In message <1865905.upRAyxzUy2@liber> on Thu, 13 Feb 2014 20:43:19 +0100,
Tobias Ellinghaus <[email protected]> said:
houz> Am Donnerstag, 13. Februar 2014, 20:13:23 schrieb Pascal Obry:
houz> > Francisco,
houz> >
houz> > > Photographic contests and photo exhibitions in my country (Brazil)
houz> > > usually require submission of photos with a certain DPI value, usually
houz> > > 300. I know that DPI is not a very relevant information, but it seems
houz> > > easier to set a DPI number than to try to convince people that they
houz> > > shouldn't care about it. Is there a way to do so in Darktable? If not,
houz> > > are there plans to add that as a feature?
houz> >
houz> > DPI has no meaning if not accompanied with a specific paper size. DPI
houz> > for a numeric image to display on screen has no meaning. In other word,
houz> > DPI (Dot per Inch) have a meaning where there is inches :)
houz>
houz> And to make matters even worse: in this case it's not DPI but PPI since
we are
houz> talking about pixels and not printed dots.
houz>
houz> That being said: no, there are no plans whatsoever to allow setting these
houz> values from within darktable. I guess that you can use exiv2 or exiftool
to
houz> set the corresponding value afterwards.
The resolution information isn't stored in the EXIF (APP1) data, but
in the JFIF (APP0) data, and is therefore not reachable with exiv2 or
exiftool (although I've read somewhere that one can set the resolution
in EXIT as well, but that has me wonder what takes priority, JFIF or
EXIF?).
I totally agree that on screen, DPI has no meaning whatsoever.
However, Francisco's problem is with printing, where DPI counts. Many
image printing services has the option to ignore what is in the JFIF
data and set some arbitrary resolution that gives the desired printing
size or set a desired printing size and ignore DPI entirely. Not all
to that though, it would seem.
Anyway, instead of joining in with the rebutal, here's a command line
using ImageMagick that can help you change the resolution:
convert -units PixelsPerInch input.jpg -density 300 output.jpg
(ref:
http://superuser.com/questions/479197/i-want-to-change-dpi-with-imagemagick-without-changing-the-actual-byte-size-of-t)
Is there a way to avoid setting the resolution in the JFIF data? If
there is (with Units=0 perhaps?), wouldn't it be a good idea to have
darktable avoid it, instead of hardcoding 72x72?
Cheers,
Richard
--
Richard Levitte [email protected]
http://richard.levitte.org/
"Life is a tremendous celebration - and I'm invited!"
-- from a friend's blog, translated from Swedish
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