[Gimp-developer] How "Print Size" can save pixel density into e.g. png file?

[Andrey Utkin <andrey krieger utkin gmail com>]

I use the feature of changing image print density (in dpi) in GIMP to
get predictable size of printed image. Now i want to do this
programmaticaly. I tried to grep the code, but it would take me long
time to figure this out by myself. Could please somebody describe in
which way png file carries pixel density information, or point to the
place in code that actually does this information saving to file.
Thanks in advance.
--
Andrey Utkin