Color matching; matching skin color in facial prosthesis via the spectrophotometer with special reference to dental restorations demanding color fidelity.
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Dental Prosthesis↗
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Limitations of color flow Doppler imaging in the quantification of valvular regurgitation: velocity of regurgitant jet, rather than volume, determines size of color Doppler image.
The objective of this study was to determine the validity of estimation of regurgitant volume by visual assessment of color flow Doppler display. An experimental apparatus was designed that is capable of ejecting precise volumes of echogenic material from one chamber to another under continuous color flow Doppler monitoring. The velocity of flow was altered independently by changing either the size of the orifice through which flow occurred or the ejection rate. In this manner the differential effects of volume and velocity on the color flow Doppler image could be examined. The maximum area encompassed by the color flow Doppler pattern for each ejection was planimetered by using commercially available on-line software. In addition the reviewer in each case applied a subjective grade to the appearance of the color flow jet (1+ to 4+). Comparison was then made of the color flow Doppler appearance of equal volumes flowing at different velocities and of different volumes flowing at different velocities. In the initial series a solution of agitated hetasarch was used. When equal volumes were imaged at different velocities the higher-velocity jet appeared larger, both subjectively (3+ vs 1+) and by measuring the area encompassed in the Doppler flow profile (40.3 +/- 1.8 vs 22.0 +/- 1.4 cm2, p = 0.0001). Furthermore, when different volumes were imaged at different velocities, the smaller volume (3 ml vs 6 ml) appeared larger when it was flowing at higher velocity (3+ vs 2+, 40.3 +/- 1.8 vs 32.4 +/- 1.3 cm2, p = 0.0006). These experiments were repeated with blood, confirming the results of the initial study.(ABSTRACT TRUNCATED AT 250 WORDS)
Blood Flow Velocity↗
Color opponencies in the system of the uniform color scales of the Optical Society of America.
Many problems regarding color opponency are still unsolved. In this study the system of the uniform color scales of the Optical Society of America (OSA-UCS) is analyzed with the aim of obtaining answers to very general questions on color opponency. The perceptual color opponencies in the OSA-UCS system, represented by its coordinates (j, g), appear to work in a mutually interacting way. On the hypothesis that such an interaction is due to a linear mixing of a pair of independent opponent mechanisms with scales satisfying a proper Weber fraction, three chromatic opponency functions are derived, whose sum is equal to zero. These functions are the logarithms of the ratios of two tristimulus values in a proper reference frame (called the "main reference frame") and therefore are antisymmetric and zero-degree homogeneous functions of these tristimulus values. Any pair of these three functions is a set of two independent functions. A new formula for color opponency in the OSA-UCS system is derived in which the perceptual color opponencies (j, g) are written as products of the lightness by a proper linear mixing of any pair of the three chromatic opponency functions. All this is possible because the lattice of the OSA-UCS system is composed of geodesic lines.
Journal Article↗
An acquired color defect of the opponent-color system.
An acquired unilateral color defect in a 22-year-old man has been investigated with standard clinical tests and by using techniques which, it is thought, test specifically for the sensitivity of the luminance and opponent-color systems. The spectral sensitivity of the defective left eye, using 1 degree 200 ms. test flashes on a white background, has a single broad peak at about 550 nm. and resembles the photopic luminosity curve; in contrast, the normal curve, measured in the same conditions, has three peaks at about 440, 520, and 600 nm. However, the subject's spectral sensitivity curve for detecting 20 Hz. flicker is quite normal and is similar to his curve for 200 ms. flashes. It has recently been proposed that the three peaks of the normal curve for 200 ms. flashes reflect the activity of the opponent-color system, whereas the single peak for flicker detection is related to the luminance system. The preceding observations may thus be interpreted in terms of a specific loss of the subject's opponent-color system and this would explain his poor color discrimination. His luminance system appears to be normal, and evidence is presented for the maintained function of red- and green-sensitive (but not blue-sensitive) cones. The spectral sensitivity of the subject's right eye is nearly normal, suggesting a precortical origin of the defect; however, there seems to be some abnormality in this eye, indicating a less developed form of the same defect.
Adult↗
Effects of color CRT display on pupil size in color-blind subjects.
The effects of color cathode ray tube (CRT) display on the pupil size in color-blind subjects were studied experimentally. Red, magenta, green, cyan, yellow, and white were presented on the CRT. Five protan subjects, five deutans, and five normal subjects were tested using infrared pupillography. In the protan group, the pupils were significantly less sensitive to red (wavelength: 600 nm) targets compared to the other colors. In the deutans and the control group, there were non-significant changes in pupil size in response to the colors. Dominant wavelengths above 600 nm in color CRTs should be avoided in routine work presentation because of less sensitivity in protanopias.
Adult↗
[Study of color perception using a new color test and desaturated panel D 15 in normal subjects and diabetics].
The authors used two tests (the Lanthony's New Color Test and the desaturated Panel D 15 test) to evaluate color vision in 235 subjects (235 eyes) of which 80 normal and 155 diabetic (85 with background retinopathy and 70 without retinopathy, as demonstrated by fluorescein angiography). The diabetic patients with maculopathy or macular oedema, with mixed or proliferative retinopathy, or with any form of advanced degenerative retinopathy were excluded from this study. The New Color Test was performed in accordance with Lanthony's standardized method, applying only the separation phase (to quantifying the color perception defect, if any) in photopic illuminance conditions at 250 lux. The desaturated Panel D 15 (qualitative classification test) has been performed at illuminance of 500 lux. Both normal and diabetic subjects were divided into two age groups (below and above 45 years) and the discriminatory value of two tests has been assessed in relation to age, diabetes and background retinopathy. The New Color Test showed a highly significant difference between normal subjects and diabetics of comparable age with background retinopathy. There was also a highly significant difference between diabetics with and without retinopathy. On the other hand, the difference between normal subjects and diabetics without retinopathy proved significant in the below-45 age group and no-significant in the above-45 age group. The results obtained in the desaturated Panel D 15 test have been similar: below the 45 years of age all differences among the three subject groups proved significant, whereas in the above-45 age group no significant differences were observed.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Color categorization and color constancy in a neural network model of V4.
We develop a neural network model that instantiates color constancy and color categorization in a single unified framework. Previous models achieve similar effects but ignore important biological constraints. Color constancy in this model is achieved by a new application of the double opponent cells found in the "blobs" of the visual cortex. Color categorization emerges naturally, as a consequence of processing chromatic stimuli as vectors in a four-dimensional color space. A computer simulation of this model is subjected to the classic psychophysical tests that first uncovered these phenomena, and its response matches psychophysical results very closely.
Animals↗
Retinal inputs to the geniculate relay cells in the eastern chipmunk (Tamias sibiricus asiaticus): a comparison between color and non-color sensitive cells.
Single unit recordings were made from the relay cells of the lateral geniculate nucleus in the eastern chipmunk. Of 362 relay cells, 47 cells (13%) were classified as color sensitive and the rest as non-color sensitive cells. Non-color sensitive cells were further classified into 5 subclasses: off-phasic, on-phasic, on-off-phasic, on-tonic and uncommon types. Within the color sensitive cells there were 3 subclasses; blue excited and green inhibited (+B-G), blue inhibited and green excited (-B+G), and blue excited (+B) cells. Retinal afferents to color sensitive relay cells had the following characteristics: ganglion cells of their origin were distributed in the central high density areas of the retina and axonal conduction velocities were in the intermediate range, though they were somewhat slow in +B cells.
Animals↗
Temporal differences between color pathways within the retina as a possible origin of subjective colors.
We propose a model of temporal signal processing within the retina based on temporal differences between the color pathways which may explain the phenomenon of subjective color. We quantify the model by inferring impulse response functions from physiological data, and predict the output of the different color pathways to temporally modulated achromatic signals which produce the sensation of color. Certain achromatic temporally modulated signals create imbalances between the color pathways which are analogous to those produced by stationary chromatic signals.
Color Perception↗
Proximity judgments in color space: tests of a Euclidean color geometry.
We describe two tests of the hypothesis that human judgments of the proximity of colors are consistent with a Euclidean geometry on color matching space. The first test uses proximity judgments to measure the angle between any two intersecting lines in color space. Pairwise estimates of the angles between three lines in a plane were made in order to test the additivity of angles. Three different color proximity tasks were considered. Additivity failed for each of the three proximity tasks. Secondly, we tested a prediction concerning the growth of the variability of judgments of similarity with the distance between the test and reference stimuli. The Euclidean hypothesis was also rejected by this test. The results concerning the growth of variability are consistent with the assumption that observers use a city-block metric when judging the proximity of colored lights.
Color Perception↗
Color terms and color concepts.
In their lead articles, both Kowalski and Zimiles (2006) and O'Hanlon and Roberson (2006) declare a general relation between color term knowledge and the ability to conceptually represent color. Kowalski and Zimiles, in particular, argue for a priority for the conceptual representation in color term acquisition. The complexities of the interaction are taken up in the current commentary, especially with regard to the neuropsychological evidence. Data from aphasic patients also argue for a priority for abstract thought, but nevertheless it may still be that the use of color terms is the only way in which to form color categories even if both linguistic and attentional factors play an important role.
Aptitude↗
When a line is a number: color yields magnitude information in a digit-color synesthete.
The phenomenon of synesthesia has received a great deal of interest recently in the scientific literature. Many previous studies stressed the unidirectional nature of this phenomenon. For example, color-grapheme synesthetes automatically perceive achromatic numbers as colored (e.g. 7 is turquoise). Conversely, colors do not automatically give rise to any sort of number experience (e.g. turquoise is 7). In contrast to the common view, we report on a digit-color synesthete in whom colors can evoke numerical representations in the absence of any digit presentation. It is concluded that in synesthesia there is a reciprocal rather than unidirectional flow of information between dimensions.
Adult↗
Synesthetic colors determined by having colored refrigerator magnets in childhood.
Synesthesia is a condition in which percepts in one modality reliably elicit secondary perceptions in the same or a different modality that are not in the stimulus. In a common manifestation, synesthetes see colors in response to spoken or written letters, words and numbers. In this paper we demonstrate that the particular colors seen by a grapheme-color synesthete AED were learned from a set of refrigerator magnets and that the synesthesia later transferred to Cyrillic in a systematic way, with the colors induced by the Cyrillic letters determined by their visual or phonetic similarity to English letters. Closer examination of the data reveals that letters of either language that are more visually similar to the English capitals in the magnet set are also more saturated. In order to differentiate AED's synesthesia from ordinary memory, we use a novel psychophysical method to show that AED's synesthetic colors are subject to ordinary lightness constancy mechanisms. This suggests that the level of representation at which her synesthesia arises is early in the stream of visual processing.
Adult↗
Aging effect on the pigment composition and color of Vitis vinifera L. Cv. Tannat wines. Contribution of the main pigment families to wine color.
Red wines made from Vitis vinifera L. cv. Tannat grapes are known to possess high contents of tannins and intense color, features that are responsible for the originality of these wines. This work aimed to study the evolution of the pigment composition and CIELAB color parameters as Tannat wines become older, as well as to establish the contribution to wine color of the main pigment families. Tannat wines produced in Uruguay from grapes of the same vineyard in six consecutive vintages (1998-2003) and Tannat grapes of the 2003 harvest were analyzed by means of HPLC-DAD-MS and UV-vis spectrometric techniques. The correlations between the different pigment families and the CIELAB parameters revealed the importance of the variations of the percentage, found in anthocyanins and flavanol-anthocyanin acetaldehyde-mediated condensation products (decrease) and pyranoanthocyanins and direct condensation products (increase), in the modification of the color from purple-red hues to more orange-red ones. The color suffered qualitative rather than quantitative changes, that is, the hue (h*ab) increased, whereas the chroma (C*ab) and lightness (L) did not show a defined trend with time.
Chromatography, High Pressure Liquid↗
Why do non-color words interfere with color naming?
In the non-color-word Stroop task, university students' response latencies were longer for low-frequency than for higher frequency target words. Visual identity primes facilitated color naming in groups reading the prime silently or processing it semantically (Experiment 1) but did not when participants generated a rhyme of the prime (Experiment 3). With auditory identity primes, generating an associate or a rhyme of the prime produced interference (Experiments 2 and 3). Color-naming latencies were longer for nonwords than for words (Experiment 4). There was a small long-term repetition benefit in color naming for low-frequency words that had been presented in the lexical decision task (Experiment 5). Facilitation of word recognition speeds color naming except when phonological activation of the base word increases response competition.
Analysis of Variance↗
Evaluation of induced color changes in chicken breast meat during simulation of pink color defect.
The objective of the study was to establish a pink threshold and simulate the pink defect in cooked chicken breast meat with treatment combinations that would induce significant changes in the color of raw and cooked meat. The subjective pink threshold used in judging pink discoloration was established at a* = 3.8. Samples of three color groups (normal, lighter than normal, and darker than normal) of boneless, skinless chicken breast muscles were selected based on instrumental color values. The in situ changes were induced using sodium chloride, sodium tripolyphosphate, sodium erythorbate, and sodium nitrite at two levels: present and not present. Fillets in all treatments were subjected to individual injections, followed by tumbling, cooking, and chilling. Samples were analyzed for color [lightness (L*), red/green axis (a*), yellow/blue axis (b*)] and reflectance spectra. Simulation of the pink defect was achieved in eight of the 16 treatment combinations when sodium nitrite was present and in an additional two treatment combinations when it was absent. Pinking in cooked samples was affected (P < 0.05) by L* of raw meat color. Results confirmed that it was possible to simulate the undesired pinking in cooked chicken white meat when in situ conditions were induced by sodium chloride, sodium tripolyphosphate, and sodium nitrite. The continuation of the simulation study can aid in developing alternative processing methods to eliminate potential pink defects.
Animals↗
Color to gray and back: color embedding into textured gray images.
We have developed a reversible method to convert color graphics and pictures to gray images. The method is based on mapping colors to low-visibility high-frequency textures that are applied onto the gray image. After receiving a monochrome textured image, the decoder can identify the textures and recover the color information. More specifically, the image is textured by carrying a subband (wavelet) transform and replacing bandpass subbands by the chrominance signals. The low-pass subband is the same as that of the luminance signal. The decoder performs a wavelet transform on the received gray image and recovers the chrominance channels. The intent is to print color images with black and white printers and to be able to recover the color information afterwards. Registration problems are discussed and examples are presented.
Algorithms↗
Color appearance under chromatic adaptation varied along theoretically significant axes in color space.
Changes in color appearance caused by chromatic adaptation were measured with a wide range of adapting fields. Observers viewed a 39'-55' annular test field composed of an admixture of lights from the red phosphor and the green phosphor of a CRT. The annular mixture field was centered and superimposed upon a 4.7 degrees steady, circular background field. After the observer was completely adapted to the background, the luminance of the red phosphor in the test was held fixed while the observer adjusted the luminance of the green phosphor until the test appeared neither reddish nor greenish. Twenty-two equiluminant backgrounds (4.5 cd/m2, approximately 50 Td) were systematically selected along two axes in Judd chromaticity space. One axis was along tritanopic confusion lines, with middle-wavelength-sensitive- (M-) and long-wavelength-sensitive- (L-) cone stimulation held constant. The other axis maintained constant short-wavelength-sensitive- (S-) cone stimulation. The results show that adapting backgrounds that were varied along tritanopic confusion lines do not have a differential effect on color appearance at high test levels (well above the adapting level). At lower test levels there is a systematic change in color appearance of the test light, which is quantitatively described by additive redness. Along constant S-cone-stimulation lines, adapting backgrounds differentially affect color appearance in a systematic way, reflecting changes in receptoral gain and the additive contribution. The measurements taken with adapting fields throughout color space are described by the two-process model of chromatic adaptation.
Adaptation, Ocular↗