Tone-true: softer skin, same color
Tone-true is the rule behind Sfuma, the iPhone portrait editor made by NameVerse, Inc.: smoothing may change the texture of your skin, never its color balance or brightness. This page says what that means, how it is measured, and which test checks it.
Does Sfuma’s smoothing change skin tone?
No. Smoothing is built so that, at any Soften value, the color balance and the brightness of the skin stay where they were. Only texture changes. The test checks the heaviest setting on six portraits from roughly Fitzpatrick II to VI.
Proof: the rule is a test in the app’s own test suite, run on real portraits, not a line in a brochure.
Why do most filters shift skin color?
Many beauty filters smooth by blurring and then brightening the whole face, or by applying a color look on top of the skin. Both move the skin toward one target: lighter, pinker, more uniform. On light skin the shift is easy to miss. On medium and deep skin it is obvious, and it is the reason a selfie can come back looking like someone else.
Sfuma separates texture from color before it does anything. Smoothing works on the luminance detail layer only, inside a skin mask that stops at the eyes, brows, lips and hairline. The color layer is passed through untouched.
How is it measured?
The tone-lock test renders each of the six frontal portraits in the test set with Soften at 100 and Even tone at 80, the heaviest combination a user can set. It then compares the center of the face before and after, where skin dominates.
| Measure | Limit | In plain words |
|---|---|---|
| Red–green balance shift | under 0.012 | less than 1.2 percent of the full color range |
| Green–blue balance shift | under 0.012 | less than 1.2 percent of the full color range |
| Brightness shift | under 0.02 | less than 2 percent of the full range, in either direction |
Any image over any limit fails the test.
Proof: the thresholds above are quoted from the test itself. The current test set spans roughly Fitzpatrick types II to VI; extending it to a licensed set of 30 or more portraits across I to VI and three lighting conditions is the target in our feature plan.
What else does the same rule cover?
- Small faces. A face at the back of a group photo is smoothed like a close-up selfie, and keeps its own color even against a wall or hair of a different tone.
- Under-eye. Dark circles soften toward your own cheek color; they are not brightened toward white.
- Looks. A look is meant to change color, so it is not held to the tone lock. Every look is tested so that very bright areas keep their highlights.
- Teeth and eyes. Whitening and brightening act inside the mouth and the eye only, and leave skin alone.
What will this page show per release?
The plan is to publish the per-band color table from the test run for every App Store release here, so the marketing claim and the engineering result are the same table. Until the extended licensed test set exists, the limits above and the roughly Fitzpatrick II–VI coverage are what the test checks today.
Proof: publishing the per-release table is part of the tone-true acceptance criteria in Sfuma’s feature plan (B1).
Sources
- Fitzpatrick TB. The validity and practicality of sun-reactive skin types I through VI. Archives of Dermatology, 1988;124(6):869–871. The scale the test set’s range is described in.
- Google. The Monk Skin Tone Scale. A ten-point scale built to describe a broader range of skin tones in imaging work.
- Apple. Core Image documentation. The framework Sfuma’s color and texture work runs on.
- Apple. Vision documentation. The on-device face detection that places the skin mask.
See it on your own skin
Hold the photo in the editor to compare with the original at any time. Touch Up tools.
Coming to the App Store — first in Turkey.
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