Quote:
Originally Posted by ApK
Wait a sec, this is driving me batty:
The problem with that is you first calculate a result of 1000 by ASSUMING 167 dpi for the diagonal. Then you are using that result in the theorem as a given, but it's only based on your assumption in the first place.
The problem with using the Pythagorean theorem for diagonal dpi, is that the theorem uses scalar units that would measure the same in any direction. Pixels are in fixed positions in a matrix, so you can't equate them with scalar units like inches. You will count a different number of them per inch depending on the angle you measure them on.
I think, after going back and forth a few times, that DT is right.
And nomenclature-wise, where has any manufacture used the term "diagonal dpi?"
|
When was last time you bought a computer monitor, tablet, smartphone, or eInk reader that listed the horizontal and vertical dpi along with the horizontal and vertical screen widths? Probably never. You might find some info buried deep in the specs, but they don't advertise screens like that. Instead, computer monitors, tablets, smartphones, and eInk readers are advertised by their DIAGONAL lengths and a single dpi amount that just happens to equal that shown in the formula I listed. A 6" eInk screen is approximately 6" across the diagonal dimension. A 27" eInk screen is approximately 27" across the diagonal dimension. Et cetera. I agree that dpi would most likely vary in each direction you might measure it, and I agree that the dpi across the diagonal dimension probably isn't accurate, but that sure seems to be what they are doing to calculate the dpi. If you have the actual screen dimensions for vert. and horz. then you can easily calculate the true dpi based on the listed number of pixels in that direction. But eInk really doesn't have pixels like LCD screens. I seem to recall that they overlap in eInk and are not nice little rectangles. So a dpi for eInk is probably not the same as a dpi in LCD screens anyway. But even for LCDs, the dpi seems to be a calculation based on the Pythagorean theorem which takes into account the number of vert. and horz. pixels (dots, points, whatever) in relation to the diagonal screen size to give us a single dpi amount. Is it highly accurate? Probably not. Does it make a lot of sense? No. Does much in marketing make a lot of sense? No. Is marketing filled with lots of BS? Yes!