Laurent Blonde

Effect of the accommodation-vergence conflict on vergence eye movements.

With the broader use of stereoscopic displays, a flurry of research activity about the accommodation-vergence conflict has emerged to highlight the implications for the human visual system. In stereoscopic displays, the introduction of binocular disparities requires the eyes to make vergence movements. In this study, we examined vergence dynamics with regard to the conflict between the stimulus-to-accommodation and the stimulus-to-vergence. In a first experiment, we evaluated the immediate effect of the conflict on vergence responses by presenting stimuli with conflicting disparity and focus on a stereoscopic display (i.e. increasing the stereoscopic demand) or by presenting stimuli with matched disparity and focus using an arrangement of displays and a beam splitter (i.e. focus and disparity specifying the same locations). We found that the dynamics of vergence responses were slower overall in the first case due to the conflict between accommodation and vergence. In a second experiment, we examined the effect of a prolonged exposure to the accommodation-vergence conflict on vergence responses, in which participants judged whether an oscillating depth pattern was in front or behind the fixation plane. An increase in peak velocity was observed, thereby suggesting that the vergence system has adapted to the stereoscopic demand. A slight increase in vergence latency was also observed, thus indicating a small decline of vergence performance. These findings offer a better understanding and document how the vergence system behaves in stereoscopic displays. We describe what stimuli in stereo-movies might produce these oculomotor effects, and discuss potential applications perspectives.

Forensic characterization of camcorded movies: digital cinema vs. celluloid film prints

Digital camcording in the premises of cinema theaters is the main source of pirate copies of newly released movies. To trace such recordings, watermarking systems are exploited in order for each projection to be unique and thus identifiable. The forensic analysis to recover these marks is different for digital and legacy cinemas. To avoid running both detectors, a reliable oracle discriminating between cams originating from analog or digital projections is required. This article details a classification framework relying on three complementary features : the spatial uniformity of the screen illumination, the vertical (in)stability of the projected image, and the luminance artifacts due to the interplay between the display and acquisition devices. The system has been tuned with cams captured in a controlled environment and benchmarked against a medium-sized dataset (61 samples) composed of real-life pirate cams. Reported experimental results demonstrate that such a framework yields over 80% classification accuracy.

Individual Colorimetric Observer Model

This study proposes a vision model for individual colorimetric observers. The proposed model can be beneficial in many color-critical applications such as color grading and soft proofing to assess ranges of color matches instead of a single average match. We extended the CIE 2006 physiological observer by adding eight additional physiological parameters to model individual color-normal observers. These eight parameters control lens pigment density, macular pigment density, optical densities of L-, M-, and S-cone photopigments, and λmax shifts of L-, M-, and S-cone photopigments. By identifying the variability of each physiological parameter, the model can simulate color matching functions among color-normal populations using Monte Carlo simulation. The variabilities of the eight parameters were identified through two steps. In the first step, extensive reviews of past studies were performed for each of the eight physiological parameters. In the second step, the obtained variabilities were scaled to fit a color matching dataset. The model was validated using three different datasets: traditional color matching, applied color matching, and Rayleigh matches.

A handy calibrator for color vision of a human observer

The variability among human observers is a challenge to the calibration of modern displays based on Light Emitting Diodes (LED) and lasers. The spectra of the displayed colors are so peaky that slight differences in the cone sensitivities in human color vision are sufficient to make two observers perceiving different colors on the same screen. Recently published results give evidence to the existence of a small number of classes of human observers. In this paper, we present first results on the development of a prototype for a lightweight, inexpensive, temporally stable and easy to calibrate and easy to use instrument that allows classification of an observer with normal color vision in a small number of categories. The instrument employs a set of LEDs having specific wavelengths and is controlled by a computer interface. The use of such an instrument will allow adapting displays and viewing conditions to individual observers in color-critical applications.

55.1: Diversity and Coherence of 3D Crosstalk Measurements

3D crosstalk is a major contributor to 3D quality loss and visual fatigue on stereoscopic displays. This paper presents several 3D crosstalk measurement methods and discusses the coherence between methods, towards the derivation of meaningful quality indicators. It also identifies the need of synthetic indicators for complex crosstalk effects.

Inverse display characterization: A two-step parametric model for digital displays

— A simple additivity model is often used as a basic model for digital-display characterization. However, such a simple model cannot satisfy the needs of demanding color-management applications all the time. On the other hand, systematic sampling of the color space and 3-D interpolation is an expensive method in terms of measurement and computation time when precision is needed. This paper presents an enhanced method to characterize the XYZ-to-RGB transform of a digital display. This parametric method exploits the independence between the luminance variation of the electro-optic response and the colorimetric responses for certain display types. The model is generally applicable to digital displays, including 3-DMD projectors, single DMDs, CRTs, LCDs, etc., if the independence condition is satisfied. While the problem to solve is a 3-D-to-3-D transformation (from XYZ to RGB), the proposed parametric model is the composition of a 2-D transform followed by a 1-D transform. The 2-D transform manages the chromatic aspects and, in succession, the 1-D transform manages the luminance variations. This parametric digital model is applicable in the field of color management, with the objective of characterizing digital displays and applying a reference look such as a film look.

Depth-of-Focus Affects 3D Perception in Stereoscopic Displays.

Stereoscopic systems present binocular images on planar surface at a fixed distance. They induce cues to flatness, indicating that images are presented on a unique surface and specifying the relative depth of that surface. The center of interest of this study is on a second problem, arising when a 3D object distance differs from the display distance. As binocular disparity must be scaled using an estimate of viewing distance, object depth can thus be affected through disparity scaling. Two previous experiments revealed that stereoscopic displays can affect depth perception due to conflicting accommodation and vergence cues at near distances. In this study, depth perception is evaluated for farther accommodation and vergence distances using a commercially available 3D TV. In Experiment 1, we evaluated depth perception of 3D stimuli at different vergence distances for a large pool of participants. We observed a strong effect of vergence distance that was bigger for younger than for older participants, suggesting that the effect of accommodation was reduced in participants with emerging presbyopia. In Experiment 2, we extended 3D estimations by varying both the accommodation and vergence distances. We also tested the hypothesis that setting accommodation open loop by constricting pupil size could decrease the contribution of focus cues to perceived distance. We found that the depth constancy was affected by accommodation and vergence distances and that the accommodation distance effect was reduced with a larger depth-of-focus. We discuss these results with regard to the effectiveness of focus cues as a distance signal. Overall, these results highlight the importance of appropriate focus cues in stereoscopic displays at intermediate viewing distances.

Perceived Rigidity in Motion-in-Depth Increases with Contour Perspective

When observers are asked to match the depth of an object according to its height, they often report systematic errors depending on viewing distance. Systematic biases can also arise while vergence distances are induced by binocular disparities. Observers of stereoscopic images tend to overestimate the depth of objects displayed in front of the screen, while the depth of objects displayed behind the screen plane is underestimated. This phenomenon creates a serious problem in that veridicality in depth perception appears distorted when one attempts to render the metrics of a captured 3-D world. These distortions could also subsist with structure-from-motion information and during motion-in-depth. Observers judged the circularity of transparent rotating cylinders that were either static or moving in depth. Crossed results show that participants could precisely retrieve the best modulation between presented depth and width. As this effect could be amplified with stimuli containing stronger perspective cues (ie contour perspective), participants judged the rigidity of spinning cubes, moving along the line of sight, which were either edges-defined or defined by randomly textured surfaces (dots). The results showed that, although depth constancy was not improved by contour perspective, perceived rigidity was increased by perspective when the best scaling estimate was displayed. This finding suggests that appropriate binocular disparity information in combination to monocular signal is necessary for stereoscopic depth perception.

Visual storytelling in 2D and stereoscopic 3D video: effect of blur on visual attention

Visual attention is an inherent mechanism that plays an important role in the human visual perception. As our visual system has limited capacity and cannot efficiently process the information from the entire visual field, we focus our attention on specific areas of interest in the image for detailed analysis of these areas. In the context of media entertainment, the viewers’ visual attention deployment is also influenced by the art of visual storytelling. To this date, visual editing and composition of scenes in stereoscopic 3D content creation still mostly follows those used in 2D. In particular, out-of-focus blur is often used in 2D motion pictures and photography to drive the viewer’s attention towards a sharp area of the image. In this paper, we study specifically the impact of defocused foreground objects on visual attention deployment in stereoscopic 3D content. For that purpose, we conducted a subjective experiment using an eyetracker. Our results bring more insights on the deployment of visual attention in stereoscopic 3D content viewing, and provide further understanding on visual attention behavior differences between 2D and 3D. Our results show that a traditional 2D scene compositing approach such as the use of foreground blur does not necessarily produce the same effect on visual attention deployment in 2D and 3D. Implications for stereoscopic content creation and visual fatigue are discussed.

Towards adapting current 3DTV for an improved 3D experience

Recent upgrades of HDTV into 3DTV resulted in impairments in displaying stereo contents. One of the most critical flaws is probably crosstalk and the resultant ghosting effect impairing the 3D experience. The purpose of this study is to identify the primary source of crosstalk, throughout the full image generation and viewing chain, for a selection of 3D displays: Liquid Crystal Display (LCD) and Plasma Display Panel (PDP) combined with different active glasses technologies. Time measurements have been carried out on various display panels and shutter glasses technologies. For each technology, the crosstalk is a complex combination of several factors depending on display panels, shutter glasses and their synchronization, and ghost busting. The study tried to discriminate the main sources of crosstalk in each case, and to simulate the effect of various display panels or shutter glasses performance optimizations. Analysis and conclusions vary depending on the display technology. For LCD, light leakage at the panel level appears the first cause of crosstalk, and, in a second step, optimization of the shutter glasses. For PDP the use of more adapted shutter glasses can mitigate color distortion effects.