Chromatic Adaptation Research Articles

Color appearance of color chips under light‐emitting diodes lamps part II: Hue shift direction

AbstractOur previous experiment showed that the color appearance of color chips changes depending on the color of illumination. In this article, we continued to analyze the previous data of 23 color chips under six vivid colored illuminations (red, yellow, green, cyan, blue, and magenta) that were assessed by 100 subjects. We found that there were usually two directions of shifted color under vivid illumination. For example, color chips would change to either a dark blue or orange direction under vivid red illumination depending on the color of the color chips. We also found that there is a similar mechanism behind the chromatic adaptation in relation to the complementary color.

Magnetoencephalography contrast adaptation reflects perceptual adaptation.

Contrast adaptation is a fundamental visual process that has been extensively investigated and used to infer the selectivity of visual cortex. We recently reported an apparent disconnect between the effects of contrast adaptation on perception and functional magnetic resonance imaging BOLD response adaptation, in which adaptation between chromatic and achromatic stimuli measured psychophysically showed greater selectivity than adaptation measured using BOLD signals. Here we used magnetoencephalography (MEG) recordings of neural responses to the same chromatic and achromatic adaptation conditions to characterize the neural effects of contrast adaptation and to determine whether BOLD adaptation or MEG better reflect the measured perceptual effects. Participants viewed achromatic, L-M isolating, or S-cone isolating radial sinusoids before adaptation and after adaptation to each of the three contrast directions. We measured adaptation-related changes in the neural response to a range of stimulus contrast amplitudes using two measures of the MEG response: the overall response amplitude, and a novel time-resolved measure of the contrast response function, derived from a classification analysis combined with multidimensional scaling. Within-stimulus adaptation effects on the contrast response functions in each case showed a pattern of contrast-gain or a combination of contrast-gain and response-gain effects. Cross-stimulus adaptation conditions showed that adaptation effects were highly stimulus selective across early, ventral, and dorsal visual cortical areas, consistent with the perceptual effects.

Micron-Scale Biogeography of Seawater Biofilm Colonies at Submersed Solid Substrata Affected by Organic Matter and Microbiome Transformation in the Baltic Sea.

The aim of this research was to determine temporal and spatial evolution of biofilm architecture formed at model solid substrata submersed in Baltic sea coastal waters in relation to organic matter transformation along a one-year period. Several materials (metals, glass, plastics) were deployed for a certain time, and the collected biofilm-covered samples were studied with a confocal microscopy technique using the advanced programs of image analysis. The geometric and structural biofilm characteristics: biovolume, coverage fraction, mean thickness, spatial heterogeneity, roughness, aggregation coefficient, etc., turned out to evolve in relation to organic matter transformation trends, trophic water status, microbiome evolution, and biofilm micro-colony transition from the heterotrophic community (mostly bacteria) to autotrophic (diatom-dominated) systems. The biofilm morphology parameters allowed the substratum roughness, surface wettability, chromatic organisms colony adaptation to substrata, and quorum sensing or cell to cell signaling effects to be quantitatively evaluated. In addition to the previous work, the structural biofilm parameters could become further novel trophic state indicators.

CVD-MET: an image difference metric designed for analysis of color vision deficiency aids.

Color vision deficiency (CVD) has gained in relevance in the last decade, with a surge of proposals for aid systems that aim to improve the color discrimination capabilities of CVD subjects. This paper focuses on the proposal of a new metric called CVD-MET, that can evaluate the efficiency and naturalness of these systems through a set of images using a simulation of the subject's vision. In the simulation, the effect of chromatic adaptation is introduced via CIECAM02, which is relevant for the evaluation of passive aids (color filters). To demonstrate the potential of the CVD-MET, an evaluation of a representative set of passive and active aids is carried out both with conventional image quality metrics and with CVD-MET. The results suggest that the active aids (recoloration algorithms) are in general more efficient and produce more natural images, although the changes that are introduced do not shift the CVD's perception of the scene towards the normal observer's perception.

Spectral tuning of bioluminescence and visual sensitivity in males of Brazilian firefly species inhabiting dim light environments (Coleoptera: Elateroidea: Lampyridae).

Bioluminescence in fireflies is essential for sexual communication, and each species has evolved a specific bioluminescence emission capable of being detected by its visual system. This spectral "tuning"between visual sensitivity and bioluminescent emission has been established in 14species of North American fireflies inhabiting diverse photoecological niches. Here we extend that research to three Brazilian species. Macrolampis omissa inhabits the Cerrado (savannas), while Photinus sp1 and Pyrogaster moestus are often sympatric species inhabiting borders of mesophyll rain forests and secondary growth. P. moestus particularly favors humid areas of the forest. M. omissa and Photinus sp1 are twilight-active fireflies emitting yellow bioluminescence. P. moestus is a "twi-night" species emitting green bioluminescence. It initiates flashing at the end of twilight and continues activity into the night. The visual spectral sensitivity of dark-adapted compound eyes in these three species is similar, showing a maximum in the yellow-green wavelengths and a secondary peak in the near-UV, suggesting the presence of two receptors. The bioluminescence emission spectrum in each species is tuned to its yellow-green visual sensitivity peak. Green chromatic adaptation experiments on Photinus sp1 and P. moestus suggest the presence of a blue receptor. The presence of near-UV, blue, and long-wavelength receptors in the compound eyes would enable a trichromatic color vision in Brazilian firefly species active in dim illumination.

Chromatic Acclimation Processes and Their Relationships with Phycobiliprotein Complexes.

Chromatic acclimation (CA) is a widespread mechanism for optimizing the composition of phycobiliprotein complexes to maximize the cyanobacterial light capture efficiency. There are seven CA types, CA1-CA7, classified according to various photoregulatory pathways. Here, we use sequence analyses and bioinformatics to predict the presence of CA types according to three GAF (cGMP phosphodiesterase/adenylyl cyclase/FhlA)-containing photoreceptors, CcaS (cyanobacterial chromatic acclimation sensor), RcaE (regulator of chromatic adaptation), and RfpA (regulator for far-red photoacclimation). These photoreceptors were classified into three different phylogenetic groups leading different CA types in a diverse range of cyanobacteria. Combining with genomic information of phycobilisome compositions, the CA capabilities of various cyanobacteria were conjectured. Screening 65 accessible cyanobacterial genomes, we defined 19 cyanobacteria that have the capability to perform far-red light photoacclimation (FaRLiP) under the control of RfpA. Forty out of sixty-five cyanobacteria have the capability to perform green/red light photoacclimation, although they use different photoreceptors (RcaE and/or CcaS) and photoregulatory pathways. The reversible response of photoreceptors in CA regulation pathways trigged by changed light conditions reflects the flexibility of photoregulatory mechanisms in cyanobacteria and the putative independent evolutionary origin of photoacclimation types.

Preservation of Perceived Colorfulness of Down-Mapped, Hybrid Log-Gamma (HLG) to Standard Dynamic Range Content Using a Color Appearance Model (CAM)

Most of today’s high dynamic range (HDR) hybrid log-gamma (HLG) to standard dynamic range (SDR) conversions rely on a mathematical approach for color volume reduction from an International Telecommunication Union-Radioommunication (ITU-R) Recommendation BT.2100 container into an ITU-R BT.709 one, typically through “tone-mapping” applied to a luminance signal. However, this might not be the only plausible option for HLG to SDR conversion. A color appearance model (CAM) has been extended in this work to compute HLG to SDR down-mapping. This alternative down-mapping approach can be carried out through a CAM combined with a chromatic adaptation transform (CAT). The CAT transforms the image into a uniform color space (UCS), and the CAM calculates values of perceived quantities of the viewed media, such as lightness and colorfulness given specific display parameters. Perceptual quantities in the model are, for the most part, conserved to compute the down-mapping. This method has shown great promise in several natural images and colors, while having limitations with engineering test signals. SDR footage derived from an HDR capture using a CAM look-up table (LUT) results in natural pictures that are more visually accurate than those from conventional conversion technologies or SDR capture since many colors in nature exist outside of a BT.709 container. Other examples of down-mapping can be found in the ITU-R report BT.2446. Such down-mapping conversions attempt to maintain color fidelity between the two visual representations and are usually implemented in a 3D LUT. Such approaches, however, cannot take full account of psychovisual factors and may struggle to differentiate between colors such as yellow and brown that are similar in hue but vary in luminance. A CAM-based approach may not deliver mathematically ideal output values for artificial test patterns, so the article will also discuss what changes may need to be made to TV production workflows if the improvements offered by CAM-based down-mapping are to be fully realized.

Probing Perceptual Phenomena for Color Management

Advancement of color management techniques is required to accommodate for emerging formats and devices. To address this, experiments were conducted by the authors in order to characterize and account for the effect of metamerism error, chromatic adaptation to the surround, contrast adaptation to display dynamic range, and viewing size dependent effects of retinal signal pooling. These topics were assembled to address perceptual representation inconsistencies which are becoming more common with the popularity of mobile, High Dynamic Range (HDR), and Wide Color Gamut (WCG) displays. In this paper, we briefly summarize the findings of these efforts and compile a series of takeaways which are key to the problem of perceptual color management. Furthermore, we discuss the implications of these take-aways on the advancement of the field.

Accurate Recognition of Motion Patterns Based on Artificial Visual Neural Network

In order to improve the accuracy of motion pattern recognition, this paper combines the artificial visual neural network to construct a motion pattern recognition system. Moreover, this paper discusses the psychological perception properties of human eyes to color stimuli and gives a description of the observation field of view where the color stimuli are located. At the same time, this paper analyzes the phenomenon of color adaptation and provides a method of color appearance matching through modeling to achieve color appearance matching under variable observation conditions. Based on the chromatic adaptation transformation, a chromatic appearance model is given, which can predict the corresponding color and also predict the chromatic appearance properties of color stimuli under given observation conditions. In addition, this paper constructs an intelligent motion pattern recognition system combined with artificial visual neural network. The experimental results show that the motion pattern recognition system based on artificial visual neural network can accurately identify the motion pattern category.

Contrast sensitivity functions in autoencoders.

Three decades ago, Atick et al. suggested that human frequency sensitivity may emerge from the enhancement required for a more efficient analysis of retinal images. Here we reassess the relevance of low-level vision tasks in the explanation of the contrast sensitivity functions (CSFs) in light of 1) the current trend of using artificial neural networks for studying vision, and 2) the current knowledge of retinal image representations. As a first contribution, we show that a very popular type of convolutional neural networks (CNNs), called autoencoders, may develop human-like CSFs in the spatiotemporal and chromatic dimensions when trained to perform some basic low-level vision tasks (like retinal noise and optical blur removal), but not others (like chromatic) adaptation or pure reconstruction after simple bottlenecks). As an illustrative example, the best CNN (in the considered set of simple architectures for enhancement of the retinal signal) reproduces the CSFs with a root mean square error of 11% of the maximum sensitivity. As a second contribution, we provide experimental evidence of the fact that, for some functional goals (at low abstraction level), deeper CNNs that are better in reaching the quantitative goal are actually worse in replicating human-like phenomena (such as the CSFs). This low-level result (for the explored networks) is not necessarily in contradiction with other works that report advantages of deeper nets in modeling higher level vision goals. However, in line with a growing body of literature, our results suggests another word of caution about CNNs in vision science because the use of simplified units or unrealistic architectures in goal optimization may be a limitation for the modeling and understanding of human vision.

Color Compensatory Mechanism of Chromatic Adaptation at the Cortical Level.

Reportedly, some chromatic adaptations have extremely short temporal properties, while others have rather long ones. We aimed to dynamically measure the transition of a neutral point as an aftereffect during chromatic adaptation to understand the temporal characteristics of chromatic adaptation. The peripheral retina was exposed to a yellow light to progress color adaptation, while the transition of a neutral point was measured at the fovea. In Experiment 1, the aftereffect had initially progressed but subsequently recovered despite ongoing chromatic adaptation and regardless of the retinal exposure size, suggesting that the adaptation mechanism at the cortical level continues to readjust the color appearance based on daylight conditions. Experiment 2 was similar to Experiment 1, except that it included participants of varying ages. Older eyes behaved in a homologous manner with younger eyes in Experiment 2, albeit quantitative differences. Regardless of age, similar recalibration of neutral points shifted by color adaptation suggests the color compensation function in older eyes may not change due to long-term chromatic adaptation by optical yellowing. In conclusion, the chromatic adaptation mechanism at the cortical level readjusts color perception, even in younger eyes, according to the daylight neutral point. This daylight information may be stored in the neural mechanism of color vision.

Phytoplankton diversity emerging from chromatic adaptation and competition for light

The phytoplankton absorption cross-section is a fundamental quantity in biogeochemical ocean models that alters the underwater spectral light field and the photosynthetic response of phytoplankton. Phytoplankton taxa are characterized by absorption spectra with defined absorption bands in the visible region of the light spectrum that govern the capability of different taxa of phytoplankton to exploit light as a resource for growth. The interplay between the spatial and temporal gradients of underwater spectral light and the light absorption characteristics of different phytoplankton types contribute to the interactions and selection among groups and hence can be a determinant in shaping phytoplankton diversity and biogeography. In this work, we used a biogeochemical model of the Mediterranean Sea to simulate nine optically different phytoplankton functional types (PFTs) and coupled it to a radiative transfer model to simulate the spectral underwater light field where the PFTs interact. We investigated the competitive advantage provided by the different absorption spectra and the possibilities of coexistence emerging from the availability of different light habitats. By considering non-spectrally resolved optical differences among PFTs, our model results led to the dominance of Synechococcus sp. within picophytoplankton, coccolithophores within nanophytoplankton and dinoflagellates within microphytoplankton. By including the spectral dependency of photosynthesis, we observed how the availability of different spectral light habitats led to the coexistence of picophytoplankton groups in clear waters, whereas for nano- and microphytoplankton PFTs, the extent of coexistence permitted by light fluctuations was minimal. By combining optical and functional differences in the PFT description, we obtained PFT distributions that were in relative agreement with observed phytoplankton distributions in the Mediterranean Sea estimated from satellite and in situ high-performance liquid chromatography sampling. This result suggests that combining spectrally resolved optical traits with functional traits in the description of the autotrophic community can be a valuable tool to improve simulations of the diversity and biogeography of primary producers in the ocean.

Polyphasic Identification and Genomic Insights of Leptothermofonsia sichuanensis gen. sp. nov., a Novel Thermophilic Cyanobacteria Within Leptolyngbyaceae

Thermal environments are an important reservoir of thermophiles with significant ecological and biotechnological potentials. However, thermophilic isolates remain largely unrecovered from their habitats and are rarely systematically identified. In this study, we characterized using polyphasic approaches a thermophilic strain, PKUAC-SCTAE412 (E412 hereafter), recovered from Lotus Lake hot spring based in Ganzi prefecture, China. The results of 16S rRNA/16S-23S ITS phylogenies, secondary structure, and morphology comparison strongly supported that strain E412 represent a novel genus within Leptolyngbyaceae. This delineation was further confirmed by genome-based analyses [phylogenomic inference, average nucleotide/amino-acid identity, and the percentages of conserved proteins (POCP)]. Based on the botanical code, the isolate is herein delineated as Leptothermofonsia sichuanensis gen. sp. nov, a genus adjacent to recently delineated Kovacikia and Stenomitos. In addition, we successfully obtained the first complete genome of this new genus. Genomic analysis revealed its adaptations to the adverse hot spring environment and extensive molecular components related to mobile genetic elements, photosynthesis, and nitrogen metabolism. Moreover, the strain was capable of modifying the composition of its light-harvesting apparatus depending on the wavelength and photoperiod, showing chromatic adaptation capacity characteristic for T1 and T2 pigmentation types. Other physiological studies showed the strain’s ability to utilize sodium bicarbonate and various sulfur compounds. The strain was also shown to be diazotrophic. Interestingly, 24.6% of annotated protein-coding genes in the E412 genome were identified as putatively acquired, hypothesizing that a large number of genes acquired through HGT might contribute to the genome expansion and habitat adaptation of those thermophilic strains. Most the HGT candidates (69.4%) were categorized as metabolic functions as suggested by the KEGG analysis. Overall, the complete genome of strain E412 provides the first insight into the genomic feature of the genus Leptothermofonsia and lays the foundation for future global ecogenomic and geogenomic studies.

Predictive performance of the standard and the modified von Kries chromatic adaptation transforms.

To investigate chromatic adaptation and develop chromatic adaptation transforms (CATs), many psychophysical experiments have been conducted to collect corresponding colors (CC) under various illumination conditions. Most modern CATs have been developed based on a database of CC sets collected in the 20th century. More recently, several additional CC sets have been collected by Smet et al., Wei et al., and Ma et al. using memory color matching or achromatic matching methods. The analysis of these CC data indicates that for yellowish (located on or close to the Planckian locus) and greenish illuminations, the short-wave (S) sensitive cones show a lower degree of adaptation compared to the long-wave (L) and medium-wave (M) sensitive cones. This can result in a large prediction error of the standard von Kries CAT, which adopts a single degree of adaptation value for all three cone types. A modified von Kries CAT is proposed that accounts for these differences between the L-, M- and S-cone signals by applying a compression to the rescaling factor for the S-cones. It outperforms the standard von Kries CAT for the Breneman-C, Smet, Wei, and Ma data, while for other data sources the two CATs have similar performance.

Study of display white point based on mixed chromatic adaptation.

In this study, the settings of the display white points were investigated, which presented the color appearance matched with a neutral surface as observed in the state of mixed chromatic adaptation. A psychophysical experiment was conducted under 20 illumination and viewing conditions via successive binocular color matching. It is discovered that the metameric light sources have generally equivalent effects on the observers' adaptation states and the resulting white points. The correlated color temperature (CCT) of the illumination and the adapting luminance, both with a significant influence on the mixed chromatic adaptation, exhibit a positive and a negative relation to the white point CCT, respectively. The immersive illumination affects the white point through the adaptation ratio and the baseline illuminant. Finally, the experimental results were verified to be predictable with an amended mixed chromatic adaptation model, which produced a mean chromaticity error of only 0.0027 units of CIE 1976 u'v'.

COLOR PERCEPTION ESTIMATIONS OF METAMERIC PAIRS UNDER DIFFERENT ILLUMINANCE LEVELS

LEDs or light emitting diodes of the lighting class dominate both the indoor and outdoor lighting industries today due to their accuracy and consumer-friendly color temperature. In the context of color science, it is necessary to analyze both the spectral power distribution of lighting and the human characteristics of color perception under these lights. In this article, we provide estimates of the appearance of eleven metameric pairs under LEDs with four correlated color temperatures and six illuminance levels, using color difference formulas based on the CIELAB, CAM02-UCS, and CAM16-UCS models to verify our estimates. We followed ASTM D4086 standard visual methods for detecting metamerism and for estimating the magnitude of a metameric color difference. Our investigations found that color appearance models are more reliable than CIELAB in evaluating color difference under various LED conditions. CAM16-UCS more accurately predicted the color difference estimates between all three formulas. Our comparative study confirms that the variation in the estimates with the CCT and illuminance levels of the LED sources depends on the color appearance model used. The results also showed that in order to determine the color difference of metameric pairs, optimal conditions regarding the colorimetric properties of the samples and the variability of the observer should be considered separately. We noticed an increasing correlation trend with increasing illuminance. However, there was no such increase or decrease trend in CCTs. The trend of the STRESS change in the color appearance models showed the influence of the chromatic adaptation, but the establishment of adaptation patterns is far beyond the scope of this work. Although our research has had limitations on correlated color temperature and illuminance, we believe that it can be beneficial for the lighting application to ensure correct lighting decisions when assessing the color differences of metameric pairs.

Color inconstancy in CIELAB: A red herring?

AbstractColor constancy is something we take for granted. An apple appears red despite monumental changes in the intensity and spectral balance of illumination. There are many components to the human visual system that make this illusion possible. Nonetheless, the system is imperfect. Objects will change apparent color under different illumination. The CIELAB color space allows for the computation of color values under any illuminant. CIELAB values will, in general, change as the illuminant changes. It would be natural to assume that these changes in CIELAB values would agree with the apparent color change that a human would experience. But the chromatic adaptation built into CIELAB is known to be less than optimal due to an imperfect emulation of how the adaptation process is performed in the human visual system. As a result, at least part of the illuminant color change implied by the CIELAB values is an artifact of this imperfect emulation. This paper investigates the magnitude of this artifact by comparing color changes implied by CIELAB with color changes in a color system that mimics CIELAB, except that it more closely emulates the human visual system. The difference between the two estimates of color change is assumed to be an artifact of CIELAB's poor emulation of the chromatic adaptation process. As color manufacturers are dealing with a wider spectrum of illumination sources, they may wish to consider the issue of color constancy; what colors and what formulations of colors exhibit better color constancy? Can CIELAB be used to quantify this? Or are color spaces that are based on LMS rather than XYZ more appropriate?

A method to prepare reference colors for chromatic adaptation experiments

AbstractThe preparation of the reference colors is the hardest and the most time‐consuming part of chromatic adaptation experiments. In this paper, a new method is proposed to prepare high‐quality reference color arrays for chromatic adaptation experiments. The reference color arrays are defined in the a*b* plane of CIELAB color space. The initial arrays are calculated by the CAT02 and the desired color differences. Then the arrays are output and two visual experiments are organized, the chromatic adaptation experiment and the color difference estimating experiment. The former is to check if the color gamut of the reference colors is fit for the experiment. The latter is to check the uniformity of the color differences of the arrays. According to the fitting curves from the color differences estimating experiment, the reference color arrays can be optimized to be more uniform in the color differences. The method is proved effective and suitable for different media.

Considering chromatic adaptation in camera white balance

Chromatic adaptation is an important mechanism in the human visual system. It helps to maintain the color appearance of illuminated objects relatively constant by automatically removing the color cast of the illumination. White balance, an important step in camera ISP pipeline, is designed to simulate the chromatic adaptation mechanism by automatically or manually specifying the white point of a captured scene. Conventional white balance algorithms simply adjust the color appearance of the captured scene to how it would appear under daylight, regardless of the illumination of the scene. Recent studies, however, clearly suggested that incomplete chromatic adaptation happened under some illumination conditions, which should be considered in white balance. In this study, we systematically varied the chromaticities of the illumination in a viewing booth, and also the chromaticities of the illumination in two viewing booths. The observers viewed the viewing booth(s) first and then adjusted the color appearance of the image of the booth(s) shown on a smartphone display by adjusting the image white point. The results clearly suggested the necessity to consider the degree of chromatic adaptation in camera white balance and provided guidance on how white balance should be performed.

Non-standard colorimetry in ICC colour management

In ICC v4 colour management, data is exchanged between different colour encodings via a fixed Profile Connection Space (PCS), in which colorimetry is based on the D50 illuminant, and the CIE 1931 standard observer. According to the ICC specification, colorimetry that is based on a different illuminant, or observer should be transformed into the fixed PCS; however, while a chromatic adaptation method is specified for when illuminants are different, there is no method specified for differences in observer. The Waypoint method has been proposed as a means of transforming between different colorimetric data encodings. In this study a Waypoint-based method recommended by ICC was evaluated as a mechanism for transforming into the ICC PCS, as applied to a use case in digital textile printing in which source colorimetry is based on the D65 illuminant and the CIE 1964 observer. It was compared with an alternative approach in which a non-ICC PCS was used within a conventional ICC colour management framework. The results show that when both source and destination colorimetry are based on D65/10-degrees, both methods perform equally well. However, when the source and destination colorimetry do not match, the ICC approach of transforming via the standard PCS yields better results.