Hair is not a hard-edged object
A portrait can have a clean shoulder outline and a difficult hair edge in the same image. The shoulder is mostly opaque with a distinct boundary. Loose hair contains fine strands, gaps, and pixels where hair and background were recorded together. Treating both edges with the same broad eraser stroke is a quick way to make a portrait look cut out with scissors.
Separating foreground from background is often described as segmentation. Estimating how much foreground belongs in a partially covered pixel is a matting problem. In practice, a useful hair cutout needs some partial transparency, not just fully opaque hair next to fully empty space. A PNG can store those values, but the format cannot determine whether they are correct.
Read the sample in three regions
In the portrait above, start at the top of the head. Fine wisps sit in front of both light and dark parts of the blurred background. A single brightness threshold would not separate all of them reliably. Next, inspect the loose strands extending toward the viewer's right: preserving a strand also means removing the spaces beside it, not restoring a whole rectangle around it.
Finally, compare the red shoulder with those hair regions. Its boundary is broader and more continuous, so small mask errors are easier to recognize. Use it as a reference for judging whether the result has lost a solid piece of the subject. These are inspection targets in the bundled photo, not a claim that every strand in the supplied cutout has been recovered.
Use backgrounds to diagnose, not to hide defects
Inspect the same region on white, a dark color, and the intended final background. If a pale rim appears only on dark backgrounds, it may contain color from the original scene. If a solid patch follows the hair across all backgrounds, it may be unwanted pixels left in the mask. If a real lock of hair disappears compared with the source, it needs restoration rather than more erasing.
A checkerboard alone is a poor final judge because its alternating tones can disguise both light and dark remnants. At the same time, an extreme zoom can make normal soft pixels look alarming. Diagnose at a close zoom, then decide whether the correction helps at the size where the portrait will actually appear.
Make a local correction, then reassess
Cutout Lab's Restore area control paints from the original photo. It does not find a strand inside your brush stroke and intelligently discard everything around it. A brush wider than a loose strand can bring back more background than hair. When that happens, undo rather than building up more alternating erase and restore strokes.
- Pick one visible defect, such as a detached background patch outside the hair. Avoid changing the full outline at once.
- Use Erase on the patch with a brush that stays clear of the subject. Leave soft, partly transparent hair pixels alone unless they are visibly wrong.
- For a missing lock, compare its exact position with the original, then try a small Restore area stroke. Undo if the old scene reappears between the strands.
- Return to the final background and normal display size. Keep the change only if it improves the silhouette without making the hair look unnaturally solid.
When a brush is the wrong tool
Color spill and missing detail are different problems. Hair photographed next to a strongly colored wall may contain that reflected color even where the mask is correct. Erasing those pixels thins the hair; restoring them restores the same color. This needs edge-color correction or a better source photo, not more confident brushwork. Cutout Lab does not currently offer dedicated color decontamination.
For a new portrait, use soft light, leave space around flyaway hair, and choose an uncluttered background that contrasts with the hair without casting strong color onto it. For an existing portrait with blur or low contrast, accept that preserving every strand may require a dedicated masking workflow. Keep a transparent master and check clothing and shoulders as carefully as the hair before publishing.