Scanpath Analysis of Fused Multi-Sensor Images with Luminance Change: A Pilot Study
Timothy D. DixonJ. LiJan NoyesT. TrosciankoS.G. NikolovJ. LewisEduardo Fernández CangaD.R. BullC.N. Canagarajah
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Image fusion is the process of combining images of differing modalities, such as visible and infrared (IR) images. Significant work has recently been carried out comparing methods of fused image assessment, with findings strongly suggesting that a task-centred approach would be beneficial to the assessment process. The current paper reports a pilot study analysing eye movements of participants involved in four tasks. The first and second tasks involved tracking a human figure wearing camouflage clothing walking through thick undergrowth at light and dark luminance levels, whilst the third and fourth task required tracking an individual in a crowd, again at two luminance levels. Participants were shown the original visible and IR images individually, pixel-averaged, contrast pyramid, and dual-tree complex wavelet fused video sequences. They viewed each display and sequence three times to compare inter-subject scanpath variability. This paper describes the initial analysis of the eye-tracking data gathered from the pilot study. These were also compared with computational metric assessment of the image sequencesA visual experiment was carried out to obtain the BCD luminance of a blinking light under the conditions of 0.1 to 100cd/m2 of background luminance and a 1 to 16 Hz blink rate. The test light was a circle with diameter of 3 minutes (6.0×10-7 sr). The experimental results showed that BCD luminance was highest in the case of a steady light with any background luminance, the BCD luminance was the lowest at around 5 to 8 Hz, and the blinking frequency corresponding to the minimum BCD luminance increased in parallel with an increase in the background luminance. Also it was found that the BCD luminance of the blinking light increased in parallel with an increase in the background luminance, a trend which was similar to the relationship between the BCD luminance of a steady light and the background luminance.
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Effects of the Uniform Surrounding Luminance On the Luminance Difference Thresholds of Foveal Vision
The physical veiling in the eye arising from stray light falling on the fovea from the surrounding fi eld of view causes a rise in the physiological adapting luminance of the fovea and a rise in the physical luminance of the test stimuli (object and its background). Using a uniform surrounding field with an outer diameter of 33° and with an inner diameter of 3°, the effects, on the luminance difference threshold of foveal vision, of increasing the physiological adapting luminance and of increasing the physical background luminance, caused by physical veiling, have been investigated independently.The results of the experiments show that the rise in the physiological adapting luminance caused by the surrounding field has a decreasing upon the luminance difference threshold as the luminance of the surrounding field increases.The effect of the rise in the physical luminance of the test stimuli determines mainly the luminance difference threshold caused by the surrounding field, provided that the luminance of the surrounding fi eld is above about 100 cd/m2.
Stray light
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Abstract Contrast sensitivity functions (CSFs) have been typically measured under persistent adaptation to a uniform background. However, this is an unusual situation, considering that visual scenes in our daily lives are typically filled by objects of various luminance levels in a wide dynamic range. We investigated the interactions between the luminance range of textured adapting background and test luminance (luminance of an immediate surround) to see how the contrast sensitivities adapt to background luminance distributions. The background was a random array of one‐dimensional lines, which had a maximum luminance range of approximately 1:520 000, and the test stimulus was a Gabor patch presented on an immediate uniform surround with various luminance levels. The carrier orientation of the Gabor patch was orthogonal to that of the background lines. In the results, the sensitivity was highest near the mean of background luminance, and the luminance range with the highest sensitivity became wider (i.e., the selectivity of sensitivity optimization weakened) as the background luminance range became larger. This sensitivity optimization was significant mainly in the lower spatial frequency. These results indicate that the overall contrast sensitivity is adjusted to the luminance range of the visual scene and the sensitivity optimization is more flexible in relatively lower spatial frequency.
Spatial frequency
Contrast ratio
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In luminance measurements of, for example, relatively dark tunnels from the approach road in daytime, considerable errors are sometimes involved. With systematic measurements it has been found that the light from the surrounding field, i.e., outside the measuring field of the luminance meter, causes a considerable amount of veiling luminance, due to scattering in the optical elements incorporated in the luminance meter, which is superimposed on the luminance of the object to be measured. It was found that the angular characteristics of scattering in the optical elements are similar to those in human eyes regarding the equivalent veiling luminance.
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Relationship between Adaptation Luminance and Threshold Zone Luminance for Vehicular Traffic Tunnels
PURPOSES : This study has been performed with the objective to determine threshold zone luminance of adaptation luminance by target safety level in a vehicular traffic tunnel with design speed set at 100km/h. METHODS : The study made a miniature capable of portraying changes in luminance distribution within $2{\times}10^{\circ}$ conical field of view of the driver approaching to the tunnel for the test. Test conditions were set based on justifications for CIE 88-1990's threshold zone luminance used as a reference by domestic tunnel light standards (KS C 3703 : 2010). Luminance contrast of object background and object is 23%, object presentation duration is 0.5 seconds, and size of the object background is $7.3{\times}11.5m^2$ RESULTS : Threshold zone luminance was set within adaptation luminance of $100{\sim}3,000cd/m^2$ . Adaptation luminance and threshold zone luminance based on 50%, 75% and 90% target safety level all showed a relatively high linear relationship. According to findings in the study, it is not appropriate to specify the relationship between adaptation luminance and threshold zone luminance as luminance ratio. Rather, direct utilization of the linear relationship gained from the study findings appears to be the better solution. CONCLUSIONS : Findings of this study may be used to determine operation of threshold zone luminance based on target safety level. However, a proper verification and validity of test results are required. Furthermore, a study to determine proper threshold zone luminance level considering target safety level reviewed in this study and various decision-making factors such as economic conditions in Korea and energy-related policies should be carried out in addition. Additional tests on adaptation luminance greater than $3,000cd/m^2$ will be performed, through which application scope of the test findings will be broadened.
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Recent studies show that dark adaptation in the visual system depends on local luminance levels surrounding the viewing direction. These studies, however, do not explain to what extent veiling luminance is responsible for the outcome. To address the latter, in this study dark adaptation was measured for three different spatial luminance distributions surrounding a target to be detected, while keeping the veiling luminance at the location of the target equivalent. The results show that a background with bright areas close to the viewing direction yields longer adaptation times than a background with bright areas at a larger visual angle. Therefore, we conclude that dark adaptation is affected to a great extent by local luminance, even when controlling for veiling luminance. Based on our results, a simple but adequate model is proposed to predict the adaptation luminance threshold for backgrounds having a nonuniform luminance distribution.
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For designing a comfortable visual environment, it is necessary to estimate adaptation luminance of the whole visual field with complicated luminance distribution. It is thought that such adaptation luminance is estimated by considering the summation of the adaptation luminance increase that is the effective luminance brought by a partial luminance of visual fields. For estimating the adaptation luminance, the additibity of adaptation luminance increase should be confirmed to the whole visual field.Under the various patterns of high luminance surfaces arrangement covering the whole visual field, the luminance difference threshold is determined to each subject for getting adaptation luminance. From the result of such subjective experiments, the additivity of adaptation luminance increase was confirmed in this paper.
Additive function
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Luminance measurements are the least frequent of all photometric measurements. This article characterizes and systematizes the various methods of luminance measurement. In particular, the method of direct luminance measurement using modern luminance meters (ILMD) is described in detail. This paper presents the results of the study on the influence of the measurement distance on the luminance measurement results. Two ILMD meters (laboratory and portable) and a luminance standard were used in this study. The conducted research showed that an incorrectly chosen measuring distance can lead to significant measurement errors of up to several tens of percent. In addition, the possible impact of incorrect measurements on the design of an interior lighting installation was presented. It was shown that the selected interior lighting installation can consume more than 40 percent more electricity compared to the installation based on the correct luminance measurements of the luminaires with diffuse shades. In the final stage of the study, the definition of the photometric test distance for luminance measurements using ILMD was proposed. The test results can be particularly useful for the luminance measurements of OLEDs or the luminaires with diffuse luminous character. However, these results can also be used for luminance measurements of other light sources and luminaires.
Luminous efficacy
Luminous flux
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As the standard lighting required in the threshold zone of a road tunnel is determined by the enough contrast. Lighting design, therefore, must be determined by the calculation method of threshold luminance based on the adaptation luminance of the driver approaching the tunnel. The veiling luminance and the luminance in the access zone were measured at different time and in different weather using the veiling luminance method, a kind of perceived contrast methods, and the L20 method when the range of vision was 20 degrees. On the basis of the measured data each threshold luminance was calculated and its results were analyzed.
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