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Development and Testing of a Color Space (IPT) with Improved Hue Uniformity
Abstract
A simple, uniform color space (the IPT color space) has been derived that accurately models constant perceived hue. The model accurately predicts hue without detrimentally affecting other color appearance attributes. Several psychophysical data sets have been modeled in the new color space and appear to perform as well as or better than CIELAB and CIECAM97s color spaces. Data sets tested and compared to CIELAB and CIECAM97s include Munsell renotation colors at Value 5, OSA color system uniform scale data, MacAdam's (observer PGN) equi-luminant color tolerance ellipses, suprathreshold color-difference ellipsoids (RIT-DuPont visual color difference data), lightness of chromatic object colors (Helmholtz-Kohlrausch effect), and the two constant hue data sets. Quantitative analysis is discussed for the constant hue data sets and the Helmholtz-Kohlrausch effect data. A verification experiment that compares the new space to Hung and Berns', and Ebner and Fairchild's constant hue data sets has been performed. Results show that the new space is judged to be at least as uniform as table based hue corrections derived from the data sets.
... Its performance is similar to CAM16-UCS except that it performed slightly worse than CAM16-UCS in the SCD-surface group. However, its constant hue perception character is much more linear than that of CAM16-UCS and the same performance as the IPT [18]. For the sCAM, it predicts equally well to the CIECAM16 using the LUTCHI data, especially performing the best for its brightness subset. ...
... Gamut mapping is a well-studied problem in digital imaging [1], important for ensuring that colors remain consistent when images undergo tone mapping and other transformations. However, existing methods often rely on complex operations in perceptually uniform color spaces such as CIELAB or IPT [2], which can be computationally intensive and challenging to implement in hardware. ...
... Furthermore, the Munsell dataset currently stands as the sole dataset encompassing WCG by describing large CDs. Its extensive utilization [5,7,8,9,10,11,12] reinforces the need to validate the correctness and consistency of the dataset. In this paper, we demonstrate the presence of errors, including misprints, in the published Munsell "Re-renotation" dataset. ...
... Once the shadow region is known, there are a number of sophisticated methods that can be used to remove it while preserving the underlying texture of the region. [6][7][8][9][10][11][12] We used the simple method of increasing the intensity on the shadow region, in the log domain, and that produces comparable results. ...
... At the very least, any assessment of color constancy should be done with a color space that it built on the cone functions. Examples of this include IPT [7], CIECAM02 [8], and CIECAM16 [9]. ...
When a spot color ink is initially formulated, the ink technician needs to decide between many potential combinations of base inks that could yield the desired color under the desired illuminant. One of the primary criteria for selection is to restrict the number of base inks that are used. A second criterion which is commonly used is the metameric index. This is the color difference as computed between the spectrum of the target color and predicted spectrum of the recipe under consideration. A third potential criterion is color constancy-the formulation should, as much as possible, maintain its appearance under different illuminants. This criterion is never used, at least in part because we don't know how to measure it! This paper considers a few possible metrics for color constancy, specifically whether a smooth spectrum is an indicator of a spectrum that will prove to be more color constant.
... Their data revealed that the existing models could not avoid inter-dependence between chroma and hue and were not suitable for the imaging application such as gamut mapping. The uniform color space IPT was developed to provide improved hue linearity [25]. The other datasets were produced to investigate hue linearity for the unitary hues (pure red, yellow, green and blue), including Xiao et al., Zhao and Luo. ...
A new color appearance model named sCAM has been developed, including a uniform color space, sUCS. The model has a simple structure but provides comprehensive functions for color related applications. It takes input from either XYZ D65 or signals from an RGB space. Their accuracy has been extensively tested. sUCS performed the best or second-best to the overall 28 datasets for space uniformity and the 6 datasets for hue linearity comparing the state of the art UCSs. sCAM also performed the best to fit all available one- and two-dimensional color appearance datasets. It is recommended to have field tests for all color related applications.
Hue can be described with two types of scales for hue discrimination and hue appearance purposes. A fundamental and physiologically plausible model, called FHS for Fundamental Hue Scales, with both types of hue scales, built directly from cone fundamentals, was introduced in the previous study. In the current study, the FHS model was improved. The first step of the FHS model is a simple conversion of the LMS cone responses into the opponent axes. The opponent axes can be converted into a hue discrimination scale using a rotation matrix that is generated based on five principal hues, or they can be converted into a hue appearance scale using a rotation matrix based on four unique hues. The hue discrimination scale is called , and the hue appearance scale is called . The proposed hue model was evaluated in terms of linearity, spacing, and hue quadrature using traditional datasets including the Munsell, NCS, Hung–Berns, and Ebner–Fairchild. In addition to the available datasets, three experiments were completed to evaluate the FHS model for stimuli with higher saturation and higher luminance levels. In the first experiment, constant hue surfaces of eight hue angles were found to assess the linearity of the hue scales. In the second experiment, the spacing between 10 pairs of constant hue surfaces was examined. The third experiment was conducted to evaluate the hue quadrature of intermediate hues. Results showed that the FHS is successful in terms of linearity, spacing, and hue quadrature prediction. The FHS hue scales are mathematically very simple, physiologically and perceptually plausible, and directly based on cone fundamentals to allow easy generalization to individual observers and perform at least as well as more complicated models.
Within this third part of our mini-series, searching for the best and worst automotive in-vehicle lighting settings, we aim to extend our previous finding about white light illumination preferences by adding local cortical area activity as one key indicator. Frontal electrical potential asymmetry, measured using an electroencephalogram (EEG), is a highly correlated index for identifying positive and negative emotional behavior, primarily in the alpha band. It is rarely understood to what extent this observation can be applied to the evaluation of subjective preference or dislike based on luminaire variations in hue, chroma, and lightness. Within a controlled laboratory study, we investigated eight study participants who answered this question after they were shown highly immersive 360° image renderings. By so doing, we first subjectively defined, based on four different external driving scenes varying in location and time settings, the best and worst luminaire settings by changing six unlabeled luminaire sliders. Emotional feedback was collected based on semantic differentials and an emotion wheel. Furthermore, we recorded 120 Hz gaze data to identify the most important in-vehicle area of interest during the luminaire adaptation process. In the second study session, we recorded EEG data during a binocular observation task of repeated images arbitrarily paired by previously defined best and worst lighting settings and separated between all four driving scenes. Results from gaze data showed that the central vehicle windows with the left-side orientated colorful in-vehicle fruit table were both significantly longer fixed than other image areas. Furthermore, the previously identified cortical EEG feature describing the maximum power spectral density could successfully separate positive and negative luminaire settings based only on cortical activity. Within the four driving scenes, two external monotonous scenes followed trendlines defined by highly emotionally correlated images. More interesting external scenes contradicted this trend, suggesting an external emotional bias stronger than the emotional changes created by luminaires. Therefore, we successfully extended our model to define the best and worst in-vehicle lighting with cortical features by touching the field of neuroaesthetics.
A split-field technique was developed and llsed to produce colour reflection prints and projected transparencies, in which one area could be altered in colour while keeping the rest of the picture constant. The variable area was arranged to contain only either blue sky, green grass or Caucasian skin. Colour pictures of this type were judged by groups of observers for the quality of the reproduction in the test areas, and chromaticities corresponding to preferred and acceptable colour reproduction were obtained. In rerlection prints, preferred blue sky was found to have a higher purity than average real blue sky, but preferred green grass and Caucasian skin had similar purities but were slightly yellower than average real samples; in transparencies projected with tungsten-halogen lamps, the preferred and acceptable chromaticities are considerably more orange because of visual adaptation to the light of the projector. Comparison of the results with older studies using photographic materials of more limited colour gamuts suggests that these gamuts may have tended to reduce the purities then obtained.
Résumé
On a mis au point et utilisé une technique de champ sectionné permettant d´obtenir des épreuves couleur observables par réflexion et des diapositives de projection dans lesquelles les couleurs d´une régión peuvent être modifiées tandis que le reste de l'image reste 'nchangé. La zone variable est adaptée de façon à ne contenir que du ciel bleu, ou de l´herbe verte ou de la peau teinte chair de Caucasien.
Ces images couleur ont été examinées par des groupes d´observateurs qui ont considéré la qualité de la reproduction dans les zones d´essai et déterminé les chromaticités correspondant aux reproductions de couleurs préférées et acceptables.
Il a été observé que pour les images vues par réflexion, le bleu du ciel préféré a une pureté plus élevée que la moyenne du bleu du ciel :eel, tandis que le vert de l'herbe et la teinte de la chair de Caucasien préférés ont la même pureté mais sont légèrement plus jaunes que les echantillons moyens réels.
Pour les diapositives projetées avec des lampes halogène-tungstène, les chromaticités préférées et acceptables sont considérablement plus oranges en raison de l´adaptation visuelle à la lumière du projecteur. La comparaison de ces résultats avec ceux d´études plus anciennes faites sur des matériaux photographiques ayant des éventails de couleurs plus limités suggère que ces éventails devaient avoir tendance à réduire os puretés obtenues à cette époque.
Zusammenfassung
Es wurde ein Verfahren zur Herstellung farbiger Aufsichtsbilder und Diapositive entwickelt, bei dem jeweils ein Teil der Bildfläche in der Farbe veràndert werden konnte, wàhrend das restliche Bild unveràndert blieb. Die verànderliche Bildflàche àthielt bei den hier beschriebenen Experimenten jeweils nur einen der drei Farbtöne: Himmelsblau, Grasgrün oder Hautfarbe (Caucasian okin). Serien von derartigen Farbbildern wurden von Gruppen von Beobachtern nach der Qualitàt der Farbwiedergabe in den Testflàchen eurteilt und die Farbortkoordinaten für die bevorzugte Farbwiedergabe wurden bestimmt. Bei Aufsichtsbildern wurde gefunden, daß das Vorzugte Himmelsblau eine höhere Farbsàttigung besitzt als das durchschnittliche reale Himmelsblau; die bevorzugten Farbwerte für Fasgrün und Haut zeigten àhnliche Farbsàttigung wie die durchschnittlichen realen Werte, waren jedoch gegenüber diesen etwas nach Gelb àrschoben. Bei den mit Wolfram-Halogen-Lampen projizierten Diapositiven waren die bevorzugten Farbwerte infolge der Adaption der eobachter auf das Projektionslicht betràchtlich nach Orange verschoben. Ein Vergleich dieser Ergebnisse mit àlteren Untersuchungen, bei onen photographische Materialien mit engerem Farbwiedergabebereich verwendet wurden, làßt vermuten, daß durch diese Begrenzung die damals gefundenen Sàttigungswerte herabgesetzt wurden.
Riassunto
Una tecnica a campo diviso (“split-field”) è stata sviluppata ed usata per produrre stampe a riflessione de colore e diapositive, nelle quali in una zona si possono avere variazioni di colore, mentre in altre l´immagine rimane costante.
La zona variabile si riferisce ai colori tipo blu—cielo, verde—erba e bruno tipo pelle del Caucaso.
Fotografie a colori di questo tipo sono state giudicate, da gruppi di osservatori, sia per la qualità della riproduzione sia per i valori di cromaticità corrispondenti, preferibili e ben accettabili.
Nelle stampe per riflessione, il colore blu—cielo è stato giudicato avere una più alta purezza che non la media normale dei blu. Il verde—erba, invece, ed il bruno tipo pelle del Caucaso, pur avendo purezze di colore simili, erano leggermente più giallognoli che non il tipo reale.
Nelle diapositive, proiettate con lampada a filamento di Tungsteno—Alogenuro, le cromaticità preferite ed accettate erano considerevolmente più aranciate a causa dell´adattamento visivo alla luce del proiettore.
Il paragone dei risultati ottenuti con vecchi studi che usavano materiali a colori con assai più limitata gradazione di colore, suggerisce che queste gradazioni possono avere influenzato le purezze di colore allora ottenute.
The concept of perceptual image quality and its measurements are discussed. A distinction is made between appreciation-oriented and performance-oriented quality. It is argued that in both cases psychometrical scaling is a very important method with respect to the measurement of perceptual quality and the strength of its dimensions and therefore is indispensable if one wants to relate these attributes to the physical image parameters. Scaled perceptual image quality and its validity are discussed in connection with physical image parameters such as size, gamma and spatial resolution. Scaled subjective impairments caused by quantisation errors are also dealt with. Finally, an example of scaled visual comfort and its relation with a few objective performance measures is given. It is concluded that the effect of inter-subject differences is of less concern than the effects of different scenes.
In phenomenological analyses of the visual color gestalt it has been found that color plays at least a double role from a cognitive point of view. First, the characteristics of the color gestalt have to do with how man identifies colors, and are related to emotions, connotations, semantics, and symbolism. The NCS (Natural Color System) was designed to cover the need for a descriptive color order system, based on the six characteristic elementary color attributes whiteness, blackness, yellowness, redness, blueness, and greenness, from which was derived the three-dimensional NCS color space for providing color notations. Second, the form of background and patterns in a color gestalt has to do with how man distinguishes color elements from each other by contrast and is informative about form and directions. In this article we report about one of the contrast phenomena, border distinctness between adjacent colors, which is most essential for the perception of form gestalts. Several years of phenomenological analyses and psychometric and psychophysical experiments have resulted in an equation for the prediction of the kind of contrast defined as border distinctness, called GT from the Swedish word Gränstydlighet. Based on that equation is a geometrical model for the GT color-difference space that is not Euclidean but of city-block type. The studies have led to the question of whether the phenomenon of color contrast (difference) is a perception of its own and not linearly related to the difference between two color perceptions.
The evaluation of quality of color reproduction poses many complex problems. Optimum reproduction needs to be identified. Since it depends upon the limitations of the reproduction process, as well as upon human vision and judgment, optimum reproduction will probably have to be determined for each process separately. The program is to vary the production controls in systematic manners, measure the resulting color reproduction in the best way known (e.g., the I.C.I. method at the present time), submit the reproductions to visual judgment, and study the judgment data in comparison with the measurements in order to find significant correlations. The growing experience of such studies of color photography is suggested as a guide. Preliminary estimates of optimum reproduction and of seriousness of deviations may be based tentatively on results of studies of noticeability of color differences and on fragmentary results of studies of color photography. These estimates can be improved as various parts of the program are carried out.
Citation
PARRY MOON and DOMINA EBERLE SPENCER, "Aesthetic Measure Applied to Color Harmony," J. Opt. Soc. Am. 34, 234-242 (1944)
http://www.opticsinfobase.org/josa/abstract.cfm?URI=josa-34-4-234
Color gamut mapping is required whenever two imaging devices do not have coincident color gamuts or viewing conditions. Two major gamut mapping techniques include lightness and chroma manipulations. Lightness mapping accounts for differences in white level, black level, and viewing conditions while chroma mapping accounts for differences in gamut volume. As a three dimensional space in which color gamut mapping is implemented, the 1991 Hunt model of color appearance was used utilizing dimensions of lightness, chroma, and hue. This model accounts for viewing conditions in addition to the usual device independent specification. The mapping techniques were applied to back-lit photographic transparencies in order to reproduce images using a dye diffusion thermal transfer printer. As the first experiment, a lightness mapping experiment was performed. Three different lightness mapping techniques, a linear technique and two non-linear techniques, were tested for four images. The psychophysical method of paired comparison was used to generate interval scales of preferred color reproduction. In general, the preferred technique depended on the amount of lightness mapping required and on the original image's lightness histograms. For small amounts of compression, the preferred technique was a clipping type. For large amounts of compression, the preferred technique was image dependent; low preference was caused by loss of detail or apparent fluorescence of high chroma image areas.