A typeface is made of glyphs: visual representations of letters or symbols. Today it's mostly digital, as are the media and the production tools, residing in files called fonts. It's a basic and fundamental typographic element standing at the intersection of visual communication and language: it's the matter the written message is made of, in the end.
Different uses require different typefaces. Books need typefaces easy to read with, road signs need typefaces efficiently legible night and day, at speed and from afar. Titles in a magazine need typefaces that look good in large sizes.
But also similar uses require different typefaces. One couldn't set an article in a newspaper like a comic strip; a love letter should look different from a war declaration. Because the message is not only the text: to a certain extent, a typeface may contain elements that stand for the tone of voice, the gestures, the gaze, the reputation, ... anything making so different a spoken communication. A newspaper can't also use the same typeface as another newspaper. Because readers unconsciously associate newspapers, but also brands, institutions, companies, ... to the typefaces they use. A typeface can deliver an emotional subliminal message of identification in an exact and transparent way. Reinforcing the explicit implication, or hiding it in plain sight. Just like a scent or a dress.
All of this can happen because reading is an unconscious act. For which we don't see letters but words as a whole. The glyphs must be arranged appropriately, in such a natural way that they no longer attract attention, a conscious act. Letter-fitting, in the end, is: making letters invisible.

Practically the letter-fitting work consists in determining all the relative positions of glyphs in a font. Usually, this task consists in determining sidebearing values for any glyph (where the space virtually occupied by a glyph begins and ends), also called spacing, and kerning values for many pairs of glyphs (how much two glyphs relatively displace when one follows the other after spacing). Obviously, spacing and kerning are two components of the same value, as two glyphs' relative position is just one entity. But traditionally the two concepts remained separated.
Ancient metal types had physical support made of solid matter: space physically occupied by a glyph. Kerns were the cuts applied to the rigid support to allow some relative shifting in exceptional cases.
This mental pattern survived the transition to the digital realm: it turned out that spacing and kerning, then become mere database values, were suitable for a compact representation of spatial relations between glyphs. And as such, implemented in new font editing tools. In so introducing the idea that a type designer, now potentially able to manage the entire font production process from start to finish, needed to fill a database with hundreds of sidebearing and thousands of kerning values for every font.
An iterative procedure made of many local micro-decisions, proceeding from local to global. Therefore, a consuming process, based on a tiring steadiness in visualising and keeping a constant idea of the final result. A frustrating job, because it's evident there's something repetitive in it but hard to grasp.

iKern is a mathematical model that describes the white space between the glyphs to determine the reciprocal position of glyphs. It's general, as it doesn't make any kind of assumption about the shape of its boundaries. It's abstract, as it provides structures and information. It's neutral, because it doesn't contain any form of preventive decision or learning about expected results. Since it explains a process-phenomenon, while allowing to make predictions on (numeric) data without using pre-existing data, iKern is a theory in a modern sense.
iKern is also the tool that uses the model to perform letter-fitting work, separating preliminary choices from repetitive tasks, smartly dealing with the former and automating the latter. A tool for evaluating the appropriateness of choices by the quality of the result. The algorithms in iKern identify properties. As long as they are intrinsic to the glyphs' shapes, and so computable, the tool is automatic. When they're not, representing choices to guide the process, and so parameters, the tool is an interface.

Acting on parameters implies a different way of thinking:

  • sidebearing and kerning values have to be found all at once and not created one by one;
  • letter-fitting has to be planned and designed at the beginning rather than determined at the end of a long process. Has to be designed, as a study of balancing visual tensions that the designer has merely triggered. To obtain:
  • Coherence: the initial choices are globally, indiscriminately and uniformly inherited by all the glyphs and all the pairs of glyphs;
  • Consistency: the same algorithms and the same parameters produce both spacing and kerning;
  • Correctness: text setting results, both functional and pleasant to the eye, to the highest level of accuracy.

The set of choices is the minimum that let decide everything—and exposed in a way that makes sense from a micro-typographical perspective. This way, it's possible to test key combinations of glyphs and immediately get a visual response. Parameters get adjusted iteratively until the result thus achieved coincides with the one anticipated by the eye. The goal always remains the same: to get to the desired result. But the process, now, goes from global, the setting of the model, to local, the result.

Finally, iKern is a service offered to type designers and font producers to give excellent letter-fitting to typefaces while avoiding the laborious, burdensome and costly spacing and kerning phase. iKern as a service has been fundamental to iKern as a theory and model, providing an ideal R&D environment, with always different fonts to work on and to experiment with. No good idea could have emerged and developed without this urge to generalise. Over the years, I worked on thousands of fonts, created and scrutinised by hundreds of designers: a unique and unrepeatable human and professional experience.