Add Bleed (BLED) Variation Axis

[jenskutilek]

My Homecomputer fonts use custom variation axes for visual artefacts related to display on a cathode ray tube: (horizontal) bleed (tag: BLED) and (vertical) scan lines (tag: SCAN).

I propose to add those axes to the Google Fonts axis registry:

Bleed (BLED)

On CRT screens

The horizontal "bleed" of the pixels on a CRT screen is caused by the phospor latency:

(Source: VT100 Series Technical Manual, EK-VT100-TM-002, p. 4-78)

The "Homecomputer" fonts simulate this effect by elongating the edge pixels horizontally.

BLED=0

BLED=max

Other uses

A Bleed axis could also be used to simulate the bleed of ink on paper. This is distinct from the proposed Grade axis, which adds or subtracts weight from the glyphs uniformly, whereas the Bleed axis could add or subtract weight in a way simulating the distribution of ink on paper when the printing process uses little or too much ink or pressure.

Ink bleed on typewritten text. Top row: various levels of added bleed due to differences in pressure applied to the keys of a mechanical typewriter. Bottom row: negative bleed due to typing without a ribbon and thus the color fading as a key is struck multiple times.

Axis proposal

tag: "BLED"
display_name: "Bleed"
min_value: -1000
max_value: 1000
default_value: 0
precision: 0
fallback {
  name: "Normal"
  value: 0
}
description:
  "Add or subtract weight from strokes or other forms in a uniform, random,"
  " or logical way, without any changes overall width, inter-letter spacing,"
  " or kerning, so there are no changes to line breaks or page layout."
  " Negative bleed makes the style lighter, while positive bleed makes it bolder."
  " This can be used to simulate different levels of ink bleed on paper, as"
  " commonly found in printed or typewritten materials."

[RosaWagner]

Thanks @jenskutilek
We would need at least two fallbacks per axes, one for the min value and one for max value, where either one or the other is the elided default one. Or three values if the default one doesn't match the min or max.

More descriptive fallback names could also be better, like negative bleed and positive bleed or shorter.
cc @davelab6

[vv-monsalve]

This issue was transferred to googlefonts/axisregistry#17. Please follow up there.