PerLecture 8 (AIver) - Colour Perception Lecture Notes

Practice flashcards covering the physical, biological, and psychological aspects of colour perception based on the lecture transcript.

Isaac Newton's Perception of Colour

The idea that rays of light are not themselves coloured, but possess a 'certain Power and Disposition to stir up a Sensation' of colour in the beholder.

3D Colour Perception Dimensions

The three dimensions that define perceptual colour space: Hue, Lightness, and Saturation.

Visible Spectrum Range

The range of electromagnetic radiation visible to humans, typically spanning from approximately $300\,\text{nm}$ or $400\, \text{nm}$ to $700\, \text{nm}$.

Spectral Colours

Colours that consist of just one specific wavelength of light.

Additive Mixture

The process of mixing light (such as in TV or computer monitors), where adding primary colours like Red, Green, and Blue results in brighter colours or white light.

Subtractive Mixture

The process of mixing pigments, paints, or inks where wavelength components are reduced due to absorption, leading to darker results (e.g., CMYK).

Rod Photoreceptors

Receptors in the retina responsible for vision in low light; they do not perceive colour, explaining the phrase 'All cats are grey at night.'

Cone Photoreceptors

Three types of receptors (S, M, and L) responsible for colour vision under daylight conditions.

S-cone

The short-wavelength cone, often associated with the perception of blue.

M-cone

The medium-wavelength cone, often associated with the perception of green.

L-cone

The long-wavelength cone, often associated with the perception of red.

Blind Spot

The region in the retina where the optic nerve exits and there are no photoreceptors (rods or cones).

Fovea

The central point of the retina containing a high density of cones but no rods and no S-cones at the very center.

Cone-Opponency

The second stage of colour processing involving comparisons between cone signals, creating dimensions such as $L-M$ (red-green) and $(L+M)-S$ (blue-yellow).

Trichromacy

The condition of having three types of cone photoreceptors, which allows for a three-dimensional colour space.

Lateral Geniculate Nucleus (LGN)

The subcortical part of the thalamus that processes colour information before relaying it to the primary visual cortex (V1).

Ventral Stream

Known as the 'what pathway' (including V2 and the V4 complex), this cortical pathway is primarily responsible for processing colour to identify objects.

Dorsal Stream

Known as the 'where pathway,' this cortical pathway generally does not process colour information.

Protanopia

A type of dichromacy resulting from the complete absence of L-cones.

Deuteranopia

A type of dichromacy resulting from the complete absence of M-cones.

Tritanopia

A type of dichromacy resulting from the complete absence of S-cones.

Daltonism

A common term for red-green colour blindness, caused by the absence of L-cones or M-cones; it is inherited via the X chromosome.

Ishihara-Plates

A standard vision test used for the diagnosis of colour deficiencies, where observers identify numbers within patterns of coloured dots.

Achromatopsia

Complete colour blindness, which can be retinal (due to a lack of cones, such as rod monochromatism) or cerebral (due to cortical lesions).

Colour Constancy

The ability of the visual system to perceive the stable colour of an object or surface despite variations in the physical properties of the illumination.

Adaptation

A mechanism of colour constancy where the visual system adjusts its sensitivity to specific colours over time, leading to phenomena like afterimages.

Local Contrast

A mechanism of colour constancy where the perception of a colour is determined relative to the colours immediately surrounding it in a scene.

Brightness Anchoring

A mechanism of colour constancy where the brightest part of a perceived scene is interpreted as 'white.'

Scene Interpretation

A high-level mechanism of colour constancy that accounts for shadows and transparency to determine the true lightness of a surface.

Dominant Hue

The representative colour of an object (e.g., 'a banana is yellow') derived from a polychromatic colour distribution.