Digital pathology, explained by following one piece of tissue from the operating room to a gigapixel image on a screen, with every term defined where it first matters.
Most of the journey happens before the scanner, in glass and wax. Tap a step, or use the arrow keys. Underlined terms open a definition.
A scanned slide is far too big to open as one picture. It is stored as a pyramid: the full-resolution image, plus smaller and smaller copies, each cut into tiles. The viewer only fetches the tiles you can see, from the level that matches your zoom. Drag to pan, scroll or pinch to zoom. The tissue here is drawn by code, not scanned.
Each level is a quarter of the width of the one below, so the whole pyramid adds only about a third to the file. Zoomed all the way out the viewer reads one of the small top levels; at full zoom the viewer is reading level 0, where a pixel is a quarter of a micrometre and a single nucleus spans about 25 pixels.
Why the files are measured in gigabytes. Set the size of the tissue and the scan resolution; the arithmetic is shown underneath.
Every term from the pipeline, in one place. The color strip says whether it belongs to the glass side or the pixel side.