Luminance & Contrast: Introduction, Texture and Gloss, Transparency, Contrast and Lightness

Flashcards covering key vocabulary terms from the lecture.

Illuminance, Reflectance, & Luminance

The relationship between illuminance, reflectance, & luminance; their variation in nature

Contrast Specification

How contrast is specified, and what influences it

Contrast Sensitivity Function (CSF)

Sensitivity of the eye to contrast varies with the coarseness or fineness (spatial frequency) of the viewed object

Visual Acuity

Visual acuity and the factors that influence it

Lateral Inhibition

Effect on vision

Illuminance (E)

Incident light

Luminance (L)

Emitted or reflected light

Reflectance (r)

Measure of how much light is reflected from a surface

Luminance of a Surface

Surface increases, illuminance increases, and/or reflectance of surface increases

Illuminace Units

lux

Luminance Units

candelas/square metre (cd/m2)

Logarithmic Unit

Vast range of values seen in vision science, values expressed as log units

Contrast

Ratio ΔL/L where ΔL = the difference in luminance, & L = the background luminance

Resolution

Ability to see critical detail in scene, rather than simply detecting something is there

6/6 visual acuity

At a test distance of 6 meters (numerator) you could read a letter whose critical detail subtends 1 minute of arc when the letter is at 6 metres

6/12 visual acuity

At a test distance of 6 meters (numerator) you could read a letter whose critical detail would subtend 1 minute of arc if the letter were placed 12 metres away

Contrast Sensitivity Function (CSF)

Sensitivity LOW contrast visible invisible

Low spatial frequency content of image

Coarse luminance variations (e.g. large objects, overall shape)

High spatial frequency content of image

Fine luminance variations (e.g. fine structure, details)

Receptive Fields

Retina is tiled with multiple, overlapping light-sensitive areas called receptive fields

Lateral Inhibition

The idea that one area can influence the activity of a neighbouring area

Texture

Texture

What is Texture?

Surface structures tactile texture visual texture

Texture processing Peripheral Vision Crowding

Texture processing Peripheral Vision Crowding

Gloss

Measure of how much light is scattered

Transparency in Images

Object that allows light to pass through without being scattered Transmittance = amount of light out / amount of light in may be wavelength dependent (= coloured filters)

Perceiving Transparency in Images

double-belongingness scission geometric conditions photometric conditions

Contrast and Lightness

Scaling visual sensitivity Adaption Distinguish lightness & brightness lightness constancy simultaneous contrast Mach bands Craik-O’Brien-Cornsweet illusion