Quote:
Originally Posted by jashsu
Quote:
Originally Posted by dsmid
167 ppi * 6 inches = 1000 pixels diagonally
and 800^2 + 600^2 = 1000^2 according to good old Pythagoras
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I've never heard of PPI numbers being used for diagonal measurements.
But the numbers look right. 800px/(167px/in) = 4.79in 600px/(167px/in) = 3.59in. sqrt(4.79in^2 + 3.59in^2) = 5.97in |
The way you calculate makes a little bit more sense since you base your calculations on length. If you try to "calculate" PPI over the diagonal you are in for a surprise - Pythagoras will fail you. Imagine a square display (10x10 pixel) and you draw a diagonal through it. According to Pythagoras you would get about 14.14 pixel (10 x sqrt(2)), but yet if you do it on grid paper it still is only 10 pixels. It just doesn't make sense to say that there is 14 pixel (my example) or 1000 pixel (
dsmid calculation) diagonally. I am pretty sure that
dsmid is aware of his flaw in calling it 1000 pixel per diagonal, but it does give correct results trying to estimate horizontal and vertical PPI. The only reason PPI is only one number any more is because nowadays pixel are usually square.