#53 '-keep chunkname' option

[freshlydog]

.. to use with '-strip all':

optipng -strip all -keep pHYs file.png
to keep DPI data

[freshlydog]

... or change strip syntax like:
-strip !pHYs
all except pHYs

-strip !pHYs!gAMA
all except pHYs and gAMA