Marr

Place Tokens

Set of visual primitives that correspond to oriented edge or boundary segments, to points of discontinuity in the orientations, to bars or to their terminators, or to blobs.

Primal Sketch

Theoretical result of the first stage of visual processing, involving the detection of intensity changes, the representation and analysis of local geometrical structure and the detection of illumination effects such as light sources, highlights and transparency. In viewer-centered coordinate frame.

Virtual Line

A visual token constructed between neighboring similar tokens that has the property of orientation and length.

Zero-Crossing

Intensity changes give rise to a zero-crossing in the second derivative which can be used to compute edges. (See also ²G Filter).

Zero-Crossing Segments

Oriented primitive composed of zero-crossings describing a piece of contour whose intensity slope and local orientation are roughly uniform.

2 1/2D Sketch

Theoretical result of the second stage of visual processing operating on the primal sketch to derive a retinocentric representation of the geometry of visual surfaces.

²G Filter

Method for computing zero-crossings from an image by taking the laplacian, ², and a two dimensional gaussian function, G, with a standard deviation, . The gaussian blurs the image, wiping structure at scales smaller than the standard deviation.