Re: DocView resolution for PDF on WQHD

[Yuri Khan]

On Tue, Jun 19, 2018 at 11:29 AM Van L <van@scratch.space> wrote:

> At about the time when src/macfont.h entered the source code I first 
> experienced PDF viewing inside NetBSD GNU Emacs and was blown away by the 
> crispness. I suppose HiDPI is a 4k, 5k, 8k display.

It’s not that simple. There are many factors in play.

First, there is the pixel count. This is what WQHD, 4k, 5k, 8k, and
explicitly stated pixel counts such as 2560×1440 refer to.

Second, there is the screen diagonal or screen size, usually expressed
in inches.

Given a pixel count and a diagonal, one can calculate the linear pixel
density: ld = sqrt(w^2 + h^2) / diag.

Third, there is the eye to screen distance, which can be measured in
meters, feet, or arm’s lengths. A desktop monitor is normally one
arm’s length (≈70cm) from the eye; a laptop, tablet, or phone screen
is usually at about half that distance; and a cinema screen might be
as far as twenty meters away.

Given a linear pixel density and eye to screen distance, one can
approximate the angular pixel density: ad = ld / dist.

Perceived crispness of the image, and what HiDPI is really about, is a
function of the angular pixel density.

A typical desktop monitor is about 100 dpi at arm’s length. A HiDPI
monitor is about 200 dpi at arm’s length.