Image Color Dimension Reduction. A comparative study of state-of-the-art methods

Document from the year 2016 in the subject Design (Industry, Graphics, Fashion), , course: 2016, language: English, abstract: Color is a human sensation depending on the brain's response to a specific visual stimulus and we experience color as one single attribute. Although we can precisely describe color by measuring its spectral power distribution, this leads to a large degree of highly redundant data. The reason for this redundancy is that the eye's retina samples color using only three broad bands, roughly corresponding to red (R), green (G), and blue (B) light, belonging to the response of three type of sensitive cells (cones) termed L (long), M (media), and S (short) in relation to the wavelength of frequency band they respond to. The signals from these sensors, together with those from the rods (sensitive to intensity only), are combined in the brain to provide several different sensations of the color.

Color production in digital RGB images is similar in some aspects, like in the usage of three sensors for R, G, and B lights, but unfortunately it lacks in sensors for intensity only (i.e. rods) and also in an analyzer similar to the human brain to interpret contextually and psychologically the signal from those three sensors.

The above-mentioned characteristics of color production in digital images difficult the process of interpreting color images, neglecting or reducing their chromatic content because this task becomes a problem of dimension reduction, from the three-dimensional (3D) space of the RGB representation to the two- or one-dimensional (1D) space of intensities: the color reduction and the color-to-grayscale (C2G) conversion, respectively. For some color reduction procedures, it is a problem similar to color quantization and compression of gamut dimensionality. However, in any case, there is a loss of visual information and, most of the time, the conversion usually preserves luminance contrast without an appropriate handing of the chrominance (hue and saturation) meaning. This is the case of the classical C2G image conversion methods in widespread use.