Colour contrast

The brain could be likened to a television set in which the amino acids are providing the basic positive and negative power lines, while the other NTs (the multi-coloured wires) control the colour, contrast and brightness. All are required for a perfect picture but some are obviously more important than others. 

Grigg, F. C. Colour-contrast phase microscopy. Nature 165, 368—369 (1950). 

Marty I, Bureau S, Sarkissian G, Gouble B, Audergon JM and Albagnac G. 2005. Ethylene regulation of carotenoid accumulation and carotenogenic gene expression in colour-contrasted apricot varieties (Prunus armeniaca). J Exp Bot 56(417) 1877-1886. 

The polished surfaces of polycrystalline Al, Cu, Ni and Si(p) and monocrystalline samples of Mo, Si(m) and W were tested to choose the best substrate providing maximal colour contrast. The surface of the substrate was chemically polished to provide mirror reflection. Thin blood smears of the same patient were deposited under the same experimental conditions. After air drying for 10 min, blood samples were placed on the microscope holder. The images were taken by a digital camera. 

Fig. 10.3 Colour contrast of human erythrocytes on different solid reflective substrates Al -polycrystalline aluminum Cu - polycrystalline copper Mo - monocrystalline molybdenum Ni - polycrystalline nickel Pt - chemically polished platinum Si(m) - monocrystalline silicon Si(p) - polycrystalline silicon Ti - chemically polished titanium W- monocrystalline tungsten...

The best colour contrast of red blood cells is achieved on mono- and polycrystalline silicon, and monocrystalline surfaces of refractory metals molybdenum and tungsten, which possess maximal reflectivity. 

Space contrast. Colour contrast is more important than brilliancy. This rule comes from the requirement to madce each colour clearly visible without being disturbed by the dazzle For example, when a weak blue light is placed near a strong red light, we cannot easily recognize the blue as it is overshadowed by the dazzle from the red which is more brilliant Accordingly it is the best to select colours in the same class in Table 1. Namely, if we use the blue in the S class as the petals, we should use the red in the same class S as pistils, i.e. p and m are used. This is to use the "same visibility effect" ... 

The colour contrast between the free indicator and the metal-indicator complex should be such as to be readily observed. 

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... 

A further limitation of the original CIE system is illustrated by Fig. 4.1 where the two grey patches ate physically identical, create the same local rate of photopigment absorption, and give the same cone excitations according to Equation 4.1. Yet, they appear to be veiy different in lightness because of the difference in their excitations relative to nearby areas. Thus whereas colour constancy demonstrates that patches of colour that have different tristimulus defiiutions can have the same colonr appearance, simultaneous colour contrast demonstrates that patches of colonr that have the same tristimulus definitions... 

A further physiological process is required to explain colonr appearance during successive colour contrast. A ubiquitous properly of neurones almost anywhere in the cortex is that when prolonged stimulation is temunated the firing rate of the nemones rebounds in the opposite state (De Valois and Jones, 1961). Since the visual pathways cany information in white-black or colom opponency channels, the termination of a stimnlns will lead to negative afterimages even in the absence of any further receptor stimulation. 

W35 W36 W37 W38 W39 W40 69% Task nature 1 = rough, 2 = moderate, 3 = fine, 4 = very fine Glare/reflection 0 = none, 1 = noticeable, 2 = severe Colour contrast 0 = none, 1 = noticeable, 2 = severe Luminance contrast 0 = none, 1 = noticeable, 2 = severe Task illuminance, foot candles Luminance Task > Midfield > Outerfield = yes... 

Purveslab at the Center for Cognitive Neuroscience, Duke University, has published numerous papers on the psychophysical visual effects people experience. One of the most striking examples of how the eye perceives colour in context is described by Lotto and Purves (2000). The discs, described in this paper, are similar to the two cubes with coloured squares (similar to a Rubik s cube) shown on the laboratory s website (Purveslab, 2011). The two cubes look similar, but one is shown in a blue environment, while the other one is shown in a yellow environment. The darkest squares of the cube in the yellow environment are blue. Yellow is the second-lightest colour of the cube in the blue environment. But, when the above-mentioned blue and yellow squares are isolated from their respective environments (taken out of context), all of them have the same colour The reason for this is called colour contrast. Although the spectral returns from the said squares are the same, the perception is that they exist in environments with different illumination, and therefore they elicit different colour stimuli in the brain. Camouflage patterns, with colours exhibiting this kind of behaviour, are effective in a wide range of environments. 

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