More accurately:
$ pnginfo
Usage: pnginfo [-d] [-D] <filenames>
$ man pnginfo | grep -A1 SYNOPSIS
SYNOPSIS
pnginfo [-t] [-d] [-D] <filenames>
$ wget -q https://upload.wikimedia.org/wikipedia/commons/7/70/Example.png
https://upload.wikimedia.org/wikipedia/commons/7/70/Example.png
$ grep -ai pHYs Example.png
$ diff <(pnginfo Example.png) <(pnginfo -t Example.png) | grep -i Resolution
< Resolution: 32720, 2 (unit unknown)
> Resolution: 32612, 3 (unit unknown)
As you see, the built-in help of pnginfo doesn't mention the switch `-t`,
though it is implemented. Please mention this switch (or drop the support for
`-t` altogether if there are too many irreparable bugs associated with it).
Further, if there is no resolution information (the pHYs chunk) in the PNG
file, the resolution values output with `-t` differ from those output without
`-t`. This difference is meaningless; it'd be way more consequential not to
print those out-of-thin-air values at all if the resolution information is not
supplied in the input PNG file.
Gratefully!
