Re: [artworks] Bitmap image size and DPI

  • From: Tim Powys-Lybbe <tim@xxxxxxxxx>
  • To: artworks@xxxxxxxxxxxxx
  • Date: Thu, 31 Jul 2008 22:38:51 +0100

In message of 31 Jul, 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?

Screen pixels per inch is not the same as printer dots per inch.

Screens display at around 72 dots per inch: on LCD screens they have a
known number of dots and you can measure the width in inches and
suitably divide.  So my screen displays at 88 dots per inch.  The above
image of yours will occupy a screen 23 inches wide at this display

Printer dots are much smaller than screen pixels and typically printing
is done at 300 dots per inch, though professional printing will be
around 2,000 dots per inch.  I normally print at 600 as this is what my
printer will do at full colour resolution.  So your above image will be
3.4 inches wide on my printer if my software sends it to the printer at
one pixel per dot.  Usually of course you arrange (enlarge or reduce)
your images on a graphics processing package, Art Works for instance and
to bring this on topic, so that they occupy suitable amounts of an A4

Tim Powys-Lybbe                                          tim@xxxxxxxxx
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