A shadow is not an object
When a person, a lamp post or your own phone throws a shadow across a floor, a wall or a page, nothing is missing from the picture. The tiles, the paper grain, the wood are all still there; they are just darker and, outdoors, a little bluer, because the shadow is lit by the sky instead of the sun. An eraser that treats the shadow as a hole throws that real surface away and invents a new one, which is why so many “shadow removers” leave a smeared, too-smooth patch. Shadow Lift does the opposite: it keeps every pixel's detail and changes only how brightly it is lit.
How Shadow Lift relights
First the editor works out where the shadow's hard core ends and its soft edge begins. It measures how quickly the brightness recovers as you move away from the selection, which gives the width of the soft edge — a few pixels for a shadow cast close by, tens of pixels for one cast from far away. Then it compares two samples on the same surface: the deep inside of the shadow and a band of lit surface just beyond the soft edge. From those it computes, separately for red, green and blue, how much brighter and how much more contrasty the lit side is, and maps the shadowed pixels onto the lit side's statistics. Doing it per channel is what removes the blue cast of an outdoor shadow. Across the soft edge the lift is weighted by how dark each pixel still is, so the boundary fades away instead of becoming a bright rim. Finally, if the lifted area is smoother than its surroundings — shadows hold fewer brightness levels, so lifting them can look plasticky — a little of the lit side's own grain is added back.
When it cannot help
Lifting only works if something survived under the shadow. If the shadow is clipped to black, or holds fewer than six levels of brightness, the editor says so and offers Rebuild instead, which is a normal erase that reconstructs the area from its surroundings. It is also built for cast shadows on surfaces — ground, walls, documents and products. It is not for faces or for relighting a portrait; light on a face is shaped by the face itself, and pretending otherwise produces something uncanny.
Passport and visa photos
People often ask about a shadow behind the head in an official photo. Many official photo specifications do not accept digitally altered photos, so the honest advice is to retake the photo with even light from the front and a little distance from the wall. For everything else — a document photographed on a desk, a product shot with a stray shadow, a patio picture — click the shadow and lift it. If what you want gone is the object casting the shadow too, Remove unwanted objects selects both together.