Investigating the Effect of Color Gamut Mapping Quantitatively and Visually

With the advent of various color management standards and tools, the print media industry has seen many advancements aimed towards quantitatively and qualitatively acceptable color reproduction. This research attempts to test one of the most fundamental and integral parts of a standard color management workflow, the profile. The gamut mapping techniques implemented by the ICC profiles created using different profiling application programs were tested for their congruity to the theoretical concepts, standards, and definitions documented by International Color Consortium (ICC). Once these profiling software applications were examined, the significance of the possible discrepancies were tested by establishing a visual assessment of pictorial images using these profiles. In short, this research assessed the implementations of the ICC color rendering intents in a standard or a commonly used color managed workflow, and then described the significance of these discrepancies in terms of interoperability. For this research, interoperability was defined the assessment of different ICC profiles in producing similar results, i.e., quantitatively and visually. In order to achieve the desired assessment, the two profiling applications were selected and each used to create an output profile using the same characterization data set. The two profiles were then compared for differences in the way they mapped real world colors. The results displayed that even though there were some significant quantitative color differences, visual subjective evaluation did not reflect any noticeable color differences and therefore concluded that the profiles were interoperable. These findings reveal that even though quantitative color differences may reflect significant color differences, subjective visual comparisons may not always reflect the same or agree with quantitative findings

Remote Visual Observation of Real Places Through Virtual Reality Headsets

Virtual Reality has always represented a fascinating yet powerful opportunity that has attracted studies and technology developments, especially since the latest release on the market of powerful high-resolution and wide field-of-view VR headsets. While the great potential of such VR systems is common and accepted knowledge, issues remain related to how to design systems and setups capable of fully exploiting the latest hardware advances. The aim of the proposed research is to study and understand how to increase the perceived level of realism and sense of presence when remotely observing real places through VR headset displays. Hence, to produce a set of guidelines that give directions to system designers about how to optimize the display-camera setup to enhance performance, focusing on remote visual observation of real places. The outcome of this investigation represents unique knowledge that is believed to be very beneficial for better VR headset designs towards improved remote observation systems. To achieve the proposed goal, this thesis presents a thorough investigation of existing literature and previous researches, which is carried out systematically to identify the most important factors ruling realism, depth perception, comfort, and sense of presence in VR headset observation. Once identified, these factors are further discussed and assessed through a series of experiments and usability studies, based on a predefined set of research questions. More specifically, the role of familiarity with the observed place, the role of the environment characteristics shown to the viewer, and the role of the display used for the remote observation of the virtual environment are further investigated. To gain more insights, two usability studies are proposed with the aim of defining guidelines and best practices. The main outcomes from the two studies demonstrate that test users can experience an enhanced realistic observation when natural features, higher resolution displays, natural illumination, and high image contrast are used in Mobile VR. In terms of comfort, simple scene layouts and relaxing environments are considered ideal to reduce visual fatigue and eye strain. Furthermore, sense of presence increases when observed environments induce strong emotions, and depth perception improves in VR when several monocular cues such as lights and shadows are combined with binocular depth cues. Based on these results, this investigation then presents a focused evaluation on the outcomes and introduces an innovative eye-adapted High Dynamic Range (HDR) approach, which the author believes to be of great improvement in the context of remote observation when combined with eye-tracked VR headsets. Within this purpose, a third user study is proposed to compare static HDR and eye-adapted HDR observation in VR, to assess that the latter can improve realism, depth perception, sense of presence, and in certain cases even comfort. Results from this last study confirmed the author expectations, proving that eye-adapted HDR and eye tracking should be used to achieve best visual performances for remote observation in modern VR systems

Impact of Illumination Correlated Color Temperature, Background Lightness, and Painting Color Content on Color Appearance and Appreciation of Paintings

© 2019, © 2019 Illuminating Engineering Society. Lighting design for art exhibitions has a significant impact on the enjoyment and understanding of the displayed artworks. In particular, the selection of the light sources and the design of the museum space affect the visitors' visual perceptions of the artworks and their color appearance. This project investigated some of the potential factors—the correlated color temperature (CCT) of the illumination, the overall color content of the painting and the lightness of its background—affecting a painting's color appearance and appreciation in a museum setting. The study involved a survey conducted in the laboratory with both naïve observers and lighting experts. The CCT of the lighting was found to be the main factor affecting the painting's appearance and the observers' overall preference for the lighting arrangements, whereas the overall hue content of the painting and the background lightness had a minor influence. Furthermore, it has been found that the perceived brightness increases along with the CCT. ispartof: LEUKOS vol:16 issue:1 pages:25-44 status: publishe

Optimising Light Source Spectrum to Reduce the Energy Absorbed by Objects

Light is used to illuminate objects in the built environment. Humans can only observe light reflected from an object. Light absorbed by an object turns into heat and does not contribute to visibility. Since the spectral output of the new lighting technologies can be tuned, it is possible to imagine a lighting system that detects the colours of objects and emits customised light to minimise the absorbed energy. Previous optimisation studies investigated the use of narrowband LEDs to maximise the efficiency and colour quality of a light source. While these studies aimed to tune a white light source for general use, the lighting system proposed here minimises the energy consumed by lighting by detecting colours of objects and emitting customised light onto each coloured part of the object. This thesis investigates the feasibility of absorption-minimising light source spectra and their impact on the colour appearance of objects and energy consumption. Two computational studies were undertaken to form the theoretical basis of the absorption-minimising light source spectra. Computational simulations show that the theoretical single-peak spectra can lower the energy consumption up to around 38 % to 62 %, and double-peak test spectra can result in energy savings up to 71 %, without causing colour shifts. In these studies, standard reference illuminants, theoretical test spectra and coloured test samples were used. These studies are followed by the empirical evidence collected from two psychophysical experiments. Data from the experiments show that observers find the colour appearance of objects equally natural and attractive under spectrally optimised spectra and reference white light sources. An increased colour difference, to a certain extent, is found acceptable, which allows even higher energy savings. However, the translucent nature of some objects may negatively affect the results

The influence of the skin colour on the perceived attributes

Skin colour data are important for many applications such as medical, imaging, cosmetics. The present study was aimed to collect a comprehensive skin colour database, and to study the impact of the skin colour on the variety of facial impression attributes. Although many researchers and engineers have collected skin data，few of them studied the skin colours to measure the same locations on a large number of subjects from different ethnic groups using the same colour measuring instruments. As for studying the impact of the skin colour on the visual perceptions, many studies investigated the impact of the skin colour on the attractiveness, health and youth. Limited previous studies investigated the impact of the skin colour on the other impression attributes. The present study was divided into two experiments, Experiments 1 and 2. Experiment 1 was to accumulate the skin colour database, named the Leeds Liverpool skin colour (LLSC). It included skin colours of 188 people from four ethnic groups (Caucasian, Oriental, South Asian and African) and both genders. Three colour measuring methods were used to accumulate the skin colour of each subject’s 10 locations including facial locations (forehead, cheekbone, cheek, nose tip, chin and neck) and body locations (the back of the hand, inner forearm, outer forearm and fingertip). The colour measuring methods included a tele-spectroradiometer (TSR), a spectrophotometer (SP) and a set of skin colour chart used as a visual aid. Also, a characterised digital camera controlled by an imaging system was used to collect facial images. Before the data collection, the short-term repeatability of different settings of the TSR and the SP on measuring human skin colour in vivo was determined. And this was used to settle the measurement protocols of the two instruments. The LLSC database was later used to investigate the skin colour distribution between ethnic groups, between genders, between measuring methods. A skin whiteness and blackness scales based on the CIELAB L* and Cab* scales in CIELAB was developed by referencing the vividness and depth formulae, which was developed by Berns (2000). It was found that these scales and CIELAB hue angle can describe well the property of skin colour of each ethnic group. Experiment 2 was to investigate the impact of the skin colour on the facial impression attributes. Based on the LLSC database, the gamut of skin colour was defined. Twenty-three attributes used to describe facial skin colours were accumulated. They were classified into two groups (appearance and impression). Two experiments were carried out on a monitor to understand the impact of the skin colour on the perceived facial impression attributes. The first experiment (Experiment 2.1) was to study the relationship between different attributes by 10 observers. The results showed that only four dimensions were required to describe skin facial colours, which were named Likeable, Sociable, Feminine and Youth. The health was also selected because the traditional Chinese medicine has interested in it. The second experiment (Experiment 2.2) was to scale facial images selected from two ethnic groups and both genders by using these five impression attributes by 24 Chinese observers. The experimental results showed that there were systematic patterns between the impression attributes and the whiteness and hue angle scales. There are some differences between these images for each impression. The ethnic group had an impact on the judgement, but the difference between the Oriental and Caucasian female images was limited. Finally, mathematical models were successfully developed to predict the impressions from the skin whiteness and hue angle data

The New Colour Scales based on Saturation, Vividness, Blackness and Whiteness

This research project has two goals. One is to understand the third dimension of colour scales describing the extent of chromatic contents such as saturation, vividness, chromaticness and colourfulness, which are less widely used than the other dimensions, e.g. lightness and hue. With that in mind, the first aim of this work is to derive new models that may serve as an alternative to the third-dimension scale of colour appearance on the basis of colorimetric values. The second goal is to develop important scales, blackness and whiteness. They are widely used because of the popularity of the NCS system. To achieve the first goal, a psychophysical experiment for scaling 15 attributes (Korean corresponding words of “bright”, “light-heavy”, “active-passive”, “fresh-stale”, “clean-dirty”, “clear”, “boring”, “natural-not natural”, “warm-cool”, “intense-weak”, “saturated”, “vivid-dull”, “distinct-indistinct”, “full-thin” and “striking”) using the NCS colour samples was carried out with Korean observers. Each sample was presented in a viewing cabinet in a darkened room. Naive observers were asked to scale each sample using a categorical judgement method. From the results, two scales widely used to represent the third dimension were identified: saturation and vividness. The same samples were assessed by British observers using these two scales. There was a great similarity between the results of the British and Korean observers. Subsequently, more samples were included to scale not only the new third dimension scales (saturation and vividness) but also whiteness and blackness scales. In total, 120 samples were scaled for saturation, vividness and whiteness experiments, and 110 samples were scaled for a blackness experiment. Four sets of models were developed for each of the three colour spaces (CIELAB, CIECAM02 and CAM02-UCS). Type one was based on the ellipsoid equation. Type two was based on the hue-dependent model proposed by Adams (called “the hue-based model”). Each of the above two types was used to fit the present experimental (Cho) data and the NCS data, which were measured using a spectrophotometer. In total, 39 models were developed. The newly developed models were tested using the Cho and NCS datasets. The models that were based on the present visual data were tested using the NCS data. Similarly, the models developed from the NCS data were tested using the present visual data. The results showed that both types of models predicted visual data well. This means that the two sets of data showed good agreement. It is also proposed that the four scales (saturation, vividness, blackness and whiteness) based on CIECAM02 developed here are highly reliable

N-colour separation methods for accurate reproduction of spot colours

In packaging, spot colours are used to print key information like brand logos and elements for which the colour accuracy is critical. The present study investigates methods to aid the accurate reproduction of these spot colours with the n-colour printing process. Typical n-colour printing systems consist of supplementary inks in addition to the usual CMYK inks. Adding these inks to the traditional CMYK set increases the attainable colour gamut, but the added complexity creates several challenges in generating suitable colour separations for rendering colour images. In this project, the n-colour separation is achieved by the use of additional sectors for intermediate inks. Each sector contains four inks with the achromatic ink (black) common to all sectors. This allows the extension of the principles of the CMYK printing process to these additional sectors. The methods developed in this study can be generalised to any number of inks. The project explores various aspects of the n-colour printing process including the forward characterisation methods, gamut prediction of the n-colour process and the inverse characterisation to calculate the n-colour separation for target spot colours. The scope of the study covers different printing technologies including lithographic offset, flexographic, thermal sublimation and inkjet printing. A new method is proposed to characterise the printing devices. This method, the spot colour overprint (SCOP) model, was evaluated for the n-colour printing process with different printing technologies. In addition, a set of real-world spot colours were converted to n-colour separations and printed with the 7-colour printing process to evaluate against the original spot colours. The results show that the proposed methods can be effectively used to replace the spot coloured inks with the n-colour printing process. This can save significant material, time and costs in the packaging industry