CIELAB color space boundaries under theoretical spectra and 99 test color samples

Abstract

A color space is a three‐dimensional representation of all the possible color percepts. The CIE 1976 L*a*b* is one of the most widely used object color spaces. In CIELAB, lightness L* is limited between 0 and 100, while a* and b* coordinates have no fixed boundaries. The outer boundaries of CIELAB have been previously calculated using theoretical object spectral reflectance functions and the CIE 1931 and 1964 observers under the CIE standard illuminants D50 and D65. However, natural and manufactured objects reflect light smoothly as opposed to theoretical spectral reflectance functions. Here, data generated from a linear optimization method are analyzed to re‐evaluate the outer boundaries of the CIELAB. The color appearance of 99 test color samples under theoretical test spectra has been calculated in the CIELAB using CIE 1931 standard observer. The lightness L* boundary ranged between 6 and 97, redness‐greenness a* boundary ranged between −199 and 270, and yellowness‐blueness b* boundary ranged between −74 and 161. The boundary in the direction of positive b* (yellowness) was close to the previous findings. While the positive a* (redness) boundary exceeded previously known limits, the negative a* (greenness) and b* (blueness) boundaries were lower than the previously calculated CIELAB boundaries. The boundaries found here are dependent on the color samples used here and the spectral shape of the test light sources. Irregular spectral shapes and more saturated color samples can result in extended boundaries at the expense of computational time and power.

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“…Color change was measured with a colorimeter according to the principle of CIE color space. Parameters L*, a*, and b* indicate the intensity of lightness, redness, and yellowness of the sample, respectively [19].…”

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“…The confocal laser-scanning microscopy (CLSM) analysis, with lipophilic Nile Red as an oil-phase marker, directly evidenced the formation and stabilization of the emulsions without any surfactants or emulsifiers (Figure 2c and Figure S3). The hair-coloring capability of the eight different emulsions was investigated by measuring the L* value in the CIELAB L*a*b* color space [37], after immersing a blonde hair sample for 30 min in the emulsion and shampooing (Table 1, Figure 2d and Figure S4). In the CIELAB L*a*b* color space, the L* (lightness) value is defined to be 0 for black and 100 for white.…”

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“…The lightness L * is limited to values between 0 and 100. However, a * and b * coordinates have no fixed boundaries, 42,43 although various studies have introduced chromatic components in the range between −120 and +120 20,40,44 . In a recent study by Durmus, 43 color coordinates under the extreme theoretical spectra of 99 test color samples produce the L * boundary between 6 and 97, a * boundary between −199 and 270 and b * boundary between −74 and 161.…”

“…However, a * and b * coordinates have no fixed boundaries, 42,43 although various studies have introduced chromatic components in the range between −120 and +120 20,40,44 . In a recent study by Durmus, 43 color coordinates under the extreme theoretical spectra of 99 test color samples produce the L * boundary between 6 and 97, a * boundary between −199 and 270 and b * boundary between −74 and 161. The hue angle ( h °) and chroma ( C *) of the images were also computed in this study from the L * a * b * values where C * = √( a * 2 + b * 2 ) and h ° = tan −1 ( b */ a *) 45,46 …”