Comparison of the Commercial Color LCD and the Medical Monochrome LCD Using Randomized Object Test Patterns

Workstations and electronic display devices in a picture archiving and communication system (PACS) provide a convenient and efficient platform for medical diagnosis. The performance of display devices has to be verified to ensure that image quality is not degraded. In this study, we designed a set of randomized object test patterns (ROTPs) consisting of randomly located spheres with various image characteristics to evaluate the performance of a 2.5 mega-pixel (MP) commercial color LCD and a 3 MP diagnostic monochrome LCD in several aspects, including the contrast, resolution, point spread effect, and noise. The ROTPs were then merged into 120 abdominal CT images. Five radiologists were invited to review the CT images, and receiver operating characteristic (ROC) analysis was carried out using a five-point rating scale. In the high background patterns of ROTPs, the sensitivity performance was comparable between both monitors in terms of contrast and resolution, whereas, in the low background patterns, the performance of the commercial color LCD was significantly poorer than that of the diagnostic monochrome LCD in all aspects. The average area under the ROC curve (AUC) for reviewing abdominal CT images was 0.717±0.0200 and 0.740±0.0195 for the color monitor and the diagnostic monitor, respectively. The observation time (OT) was 145±27.6 min and 127±19.3 min, respectively. No significant differences appeared in AUC (p = 0.265) and OT (p = 0.07). The overall results indicate that ROTPs can be implemented as a quality control tool to evaluate the intrinsic characteristics of display devices. Although there is still a gap in technology between different types of LCDs, commercial color LCDs could replace diagnostic monochrome LCDs as a platform for reviewing abdominal CT images after monitor calibration

The effect of image size on the color appearance of image reproductions

Original and reproduced art are usually viewed under quite different viewing conditions. One of the interesting differences in viewing condition is size difference. The main focus of this research was investigation of the effect of image size on color perception of rendered images. This research had several goals. The first goal was to develop an experimental paradigm for measuring the effect of image size on color appearance. The second goal was to identify the most affected image attributes for changes of image size. The final goal was to design and evaluate algorithms to compensate for the change of visual angle (size). To achieve the first goal, an exploratory experiment was performed using a colorimetrically characterized digital projector and LCD. The projector and LCD were light emitting devices and in this sense were similar soft-copy media. The physical sizes of the reproduced images on the LCD and projector screen could be very different. Additionally, one could benefit from flexibility of soft-copy reproduction devices such as real-time image rendering, which is essential for adjustment experiments. The capability of the experimental paradigm in revealing the change of appearance for a change of visual angle (size) was demonstrated by conducting a paired-comparison experiment. Through contrast matching experiments, achromatic and chromatic contrast and mean luminance of an image were identified as the most affected attributes for changes of image size. Measurement of the extent and trend of changes for each attribute were measured using matching experiments. Proper algorithms to compensate for the image size effect were design and evaluated. The correction algorithms were tested versus traditional colorimetric image rendering using a paired-comparison technique. The paired-comparison results confirmed superiority of the algorithms over the traditional colorimetric image rendering for the size effect compensation

The Effects of Multi-channel Visible Spectrum Imaging on Perceived Spatial Image Quality and Color Reproduction Accuracy

Two paired-comparison psychophysical experiments were performed. The stimuli consisted of six image types resultingfrom several multispectral image-capture and reconstruction techniques. A seventh image type, color-managed images from a high-end consumer camera, was also included in thefirst experiment to compare the accuracy of commercial RGB imaging. The images were evaluated under simulated daylight (6800K) and incandescent (2700K) illumination. The first experiment evaluated color reproduction accuracy. Under simulated daylight, the subjects judged all of the images to have the same color accuracy, except the consumer camera image which was significantly worse. Under incandescent illumination, all the images, including the consumer camera, had equivalent performance. The second experiment evaluated image quality. The results of this experiment were highly target dependent. A subsequent image registration experiment showed that the results of the image quality experiment were affected by image registration to some degree. An analysis of the color reproduction accuracy and image quality experiments combined showed that the consumer camera image type was preferred the least over all. The most preferred image types were the thirty-one-channel image type and both six-channel image types created using RGB filters along with a Wratten filter, with eigenvector analysis and pseudo-inverse transformations

Right-lateralised lane keeping in young and older British drivers

Young adults demonstrate a small, but consistent, asymmetry of spatial attention favouring the left side of space (“pseudoneglect”) in laboratory-based tests of perception. Conversely, in more naturalistic environments, behavioural errors towards the right side of space are often observed. In the older population, spatial attention asymmetries are generally diminished, or even reversed to favour the right side of space, but much of this evidence has been gained from lab-based and/or psychophysical testing. In this study we assessed whether spatial biases can be elicited during a simulated driving task, and secondly whether these biases also shift with age, in line with standard lab-based measures. Data from 77 right-handed adults with full UK driving licences (i.e. prior experience of left-lane driving) were analysed: 38 young (mean age = 21.53) and 39 older adults (mean age = 70.38). Each participant undertook 3 tests of visuospatial attention: the landmark task, line bisection task, and a simulated lane-keeping task. We found leftward biases in young adults for the landmark and line bisection tasks, indicative of pseudoneglect, and a mean lane position towards the right of centre. In young adults the leftward landmark task biases were negatively correlated with rightward lane-keeping biases, hinting that a common property of the spatial attention networks may have influenced both tasks. As predicted, older adults showed no group-level spatial asymmetry on the landmark nor the line bisection task, but they maintained a mean rightward lane position, similar to young adults. The 3 tasks were not inter-correlated in the older group. These results suggest that spatial biases in older adults may be elicited more effectively in experiments involving complex behaviour rather than abstract, lab-based measures. More broadly, these results confirm that lateral biases of spatial attention are linked to driving behaviour, and this could prove informative in the development of future vehicle safety and driving technology

Perceptual Modeling and Reproduction of Gloss

The reproduction of gloss on displays is generally not based on perception and as a consequence does not guarantee the best visualization of a real material. The reproduction is composed of four different steps: measurement, modeling, rendering, and display. The minimum number of measurements required to approximate a real material is unknown. The error metrics used to approximate measurements with analytical BRDF models are not based on perception, and the best visual approximation is not always obtained. Finally, the gloss perception difference between real objects and objects seen on displays has not sufficiently been studied and might be influencing the observer judgement. This thesis proposes a systematic, scalable, and perceptually based workflow to represent real materials on displays. First, the gloss perception difference between real objects and objects seen on displays was studied. Second, the perceptual performance of the error metrics currently in use was evaluated. Third, a projection into a perceptual gloss space was defined, enabling the computation of a perceptual gloss distance measure. Fourth, the uniformity of the gloss space was improved by defining a new gloss difference equation. Finally, a systematic, scalable, and perceptually based workflow was defined using cost-effective instruments

Inverse tone mapping

The introduction of High Dynamic Range Imaging in computer graphics has produced a novelty in Imaging that can be compared to the introduction of colour photography or even more. Light can now be captured, stored, processed, and finally visualised without losing information. Moreover, new applications that can exploit physical values of the light have been introduced such as re-lighting of synthetic/real objects, or enhanced visualisation of scenes. However, these new processing and visualisation techniques cannot be applied to movies and pictures that have been produced by photography and cinematography in more than one hundred years. This thesis introduces a general framework for expanding legacy content into High Dynamic Range content. The expansion is achieved avoiding artefacts, producing images suitable for visualisation and re-lighting of synthetic/real objects. Moreover, it is presented a methodology based on psychophysical experiments and computational metrics to measure performances of expansion algorithms. Finally, a compression scheme, inspired by the framework, for High Dynamic Range Textures, is proposed and evaluated

Application of PQS for image quality analysis in visible spectral imaging

An image quality investigation in visible spectral imaging was performed. Spectral images were simulated using different number of imaging channels, wavelength steps, and noise levels based on practical spectral imaging systems. A mean opinion score (MOS) was determined from a subjective visual assessment scale experiment for image quality of spectral images rendered to a three-channel display. A set of partial image distortion measures, including color difference for color images, were defined based on classified and quantified actual distortions produced by spectral imaging systems. Principal components analysis was then carried out to quantify the correlation between distortion factors. Finally, a multiple regression analysis (MRA) was carried out between the principal component vectors and the measured MOS values to determine the picture quality scale (PQS). The obtained quality metric, PQS, had high correlation with the subjective measure, MOS. The importance of contribution of the distortion factors in the image quality metric was also evaluated