Am 02.04.2017 um 10:27 schrieb Thorsten Froehlich:
> clipka <ano### [at] anonymousorg> wrote:
>> Am 02.04.2017 um 06:08 schrieb Thorsten Froehlich:
>>> "Kenneth" <kdw### [at] gmailcom> wrote:
>>>> That's an interesting question. Which I don't know the answer to :-P
>>>>
>>>> But I work around it in Photoshop: If I need to change an image's DPI, for
>>>> printing or whatever, I just go into IMAGE/IMAGE SIZE and fiddle with the
>>>> resolution there, then re-save it. (If the image is PNG, that's a lossless
>>>> re-save, quality-wise; but if JPEG, then a 2nd compression quality-loss is
>>>> incurred... which I usually live with.)
>>>>
>>>> That said, it would be nice to be able to specify a DPI setting in POV-Ray.
>>>
>>> You do realise that it is pointless to add some arbitrary number to an image
>>> file? Apart from the fact that misc image formats, JPEG included, don't have a
>>> standard DPI flag? - It isn't surprising either, as there is absolutely no use
>>> for it ... I might also add that this discussion comes up every few years. So
>>> maybe search the newsgroups for the many answers in that regard.
>>
>> If the image is intended to be printed, there /is/ use for it. You might
>> argue that it's not a strong enough case, but just because you don't see
>> a use case doesn't mean there is none at all.
> 
> At least I am in good company:
>
http://news.povray.org/povray.general/thread/%3CpdbNOSPAM-66C5AC.10595417092005%40news.povray.org%3E/

Quiz:

Q1: How many people involved in that thread had any actual experience in
the printing business?
A1: Only one, as it seems.

Q2: What was the opinion of that person?
A2: Not yours, as it seems.


In a nutshell, what that person wrote is:

If a person from the printing business asks you for an image with a
physical size of X mm by Y mm and a pixel pitch of P pixels per inch,
they _not only_ want the image to be (X,Y)*P/25.4 pixels in size, but
_also_ would like the image header to explicitly say "intended to be
printed at a pitch of P pixels per inch".

Whether this semi-requirement by the printing industry is deemed
unnecessary and confusing by most artists is irrelevant: Apparently it's
a _fact_ of the printing industry (or at leat it was, a dozen years
ago), and therefore /some/ people creating images may want to cater to that.

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