Cut out hair and fur

Set edge detail to one and this page behaves like every other background remover: it makes a yes-or-no decision about every pixel and draws the line. On a handbag that is exactly right. On a person it produces a helmet — a head-shaped outline where the hair has been rounded either up to solid or down to gone, and the result has the flat, stuck-on quality that gives a cutout away in a fifth of a second.

This page starts at thirteen pixels and sixty percent feather. Thirteen pixels of band means the boundary is not a line but a strip, and inside that strip the guided filter re-reads the photograph at full resolution and lets its real edges decide how much of each pixel is hair. Sixty percent feather means the values it finds are left roughly as found rather than pushed toward nought or one. Both are starting positions and both are on the same two sliders as everywhere else on this site.

Leave the band alone on the first pass and look at the silhouette. If the shape of the person is wrong — a hand missing, someone else included — that is a job for the keep and take-away brushes on step 3, and no amount of edge work will fix it. Get the shape right first; the band only ever refines a boundary that is already roughly in the right place.

Then widen the band until strands appear and stop at the point where the background starts appearing with them. That point is different for every photograph, and it is usually a lot lower against a bookshelf than against a wall. Last, put the cutout on the near-black backing swatch and look at the crown: a pale halo there is the surest sign the band is wider than the photograph can support.

• Similar tones beat this. The whole method rests on the subject and the ground being distinguishable by colour and contrast. Dark hair against a dark doorway gives it nothing to work with, and the honest result is a cutout that follows the head and loses everything loose around it.
• Colour picked up from behind stays. A semi-transparent hair pixel is part background by definition, and this version does not estimate and subtract that contribution. In front of a hedge you will get a faint green rim, and the fix available today is the brush rather than a slider.

Why does widening edge detail sometimes make it worse?

Because a wider band is a bigger question, not a better answer. Every pixel inside the strip is re-decided from the photograph's own contrast, so on a portrait against a plain wall a wide band finds real strands and keeps them. Against a patterned curtain, the same width hands the filter a strip full of edges that have nothing to do with the person, and it dutifully makes some of them semi-transparent. Wide bands want simple backgrounds.

What is feather doing that edge detail is not?

Edge detail decides how many pixels are allowed to be uncertain. Feather decides how that uncertainty is resolved — whether the values in the band get pushed toward a decision or left as the filter found them. At nought the ramp is steep and the cutout has a definite outline; at a hundred the ramp is left long and gentle, which reads as soft rather than as sharp-but-wrong. On hair you usually want both up.

There is a green tinge along the edge of the hair.

That is the background, still physically present in those pixels. A strand that covers a third of a pixel means two thirds of that pixel's colour came from whatever was behind it, and lifting it onto transparency carries that colour along. Estimating and subtracting it is a real technique and it is not in this version; what is here is the take-away brush, which removes the worst of the rim at the cost of the strands inside it.

Does a bigger photo give better hair?

Up to a point, yes, and it is worth knowing why. The band is solved against the picture at its real resolution, so more pixels across a strand means more pixels that can be partly there. A subject under about three hundred pixels on its long edge has strands thinner than one pixel, and there is nothing for the band to resolve — it is a coarse mask with soft edges, which is not the same thing.

• Hair, fur and every other soft edgeWhat the uncertain band is, what widening it costs, and the edges nobody wins.
• Make a picture transparentThe same four steps, with the file-format question answered on the way out.
• Why a transparent PNG can still look whiteTransparency is a channel, and every app you paste into decides what sits behind it.
• Cut the subject outOpen a photo with a clearly separable subject, let colour and contrast propose the edge, correct it by hand, save a transparent PNG.