First pass sample Kern pairs

[dberlow]

Image shows default at the bottom and use of scaling kerning using XTRA:
Default XTRA/100 = Extreme XTRA/n

Default Kern x n = Extreme Kern

[dberlow]

Kern.pair tendencies
Assume FB space/kern method.

Default = 14 pt. Its xtra will = “dxtra” and “lxtra” is local instance’s value.

Values given in first chart is approximated scale and at least direction to scale kerns to 6 lxtra adding those scales to the existing scale. 20 other defining designspace locations for wght, wdth, and opsz will then be analyzed as those scalings add up.

This approximated scaling makes negative kern values larger, and positive kern values smaller, (which may seem wrong, please confirm;).

The value list is not intended to be final as listed, but rather as a guide to the dxtra to lxtra values at first applied to the instances at 6 “sides” of the design space e.g.
opsz14, wdth50, wght400, default size & weight, width min, or
opsz144, wdth100, wght400, default weight & width, opsz max.
get scale factors differ t form so far now applied.

After analyzing the effects of the rescaling on the kerning those 6 sides.

The suggested scaling effects on those sides is in italic

The other 20 locations shown in the chart, (as list only for opsz8), then need to be looked at as the scale factors have added up in the design space.

Then:

1. Further refinement for those 6 and/or 20 instances?
2. Division of scale factors between cases, and among cases?
3. Separate treatment of positive and negative values?
4. Manual intervention?

Amstelvar Roman:
Input: opsz 008 wdth 100 wght 400 lxtra 0.98 + from dxtra...
Input: opsz 008 wdth 050 wght 400 lxtra 1.10
Input: opsz 008 wdth 150 wght 400 lxtra 1.50
Input: opsz 008 wdth 100 wght 100 lxtra 1.40
Input: opsz 008 wdth 100 wght 900 lxtra 1.05
Input: opsz 008 wdth 050 wght 100 lxtra 1.10 + lxtra 1.40
Input: opsz 008 wdth 150 wght 900 lxtra 1.50 + lxtra 1.05
Input: opsz 008 wdth 150 wght 100 lxtra 1.50 + lxtra 1.40
Input: opsz 008 wdth 050 wght 900 lxtra 1.10 + lxtra 1.05
Input: opsz 014 wdth 100 wght 400 dxtra
Input: opsz 014 wdth 050 wght 400 lxtra 1.10
Input: opsz 014 wdth 150 wght 400 lxtra 1.50
Input: opsz 014 wdth 100 wght 100 lxtra 1.40
Input: opsz 014 wdth 100 wght 900 lxtra 1.05
Input: opsz 014 wdth 050 wght 100
Input: opsz 014 wdth 150 wght 900
Input: opsz 014 wdth 150 wght 100
Input: opsz 014 wdth 050 wght 900
Input: opsz 144 wdth 100 wght 400 lxtra 1.20
Input: opsz 144 wdth 050 wght 400
Input: opsz 144 wdth 150 wght 400
Input: opsz 144 wdth100 wght 100
Input: opsz 144 wdth 100 wght 900
Input: opsz 144 wdth 050 wght 100
Input: opsz 144 wdth 150 wght 900
Input: opsz 144 wdth 150 wght 100
Input: opsz 144 wdth 050 wght 900

[djrrb]

Sorry for the delay here, these are the values I used in the initial version of the script:

Source	Multiplier	XTRA value
default	1.0	800
Amstelvar-Roman-opsz-36.ufo	0.9364	749
Amstelvar-Roman-opsz-84-wghtmin.ufo	1.0528	842
Amstelvar-Roman-opsz-84.ufo	0.8778	702
Amstelvar-Roman-opsz-max-wdthmin-wghtmax.ufo	0.18125	145
Amstelvar-Roman-opsz-max-wghtmin.ufo	1.045	837
Amstelvar-Roman-opsz-max.ufo	0.87125	697
Amstelvar-Roman-opsz-min.ufo	1.0	800
Amstelvar-Roman-wdthmax.ufo	1.4775	1182
Amstelvar-Roman-wdthmin.ufo	0.55	440
Amstelvar-Roman-wghtmax.ufo	0.625	500
Amstelvar-Roman-wghtmin.ufo	1.175	940

[dberlow]

So the six values in italic that I’ve given above, are guesses intended to be additional scales to the values that you used for those 6, but the opsz value somehow has to be distributed out over OPSZ max’s Intermediates.

Let me know thanks

[dberlow]

pinging DJR on last comment above...

[djrrb]

Again, my apologies on the delay...in the past couple days I’ve finally been able to get my brain back into the kerning.

I hope I’ve understood your comment above correctly and have manually inserted multiplier values for the italicized masters in your post. When you used "dxtra" it is relative to the default value, when you used "lxtra" it is relative to the value that I had previously calculated.

For example, where you wrote Input: opsz 014 wdth 050 wght 400 lxtra 1.10 I interpreted that to mean that for wdth-min, the previously calculated value of 0.55 is multiplied by 1.10 to become 0.605.

These values are currently hard-coded into the script, making it Amstelvar-specific. If there was some systematic logic you used to get these values that could be written into the script, let me know.

A sample font is attached here and available on Amstelvar fea-propagate-kerns.

Amstelvar-Roman-VF.ttf 2.zip

Source	Multiplier	XTRA value
default	1	800
Amstelvar-Roman-opsz-36.ufo	0.9364168734491315	749.1334987593052
Amstelvar-Roman-opsz-84-wghtmin.ufo	1.0528011786600497	842.2409429280398
Amstelvar-Roman-opsz-84.ufo	0.8778011786600497	702.2409429280398
Amstelvar-Roman-opsz-max-wdthmin-wghtmax.ufo	0.18125	145.0
Amstelvar-Roman-opsz-max-wghtmin.ufo	1.0458467741935484	836.6774193548388
Amstelvar-Roman-opsz-max.ufo	1.0454999999999999	697.0
Amstelvar-Roman-opsz-min.ufo	0.98	800
Amstelvar-Roman-wdthmax.ufo	2.21625	1182
Amstelvar-Roman-wdthmin.ufo	0.6050000000000001	440
Amstelvar-Roman-wghtmax.ufo	0.875	500
Amstelvar-Roman-wghtmin.ufo	1.2337500000000001	940

[dberlow]

How’s it look? :-)