Light passing through a stained cell loses some of its strength, like a flashlight beam cutting through a glass of tea. The denser the color, the more light is absorbed. But until now, a microscope could only show a flat shadow of this process, not its volume.

The new method takes a stack of ordinary images captured as the focus is smoothly shifted and assembles them into a three-dimensional map of how strongly each point in the sample attenuates light. No lasers, no rotating the specimen, no special labels, just a standard light microscope and math that untangles how the shadow from depth mixes with the shadow from the surface.

The same approach colored petunia petals in 3D and digitized large stained sections of human tissue that pathologists examine under a microscope. Color, once just a picture, has become a measurable quantity, like temperature or weight.

In this way, an ordinary microscope transforms from a device for looking into an instrument that sees not only shape but also substance — layer by layer, cell by cell.