Visual Color Matching Research Articles

Study of the influence of various D65 simulators on colour matching

This study investigates the influence of various D65 simulators on visual colour matching. Spectroradiometric measurements of D65 simulators and visual assessments were obtained. The spectral power distributions of three D65 simulators were measured by spectroradiometer in a colour viewing cabinet. Based on the measured spectral power distributions, the quality of the D65 simulators were assessed using CIE No.51.2 and CIE No.13.3 methods. For visual assessment, the Davidson and Hemmendinger colour rule, which is composed of highly metameric pairs, was used in this study. The colorimetric match points and visual match points under three D65 simulators were determined. Pair‐comparison t‐tests were also used to examine the statistically significant differences among visual match points. The results show that various D65 simulators influence visual colour judgement of metameric pairs. The correlation between quality rating of D65 simulators under these two CIE methods and visual assessment was evaluated.

Evaluation of visual and instrument shade matching

Statement of problem. Visual color matching to determine shades in dentistry is inconsistent and unreliable. If accurate, instrumental measurement of tooth color would provide objective, quantified data to match natural teeth to clinical shade guides. Purpose. This study evaluated and compared the ability of a new computerized colorimeter and a simple visual test to match ceramic shade guide teeth. Material and methods. Thirty-one (n = 31) observers with normal color vision were allowed unlimited time to match one set of Vita Lumin shade guide teeth to the corresponding shade guide teeth of a second Vita Lumin shade guide. The same test was administered to 14 of the observers several months later to determine within-subject variability. A computerized colorimeter (Colortron II) equipped with a positioning guide was used to measure the middle third of each shade guide tooth. Through a “match tool” present in the computer’s software, readings from one shade guide were matched with readings of the other shade guide by using CIELAB measurements and ΔE values. The mean number of correct matches by the colorimeter and of correct matches in visual test were compared with a 1-tailed t test. Repeatability for both tests was determined with a paired t test. Results. The Colortron II instrument correctly matched 8 of the 16 tabs (50% correct), whereas visual matching by examiners averaged 7.7 of 16 correct matches (48% correct) (standard deviation 2.7). No statistically significant differences existed between the 2 methods. The colorimeter demonstrated 100% repeatability and the visual test demonstrated fair repeatability (correlation coefficient r = .60). Conclusions. Shade determination by visual means was inconsistent. Accuracy of a new colorimeter in matching porcelain shade guide teeth was only slightly better. (J Prosthet Dent 1998;80:642-8.)

Optical chlorophyll sensing system for banana ripening

An optical chlorophyll sensing system was developed to detect the chlorophyll content of bananas as the fruit ripens. This system shows a high correlation to other peel colour analysis methods (spectral analysis, tristimulus colorimeter analysis, and visual colour matching). Regression equations were developed to predict the chlorophyll content of banana peels, which is primarily responsible for the change in the colour of the peel. This optical chlorophyll sensing system has the following characteristics: rapid response, simple operation, non-destructive measurement, and low cost. The potential application of this system in automatic monitoring of banana ripening is also discussed. © 1997 Elsevier Science B.V.

Field Determination of Cr(VI) in Water At Low PPB Level

Methods for determining chromium (VI) at the ppb level, in tap water and ground water, were developed. These make use of anion exchange resin beads or anion exchange membrane filters to preconcentrate the Cr(VI) and separate it from interfering cations. The color is developed by reaction with diphenylcarbazide and the quantitation is carried out using a portable UV/Vis spectrometer, in the liquid or solid phase, or by visual color matching. These methods are suitable for use in the field.

Quantitative reflectance haemoglobinometry

Conventional haemoglobinometry based upon optical transmission characterisation involves volumetric measurements and chemical processing in liquid media, thus making the procedures cumbersome. Reflection measurements being simple in practice, the now obsolete Tallqvist's reflection and visual colour matching technique has been scientifically reassessed. Three factors identified to be contributing to variable results from this method are: inadequate haemolysis of red blood cells; oxygenation variations; and no blood volume control. Based upon this identification, a new technique has been formulated which overcomes all the limitations of the Tallqvist's method. Consistent results are obtained even without volumetric control. Saponin and sodium nitrite impregnated into filter paper induce haemolysis and conversion of blood to a stable form independent of oxygen concentration. Thus the sources of errors are removed. Since reflectance measurement at a narrow wavelength range is adequate, the approach can lead to a simple haemoglobinometer.

Calculation of Soil Color from Reflectance Spectra

AbstractProcedures were developed for obtaining visible spectra of dry and moist soil powders on a Cary 17D spectrometer. Accuracy and precision were checked by measuring the colors of: (i) 28 chips of the Inter‐Society Color Council‐National Bureau of Standards (ISCC‐NBS) Centroid Color Chart, (ii) 279 chips of the Munsell Soil Color Chart, and (iii) 12 selected soil samples. Measured Munsell values were not significantly different from nominal values. Measured hue and chroma were significantly different from nominal hue and chroma, but the difference was approximately 0.25 units of chroma and, thus, is relatively small. Average deviations for duplicate measurements of Munsell hue, value, and chroma of 12 silt loam and silty clay loam soil samples were <0.1 unit of hue, value, or chroma and maximum deviations were <0.2 units. Precision was similar for both dry and moist samples. Increased accuracy and precision make it possible to quantify small differences in soil color that are difficult to quantify using only visual color matching.

Tachistoscopic tests of colour naming and matching in schizophrenia: evidence for posterior callosum dysfunction?

Neuropsychological studies have shown that the integrity of the posterior corpus callosum is necessary for accurate colour naming in the left visual field (LVF) and colour matching across hemifields. Using this model, 22 schizophrenics, 14 depressive and 16 healthy matched controls were given a battery of tachistoscopic tests of colour perception. The schizophrenics made significantly more errors, in naming colours in the LVF compared to depressives, and in matching colours across fields compared to depressives and normals. There were no differences between groups for right visual (RVF) colour naming or matching within right and left visual fields. These findings support the hypothesis that trans-callosal transmission may be impaired in schizophrenia and are unlikely to be due to a specific disorder of colour perception, neuroleptic drugs or generally impaired performance. Those schizophrenics whose LVF naming errors exceeded RVF errors were more likely to have first rank symptoms and showed less cerebral atrophy but did not differ on other variables. The techniques described may be useful for further research into interhemispheric function in schizophrenia.

The Development of Pass/Fail Colour Matching Formulae for Single Number Shade Passing

A series of modifications to the ANLAB colour–difference formula is described which has progressively improved the agreement between the formula and the pass/fail decisions of visual observers. The latest modification, the JPC 79 formula has been suggested as a viable alternative to visual colour matching.

Visual Function in Acute Posterior Multifocal Placoid Pigment Epitheliopathy

We examined a 19-year-old woman with acute posterior multifocal placoid pigment epitheliopathy one week after she noted blurring of central vision. Her corrected visual acuity was R.E.: 6/7.5 (20/25), and L.E.: 6/12 (20/40). The visual fields showed 10-degree pericentral scotomas. A color vision defect and an abnormal Stiles-Crawford effect were present. Dark adaptation showed a delayed time course, with normal final thresholds. The electro-oculogram was subnormal, suggesting widespread abnormality of the retinal pigment epithelium. Active lesions resolved within three weeks, but fluorescein angiography showed characteristic widespread residual changes. Within three weeks, she had normal visual acuity and a normal electro-oculogram. Other tests of visual function showed recovery with a slower time course. By one year, the visual fields, color matching, Stiles-Crawford effect, and dark adaptation were almost normal. Analysis of the color-matching data and Stiles-Crawford effect indicated that the abnormalities of macular function were caused by an underlying lesion of the pigment epithelium and photoreceptors. This caused a physical distortion of the photoreceptor layer and metabolic disfunction of the photoreceptors.

歯周疾患患者における歯齦色の色彩学的研究

Remodelled ophthalmic funds camera for human gingiva was employed to take a photograph of upper and lower anterior interdental palillaes and lower lip. The photoelectric colorimeter was used to estimate the light extinction of the developed reversal color film.In this study R value (the light extinction of gingival color to lower lip color) and visual color matching were applied to estimate the gingival color.The purposes of this investigation were to compare the gingival colors of normals and periodontal patients and to study the gingival color changes following periodontal treatments.The results were as follows1 In non mottled gingiva statistically significant higher R values were observed in periodontal patients than the normals. By visual color matching the hue of the gingival colors in periodontal patients inclined to the direction of RP, the value was lower than that of healthy gingiva, and the chroma was higher than that of healthy gingiva. In melanin pigmented gingiva, little difference was observed in R value. The hue of gingival colors in periodontal patients distributed in the direction of RP than that of healthy gingiva. Little difference, however, was observed in value and chroma.2 The close relationship was observed in the gingival color estimations between by absorptimeter and by visual color matching in normals and periodontal patients, even in gingival color estimations following periodontal treatments.3 Following scaling significant R value reduction was observed in 1 week, while after 6 weeks treated gingival color showed healthy. By visual color matching, gingival color following scaling seemed to be healthy after 6 weeks.4 Following subgingival curettage significant R value reduction was observed from 1 to 2 weeks, while after 6 weeks treated gingival color showed healthy. By visual color matching, gingival color following subgingival curettage seemed to be healthy after 6 weeks.5 Significant R value reduction was observed from 2 to 4 weeks following gingivectomy while after 9 weeks little reduction was observed. After 12 weeks, R value showed a little higher than that of normal gingiva. By visual color matching it was demonstrated that after 12 weeks following gingivectomy hue was distributed slightly in direction of RP, value and chroma seemed to be normal.6 Significant R value reduction was observed from 2 to 4 weeks following flap operation, while after 9 weeks little changes was observed and after 12 weeks R value was a little lower than that of normal gingiva. By visual color matching, it was shown that after 12 weeks following flap operation hue seemed to be normal, and value was higher and chroma was lower than that of normal gingiva.7 The gingival color changes following subgingival curettage and flap operation were similar except that the gingiva treated by flap operation takes 7 to 10 days longer to the healthy gingival color than by subgingival curettage.

The color of gingiva studied by visual color matching. Part I. Experimental studies on the discrimination threshold for color difference and effect of training.

As a preliminary experiment on the gingival color indicated by Munsell system, the makings or the qualities for color sensation of the individual were checked with regard to (1) discrimination threshold for color difference with certain color range of gingiva (paired difference test for color comparison) and (2) promotion of memorial power by training (test for memory color). A total of 20 males and females (20-30 years old) participated in this preliminary study as experimental subjects and the following results were obtained: (1) the average color discrimination threshold for color difference among subject trained for color memory is 0.8 Lab. (Hunter), and is assumed to be greater in the actual colorimetry of gingiva, (2) the similarity of discrimination is more frequent among the subjects trained for color memory than among those who were not trained, and (3) training for color memory is found to be effective in promoting the ability for color discrimination.

An assessment of the Azostix strip test.

The approximate concentration of urea in a single, unmeasured drop of blood may be estimated with an Azostix strip in a little over a minute, without the use of laboratory equipment. The test has been assessed by comparing 488 strip readings made by two observers on 331 specimens of blood from patients with plasma urea concentrations determined by the Auto-Analyzer diacetyl monoxime method. Observations were also made on inter- and intra-observer reading differences, on the effect of the period of contact of blood with the reagent zone of the strip and on the effect of different types of illumination. Difficulties with visual colour matching inevitably limit the performance of this type of test. Azostix strips cannot replace laboratory methods, but, provided their limitations are appreciated, and proper technique is observed, they should provide a screening test for azotaemia when laboratory facilities are not readily available. Their place in hospitals would seem to be confined to emergency use as a screening test for severe azotaemia. In general and domiciliary practice they should provide a convenient screening test for azotaemia provided that readings greater than ;20 mg/100 ml' are taken as an indication for further investigation.

Visual versus Instrumental Colour Matching

The paper describes studies that have been made of both visual and instrumental colour matching and attempts to measure those factors that must be taken into account when replacing visual with instrumental colour matching. The factors in visual colour matching examined are lighting source, viewing geometry, size of specimen, age, sex and colour‐vision defects of observer, and consistency of observers. Those in instrumental colour matching are lighting source, choice of 2° or 10° Standard Observer data, effect of viewing geometry, textile structure, lustre (or specular reflection), dichroism, fluorescence, metamerism of specimen, choice of colour‐difference formulae, and uniformity of visually uniform colour space. Mechanical and electrical reliability of instruments, short‐and long‐term reproducibility, and absolute and relative accuracies of instruments are discussed.

FRIDAY MORNING, 17th SEPTEMBER 1965

It is shown that accusations of inconsistency on the part of colour matchers are justified in degree. This is because visual colour matching is not only a function of the eye, but also of the brain and the stored preferences and psychological responses of the individual. Instrumentation has come a long way and can perform this function objectively, but the data still require interpretation and this will tend to reintroduce some measure of personal bias. The new instrumentation is colorimetrically very precise and is an excellent complement to spectrophotometers and computers, which are now being used extensively to solve the textile industry's problems. Much more can be expected from the use of instrumentation, in particular a substantial assistance in understanding the fundamental relations of the dyes and fibres and the influences of various factors in processing and in use.

Photometry and Colorimetry of Natural Objects

Apparent luminances and colors of natural objects were measured by three types of telephotometers, which were designed originally as telephotometers to measure distant light sources and extinction of light in the atomsphere, but used as brightness meters in this study. Two of them are based on the photoelectric and photographic spectroradiometric methods and the third on the visual color matching with a comparison light consisting of an incandescent lamp and three Lovibond glasses.The range of the luminance observed in the daytime for the sky near the horizon is 6, 600-7, 400 cd/m2 on a clear day and 1, 200-5, 500 cd/m2 on an overcast day. The luminance of the snow surface in the vicinity of the instrument on a clear day. ranging 10, 000-14, 300 cd/m2, is largest among the natural objects. The luminance of other objects near the observer is generally much smaller than that of the sky. But with the increasing distance it approaches the luminance of the sky.The colors of natural objects are chiefly yellow green or yellow when the distances are small. With the increasing distance their chromaticity points on the chromaticity diagram move into blue green region along the blackbody locus. The domain, in which the chromaticity points of natural objects aredistributed, is fairly wide in the direction extending from blue to yellow green approximately parallel blackbody to the locus but much narrower in the direction vertical to it. Foliage at a distance less than 1 kilometer has yellow-greenish colors of dominant wavelength 542-582 mμ. Field crops and vegetables have a dominant wavelength of 561-570 mμ. Their colors are most saturated among the observed objects, having a maximum excitation purity of 52%. Earth colors are yellow of 561-585 mμ. With the increasing distance the colors of natural objects changes to blue. The chromaticity points for buildings, sea, snow, sky and distant objects are distributed over a small area around the achromatic point and its blue side.Spectral distribution curves for natural objects are characterized by their flat appearance, especially when the distances are large, in accord to the low saturation of their apparnet colors.These data were applied for discussing the visual range of colored lights, for instance signal lights, and objects through the atmosphere in the daytime.

Propagation of Errors in Colorimetric Transformations

A common colorimetric transformation is a homogeneous linear transformation of tristimulus values from one primary system to another. The transformation coefficients are obtained by spectrophotornetry and/or visual color matching and consequently are subject to certain errors. These errors, together with those associated with the given tristimulus values, propagate into the tristimulus values to be computed by means of the transformation equations. The theory of the propagation of such errors is outlined and illustrated by an example.

Visual Selection of Color Film Neutrals

Neutral areas on color film were selected by a visual color matching technique as a basis for comparing real observers with the CIE standard observer. Data from 29 observers show low precision of visual selection as compared to standard physical techniques, and possible deviance from the CIE standard observer in the blue direction. A comparison of Stiles’ tentative mean observer with the CIE standard observer showed that the latter is the more representative of our real observers.

Determination of Copper in Rubber Latex

Abstract Small amounts of copper in rubber latex can be determined by following a dry-ashing procedure for removal of organic matter and concluding with a colorimetric determination of the copper in the ash. Provided the ignition is not undubly prolonged, the ashing temperature can safely rise to 800° C, and recovery of the copper is complete from the ash when a mixture of nitric and hydrochloric acids is used. Results are slightly higher than those obtained by the wet oxidation process. Assay of the copper can be carried out on the solution of the ash, either in aqueous medium or in carbon tetrachloride solution, depending on the extent of interference anticipated from iron and insoluble ingredients, such as clay, and on the degree of accuracy required. Visual color matching in aqueous solution is simpler and quicker, but insoluble material may give rise to considerable personal error. In aqueous solution, the copper equivalent of ferric iron is about 1/100, i.e., the coloration is about 100 times more intense for copper than for iron. for more accurate work, measurement of the color of a carbon tetrachloride solution of the copper diethyldithiocarbamate complex by means of a suitable colorimeter is recommended. The tendency of the complex to fade is overcome by replacing the sodium diethyldithiocarbamate by the zinc salt dissolved in carbon tetrachloride. In such a solution the copper equivalent of ferric iron is about 1/1000, but actual experimental conditions can vary this figure between wide limits. A more satisfactory procedure is, therefore, to measure the total color developed in carbon tetrachloride, and then bleach out the color due to copper with potassium cyanide. The residual (interfering) colors can thus be estimated, and the difference between the readings gives a direct measure of the concentrations of copper in the test solution.

Photo-electric colour-matching

In order that photo-electric photometry shall be successful, a method, more accurate than visual colour-matching, must be available for determining the colour of the source. Colour, for our present purpose, may be replaced by equivalent temperature. An attempt is made to found such a method on the comparison of currents excited by the source in two photo-electric cells of different frequency-sensitivity characteristics. Cells filled with rubidium and sodium were used for this purpose. The conditions that must be fulfilled if the method is to be successful are examined critically. An apparatus designed to embody these conditions is described. It is very sensitive, and will detect a change of 0??5 in the temperature of a source at 2400? K. But one of the necessary conditions, namely, that the photo-electric current should be proportional to the intensity of the light, is not yet accurately fulfilled. This defect can probably be removed by a more suitable design of the cells. If cells filled with the same chemically pure metal could be made to have accurately the same frequency-sensitivity characteristic, it would be possible to define a complete scale of high temperature in terms of the temperature of a single lamp and the properties of the alkali metals.