Excel Worksheet: Pixels Per Inch

[MartyTX]

I’m thinking about adding a tablet to my electronic gadget lineup. I already have a desktop, laptop, iPhone and Nook ST.

The 1st generation iPad at Walmart for $200 net on Black Friday seems too good to pass up, but I’ve read several reviews about its low resolution. I’ve also read that Pixels Per Inch (PPI) is a better determinant of screen clarity than just resolution. 800x600 looks fine on my 6” Nook, but not so fine on a 21” monitor.

So, I did some browsing and some messing around with Excel, and made a worksheet that easily calculates Pixels Per Inch.

To use the worksheet you have to enter the screen resolution (pixels) and the screen diagonal (inches) into the GREEN cells. This info seems to be given in most advertisements. All the other cells are filled by the formulas. I’ve populated the sheet with the devices that I already own and some I’m thinking about. Simply erase the GREEN cells and enter your own data.

NOTE: Some devices can be read in portrait and landscape mode. For consistency, I listed the larger number first for all devices. For example, even thought the Nook is read in portrait mode 600w x 800h (3:4), I’ve listed it as 800x600 (4:3). Regardless of which number you call the width and which you call the height, as long as you enter both dimensions the PPI stays the same.

Hope some Excel users will find this sheet useful.

Marty

[fjtorres]

The effect of pixel density is a function of viewing distance. So, unless you watch the bigger device from the same distance as the smaller, you need a correction factor for viewing distance.

[MartyTX]

Hi fjtorres,

Thanks for your input.

I'm aware of the viewing distance factor from posts on MobileRead and elsewhere. Also, have read several articles stating that the human eye generally can't differentiate individual pixels beyond 300 PPI when viewed 10 to 12 inches from the eyes. PPI is just one of many factors involved in determining what makes a "good eReader".

This reminds me of audio "high fidelity" discussions of the 60's & 70's. "Frequency Response Range" was the hot topic back then.

The limits of normal human hearing are defined as 20-20,000 Hz. However, many equipment manufacturers were touting frequency ranges inaudible to the human ear, well beyond the 20,000 Hz threshold.

My worksheet is user editable if someone wants to tackle adding a correction factor for viewing distance.

Marty

[Penforhire]

There are nuances to the current debate over displays (don't forget about viewing angle, color gamut, brightness, reflections, and contrast). Resolution as the primary measure of goodness is still a weak measure.

On your analogy, my own hearing tested up to around 25 kHz and I'm only a tiny bit of a freak o' nature.

[MartyTX]

Originally Posted by Penforhire

On your analogy, my own hearing tested up to around 25 kHz and I'm only a tiny bit of a freak o' nature.

I'm envious of your 25 kHz hearing! Recently had mine tested and have the typical high frequency "old-timer" roll-off. Likewise, my vision is definitely not what it used to be.

But my mind is still tharp as a sack ...

Marty