DPI & PPI - help! (Full Version)

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RickP -> DPI & PPI - help! (5/2/2005 14:43:00)

Can anyone explain the relationship between dpi & ppi on a monitor?

All the books cite that "monitors usually run at 72DPI" - now... If I can alter the pixel resolution of my monitor (PPI) making more, or less pixels per inch how can it be said that most monitors still run at 72DPI ? 

Pixels per inch increasing or decreasing as I adjust settings I understand but what are the 72 DOTS per inch that, according to all and sundry, seem to remain the same regardless of my choice of pixel resolutions settings?

Sorry if this is a confusing question but it is sure bothering me!!![image]http://www.frontpagewebmaster.com/image/s6.gif[/image]



bobby -> RE: DPI & PPI - help! (5/2/2005 17:45:07)

As I understand it, a pixel and a dot are interchangable...

Also, Mac's run at 72 dpi and PC typically default at 96 dpi





RickP -> RE: DPI & PPI - help! (5/2/2005 18:15:03)

But that doesn't make sense (to me at least)!

If they are one and same (for monitor purposes) then how is it that books and sites everywhere seem to say that monitor resolutions are all either 72 OR 96 dpi/ppi. (also PSP & PS seem to default to these precise resolutions when optimising a gif graphic)

Now, thinking out loud here...

If I run a monitor at 800x600 pix - I have 800 pixels from the left to the right of my monitor - now my monitor is 17inch (diagonal of course) which makes it about 13 inches across...

800 divided by 13 = 61.5 approx - that means that I have 61.5 pixels per inch (PPI & DPI are measured in one inch 'lines' not square inches of course)

Now, for starters, anyone with a 14inch monitor must, at the same pixel resolutions, cram in more pixels per inch - yes? It can't be the same as on my 17 inch monitor!

Another way to look at it:

Lets say I increase my PIXEL resolutions to 1024 by 768...
I now have 1024 pixels going across my monitor - but it is still 13 inches across
1024 divided by 13 = 79 (approx) Pixels per inch

IF PPI and DPI are synonymous when talking of MONITOR resolutions then it would make sense to me if these books and sites stated that "monitors usually run at AROUND 60 - 100 DPI/PPI"

Now, if they said that then what you are saying makes sense but they all seem to be so emphatic that it is either 72 OR 96!!!

I don't get it[:(]



Reflect -> RE: DPI & PPI - help! (5/3/2005 10:42:57)

I will take an uneducated stab...

Think of DPI for scanning in pictures and printing. When I scan I bump DPI down to 72 DPI. I know that at this setting the picture will look acceptable and also print acceptable. It will also keep the images size to an acceptable level when adding all weight that is associated to a page for download freindleness.

On PPI I link this to dots on the monitor or how many pixles fit in a given space for display purposes.

HTH,

Brian



bobby -> RE: DPI & PPI - help! (5/3/2005 11:15:46)

think of the dots/pixels as growing/shrinking too... they don't necessarily stay the same size as resolutions change.

Also keep in mind that your 17" monitor doesn't necessarily always display 17" of content... it depends on so many settings it would really make your head spin.

My best advice is not to worry about it and just accept that you may never fully grasp the concept.  That's what I've done with most things in life and it's worked pretty well for me so far.

Then have a beer...

[:D]



RickP -> RE: DPI & PPI - help! (5/3/2005 13:37:26)

Reflect - thank you for your offering (still not sure though!)

Bobby - what else is there to be said but... "cheers" [:D]



d a v e -> RE: DPI & PPI - help! (5/3/2005 13:44:27)

there is some info on this at http://www.nw-media.com/ps_intro/html/lesson_1/lesson1_pg3.html (the link given in your post on raster and vector.

If i remember rightly images for are prepared at 1.5-2 times the lines per inch so for a typical newspaper that uses say 150 lpi images would be say 300 ppi - pixels per inch. glossy magazines/publications would use images at around 1200ppi -2400ppi or thereabouts.

if you having something preofessionaly printed then you're best always asking the printers for advice on their requirements e.g. what res pictures to use in ppi.



RickP -> RE: DPI & PPI - help! (5/3/2005 13:48:09)

Thanks Dave - will read



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