> Date: Wed, 8 May 2013 10:34:29 +0300 > From: [email protected] > To: [email protected] > Subject: [Gimp-developer] How "Print Size" can save pixel density into e.g. > png file? > > I use the feature of changing image print density (in dpi) in GIMP to > get predictable size of printed image. Now i want to do this > programmaticaly. I tried to grep the code, but it would take me long > time to figure this out by myself. Could please somebody describe in > which way png file carries pixel density information, or point to the > place in code that actually does this information saving to file. > Thanks in advance. > -- > Andrey Utkin > _______________________________________________ > gimp-developer-list mailing list > [email protected] > https://mail.gnome.org/mailman/listinfo/gimp-developer-list
Sounds like you need to look at the PNG specs themselves, not necessarily GIMP's method of writing to them: http://www.libpng.org/pub/png/spec/1.2/PNG-Contents.html http://www.libpng.org/pub/png/spec/1.2/PNG-Structure.html Specifically, DPI is encoded into the PNG file in the "pHYs" data chunk, as a pair of 4-byte unsigned integers representing "pixels per unit" along each axis, followed by a single byte specifying the unit of measure (note the only supported unit is "meter", not "inch"). http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.pHYs -- Stratadrake [email protected] -------------------- Numbers may not lie, but neither do they tell the whole truth.
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