Reference Work Entry

Computer Vision

pp 562-564

Date:

Opacity

  • Ivo IhrkeAffiliated withMPI Informatik, Saarland University

Synonyms

Opaque

Related Concepts

Polarization; Transparency and Translucency

Definition

Opacity describes the degree to which an object or material is not transmitting light. Sometimes the opposite is referred to as transmittance (mostly in physics). In computer graphics, the opposite of opacity is typically referred to as transparency.

Background

Most computer vision algorithms, whether designed for 3D reconstruction, object detection, object classification, etc., require the scene and the objects it consists of to be opaque. More precisely, objects are required to be diffusely opaque. Specularly reflective objects, e.g., are opaque by definition but most vision techniques cannot handle them.

A multitude of research has gone into lifting the restriction on scene opacity. When going beyond opaque objects, images are typically enhanced by an alpha channel – a fractional measure of opacity, or the amount by which an object obscures the background in an image.

In television and film production, th ...

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