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The light density, direction and diffuseness are important indicators of the spatial and form-giving character of light. Mury presented a method to describe, measure and visualise the light field’s structure in terms of light density and direction variations in three-dimensional spaces. We extend this work with a theoretical and empirical review of four diffuseness metrics leading to a novel metric proposal DXia. In particular, the relationships between these diffuseness metrics were studied using a model named ‘probe in a sphere’. Diffuseness metric DXia re-frames the diffuseness metric of Cuttle in an integral description of the light field. It fulfils all diffuseness criteria and has the advantage that it can be used in a global, integrated description of the light flow and diffuseness throughout three-dimensional spaces. [ABSTRACT FROM AUTHOR]

We introduce a way to simultaneously measure the light density, light vector and diffuseness of the light field using a cubic illumination meter based on the spherical harmonics representation of the light field. This approach was applied to six light probe images of natural scenes and four real scenes built in our laboratory, and the results were compared to those obtained using Cuttle’s method. We also demonstrated a way to simultaneously and intuitively visualise the global structure of the light distribution using light tubes and colour coding for the light density, light flow and diffuseness variations through the space. Together with Mury’s work, we have a complete way to describe, measure and visualise the local and global low-order properties of light distributions in three-dimensional spaces. [ABSTRACT FROM AUTHOR]

This paper investigates the interaction between retail lighting and textiles to provide retailers and lighting designers with a set of physical textile objects that can be used to test the visual effect of a lighting setting. Since the relationships between optical aspects of lighting-textiles interactions and subjective qualities associated with them have not been systematically investigated, we conducted two experiments to study those relationships. The first experiment concerned photometric measurements of textiles in order to categorize the reflectance types. The second experiment examined human observers' judgments of a range of material-expressing qualities, such as shininess and softness, in two canonical types of lighting. The textiles for which the differences in those qualities were maximal were used in designing a lighting probe set. [ABSTRACT FROM AUTHOR]

At the start of the 20th century, Moritz von Rohr invented the synopter: a device that removes 3D depth cues that arise from binocular disparities and vergence. In the absence of these visual cues, the observer is less aware of the physical flatness of the picture. This results in a surprisingly increased depth impression of pictorial space, historically known as the 'plastic effect'. In this paper we present a practical design to produce a synopter and explore which elements of a painting influence the plastic effect. In the first experiment we showed 22 different paintings to a total of 35 observers, and found that they rate the synoptic effect rather consistent over the various paintings. Subsequent analyses indicated that at least three pictorial cues were relevant for the synoptic effect: figure-ground contrast, compositional depth and shadows. In experiment 2, we used manipulated pictures where we tried to strengthen or weaken these cues. In all three cases we found at least one effect that confirmed our hypothesis. We also found substantial individual differences: some observers experience little effect, while others are very surprised by the effect. A stereo acuity test revealed that these differences could not be attributed to how well disparities are detected. Lastly, we informally tested our newly designed synopter in museums and found similar idiosyncratic appraisal. But the device also turned out to facilitate discussions among visitors. [ABSTRACT FROM AUTHOR]

At the start of the 20th century, Moritz von Rohr invented the synopter: a device that removes 3D depth cues that arise from binocular disparities and vergence. In the absence of these visual cues, the observer is less aware of the physical flatness of the picture. This results in a surprisingly increased depth impression of pictorial space, historically known as the 'plastic effect'. In this paper we present a practical design to produce a synopter and explore which elements of a painting influence the plastic effect. In the first experiment we showed 22 different paintings to a total of 35 observers, and found that they rate the synoptic effect rather consistent over the various paintings. Subsequent analyses indicated that at least three pictorial cues were relevant for the synoptic effect: figure-ground contrast, compositional depth and shadows. In experiment 2, we used manipulated pictures where we tried to strengthen or weaken these cues. In all three cases we found at least one effect that confirmed our hypothesis. We also found substantial individual differences: some observers experience little effect, while others are very surprised by the effect. A stereo acuity test revealed that these differences could not be attributed to how well disparities are detected. Lastly, we informally tested our newly designed synopter in museums and found similar idiosyncratic appraisal. But the device also turned out to facilitate discussions among visitors. [ABSTRACT FROM AUTHOR]

In four experiments, we tested whether haptic comparison of curvature ranging from -4/m to +4/m is qualitatively the same for static and for dynamic touch. In Experiments 1 and 3, we tested whether static and dynamic curvature discrimination are based on height differences, attitude (slope) differences, curvature differences, or a combination of these geometrical variables. It was found that both static and dynamic hepatic curvature discrimination are based on attitude differences. In Experiments 2 and 4, we tested whether this mechanism leads to errors in the comparison of stimuli with different lengths for static and dynamic touch, respectively. If the judgments are based on attitude differences, subjects will make systematic errors in these comparisons. In both experiments, we found that subjects compared the curvatures of strips of the same length vertically, whereas they made systematic errors if they were required to compare the curvatures of strips of different lengths. Longer stimuli were judged to be more curved than shorter stimuli with the same curvature. We conclude that similar mechanisms underlie static and dynamic haptic curvature comparison. Moreover, additional data comparison showed that static and dynamic curvature comparison is not only qualitatively, but also quantitatively similar.

We investigated whether haptic comparison of the curvature of strips is influenced by the tilt (the average slope relative to the horizontal) of the curved strips. This particular stimulus manipulation was chosen to decide between two broad ways in which dynamic curvature comparison might be done: on the basis of the attitude (slope) differences over the surfaces or on the basis of the attitude (slope) differences between successively presented surfaces. For this purpose we conducted matching and discrimination experiments in which strips of constant curvature 9 cm long were touched dynamically and the tilts of the strips were varied. The results of the matching experiment showed some influence of tilt: the strips were judged to be slightly more curved if the tilt was nonzero than if it was zero. The results of the discrimination experiment did not show an effect of tilt. Because the attitude (slope) differences over the surfaces were independent of the tilt it is concluded that curvature comparison is based primarily on attitude differences over the curved surfaces.

An investigation was undertaken into whether haptic comparison of curvature and of shape is influenced by the length/width ratio of the hand. For this purpose three experiments were conducted to test the curvature matching of curved strips (experiment 1), the curvature matching of cylindrically curved hand-sized surfaces (experiment 2), and the shape discrimination of elliptically curved hand-sized surfaces (experiment 3). The orientation of the stimuli with respect to the fingers was varied. The results of the two matching experiments showed that a given curvature is judged to be more curved when touched along the fingers than when touched across the fingers. The phenomenal flatness along and across the fingers was found to be different and subject dependent. The results of the shape-discrimination experiment showed that the orientation of ellipsoidal surfaces influences the judgments of the shapes of these surfaces. This influence could be predicted on the basis of results of the second matching experiment. It is concluded that similar mechanisms underlie the (anisotropic) perception of curvature and shape. For the major part the trends in the results can be explained by the length/width ratio of the hand and the phenomenal flatnesses.

Static haptic discrimination of the curvature of convex, concave, or straight 20-cm-long strips was investigated for nine placements on the hand. In one condition, the strips were touched with the palmar side of the hand, and in the other condition, with the dorsal side. The influence of the lengths of the strips, and thus of contact lengths, was also investigated. For all placements, discrimination was poorer in the dorsal than in the palmar condition, owing to poorer cutaneous resolution on the dorsal side of the hand (the kinesthetic stimulation was the same in both conditions). Thus cutaneous stimulation is important. In both experiments, performance appeared to depend primarily on contact length. Moreover, the discrimination thresholds for all different placements and contact lengths followed the same trend. We conclude that in these experiments the effective stimulus for the discrimination of curved strips is the total difference of local surface attitude--that is, the slope difference over the far ends of the stimulus.