What Are Window and Level in DICOM?

What Are Window and Level in DICOM

A DICOM image stores far more distinct values than a display can show or an eye can separate — CT, for instance, covers thousands of Hounsfield units. Windowing chooses which part of that range becomes visible: the window width is how wide a band of values is mapped to the available shades of gray, and the window center (the level) is where that band sits.

Narrow the window and small differences become visible while everything outside the band turns pure black or white; widen it and more of the range fits on screen with less contrast between nearby values. This is why the same CT is read at one setting for lung and another for bone or soft tissue: the pixel data does not change, only the mapping.

The values are not arbitrary. A study often carries VOI LUT information — either a window width and center chosen at acquisition, or a full lookup table — and viewers add presets per modality so a reader can jump between the settings that matter for a body region.

Because windowing is display only, it never alters the stored pixels; what it does alter is what a screenshot or an exported picture will show.

In Weasis, see LUTs and window/level.