Units: pixels, ems, display resolution

Author Peter Edberg
Date 2019-05-21
Status Proposal
Feedback to pedberg (at) unicode (dot) org
Bugs CLDR-9996 Add units for  pixels , ems, and display resolution
CLDR-8076 Proposal: add units for dot density and pixel density

This is a proposal to add 7 units related to graphics, imaging, typography.

unit abbr (en) proposed category
notes
pixel
megapixel
px
MP
new category? A pixel is the smallest resolvable element of a bitmap image. In many usages it does not have a fixed size, and is just used for counting (e.g. an image has 360 pixels vertically and 480 horizontally). In some graphic usages it is specifically 1/96 inch. In CSS it is the smallest resolvable element on a display, but specifically means 1/96 inch on a printer. Thus sometimes it is a property associated with an image, and sometimes with a device.
dots-per-inch
dots-per-centimeter
dpi
dpcm
new category?
or concentr
A dot is the smallest displayable element on a device, typically used for printers. Measurements using dots per inch or centimeter are used to indicate printer resolution, and are a kind of linear density.
pixels-per-inch
pixels-per-centimeter
ppi
ppcm
new category?
or concentr
Measurements using pixels per inch or centimeter are sometimes used to indicate display resolution, and are a kind of linear density.
em em new category?
or length
A typographic em is a unit of length that corresponds to the point size of a font (so it does not have a fixed size).

We could consider adding a new category for these, say “graphics”; otherwise some of them do not fit reasonably into any existing category.

Per TC meeting 2019-05-22:
  • Use singular for the internal key name, e.g. “dot-per-inch”
  • Put all of these in a new category “graphics”

Some reference material: