Quote:
Originally Posted by jswinden
Your a bit confused. Here is the actual formula used to calculate diagonal ppi:
SQRT(horizontal pixels^2 + vertical pixels^2) / screen diagonal distance in inches = ppi
SQRT(600px^2 + 800px^2) / 6" diagonal distance = 166.66666667 ppi
SQRT(360,000 + 640,000) / 6" diagonal distance = 166.66666667 ppi
SQRT(1,000,000) / 6" diagonal distance = 166.66666667 ppi
1,000 / 6 = 167 ppi
ETA: Pixels are not necessarily square. Look at the specs for various devices and you see that the horizontal pixel dimension is often different from the vertical pixel dimension. This part of the equation SQRT(600px^2 + 800px^2) calculates how many total pixels could theoretically stretch across the entire diagonal length of the screen. Since we want to determine ppi (pixels per inch) and since the screen is 6" across the diagonal measurement, we divide SQRT(600px^2 + 800px^2) by 6 to get 167 ppi.
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You are correct, pixels are not always square. And when they are not the horizontal and vertical resolution (ppi) is different. Across the diagonal is something else entirely, especially as the angle changes with aspect ratio of the entire screen. If you only allow a non-aliased line as diagonal, then that line is only made up by as many pixels as the longer of both sides has. In 600x800 screen that would be 800.
It makes absolutely no sense to say that the screen has 167ppi diagonally.