Jussi Hakala

Visual Performance With Small Concave and Convex Displays.

Objective: In this study, we aim to investigate how users’ visual performance with a small flexible display changes based on the direction (i.e., convex, concave) and the magnitude (i.e., low, high) of the display curvature. Background: Despite the wide interest in flexible display materials and deformable displays, the potential effects of nonplanar display surfaces on human perception and performance have received little attention. This study is the first to demonstrate how curving affects visual performance with an actual flexible display (4.5-in. active-matrix organic light-emitting diode). Method: In a series of three experiments, we compared the performance with a planar display to the performance with concave and convex display surfaces with low and high curvature magnitudes. Two visual search tasks were employed that required the subject to detect target letters based on their contrast (Experiments 1 and 2) and identity (Experiment 3). Performance was measured as the sensitivity of target detection (d′) and threshold time of the search, respectively. Results: There were similar sensitivities for targets across the curvature variants, but the high-magnitude curvatures resulted in prolonged search times, especially for the convex form. In both of the tasks, performance was dependent on the display location, which was defined as the target’s distance from the display center. Conclusion: High curvature magnitudes should be avoided, even in small displays, because large local changes in visual stimuli decrease processing speed outside the central display. Application: The findings have implications for the development of technologies, applications, and user interfaces for flexible displays and the design of visual display devices.

Depth Artifacts Caused by Spatial Interlacing in Stereoscopic 3D Displays

Most spatially interlacing stereoscopic 3D displays display odd and even rows of an image to either the left or the right eye of the viewer. The visual system then fuses the interlaced image into a single percept. This row-based interlacing creates a small vertical disparity between the images; however, interlacing may also induce horizontal disparities, thus generating depth artifacts. Whether people perceive the depth artifacts and, if so, what is the magnitude of the artifacts are unknown. In this study, we hypothesized and tested if people perceive interlaced edges on different depth levels. We tested oblique edge orientations ranging from 2 degrees to 32 degrees and pixel sizes ranging from 16 to 79 arcsec of visual angle in a depth probe experiment. Five participants viewed the visual stimuli through a stereoscope under three viewing conditions: noninterlaced, interlaced, and row averaged (i.e., where even and odd rows are averaged). Our results indicated that people perceive depth artifacts when viewing interlaced stereoscopic images and that these depth artifacts increase with pixel size and decrease with edge orientation angle. A pixel size of 32 arcsec of visual angle still evoked depth percepts, whereas 16 arcsec did not. Row-averaging images effectively eliminated these depth artifacts. These findings have implications for display design, content production, image quality studies, and stereoscopic games and software.

Effect of camera separation on the viewing experience of stereoscopic photographs

This study presents a geometric and subjective analysis of typical mobile stereoscopic 3-D images. The geometry of the stereoscopic pipeline from the scene to the eyes of the viewer is a highly relevant issue in stereoscopic media. One important factor is camera separation, because it can be used to control the perceived depth of stereoscopic images. The geometric analysis included consideration of disparity and roundness factor within typical mobile stereoscopic imaging scenes. These geometric properties of stereoscopic 3-D images were compared to subjective evaluations by varying camera separation in different scenes. The participants in this study evaluated the strength and naturalness of depth sensation and the overall viewing experience from still images with the single-stimulus method. The results showed that participants were able to perceive the change of depth range even though the images were shown in random order without a reference depth scale. The highest naturalness of depth sensation and viewing experience were achieved with 2 cm to 6 cm camera separation in every content. With these preferred camera separations, the disparity range was less than ±1 deg⁡ and cardboard effect (quantified with roundness factor) did not negatively affect the naturalness of depth sensation.

Estimation of subjective quality for mixed-resolution stereoscopic video

In mixed-resolution (MR) stereoscopic video, one view is presented with a lower resolution compared with the other one; therefore, a lower bitrate, a reduced computational complexity, and a decrease in memory access bandwidth can be expected in coding. The human visual system is known to fuse left and right views in such a way that the perceptual visual quality is closer to that of the higher-resolution view. In this paper, a subjective assessment of mixed resolution (MR) stereoscopic videos is presented and the results are analyzed and compared with previous subjective tests presented in the literature. Three downsampling ratios 1/2, 3/8, and 1/4 were used to create lower-resolution views. Hence, the lower-resolution view had different spatial resolutions in terms of pixels per degree (PPD) for each downsampling ratio. It was discovered that the subjective viewing experience tended to follow a logarithmic function of the spatial resolution of the lower-resolution view measured in PPD. A similar behavior was also found from the results of an earlier experiment. Thus, the results suggest that the presented logarithmic function characterizes the expected viewing experience of MR stereoscopic video.

Cross-lab study on preference of experience in 3DTV: Influence from display technology and test environment

Quality of Experience (QoE) in 3DTV may be influenced by many factors, such as the viewing conditions, the characteristics of the panel of viewers, etc. In this study, the impact of two factors, namely the test environment and the display technology are analyzed. Particularly, two paired comparison experiments have been carried out to assess the overall preference of experience (PoE) for a set of 3D video sequences. The first experiment, performed at University of Nantes, allows comparing the results obtained in a standard laboratory versus living-room-like environment. No significance difference has been found. The second experiment, performed at Brno University, allows comparing the results obtained using stereoscopic display with shutter glasses versus polarized glasses. Significance difference could be identified depending on the video content. Since the same test material has been used in both locations, inter-laboratory correlation is also analyzed.

Effect of image scaling on stereoscopic movie experience

Camera separation affects the perceived depth in stereoscopic movies. Through control of the separation and thereby the depth magnitudes, the movie can be kept comfortable but interesting. In addition, the viewing context has a significant effect on the perceived depth, as a larger display and longer viewing distances also contribute to an increase in depth. Thus, if the content is to be viewed in multiple viewing contexts, the depth magnitudes should be carefully planned so that the content always looks acceptable. Alternatively, the content can be modified for each viewing situation. To identify the significance of changes due to the viewing context, we studied the effect of stereoscopic camera base distance on the viewer experience in three different situations: 1) small sized video and a viewing distance of 38 cm, 2) television and a viewing distance of 158 cm, and 3) cinema and a viewing distance of 6-19 meters. We examined three different animations with positive parallax. The results showed that the camera distance had a significant effect on the viewing experience in small display/short viewing distance situations, in which the experience ratings increased until the maximum disparity in the scene was 0.34 - 0.45 degrees of visual angle. After 0.45 degrees, increasing the depth magnitude did not affect the experienced quality ratings. Interestingly, changes in the camera distance did not affect the experience ratings in the case of television or cinema if the depth magnitudes were below one degree of visual angle. When the depth was greater than one degree, the experience ratings began to drop significantly. These results indicate that depth magnitudes have a larger effect on the viewing experience with a small display. When a stereoscopic movie is viewed from a larger display, other experiences might override the effect of depth magnitudes.

Stereoscopy Amplifies Emotions Elicited by Facial Expressions

Mediated facial expressions do not elicit emotions as strongly as real-life facial expressions, possibly due to the low fidelity of pictorial presentations in typical mediation technologies. In the present study, we investigated the extent to which stereoscopy amplifies emotions elicited by images of neutral, angry, and happy facial expressions. The emotional self-reports of positive and negative valence (which were evaluated separately) and arousal of 40 participants were recorded. The magnitude of perceived depth in the stereoscopic images was manipulated by varying the camera base at 15, 40, 65, 90, and 115 mm. The analyses controlled for participants’ gender, gender match, emotional empathy, and trait alexithymia. The results indicated that stereoscopy significantly amplified the negative valence and arousal elicited by angry expressions at the most natural (65 mm) camera base, whereas stereoscopy amplified the positive valence elicited by happy expressions in both the narrowed and most natural (15–65 mm) base conditions. Overall, the results indicate that stereoscopy amplifies the emotions elicited by mediated emotional facial expressions when the depth geometry is close to natural. The findings highlight the sensitivity of the visual system to depth and its effect on emotions.

Perception of stereoscopic direct gaze: The effects of interaxial distance and emotional facial expressions

Gaze perception has received considerable research attention due to its importance in social interaction. The majority of recent studies have utilized monoscopic pictorial gaze stimuli. However, a monoscopic direct gaze differs from a live or stereoscopic gaze. In the monoscopic condition, both eyes of the observer receive a direct gaze, whereas in live and stereoscopic conditions, only one eye receives a direct gaze. In the present study, we examined the implications of the difference between monoscopic and stereoscopic direct gaze. Moreover, because research has shown that stereoscopy affects the emotions elicited by facial expressions, and facial expressions affect the range of directions where an observer perceives mutual gaze-the cone of gaze-we studied the interaction effect of stereoscopy and facial expressions on gaze perception. Forty observers viewed stereoscopic images wherein one eye of the observer received a direct gaze while the other eye received a horizontally averted gaze at five different angles corresponding to five interaxial distances between the cameras in stimulus acquisition. In addition to monoscopic and stereoscopic conditions, the stimuli included neutral, angry, and happy facial expressions. The observers judged the gaze direction and mutual gaze of four lookers. Our results show that the mean of the directions received by the left and right eyes approximated the perceived gaze direction in the stereoscopic semidirect gaze condition. The probability of perceiving mutual gaze in the stereoscopic condition was substantially lower compared with monoscopic direct gaze. Furthermore, stereoscopic semidirect gaze significantly widened the cone of gaze for happy facial expressions.

Geometric and Subjective Analysis of Stereoscopic I3A Cluster Images

This paper presents a geometric and subjective analysis of stereoscopic versions of close range I3A clusters (Subject- Camera distances below 5 m). The geometry of the stereoscopic pipeline from the scene to the viewers eyes is a very relevant issue in stereoscopic media. One important factor is the camera separation, because it can be used to control the perceived depth of stereoscopic images. The computational camera separations were compared to subjectively preferred camera separations. Participants evaluated the strength and naturalness of depth sensation and overall viewing experience from the still images with single-stimulus method. Results showed that participants were able to perceive the change of depth range even though the images were shown in random order without a reference depth scale. A mild depth sensation was preferred over strong depth sensations. The computational camera separation differed from the subjectively preferred camera separation when the depth range of the scene was narrow. This result indicates that scenes with narrow depth should not be imaged with a long camera separation just to fill the depth budget of the display.