Random walker algorithm how a gray-level image can be 3D?

Question

• I was reading the source of the random walker algorithm in scikit-image library, and it's written there that:

Parameters

---

data : array_like
    Image to be segmented in phases. Gray-level `data` can be two- or
    three-dimensional

My question is: what do they mean by 3D gray-level image?

Answer 1

A 2D image is an image that is indexed by (x,y). A 3D image is an image that is indexed by (x,y,z).

A digital image samples the real world in some way. Photography produces a 2D projection of the 3D world, the digital photograph is a sampling of that projection. But other imaging modalities do not project, and can sample all three dimensions of the 3D world. For example:

• Confocal microscopy
• Computed tomography
• Magnetic resonance imaging

Besides these, a 2D time-series (a movie) is sometimes also treated as a 3D image, applying algorithms that work on 3D images.