Peter Bodrogi

Mesopic visual efficiency IV: A model with relevance to nighttime driving and other applications

The authors represent a research consortium1 which has adopted a task performance based approach for nighttime driving to establish a system for photometry in the mesopic region. This article analyses the experimental investigations described in earlier articles on visual performance in the mesopic domain using reaction time, detection threshold, and discrimination threshold techniques. These results are used to develop a system for mesopic photometry, which balances the quality of the fit to the experimental data with the ease of practical implementation by the lighting industry. A more complex model is also described, which takes account of the chromatic visual response channels and thus provides a better fit to some of the experimental results (particularly those involving monochromatic stimuli), but describes the totality of the data less well and is furthermore less suitable for practical photometric measurements.

Mesopic models : from brightness matching to visual performance in night-time driving: a review

At present, suitable methods to evaluate the visual effectiveness of lighting products in the mesopic region are not available. The majority of spectral luminous efficiency functions obtained to date in the mesopic range have been acquired by heterochromatic brightness matching. However, the most recent studies in the mesopic field have adopted a task performance-based approach. This paper summarizes the major mesopic models proposed so far, presenting in detail the experimental conditions of these studies. The authors represent a research consortium which has adopted the task performance-based approach for night-time driving in which mesopic visual performance has been divided into three subtasks. Data for each sub-task will be generated by using a set of common parameter values and 120 observers. The approach and methods used by the consortium are presented.

Chromaticity contrast in visual search on the multi-colour user interface

Abstract Observers had to find one of fifteen different meaningful white and coloured computer commands on a simulated multi-colour user interface. Average search time was recorded as a function of chromaticity, position, and length of the search commands. After eliminating the effects of display position and command length, the range of search time values was found to extend by a factor of 2 when the search objects became coloured by different types of chromaticity contrast. This implies that chromaticity contrast is an efficient tool to control the conspicuity of the display elements. It was suggested to put the coloured display items (symbols, characters, etc.) on several ‘conspicuity levels’ depending on the designers intent of emphasis. A formula and guidelines for an algorithm have been suggested. The relationship between conspicuity and the concept of brightness was discussed.

LED Lighting: Technology and Perception

Promoting the design, application and evaluation of visually and electrically effective LED light sources and luminaires for general indoor lighting as well as outdoor and vehicle lighting, this book combines the knowledge of LED lighting technology with human perceptual aspects for lighting scientists and engineers. After an introduction to the human visual system and current radiometry, photometry and color science, the basics of LED chip and phosphor technology are described followed by specific issues of LED radiometry and the optical, thermal and electric modeling of LEDs. This is supplem

Testing a calibration method for colour CRT monitors. A method to characterize the extent of spatial interdependence and channel interdependence

Abstract The performance of a colorimetric calibration method for colour CRT monitors has been investigated experimentally for six monitor types representing different quality levels. The colour of luminous patches in the presence of different border and background colours on the screen was measured. Systematic deviation from the calibration method described in CIE Technical Report, Guide to Characterizing the Colorimetry of Computer-Controlled Displays (1993) was found that can only be explained by the violation of two basic assumptions of the calibration method used: spatial independence and channel independence. Measurements were carried out to see the effect of spatial and channel interdependence separately. We recommend a new method to characterize the extent of channel and spatial interdependence of a given monitor set-up. With the help of this method it is possible to predict the CIE XYZ tristimulus values of displayed colours even in the case of such monitors that show channel- and/or spatial-interdependence. This method is especially important if colours have to be displayed accurately on different screen backgrounds.

Colour preference varies with lighting application

Numerous efforts have been made to investigate how to characterize the effect of light sources on colour preference. This paper describes a psychophysical experiment to compare the colour preference evaluation among three sources for different lighting applications. Three lighting applications – restaurant, retail display, and supermarket – were created in two side-by-side full-scaled rooms. It was found that the colour preference varied with the lighting applications. Although none of the existing single-value measures can predict the preference for all three applications, a single measure is necessary for general consumer use given a careful definition of general lighting. In addition, lighting application specific measures could be useful for lighting professionals and experts. To provide detailed information, a colour distortion icon, with improved test colour samples will be useful.

Luminance contrast and chromaticity contrast preference on the colour display for young and elderly users

Abstract The human visual system changes with aging and one of the most important changes is the decrease of spatial contrast sensitivity. We investigated this change both for luminance contrast and chromaticity contrast, and both for threshold contrast and preferred contrast, (preferred by users to carry out a visual recognition task), in a series of psycho-physical experiments with achromatic and chromatic sinusoid gratings of different values of spatial frequency, hue, and luminance level, and with two observer groups: young and elderly observers. We investigated the spatial frequency range of 0.1–10 cycles per degrees. Our results indicate that, beyond the expected luminance contrast sensitivity decline of the elderly observers, the difference between the preferred luminance contrast of the elderly and the preferred luminance contrast of the young is even more significant than the threshold difference. The small preference differences between the age groups for chromaticity contrast compared to luminance contrast suggests that while with increasing age both the chromatic and the achromatic contrast sensitivity drops, preferred contrast stays more stable for chromaticity contrast than for luminance contrast.

On the use of the sRGB colour space: the 'Gamma' problem

Abstract The dependence of the luminous output of computer-controlled CRT monitors on the digital colour values was measured on 11 different monitors. This dependence was called the channel function. Different settings of the monitors (gain/offset, position and size of the test colour patch, screen size) were investigated. It was concluded that the use of the default sRGB channel function instead of the measured channel function can lead to mean chromaticity errors of up to Δ u ′ v ′=0.06 and colour differences of up to Δ E ab ∗ =33. Changing the graphics card did not influence the channel functions significantly.

Colour preference, naturalness, vividness and colour quality metrics, Part 1: Experiments in a room:

In Part I of this work, observers scaled colour preference, naturalness and vividness visually on interval scales (0–100) labelled by semantic categories (e.g. ‘moderate’, ‘good’ and ‘very good’) in the context of office lighting. Five customary light sources without object saturation effect illuminated a table with coloured objects in a real room. The observers’ assessments were predicted by recent colour quality indices and selected pairs of indices combined linearly. Criterion values of the indices for ‘good’ colour preference and vividness were determined to provide a usable acceptance limit for the spectral design and evaluation of light sources. To predict colour preference, correlated colour temperature turned out to be useful. In Part 2 of this work, another experiment with the same method but using multi-LED spectra with more object saturation will be analysed and the two datasets will be merged.

Optimal color primaries for three- and multiprimary wide gamut displays

We present a collection of principles to compare two sets of color primaries for wide gamut displays. A new, algorithmic threedimensional method to find optimal color primaries both for threeprimary and multiprimary displays is described. The method was implemented in a computer program. The resulting optimal color primary sets are discussed. We show that two-dimensional methods to find optimal color primaries by using a chromaticity diagram are inferior to three-dimensional optimization techniques that include luminance information.