How to whiten teeth in a photo — in Facetune, and why it goes wrong

The steps, in Facetune

Facetune is the app most people mean when they ask this, and its whitening tool is a brush. You paint the effect onto the teeth yourself, which is both why it is precise and why it is easy to get wrong.

• •Open the photo in Facetune.
• •Go to Retouch, then Whiten.
• •Brush over the teeth. The app detects teeth and tries to keep the effect inside them, but the brush is still yours to place.
• •Pull the intensity down. This is the step people skip, and it is the one that decides whether the result is believable.

Keep it around a quarter of the way up

The single most repeated piece of advice from people who edit photos for a living is to stop at roughly 20–30% intensity. It looks like almost nothing on the small preview. It looks correct at full size, which is the size other people will see it at.

The reason is that teeth are not white. They are a pale, slightly warm off-white with visible variation between one tooth and the next, and they get darker towards the gum line and towards the back of the mouth. A whitening brush at full strength flattens all of that into one even tone, and a flat even tone is the thing the eye reads as fake — not the brightness.

If you are unsure whether you have gone too far, look at the shadows between the teeth. If they have disappeared, so has the thing that made them look like separate teeth.

The three mistakes that give it away

Almost every obviously-edited smile fails in one of the same three ways, and all three are avoidable.

• •Whitening past the teeth. The brush catches the lower lip or the gum line, and now there is a pale patch where there should be pink. This is the most common one and the most visible, because a gum lightened by even a little stops looking like tissue.
• •Losing the shading. At full strength the natural gradient from front tooth to back tooth disappears and the mouth reads as a single white shape. Front teeth are meant to be slightly brighter than the ones beside them.
• •Going bluer, not brighter. Many whitening tools shift the colour towards blue as they brighten. A little reads as clean; more than a little reads as a lit screen inside your mouth, and it fights the warmth of the rest of your face.

The bit nobody mentions: the rest of the photo

A smile that looks wrong is often not the whitening at all. It is that the teeth are now brighter than anything else in the frame.

If the photo is lit dimly, whitened teeth become the lightest thing in it, and the eye goes straight there. Brightening the whole image slightly before whitening — or instead of whitening — solves more of these photos than any brush setting.

This is worth trying first. A lot of people whiten teeth when what they actually wanted was a better-lit photo.

If you would rather not brush it on

A brush gives you control and asks for a steady hand on a small area. That trade is fine on a laptop and awkward on a phone, which is where most people are doing this.

The alternative is a tool where the constraint is written into the instruction rather than into your hand: whiten the teeth, keep the tooth texture and shading, do not touch the lips or gums, match the edges to the surrounding skin tone. Those are the same three failures above, stated as rules before anything is edited.

Neither approach is better in the abstract. A brush is better when you want one tooth handled differently from the others. An instruction is better when you want the ordinary result and do not want to think about the edges.

What none of this can do

Photo whitening is photo whitening. It does not preview a dental treatment, and it is not a reliable guide to what whitening strips or a dentist would achieve on your teeth, which depends on whether the staining is on the surface or inside the tooth.

It also cannot rescue a photo where the teeth are barely visible or badly out of focus. Teeth occupy a very small number of pixels in most photographs, and there has to be enough detail there to work with. A closed-mouth smile gives a whitening tool nothing at all.