JOURNAL OF COSMETIC SCIENCE 456 The refl ective properties of surfaces are most generally and completely described by the bi-directional refl ectance distribution function (BRDF), which is a function of the direc- tion of light incidence, the direction of observation, the wavelength of light, and its state of polarization. Assessment and evaluation of the refl ective properties of surfaces can be realized (usually) by motorized scanning of a range of observation directions with a pho- tometric or spectroradiometric receiver for one direction of light incidence. This can be done with complex and bulky high-precision mechanisms called goniophotometers or goniospectroradiometers. An alternative way of scanning the directions of observation without moving parts, which is also realized in the opsira Shine-Box, is given by analysis of the spreading of a point or line source of illumination. The variation of the scattering properties of a fl exible specimen with an angle of observation within a fi xed plane of ob- servation (in-plane BRDF) can most conveniently be evaluated in a cylindrical geometry (as used in the opsira Shine-Box, see Figure 1B) by analysis of the spread of a linear illu- mination source. In that confi guration, the angle of light incidence and the angle of obser- vation both vary with their position on the circumference of the cylinder, thus generating a wide range of angles between incident and refl ected light beams. As a consequence, this cylindrical geometry can be used to evaluate the in-plane BRDF of a roll of hair fi bers in one single image of an adequaltely calibrated camera (imaging photometer or colorime- ter). From such images, e.g., the sheen (luster) of the hair can be determined, or with some modifi cations in the geometry of illumination, other characteristics like sparkle can also be measured and evaluated. Using BRDF, it is also possible to determine the half width (HW), or more precisely, full width at half maximum, of specular refl ection (Figure 2). The objective shine value or luster (L) is characterized by the equation of Reich/Robbins (4) as standard specular RS×HW L RD×HW (Eq. 1) where RS is the integrated intensity of specular refl ection • RD is the integrated intensity of diffuse refl ection • HW • standard is the half width of an optimally refl ecting area (representing the carrier without mounted hair tresses HW • specular is the half width of specular refl ection of the mounted hair tress Figure 2. Specular and diffuse refl ection of a human hair mounted on the carrier of the Shine-Box. HW denotes the half width of specular refl ection, or more precisely, full width at half maximum.

AUTOMATED DEVICE TO ASSESS HAIR SHINE 457 Thus, the higher the contrast between specular refl ection and its background (i.e., the lower diffuse refl ection and the half width of specular refl ection), the higher the shine value. By inclusion of the standard half width of a black metal cylinder into the above equation, the calculated objective shine value L has no dimension. Objective sparkle value. Sparkle effects are characterized by a short angular lifetime. The sparkle effect results from a total refl ection of the incident light within the hair fi ber in the direction of the observer, who perceives this light as a bright spot. The effect strongly depends on the angle of the incident light, the actual geometry of the hair, and the posi- tion of the observer. Therefore, hair seems to sparkle due to the movement of the head or the observer. Since dark hair absorbs most of the incident light, sparkle is most promi- nent with blond hair and contributes to the subjective perception of hair shine. In the opsira Shine-Box, sparkle is quantifi ed by illuminating hair tresses via a segment of a ring illumination device (see Figure 1A) from slightly different angles (±5.6° and ±2.8°) and recording pictures for each individual illumination angle. According to the defi nition of sparkle, a sparkle spot must only occur under one illumination angle. To identify sparkle spots using the opsira Shine-Box, means and standard deviations of in- tensities of corresponding pixels from four pictures (taken under different illumination angles) are calculated, and sparkle spots are defi ned as pixels with a very high standard deviation (i.e., exceeding a defi ned threshold of standard deviation). The number of spar- kle spots is counted for each individual hair tress and makes up the sparkle value. A typical series of four pictures and the calculated results picture are shown in Figure 3. Parallelism. To allow an accurate determination of shine and sparkle, a hair tress to be evaluated has to be well combed and parallel. Using the opsira Shine-Box, parallelism is routinely assessed as a quality control, and tresses with insuffi cient parallelism are ex- cluded from analysis until better parallelism is gained by additional combing. Under ideal conditions of a perfectly cylindrical body (e.g., the carrier without a mounted hair tress), the vertical intensity distribution follows a bell-shaped distribution, and the hori- zontal intensity distribution at a given position has a constant value. This horizontal and vertical distribution pattern changes when the surface is altered, e.g., by mounting a hair tress on the carrier. To quantify the parallelism of a given hair tress mounted on the car- rier, the entire object is divided into a defi ned number of vertical columns. At each posi- tion in a given row, the average horizontal intensity is calculated (Figure 4). Averaging is done to not give individual hairs in a given row too big a weight. In an ideally combed tress, the vertical distribution of the average horizontal intensities of all rows should be identical. In contrast to this, the vertical distribution of uncombed tresses can be expected to be different in each individual row. The variance of intensity distribution between in- dividual rows contains the information about the parallelism and quality of combing. RESULTS HAIR SHINE Correlation of objective shine values with subjective panel results. According to the equation of Reich/Robbins (eq. 1), the objective shine value can be increased by increasing the inte- grated intensity of specular refl ection (RS) in the numerator of the fraction, or by decreasing