Smile changes not only the mouth: it involves cheeks, eyes and the entire lower part of the face.
If the model has painted white teeth, but left neutral eyes and fixed cheeks, the expression looks glued; if the intervention is too broad, age and recognition change with the smile.
This expression is assembled from several agreed modifications
The lower eyelid rises slightly, the look remains alive.
The volume shifts upward and affects the folds near the nose.
The corners change position, but the shape of the mouth remains recognizable.
An open smile changes the distance between your lips.
The stronger the new emotion, the higher the risk of getting another face.
A light smile usually requires a little local editing. Open-mouthed laughter rearranges the cheeks, chin, eyes and visible part of your teeth. If you want one like that, it's more useful to give a reference to your own facial expressions than to ask the model to guess them.
Ideal identical teeth make a smile less plausible
The natural tooth arch obeys perspective: the lateral teeth are narrower and darker, the upper lip casts shadow, there are no identical black lines between the teeth. Don't demand a "Hollywood smile" if the goal is to preserve the person.
Set the power of emotion and protected traits
ExampleAdd a light natural smile with your mouth closed. Raise the corners of your lips and cheeks slightly, keep your eyes calm. Don't change the shape of the face, nose, eyes, eyebrows, age, skin texture and head turn. Expression is friendly but restrained.
Close your mouth on the screen with your hand and check the rest of your face.
If you don't have the lip area, your eyes and cheeks are completely neutral, the new emotion is not collected. Then close the top of your face: the shape of the lips and chin should remain similar to the original person.
Compare not a smile, but stable facial features
Put the source and the result side by side on the same scale. First, close your mouth and compare the line of eyes, eyebrows, nose, oval and distance between features. Then cover the upper half of your face and check the shape of the lips, chin and nasolabial area, which separates the change in emotion from the subtle substitution of appearance.
It's safer to change one sign at a time: a light smile, the direction of your gaze or eyebrow tension. Asking you to simultaneously "make it happier, younger and more attractive" doesn't set a verifiable limit and almost inevitably changes the person.
Don’t use synthetic emotion as a document of an actual event.
For an avatar or a creative portrait, mild correction is acceptable. For a reportage, review or photograph where the expression has actual meaning, it's better to choose the real adjacent frame.
Change the intensity of expression, not facial anatomy
For mild facial expressions, a narrow instruction is enough; for strong emotions, you need your own reference and a more rigorous similarity check.