The equivalence numbers are what dpi of black and white dots you'd need to make a geyscale display with the ppi. It's only a guide, but for example:
For 4 grey levels, (white, light grey, dark grey, black) you need a pixel containing three black or white dots. So to convert a 4 level ppi to dpi you multiply by the square root of three. and vice-versa.
It's only approximate, but it's about right. Obviously, if you're only displaying pure black or white, the extra grey levels do you no good. But even with text, some anti-aliasing can improve the apparent resolution of the text.
The trouble with increasing the resolution is that each pixel requires a transistor - the more that are needed, the smaller they are, and the likelier that there'll be a flaw in any one of them, and as there are a lot more of them, the chance of a flaw somewhere in the display gets bigger rapidly.
So for now, I'd settle for something with faster refresh and no glass. Lets hope we see it this year.
Quote:
Originally Posted by Xenophon
Yes, PPI and DPI really are different. And greyscale PPI indeed relates to a larger-numbered DPI value. I've not previously seen 'equivalence' numbers; where did you get them from? That's curiosity, not doubt, btw.
All that said, I long ago concluded that 300DPI was thoroughly inadequate. I'm OK with a good 1200DPI laser printer, but setting my inkjet to 720DPI instead of 1440DPI gets low enough to bother me (thinking text here, not images). So I really REALLY want that 1200DPI-equivalent eInk display. You know, the one that's made of 100% pure unobtanium, with a bolonium back-plane. 
Xenophon |