

The Sad Story of PNG Gamma “Correction” - kinetik
http://hsivonen.iki.fi/png-gamma/

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blasdel
DPI metadata in PNGs is even worse than Gamma 'correction', since it serves no
purpose whatsoever.

DPI is only remotely meaningful when dealing with something that was once
printed (set it on scans so you know the original size), or soon will be (know
how big to print it). In practice there's so much completely bogus DPI
metadata out there that little software will respect it on output. For further
brokenness, DPI is cleverly stored as a Rational in most formats, but nearly
all metadata libraries expose it only as a float!

There's a ton of software out there written by some twit that read on the
internet somewhere that "Macs are 72dpi, everything else is 96dpi", and then
goes on to set that in every file it outputs depending on the platform.
Inkscape does this and it is incredibly obnoxious.

~~~
sesqu
And shouldn't it be PPI? DPI is a property of printers and CRTs, not scanners
or prescaled images.

edit: oh! and speaking of tagging digital formats with physical scale
information, it took me ages to understand why text processors measure font
size in points, which here refers to absolute size when printing, but don't
display the text at that size on the screen (which is where it matters more,
imho). maybe things are different now, but the only thing I remember from the
adventure was that I decided never to touch anything typographic.

