Why skin-colour tables fail darker skin
Many retouching tools decide what counts as skin by checking each pixel against a fixed colour range. Those ranges were measured on mostly light faces, and a darker face falls partly outside them. Here is what that does to a retouch, and how the skin gate on this site decides instead.
A smoothing tool needs to know where the skin is. Smooth the eyebrows and they turn to fog; smooth the hair and it turns to felt; smooth the background and the photo looks unfocused. So before anything is softened, something has to draw a mask: these pixels are skin, those are not.
The cheap way to draw that mask is a table. Convert each pixel to a brightness-and-colour space (often called YCbCr), and keep it if its two colour numbers fall inside a fixed box. The box comes from a paper or a dataset: someone photographed a set of faces, plotted their skin pixels and drew a boundary around the cloud.
Where the box comes from decides who it fits
A box is only as fair as the faces it was drawn around. When the faces are mostly light, the box hugs light skin: the colour numbers of a very dark cheek, a deep shadow on a brown face, or a warm face under tungsten light land near or past its edge. The pixels that fall outside are simply not skin to the tool.
The result is not dramatic. It is a mask with holes: the lit side of a darker face is smoothed, the shadowed side is not, and the two halves of one face end up with different textures. Or the opposite fault, when a box is drawn wide to compensate: lips, hair and a wooden background start to count as skin and get softened too.
What the gate here does instead
The skin gate on this site never consults a table. It looks at the region you placed over the face — by hand, or with the face finder — and takes the median brightness and colour of that region. The median, not the average, so a patch of hair or a bright earring inside the oval does not drag it. Then it keeps the pixels whose colour is within a tolerance of that median, and lets the rest fall away with a feathered edge.
- Reference colour
- the region's own median, sampled from this photo
- Tolerance
- 20 colour units by default, adjustable
- Off switch
- Keep hair, eyes and background out — off means the oval alone decides
- Check
- M paints the mask; the coverage figure is written beside it
Because the reference is the face in front of it, a very dark face and a very light one are treated the same way: each is measured against itself. Shadows that keep the same colour but drop in brightness stay in, because the gate tests colour, not brightness.
And the layers keep the colour
A mask is half the problem. The other half is what the layers do inside it. Every tonal layer here — skin smoothing, tone evening, under-eye, shine, dodge and burn — changes brightness only and writes each pixel’s colour back as it was read. Nothing here can make skin lighter or fairer in colour: that is measured on every build, on nine synthetic tones, and published on the skin-tone test page.
It is still worth looking. Press M on your own photo and see what the gate kept. If it missed part of a face, raise the tolerance or move the oval; if it kept hair, lower it. The figure beside the switch tells you how much of the region is in.
Read next
- Skin-tone testEvery layer measured for hue and chroma drift across nine synthetic skin tones, failures included.
- Skin smoothingOpens with the skin layer at 25 per cent, which leaves three-quarters of the texture.
- Even skin toneThe tone band evened at 30 per cent with texture removal at zero, so every pore stays.
- What frequency separation isThe split, the radius, and why a blur destroys the band that makes skin look like skin.