Tuesday, February 17, 2009

DPI question

Maybe somebody can enlighten me: I've noticed that many people who sell pictures on the Net give size information in DPI, like the pictures are "300 DPI" or "72 DPI". But this is meaningless without any dimensions in inches. If I open a picture and change its info from 200 DPI to 300 DPI without rescaling, I have not changed anything meaningful about the picture at all, except how big my printer decides to print it.

So, are all those people confused, or am I missing something?

[A different issue is that when people use "DPI" (dots per inch) they usually mean "PPI" (pixels per inch), but I've given up on that one.]

3 comments:

Bert said...

That one is yet another legacy from the traditional printing business, just like measuring type in points (1/72") and picas (1/72 foot or 12 points). A DPI guideline was relevant when images were supplied on photo paper and the printer needed to know how to process them, but nowadays is only a source of confusion, if you ask me.

eolake said...

Thank you! That's about what I thought.

Sometimes it's like I'm speaking Chinese when I try to explain to people that it does not make sense to use DPI about web images.

Dibutil Ftalat said...

"....nowadays is only a source of confusion...." - not really. Any page layouting software like Quark Express (I shall not mention MS software in this blog!) scales the freshly imported image to the size set by DPI. Of course, you can re-scale it to your liking and most of the common software will not loose data - it will just internally change the associated DPI of the image, keeping the actual pixels.