Evaluation of the color image and video processing chain and visual quality management for consumer systems

With the advent of novel digital display technologies, color processing is increasingly becoming a key aspect in consumer video applications. Today’s state-of-the-art displays require sophisticated color and image reproduction techniques in order to achieve larger screen size, higher luminance and higher resolution than ever before. However, from color science perspective, there are clearly opportunities for improvement in the color reproduction capabilities of various emerging and conventional display technologies. This research seeks to identify potential areas for improvement in color processing in a video processing chain. As part of this research, various processes involved in a typical video processing chain in consumer video applications were reviewed. Several published color and contrast enhancement algorithms were evaluated, and a novel algorithm was developed to enhance color and contrast in images and videos in an effective and coordinated manner. Further, a psychophysical technique was developed and implemented for performing visual evaluation of color image and consumer video quality. Based on the performance analysis and visual experiments involving various algorithms, guidelines were proposed for the development of an effective color and contrast enhancement method for images and video applications. It is hoped that the knowledge gained from this research will help build a better understanding of color processing and color quality management methods in consumer video

Appearance-based image splitting for HDR display systems

High dynamic range displays that incorporate two optically-coupled image planes have recently been developed. This dual image plane design requires that a given HDR input image be split into two complementary standard dynamic range components that drive the coupled systems, therefore there existing image splitting issue. In this research, two types of HDR display systems (hardcopy and softcopy HDR display) are constructed to facilitate the study of HDR image splitting algorithm for building HDR displays. A new HDR image splitting algorithm which incorporates iCAM06 image appearance model is proposed, seeking to create displayed HDR images that can provide better image quality. The new algorithm has potential to improve image details perception, colorfulness and better gamut utilization. Finally, the performance of the new iCAM06-based HDR image splitting algorithm is evaluated and compared with widely spread luminance square root algorithm through psychophysical studies

A Modeling of Chroma Subsampling Artifact Assessment Metric

Department of Human Factors EngineeringAs digital broadcasting develops alongside advancements in display, video quality of broadcasting has emerged as an important issue. When the broadcasting digital signal transfers from the camera into the display TV, the optical signal changes to an electrical one before the transmittance begins. After converting to an electrical signal, the chroma subsampling, the method of compression usually used, process is implemented for compressing the digital signal. The artifact decreases the video quality, so an assessment metric is needed for increasing the video quality. The aim of this research is to investigate the effect factors of artifact estimation with qualitative and quantitative analyses and to devise an assessment metric that can predict the 4:2:0 chroma subsampling artifact based on a psychophysical experiment. The perceived degree of artifact was estimated by conducting a psychophysical experiment. Stimuli with a striped pattern and the 1-pixel artifact was used for estimation. Participants evaluated the magnitude of artifact in test stimuli with the reference patch, randomly shown on the monitor, having a value of 5. If the participant perceives the artifact error more than reference, they gave the value of over 5. A total of 150 test stimuli were evaluated and 10 people participated. In the results of the experiment, 4 effect factors of artifact estimation are found: The color difference between the original and subsampled artifact, the surrounding colors effect, the neighboring colors effect, and the effect of the pixel structure. These effects help us determine the characteristics of artifact estimation. First, the color difference between the original and the subsampled artifact has the highest correlation with artifact estimation. Second, as surrounding colors have a larger difference, people underestimate the chroma subsampling error. Third, if the artifact has a similar color with one of the neighboring colors, it isn???t perceived well. The effect of pixel structure was occurred by R, G, B sub-pixel structure of LCD monitor. However, this effect factor varies depending on the pixel structure of the monitor. Those effect factors were used to model the error assessment metric. The performance test of modeled metric was conducted with 5 participants, who were asked to select between the existing metric (dE00) and the new one modelled in this research. Most respondents selected the latter. In a further study, the new metric can be used for evaluating chroma subsampling artifacts based on human perception. The encoding process of image and video can also be developed by applying this method, decreasing the chroma subsampling artifact.clos

Computing Chromatic Adaptation

Most of today’s chromatic adaptation transforms (CATs) are based on a modified form of the von Kries chromatic adaptation model, which states that chromatic adaptation is an independent gain regulation of the three photoreceptors in the human visual system. However, modern CATs apply the scaling not in cone space, but use “sharper” sensors, i.e. sensors that have a narrower shape than cones. The recommended transforms currently in use are derived by minimizing perceptual error over experimentally obtained corresponding color data sets. We show that these sensors are still not optimally sharp. Using different computational approaches, we obtain sensors that are even more narrowband. In a first experiment, we derive a CAT by using spectral sharpening on Lam’s corresponding color data set. The resulting Sharp CAT, which minimizes XYZ errors, performs as well as the current most popular CATs when tested on several corresponding color data sets and evaluating perceptual error. Designing a spherical sampling technique, we can indeed show that these CAT sensors are not unique, and that there exist a large number of sensors that perform just as well as CAT02, the chromatic adaptation transform used in CIECAM02 and the ICC color management framework. We speculate that in order to make a final decision on a single CAT, we should consider secondary factors, such as their applicability in a color imaging workflow. We show that sharp sensors are very appropriate for color encodings, as they provide excellent gamut coverage and hue constancy. Finally, we derive sensors for a CAT that provide stable color ratios over different illuminants, i.e. that only model physical responses, which still can predict experimentally obtained appearance data. The resulting sensors are sharp

Developing a flexible and expressive realtime polyphonic wave terrain synthesis instrument based on a visual and multidimensional methodology

The Jitter extended library for Max/MSP is distributed with a gamut of tools for the generation, processing, storage, and visual display of multidimensional data structures. With additional support for a wide range of media types, and the interaction between these mediums, the environment presents a perfect working ground for Wave Terrain Synthesis. This research details the practical development of a realtime Wave Terrain Synthesis instrument within the Max/MSP programming environment utilizing the Jitter extended library. Various graphical processing routines are explored in relation to their potential use for Wave Terrain Synthesis

A testing procedure to characterize color and spatial quality of digital cameras used to image cultural heritage

A testing procedure for characterizing both the color and spatial image quality of trichromatic digital cameras, which are used to photograph paintings in cultural heritage institutions, is described. This testing procedure is target-based, thus providing objective measures of quality. The majority of the testing procedure followed current standards from national and international organizations such as ANSI, ISO, and IEC. The procedure was developed in an academic research laboratory and used to benchmark four representative American museum’s digital-camera systems and workflows. The quality parameters tested included system spatial uniformity, tone reproduction, color reproduction accuracy, noise, dynamic range, spatial cross-talk, spatial frequency response, color-channel registration, and depth of field. In addition, two paintings were imaged and processed through each museum’s normal digital workflow. The results of the four case studies showed many dissimilarities among the digital-camera systems and workflows of American museums, which causes a significant range in the archival quality of their digital masters

Design Principles of Wide Gamut YCC Color Encoding Space for Effective Signal Sub-Sampling

The YCbCr color space in BT.709 suffers the image quality deterioration by color difference signal sub-sampling though reducing the number of signals are quite important issue for future television system. For the future television systems, such as UHDTV and 3DTV, new color encoding space is required which can encode large color gamut and result in good image quality even after color difference signal sub-sampling. In this study, two approaches i.e. following human visual system (CIECAM02) and using new sets of wide color gamut primaries are considered to design new color encoding space. Various YCC color encoding spaces are designed and the sub-sampled image qualities are compared. The result shows that using the opponent color signals in simplified-CIECAM02 as YCC space has the best image quality. Also it is shown that using wide color gamut primaries can improve the sub-sampled image quality significantly than the current encoding color space for HDTV