haseloff <lutz.haseloff@toppkieker.info> wrote:

First i tried the grph-downsample.lua script.
Unfortunately i get an error message
grph-downsample.lua:31: bad argument #2 to 'format' (number has no
integer representation) See attached log file.

I remember that error. The script worked up to a particular context
version. I believe a Lua upgrade broke it. The version attached
should work.

Marco