Character consistency

Character consistency is whether the illustrated child on page eleven is recognisably the same person as the one on page one. It is the single hardest technical problem in generated personalized books, and it is the one that most reliably separates a book a family keeps from one they quietly put away.

The difficulty is that each illustration is produced separately. A character has to survive being drawn from the front and the side, close up and at a distance, in daylight and in the dark, and small deviations at each step accumulate. The result is drift: a face that is close early and generic by the end.

The features that drift first are predictable, and they are the ones that identify a person. Face shape goes first, then hair texture, then skin tone. Freckles, glasses and a fringe survive least well of all, because they are small details that each new scene has an opportunity to lose.

Consistency also has a fairness dimension that is easy to overlook. Tightly coiled hair, deep skin tones and very fine fair hair are the cases generators historically handled worst, which means the failure is not evenly distributed across children. A maker's samples showing only one kind of child is a meaningful omission.

The practical way to judge it is to insist on the whole book. A single sample image proves nothing, because the first illustration is the easy one. Seeing every page before paying is the only reliable test, and a maker who offers that is telling you something about their confidence.

The same idea appears in shops and reviews as likeness consistency, character coherence, or simply likeness. In the wider technical field it belongs to identity preservation, which is the name for the general problem of keeping one specific person recognisable across a series of separately generated images.