Tooth shade from a photo: a measurement on the VITA scale

You can, but the result will mean nothing. The color in a photo is the color of the enamel multiplied by the color of the lighting and by the camera’s processing: under an incandescent bulb the same teeth come out yellow, by a window on an overcast day bluish. The white sheet gives a fixed point: we know what it should look like, we see what it does look like, and the difference gives a correction that is then applied to the tooth. Studies of photo-based shade matching without such calibration report roughly 38 per cent correct identifications — more often a miss than an answer.

Because the white sheet came out blown out — clipped at maximum brightness. Such an area contains no information: any light brighter than the limit of the scale is recorded as the same value, and the balance cannot be recovered from it in principle. Showing a “shade” from that frame would mean passing off a random number as a measurement. Lowering the exposure in the camera, stepping away from the lamp or shooting by a window without direct sun all help.

Markedly less accurate, and that is not hidden. A dentist measures with a spectrophotometer directly in the mouth, under controlled light and without a camera’s processing in between. A home photo measurement depends on the phone’s sensor, its algorithms and how you held the sheet. But it has a region where it is reliable: the DIFFERENCE between two of your own photos taken the same way. That is what the log exists for.

On the contrary, it is an honest answer. The tabs of the VITA scale sit close together in color space, and a phone photo often lands exactly between two. When the distance to the second tab is under one and a half color units, choosing between them from a photograph is not possible — only pretending to is. For tracking whitening this does not matter: the shift along the scale is counted the same either way. For choosing a crown shade you need an instrument measurement from a dentist.

The middle third of a front tooth — roughly halfway between the incisal edge and the gum. In most people the edge of the tooth is semi-transparent and looks darker and bluer than the tooth itself, while the area near the gum is yellower because the enamel is thinner there. The middle is the most representative area, and it is the one used when matching shades in a clinic. Avoid highlights: the tool tolerates small ones, but aiming at a reflection of the lamp is not a good idea.

The log is kept in this browser on this device and does not travel between your phone and your computer. For before-and-after comparison that means measuring and saving from the same device — otherwise the first measurement simply will not be next to the second. Clearing site data in the browser erases the log.