فهرست مطالب فرهاد عامری

A condition that must be satisfied for digital printers in a color management system is converting device-dependent color values into device-independent color values by a transfer model of high-quality performance. Usually, each transfer model is initially trained with some specified samples as a training set before being tested. In the present study, color charts with different quantities of color patches in an RGB space were selected and printed as training groups.  The spectral reflectances of all samples in printed color charts were measured and converted to an XYZ color space under a standard observer/illuminant combination. Using a matrix method, the RGB to XYZ transformation matrices were obtained with the algebraic operation of different degrees of polynomials and the least-square errors for the training groups.Similar operations were also performed for the well-known ProfileMaker software, which is based on a look-up table method. Finally, the statistical values of color difference (DE2000) were calculated between the actual XYZ from the printed color charts, the predicted XYZ from the matrix method, and those predicted from the ProfileMaker software. The ProfileMaker software showed a significantly lower color difference near the perception threshold for the specified training samples.

It is essential to investigate calibrated BCRA ceramic standards reference' color stability to determine the reflectance spectrophotometer's calibration period time. In this research, the color and spectral changes of a set of fourteen BCRA ceramic standards made by Avian Technologies Company were investigated over three years under repeatable conditions. Each ceramic's color changes were evaluated by calculating ∆E*ab and ∆E*00 and then analyzed using univariate statistic metrics such as MCDM and RMS (2S). Similarly, the spectral reflectance factor's variation was evaluated using univariate metrics of the standard deviation of reflectance (∆Rλ,2δ) and RMSR. This study's statistical results showed that the color and spectral reflectance factor of BCRA ceramic standards had no significant changes for three years and established good color stability. The maximum values were obtained for the statistic metric of MCDM (ΔE*ab) within about 0.08 units and the statistic metric of RMSR within about 0.02%. This result can play a significant role in reducing the recalibration costs of these reference ceramics.

The aesthetic and pleasing properties of a product are important and significantly add to the meaning and relevance of a product. There has been a strong industrial and academic interest and need to establish hardware and/or software systems in order to quantify and link appearance properties to their human response equivalences. In this study, we intend to review models which have been proposed to quantify human perceptions of appearance features. To this end the importance of Kansei Engineering in appearance is considered. This is a tool for linking consumer expectations of products with valid design parameters. In the domain of human senses, soft metrology is used as a method for metering and objective quantification of perceptual qualities of appearance.

In the present investigation four spectrophotometers from different models of the X-Rite company were compared in terms of precision and truness using BCRA standard tiles. We investigated the effect of manufacturer’s re-calibration procedure on the reduction of error for spectrophotometers in which only two of them were calibrated. The repeatability results of this research show that the precision of all spectrophotometers is acceptable and there is no significant difference between calibrated and non-calibrated devices. Moreover, the average of color difference results for a series of fourteen BCRA tiles show that only the CE7000 A as a non-calibrated spectrophotometer needs the manufacturer’s re-calibration procedure whereas the SP62 spectrophotometer which was not calibrated, shows no significant error in comparison to both other calibrated devices. Additionally for achromatic tiles, the new calibrated Ci64 device demonstrates a larger error than both SP62 and SP64 devices. Meanwhile, the average of color difference values per device for BCRA tiles are larger than acceptable values. Therefore, it seems that the acceptable value for trueness of spectrophotometers is an unreasonable expectation and needs to be revised.

In this research the effect of appearance factors of automotive finishes on their blackness perception is investigated under various types of illumination. In order to decrease the effect of colorimetric attributes on perceived blackness of panels, samples with nearly identical colorimetric properties, i.e., lightness, chroma and hue, are selected. Regarding the industrial and commercial approach of the subject, the selected panels benefit from the optimum geometric appearance factors (higher values of distinctness of image and gloss as well as lower orange peel values) which are preferred by the majority of luxury vehicles customers. The pair comparison method was used to visually rank the blackness perception of metallic black panels. Results showed that there is not any significant relationship between the geometric appearance factors of automotive finishes and their blackness perception under different types of illumination, i.e., light booth, diffuse illumination and the unidirectional illumination.

In this study the correlation between quantitative visual assessment of distinctness of image and its instrumental equivalents as measured by two types of measuring instruments namely a goniophotometer and a wavescan DOI instrument was sought after. To this end, 4 scales were prepared based on automotive achromatic samples varying in lightness i.e. black, grey, silver and white, having variable DOI values but the other geometric attributes being kept constant as far as possible. The differences in DOI of samples in each scale were visually assessed and quantified in terms of an also prepared lightness scale by a panel of 16 observers. The coefficient of determination was utilized to assess the correlation between such quantified visually assessed data and the equivalent instrument values as measured separately by a goniophotometer and a wavescan DOI instrument. Results show that irrespective of lightness of samples, the correlation of differences in visual and instrumental data was always superior for the goniophotometer than the wavescan DOI instrument. This implies that the measurement of DOI by a goniophotometer has unequivocal advantages.

In order for a color matching model to be able to predict the correct and precise amounts of colorants to achieve a certain color, numerous sets of information regarding the effective parameters of the colored system is required. These parameters include the absorbance and scattering coefficients of colorants, relations between total and internal reflection of a colored layer, basic assumptions relating to incident light interactions with and without the colored layer, geometry and size of the scattering particles, etc. Additionally a colored layer could be transparent, translucent or opaque. Various models such as physical, numerical, intelligent and hybrid models attempt to present a correct prediction of the amounts of components to give the precise color through determining the contribution of each effective parameter which may lead to new formulae. In the present study, a variety of such models and their various applications are reviewed. Most of the well-known physical models such as Kubelka-Munk, Four- Flux, Many-Flux, Chandrasekhar, inverse adding doubling, Monte Carlo, representative layer theory and even intelligent models such as artificial neural network models for optimal usage are herewith described.

In the present study, attempts were made to investigate the possibility of developing a two dimensional appearance chart to make provisions for a straightforward assessment and control of appearance quality of achromatic automotive finishes. To this end, four series of random test samples in which the three geometric appearance attributes, namely specular gloss, distinctness of image and orange peel varied simultaneously were prepared using metallic black, metallic grey, metallic silver and solid white automotive finishes. The samples were visually evaluated by a panel of 16 observers, utilizing grey scale technique. Analyzing the results of correlation between visually quantified total appearance and instrumentally measured specular gloss, distinctness of image and orange peel attributes of random samples showed that there is a good correlation between instrumentally measured distinctness of image and the Wave scan Wd parameters, and the corresponding visually evaluated data at the four investigated achromatic levels.Using these two parameters, a two dimensional appearance chart was developed for achromatic automotive finishes under investigation. Discrete acceptable, tolerable and unacceptable tolerance regions were determined for distinctness of image and Wd parameters, separately for horizontal and vertical automotive body parts, using the results of visual inspections of 6 expert auditors of the Iran Khodro car manufacturing company on 28 randomly selected car bodies with different achromatic levels.

Illumination/observation geometries have an effective role in visual assessments of geometric attributes such as gloss, distinctness of image, orange peel of automotive paints. In this research, gloss, distinctness of image and orange peel of an automotive paint were investigated under three different illumination/observation conditions namely, directional, diffuse and combination of the two(i.e. directional plus diffuse) usually achieved in a standard light cabinet. For each condition, the visual assessments were carried out at various viewing geometries. For this purpose, three scales, i.e. specular gloss, distinctness of image and orange peel were prepared for a black automotive finish. These scales were separately evaluated visually under various illumination/viewing conditions by a panel of 8 observers. The statistical parameters showed that the visual perception of gloss under directional lighting/viewing geometry of 38º/7 º along with visual perception of distinctness of image and orange peel observed in a standard light cabinet with a 45º /0º geometry gave the most reasonable results as the performance of observers in such set ups induced average stress values of less than 8%. J. Color Sci. Tech. 7(2014), 323-330©. Institute for Color Science and Technology.

Assessment of the total appearance of an automotive coating using standard methods would have a great impact in the automotive industry. These methods should have a good correlation with visual assessments. In this research, the correlation between visual assessments and the wave scan DOI results were investigated for white, metallic grey and metallic black automotive samples. The visual assessments were carried out by a panel of 14 observers, including 6 males and 8 females under a light source simulating D65 in a light cabinet with a viewing geometry of 45/0. The visual assessment method used was one of paired comparison. Such quality rankings were then converted to quantitative equivalents by the aid of the Thurston scale and the results were compared with each of the wave scan output parameters. Statistical and error estimation parameters (i.e. R 2 and stress) illustrated that amongst all wave scan parameters, only Wd, Wc, LW and in that order strongly correlated with human evaluations of geometric attributes for these achromatic paint samples. Investigation of structure spectrum showed that Wb is another important parameter indirectly influencing on the surface appearance and in fact the value of Wb is greater than Wd and Wc in the acceptable region. Therefore, there seems to be a complex relationship between these parameters which represent the short and the long waves which is of utmost importance in assessing perceived total appearance. J. Color Sci. Tech. 7(2013), 123-131©. Institute for Color Science and Technology

The aim of the present study was to investigate and compare the performance of various color matching procedures inclusive of color matching based on Allen''s rough match and an iterative procedure using the CIELAB color difference formula، spectrophotometric procedures such as McGinnis least square method، iterative method، weighted iterative method and spectrophotometric color matching based on fundamental color stimulus. To this end، 165 samples were dyed. Initially، the comparisons were made theoretically on the basis of color differences and indices of metamerism. Additionally، such comparison was extended practically by dyeing 24 real dyed samples. Practical results were in good agreement with the theoretical results، showing a relatively better performance of the spectrophotometic color matching procedure based on the fundamental color stimulus. J. Color Sci. Tech. 7 (2013)، 75-83© Institute for Color Science and Technology.

Due to their periodic structures, three dimensional photonic crystals possess some useful optical properties such as wave guiding. Sandwiching these structures between multilayered polymer films improves such properties compared to those of single-layer films because they form a nano structure. In the present investigation polymethyl methacrylate and polystyrene were dissolved in proper solvents namely, acetone and cyclohexane(plus 5ml carbon tetrachloride per 95ml of cyclohexane). Solutions and suspension of nano particles were spin-casted rotationally using specially designed machine to produce a periodic structure. The optical properties of the cast films were studied using spectrophotometric techniques. It was found that cladding three-dimensional polymer films induced a color change. A color-shift from blue to green was found to be related to refraction of light amongst polymer layers. J. Color Sci. Tech. 5(2011), 69-75© Institute for Color Science and Technology.

A monoazo disperse dye based on naphthalimide was synthesized by using 3-(6-amino-1,3-dioxo-1H-benzo[de]isoquinoline- 2(3H)-yl) propanoic acid as a diazo component and N-ethyl-N-hydroxyethyl aniline as a coupling component. The synthesized dye was purified and characterized by FTIR, 1HNMR, DSC and UV-Vis spectroscopic techniques. Thespectrophotometric characteristics of the dye were investigated in various solvents. The results showed that the synthesized dye has a positive solvatochromism. Wavelength of maximum absorption and molar extinction coefficient in acetone were 524.3 nm and 34125 l mol-1cm-1, respectively. The synthesized dye was applied to nylon, polyester and acrylic fibers and the effects of temperature, time and build up were investigated. The results showed that the synthesized dye had a good build up on nylon which gave excellent wash and rubbing fastnesses and fair light fastness. J. Color Sci. Tech. 3(2010), 257-266 © Institute for Color Science and Technology.