Re: [artworks] Bitmap image size and DPI
- From: Chris Terran <chris.terranova@xxxxxxxxxxxx>
- To: artworks@xxxxxxxxxxxxx
- Date: Thu, 31 Jul 2008 22:29:27 +0100
In message <48922362.7010709@xxxxxxxx>
Clive Bonsall <cbonsall@xxxxxxx> wrote:
> This is not specifically ArtWorks related, but members of this group may
> be well placed to supply an answer to my question ...
> I have a digital photo taken with a Canon EOS 350D camera (8
> mega-pixels, I think). The photo was taken in high quality mode. To any
> bitmap editing software I've tried, the image size appears as 2048 x
> 1536 pixels, and the Image DPI as 72 pixels/inch. The file size is 9 MB.
> To my eyes this is quite a high resolution image. Can it really be just
> 72 DPI -- or am I misunderstanding the relationship between resolution
> and DPI?
The dpi is completely arbitrary; it only governs what size the image
appears as when displayed, and says nothing about the 'true'
resolution. Some programs obey any embedded dpi information, some
don't. You can change the dpi without affecting the file size or the
pixel dimensions.
Our Canon 10D (a very similar camera) creates images at 180dpi, so
72dpi is a bit surprising. Are you looking at them on a Mac? 72dpi is
the standard figure used by Macs (90dpi on RISC OS, 96dpi on Windows).
The only meaningful dpi figure for a digital camera would be related
to the size of the sensor chip. On a 10D, this is 22.7x15.1mm and
produces images containing (for our purposes) 3072x2048 pixels. This
gives (very approximately) a dpi of about 3300. Not a terribly useful
figure ;-)
Anyway, this is indeed off-topic...
Best, Chris
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