Perception of colour

When colour is assessed on the basis of reflectance measurements, it is common to consider the three relevant attributes of perception of colour as hue, chroma (or saturation) which is the colourfulness or richness of the colour, and lightness, which refers to the amount of reflected light. These three attributes may be described using the concept of colour space, which shows the relationships of colours to one another and which illustrates the three-dimensional nature of colour, as portrayed in Figure... 

Those of us fortunate enough to possess optical powers capable of distinguishing a variety of colours will appreciate the influence that this particular sensory dimension exercises on our judgement of matters important to our well-being, such as food and drink. The perception of colour influences a taster s reception of a drink, and as a consequence there is inevitably some controversy over the use of colourings in food and drink. 

The effects of psilocybin last for a few hours. Its physical effects include pupillary dilatation, flushing, nausea, tremor, pyrexia, hyper-reflexia, tachycardia, weakness, and dizziness (5). The psychedelic effects include visual and other types of hallucinations, including enhanced perception of colours, synesthesia, time slowing, and a sensation of ego fragmentation. Psilocybin also causes illusions of motion in otherwise stationary objects (6). Psychotic reactions ( bad trips ) can occur, accompanied by fear, panic, and dangerous behavior, especially when psilocybin is used in combination with other drugs and alcohol or by psychiatrically unstable patients. During such an attack, self-mutilation can occur (7). 

Calvo, C., Salvador, A., and Fiszman, S.M. 2001. Influence of colour intensity on the perception of colour and sweetness in various fruit-flavoured yoghurts. European Food Research and Technology 213 99-103. 

A major objective of this book is to relate the psychological processes involved in the human perception of colour and its associated appearance qualities with the many components and variables encountered in the visual judgement of foods within their contexts. This book is divided into two major parts, the first dealing with the perception of appearance and measurement of the colour of food and the second on colour control in food. 

Stephen Westland continues the topic of human perception of colour in Chapter 4. He describes the retinal image and the effects of the surroundings on the perception and appearance of colour, especially the phenomena of colour constancy and colour contrast. The importance of white as a reference point in the field of human vision and its role in adaptation is presented. The development of colour appearance models is outhned and the relationship of these uniform colour space models to their use in the formation of digital image... 

The co-ordinates of L, a and b in CIELAB serve to define the location of any colour in the uniform colour space. However, in most industrial applications the object of measuring products is usually to determine how far they may be divergent from a set standard, both in colorimetric terms and in acceptability of visual match. The determination of uniform colour differences by CIELAB is not the same as the recognition of acceptability. CIELAB is based on the perception of just noticeable colour differences in the cyhndrical co-ordinates of the system. However, acceptability differences are based on the perception of colour tolerance differences of real materials of industrial interest, e.g., textiles. 

Good food can usually be distinguished from bad food by colour. This may appear to be an obvious statement, but the implications for the food industry are significant. Human perception of colour has proved very effective in determining food quality. Sorting of food products using the human eye and hand is still widely practised in regions where labour rates remain low. However, where the cost of labour has increased, so automated teehniques have been introduced. 

Colour perception in humans is initiated by the absorption of light by three different spectral classes of cone cells present in the retina, conveniently referred to as blue, green and red. Each class exhibits a different but overlapping spectral sensitivity, with maximum values at ca. 419, 531 and 558 nm respectively. The sum of the differing sensitivities is called the photonic response and displays a maximum value at 555 nm. However colour perception can be very subjective, and the description of colour differences can be quite challenging. Colorimetry and the trichromatic perception of colour are based on Grassmans laws [19, 20] ... 

Mirrors reflect colours very well For CMS the image fidelity is determined by the optical-electrical-optical transfer function. The colour range of a CMS is limited. Colours can be perceived differently by changing the angle of view on the monitor. Artifacts can affect the depiction and perception of colours... 

Chloramphenicol may cause retinal bleeding (as a symptom of aplastic anaemia), alterations in the perception of colours, and optic neuritis. The latter type of side effect has been observed especially in children with cystic fibrosis receiving chloramphenicol in relatively high doses for fairly long periods (38 ). Deficiency of B vitamins is believed to be the cause of the optic neuritis, and perhaps also of the polyneuritis, peripheral neuritis, and paraesthesiae of the legs sometimes seen after prolonged courses of treatment with chloramphenicol and thiam-phenicoL Administration of extra vitamins may protect patients from this type of reversible side effect (SED VIII, p. 610 38 ). 

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