Colour perception and sensory evaluation


Color

The modern era of for the study of the light and vision can be regarded as starting in the 17th century. More is known about the visual part of the brain than any other and hence much work has focused on visual development.

Color perception

Light entering the lens of eye is focused on the retina, where the rods and cones convert it to neural impulses which travel to the brain via optic nerve. Photo-absorption is the initial event of vision, photosensing, and ion-pumps in retinal proteins. The absorption maxima of the retinal proteins are well regulated in wide spectral range to furnish the photo-receptors with color sensitivity, whereas the proteins include a common identical chromophore, retinal. The electronic excitation energy of retinal is controlled by interaction with the apoprotein known as opsin.
          
There are some aspects of color perception that must be considered in sensory testing. These aspects include, subjects often give consistent responses about an object color even when filters are used. The gloss and texture of a surface also affect perception of color. Color vision differs amongst subjects. Subjects are influenced by adjoining or background color and the relative sizes of areas of contrasting color, blotchy appearance, as distinct from an even distribution of color, affects perception.
          
The vision has advantage over the other senses in that an observer’s appreciation of an object’s appearance can be recorded pictorially. Color vision and appearance are two different things. Vision can be regarded as the process of seeing whereas appearance is the recognition and assessment of the properties such as surface structure, opacity, color, etc. associated with the seen object. Vision is sequence of events starting with the external stimulus, the radiant flux incident on the eye, and proceeding through the reception of light on the retina to its interpretation after transmission through the visual pathway to the cortex of the brain. Vision is the psychological response to the objective stimulus generated by the physical nature of the object.
            
Different color terms are typically used to describe color experiences that vary from culture to culture, all sensations of color reduce to one of four perceptual categories (five if greyness is included): redness, yellowness, greenness and blueness. For any individual with normal color vision, there should be a specific wavelength that causes a ‘unique’ sensation of yellow that is a color percept that contains neither redness nor greenness. The same case for perceptions of red, green and blue.  The identity of this wavelength remains fairly constant from individual to individual


Definitions of the terms related to the color

Attribute

Definition

1.Color Identity

 

Color that you closely associate with the sample. Found on the color wheel i.e. white-green, yellow-green, yellow, yellow-red, red, red-purple, purple, blue-purple, blue, and blue-green.

2.Color strength

 

Also known as color intensity. The weakness or strength of the sample color.

3. Lightness

 

Lightness refers to the presence of white and the absence of black or gray in the sample color. Darkness refers to the amount of black or gray shades that is found in the sample color

4. Vividness

 

Emitting or reflecting much light from within, Vivid.

5.Color uniformity

 

Equal or even distribution of color throughout the sample. NOT streaky mottled nor speckled

6. Naturalness

 

Impression of naturalness the sample color projects. Mark on the zero point at the beginning of the scale if you find that the sample is synthetic or artificial in appearance

7. Glossiness

 

Surface lustre/ shine/ glaze

8. Opaqueness

 

Light not able to be transmitted through the sample i.e. sample impenetrable to light.

 9.Opacity uniformity

 

Equal or even distribution of opaqueness throughout the sample


References

Piggott, J.R. (1988) Sensory Analysis of Foods (second Ed.) Elsevier Applied Science, London & New York.

Imran, N. (1999) Visual cues identified by a visual profile panel in the evaluation of chilled Dairy Desserts. Journal of Sensory Studies, 14, 369-386.

Meilgaard, M., Civille, G. V. & Carr, B. T. (1999). Sensory evaluation techniques (third Ed.). Boca Raton, FL: CRC Press LLC.

Lotto, R.B. (2004) Visual Development: Experience Puts the Color in Life. Current Biology, 14, R619–R621.

Fujimoto, K., Hasegawa, J., Hayashi, S., Kato, S., Nakatsuji, H (2005). Mechanism of color tuning in retinal protein: SAC-CI and QM/MM study. Chemical Physics Letters, 414, 239–242.

Zhou, Y., Chen, A., Gong, H., Liang, P. (2005). Color information encoded by the spatiotemporal patterns of light response in ganglion cells of chick retina. Brain Research, 1059, 1-6.

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