emulating autostereoscopic lenticular designs

JOURNAL OF DISPLAY TECHNOLOGY, VOL. 8, NO. 5, MAY 2012 283

Emulating Autostereoscopic Lenticular DesignsMarc Lambooij, Karel Hinnen, and Chris Varekamp

Abstract—Optimizing performance of autostereoscopic lentic-ular displays can be achieved by altering specific interdependentdesign parameters, e.g., width and number of views, screendisparity and lenticular slant, resulting in different crosstalkdistributions and amounts of banding and consequently, differentpercepts. To allow the evaluation of an autostereoscopic lenticulardisplay, before a costly physical sample is produced, an emulatorwas build. This emulator consisted of a goggle-based stripedpolarized display, a camera-based head tracker and software forgenerating L/R stereo pairs in real-time as a function of head-lo-cation. This paper addresses the development of the emulator, itsvalidation with respect to an existing physical prototype, and theperceptual evaluation of three emulated fundamental design ex-tremes: 1) a 9-view low-cross-talk system; 2) a 9-view intermediatecrosstalk system; and 3) a 17-view high crosstalk system.

Index Terms—Emulation, human factors, perception, stereoimage processing, stereo vision, three dimensional TV (3D-TV).

I. INTRODUCTION

O NE of the drives for innovative, next-generation three-dimensional television (3D-TV) is to enrich the overall

viewing experience. 3D-TV exploits the concept that the humaneyes are horizontally separated, and therefore, have their ownperspective of the world, of which the brain extracts relativestereoscopic depth information. By providing a different viewto each eye, 3D-TV is able to present content that is perceivedboth in front and behind the display.

Nowadays, various display technologies exist to realizestereoscopic 3D perception. Current consumer technologies areglasses-based and are relatively cheap and easy to construct:passive polarization-multiplexing (left and right views are sep-arated with polarized light) and active temporal multiplexing(left and right views are occluded alternately in rapid succes-sion using shutter glasses in sync with the left-right alternatingimage information on the screen) [1].

The next innovative 3D display technology bringing 3Dmovies and games in the comfort of the living room, is ex-pected to be glasses-free or autostereoscopic display technology[1], [2]. The most popular concept is the lenticular-based LCD,consisting of a lenticular sheet (i.e., a sheet of cylindricallenses) that is placed on top of an LCD in such a way that if the

Manuscript received August 16, 2011; revised December 06, 2011; acceptedDecember 06, 2011. Date of current version April 18, 2012.

The authors are with the Viewing Experience Innovation Group, PhilipsBG TV Innovation Site Eindhoven, Eindhoven, 5656 AE, The Nether-lands (e-mail: [email protected], [email protected],[email protected]).

This paper has supplementary multimedia material available at http://www.ieeexplore.ieee.org, provided by the author. The total size of all objects is 14.7MB. Player Information: The video files are saved in avi-format and can beplayed by most players. Packing List: recording of the autostereoscopic display.avi; recording of the emulator.avi; recording of the emulator with view-overlay.avi).

Color versions of one or more of the figures are available online at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JDT.2012.2185681

correct image information is put on the pixels underneath thelenses, different views are transmitted in different directions[3]. Each cylindrical lens in the sheet covers multiple sub-pixelsof which each sub-pixel corresponds to a distinct view. Hence,multiple distinct views of a scene can then be spatially multi-plexed behind the lenses in such a way that an observer sees adifferent view in his/her left-eye and right-eye resulting in a 3Dimpression.

Autostereoscopic lenticular displays are still regarded as apromising 3-D technology since they provide 3-D viewing withseveral advantages. Firstly, it allows observers to view the stereoimage without the use of special glasses. Secondly, it supportsmotion parallax, allowing observers to look around objects bymoving their head through the views. Next, multiple observerscan be accommodated at the same time due to the repetition ofviews in multiple viewing cones. And finally, some disadvan-tages present in current stereoscopic displays are absent, e.g.,reduction in luminance as a result of the use of glasses or per-ceived flicker due to time-sequential fields.

This design choice, however, also has some disadvantages.A first disadvantage is a loss of spatial resolution due to thegeneration of the multiple views. A second disadvantage isthe perception of pseudo-stereoscopic views in a viewing conetransition, i.e., viewing the left-eye image with your right eyeand vice versa. Consequently, a conflict between the disparityand several monocular cues occurs, which confuses observersand in the worst case induces visual discomfort. Another disad-vantage is that as a consequence of the employment of crosstalk,the display suffers from a level of blur that is noticeable, andcan become annoying as screen disparity increases. Crosstalk,however, also has beneficial effects. Crosstalk reduces thepicket-fence effect (banding, i.e., the occurrence of dark bandson the screen) and minimizes image flipping (the discretetransitions between neighboring views), with the additionalbenefit that it increases light output and perceived resolutionof the screen [3], [4]. For stereoscopic displays, crosstalkpercentages should not exceed 2% to maintain a comfortableviewing experience [5], bwhereas for autostereoscopic displaysthe optimal amount of crosstalk is still an issue of debate.Wang et al. (2010) found that for an autostereoscopic two-viewparallax barrier display, crosstalk of 3% is at the edge ofbecoming perceptible and crosstalk lower than 6%–9% is stillacceptable [6]. In combination with small disparities limited tothe fore- and background regions, even higher crosstalk values(up to 40%) still stimulate stereo perception without substantialperception of ghosting [7]. These high cross-talk values forautostereoscopic displays are a consequence of the definition ofcrosstalk [8]. In contrast to two-view systems, a single view ofa multi-view system typically contains contributions of three ormore views. So for a given percentage of overall crosstalk (i.e.,the contribution of all neighboring views), the contribution ofeach neighboring view is less in terms of percentages.

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284 JOURNAL OF DISPLAY TECHNOLOGY, VOL. 8, NO. 5, MAY 2012

The design choice for a specific display performance is a bal-ance between the amount of screen disparity, annoying degreesof blur or ghosting, perceived banding, width and number of theviews, transitions between views, and the resulting percept. Inaddition, the percept also considerably depends on observer po-sition, being static or dynamic, i.e., moving through the views orthrough a cone transition. The relation between the overall per-formance and these design parameters of the imaging system isof main interest for display manufacturers in general. However,it is often very time consuming and inefficient to assess these re-lations directly, since many parameters are interdependent, andmanufacturing different lenticular displays is very expensive.A well-known design choice which is already in production isthe slanted lens proposed by Van Berkel [9], [10]. Yet to opti-mize design choices, knowledge is required about what wouldbe the preferable performance of an auto-stereoscopic lentic-ular display. To this end, an autostereoscopic display emulatorwas developed to let people experience a given lenticular dis-play design. This emulator consists of a glasses-based stripedpolarized display, a camera-based head tracker and software forgenerating L/R stereo pairs in real-time as a function of head-lo-cation. Note that only a single person can use this emulator ata given time. The emulator allows evaluation of an autostereo-scopic lenticular display even before a costly physical sampleis produced. This paper addresses the development of the em-ulator, its validation with respect to an existing physical pro-totype, and the perceptual evaluation of three emulated funda-mental design extremes: 1) a 9-view high-crosstalk system; 2) a9-view low crosstalk system; and 3) a 17-view average crosstalksystem.

II. EMULATOR SYSTEM

A. Display System

A full-HD 16:9 46” interlaced-polarized passive 3D-TVwas used for the emulation. Emulation was based on aviewing distance of 330 cm, which corresponds to about 6picture heights [11], [12]. The display was driven at 1080p1920 1080 60 Hz by a computer running Windows XP. The

color reproduction of the display was not explicitly calibrated,but it was measured in a dark room using full-screen colorpatches with a Photo Research PR-680 spectro-radiometer. Thedisplay reached a peak full-screen white level of 211.5 cd/m ,when measured without a viewing polarizer, and 86.6 cd/mand 87.5 cd/m through the left-eye and right-eye polarizers,respectively, all three with a correlated color temperature of8100 K. Its minimum black level was 0.0667 cd/m . Thewhite-to-black system crosstalk (display and glasses) is 2.9%[13]. All of these values are typical for today’s consumertelevisions.

B. Emulation Model

The emulator mimicked the position-dependent front-of-screen performance of an autostereoscopic system on agoggle-based 3D display. As a result, a single user was able toexperience the effect of moving through the views and cones.The main effect included was the position-dependent crosstalkintroduced by differences in the sub-pixel visibility. Fig. 1shows a block-scheme of the considered emulator system.

Fig. 1. Block-scheme of the autostereoscopic emulator system.

Fig. 2. Position of an observer relative to the display. The green lines denoteview boundaries and the red lines denote cone transitions. Only movement in�-direction was tracked; � was fixed at � .

A head-tracker determined the position of an observer relativeto the screen. The viewing distance of the observer was fixedat and only head movement parallel to the display wastracked. This is illustrated in Fig. 2. Hence, the head-tracker onlyneeded to establish the viewing angle or lateral displacement .

The output of the emulator was obtained by adding the lightcontribution of different views under a few assumptions; for

the emulator was viewpoint-corrected, the lateral displace-ment was sufficiently small to neglect differences in viewingangle over the display, and the views were repeated in subse-quent cones neglecting optical aberrations.

In other words, the output was modeled as a linear com-bination of the input views. As these contributions representlight, they were performed in the linear light domain. To en-able real-time operation, the conversion from and to the gammadomain was approximated by the power of two.

Let denote the image in linear light corresponding to theth view. The output for the left eye view is then obtained by

(1)

where weights represent the contribution of the th view atleft eye positions with and a total ofviews. The output image for the right eye was computed in asimilar manner. The weights and depended on the eye

LAMBOOIJ et al.: EMULATING AUTOSTEREOSCOPIC LENTICULAR DESIGNS 285

Fig. 3. Designs A, B, and C depict a schematic representation of the three tested sub-pixel and lenticular designs (top) and their visibility functions (bottom).

position relative to the views. Given the head position , the eyepositions were computed assuming a fixed inter ocular distance

orthogonal to a line through the display center. The left eyeposition is hence given by

with (2)

The weight factors and were determined by the posi-tion of the eye relative to the view boundaries. In general theview in which the eye is located will contribute most, with asteady decrease of more outer views. It was assumed that thecontribution of outer views depends only on the position of theeye relative to the view. Considering Fig. 2, the contributionwas expressed as single visibility functions and ,where

(3)

and is the width of a cone at distance . This definitionensures that corresponds to the repetition period of aview. The subtractive term ensured that view 0 is centered on

. Given the visibility function, the weight factors forthe left and right eye were computed as stated in (4).

(4)

Here and are the normalized eye positions from (3) andthe operator mod implements cone repetition. After computing

and from (1), the images were transformed to the gamma

TABLE ISUB-PIXEL VISIBILITY FUNCTIONS.

domain line and interleaved to be displayed on the passive 3Ddisplay.

In the perception experiment (Section III), three theoretical,extreme, visibility curves were implemented. The curves corre-sponded to the lenticular/panel designs shown in the top row ofFig. 3. As the LCD pixels were assumed to be in the focal planeof the lenticular and the panel has no black matrix, the sub-pixelvisibility for each is proportional to amount of light collectedalong a line parallel to the lenticular. The resulting visibilitiesare shown in the bottom row of Fig. 3. All visibility curves arenormalized in such a way that they add up to one. Table I pro-vides the functional descriptions.

To understand the visibility curves, note that parameterizesthe position of the light gathering line within a sub-pixel suchthat for the line passes through left-bottom corner ofthe considered sub-pixel, while for it passes through theright-top corner. At the line passes through the centre


Fig. 4. Camera system and display system configuration.

of the sub-pixel. The visibility of a sub-pixel for a given isproportional to the length of the line within the sub-pixel. Con-sider as an example the black lines in Fig. 3, which correspondto the case for view 7.

In design A, the black line is parallel to the sub-pixels. Theamount of visibility of a view is hence constant forand zero outside. Hence, there is no overlap between the viewsand the cross-talk between the views is 0%. For design B, theamount of light collected along the black line (slant 1/3), givesrise to the triangular shaped visibility curve shown in Fig. 3(b).The amount of cross-talk between the views is now position de-pendent. In the middle of a view (i.e., ), the crosstalkis 0%, while at the view boundaries (i.e., and ) itreaches up to 100%. Finally, in Fig. 3(c) a design with a lentic-ular slant of 1/6 is depicted. As shown, the system has trape-zoidal shaped visibility curves with considerable overlap be-tween the views. Within a view, the total crosstalk from neigh-boring views is 100%, since in contrast to design B both the leftand the right neighboring view contribute. This is also reflectedby the fact that the black line in Fig. 3(c) intersects sub-pixelswith a different view number. In addition, intermediate viewsoccur between the left and right eye, resulting in 17 views in-stead of the 9 views in design A and B.

C. Validation Emulator

To validate the functioning of the emulator, a Quad Full HDautostereoscopic lenticular display with design C and 15 viewsand its emulation were directly compared in an informal qual-itative test by 20 participants. No test data was collected, yetnone of the participants considered the system to be a poor em-ulation or indicated that there were large differences with theactual lenticular display. In addition, to demonstrate the perfor-mance of the emulator, a video was captured while moving acamera through their view transitions. To capture the videos, a

color camera from IDS Imaging (model UI-2230 ME-C-HQ)with a Schneider-Kreuznach lens (Xenoplan 1.7/17) was used.The camera was translated parallel to the display plane with theoptical axis of the lens orthogonal to the display plane. To cap-ture one view of the emulator, a polarizer was placed betweenthe lens and the camera sensor. Since the polarizer blocks light,the shutter time and the aperture of the camera were adjustedsuch that the luminance of both display setups appeared to beequal. For both display setups, the focus distance of the camerawas 3 m (optimal viewing distance of the Quad Full HD dis-play). The resulting video clips clearly show that position-de-pendent cross-talk introduced by differences in the sub-pixelvisibility and visible as depth-dependent blur was adequatelymodeled as well as the perceptual effect of cone transitions (seehttp://www. ieeexplore.ieee.org for a video recording of valida-tion).

D. View Generation

Fig. 4 depicts the geometry on which the image renderingwas based. The scenes were rendered with the ray tracing toolPovray,1 in which in a three-dimensional space objects and lightsources are created and positioned. The geometry was character-ized by six basic parameters [14]: 1) the camera base distance;2) the camera convergence distance; 3) the field of view of thecameras; 4) screen width; 5) viewing distance; and 6) interoc-ular distance. In order to render perceptually realistic images,i.e., without any depth distortions, these parameters had the fol-lowing values: parameter 1 and 6 are 63 mm [15], parameter 2and 5 are 330 cm [11], [12], parameter 4 is 102 cm and param-eter 3, which is determined by parameters 2 and 4, is 17.6 . Mul-tiple views were rendered by shifting thecamera 63 mm, while keeping convergence distance and con-vergence point constant (resulting in a toed-in configuration).

1[Online]. Available: www.povray.org


E. Head-Tracker

As mentioned in Section II-B, to detect the observer’s posi-tion a head-tracker was used that provided real-time head-lo-cation data to the display such that the appropriate images arerendered for the left- and right-eye of the tracked observer. Theviewing distance of the observer was assumed to be atand only head movement parallel to the display (in -direction)was dynamically determined.

For the head-detection with a single camera the face detectorintroduced by Viola and Jones [16] was used in OpenCV [17].Since eye locations were not estimated independently, a singlelocation steered the image of two eyes. The centre of theface window as detected by the Viola-Jones algorithm servedas reference for the location that lies exactly in the middlebetween the two eyes. A webcam communication camera wasused with a field-of-view of 56.8 degree (diagonal) at the spec-ified maximum (HD) resolution of 1280 720. To be flexible inchanging camera type and/or lens optics, we used a straightfor-ward camera calibration procedure. Assuming an ideal pinholecamera, the observed image coordinate in the -direction, , isproportional to the magnitude of the -coordinate and inverselyproportional to the z-coordinate:

(5)

where proportionality constant depends on lens focal length,sensor pixel size and camera resolution. To determine for agiven camera, a bar of length m with reflective redtape was placed parallel to the TV at a distance of m fromthe display. The ends of the bar in the image were then indicatedwith a mouse click. The constant is then calculated as

(6)

After calibrating , a given face image coordinate togetherwith assumed distance give the required -coordinatevia (5).

A VGA 640 480 input resolution at nominally 30 framesper second was used. When processing a full frame, however, asufficiently low latency could not be achieved. To decrease la-tency a tracked window of 100 100 pixels was used for theface detection. The position of this tracking window was ad-justed based on the calculated face location, such that the de-tected face remained at the center of the tracked window.

The centre coordinate of the face window was an integertaking steps that corresponded to the pixel size. Consequently,discrete changes in the image when an observer moved lateralto the screen could be perceived. To minimize the perceptualeffect of these discrete changes, a post-processing step was im-plemented, in which the head image coordinate was calculatedbased on intensity weighting in the detected face window:

(7)

where denotes the norm of the RGB color vectors ofthe camera and Window denotes a vertical strip of 11 pixelswide and a height that corresponds to the height of the detectedface window, centered on the detected face location. Equation

(7) weighs the combination of image locations of which theweight increases as function of the luminance of regions. Sincethe nose in a face is usually brighter than the eyes, these pixelswere weighted more. Yet, the biggest advantage was that thepixel discretization has less influence on the tracked location.As a final step, the following temporal filter was applied to theestimated face location (indicated by the “hat”):

(8)

Note that although the temporal filter in (8) reduced the effectsof noisy estimates, it also increased overall latency. The overalllatency is one of the critical factors in head tracked display sys-tems [18], which can be defined as the period in time from theactual head movement to the actual displaying of the scene ren-dered according to that head position. For low latencies, usersdo not perceive latency directly, but rather the consequencesof latency; scenes become unstable in space when users movetheir heads. Latencies should be no more than 50–100 ms [18],though JND’s of latency in head-tracking applications had beenfound to be around 17 ms [19] (indicating that in the perfectapplications tracking must be performed at 60 Hz). Assuminga head velocity ranging from 100 mm/s [20], and a latency of50 ms, the head displacement is about 5 mm before the imageadapts.

III. PERCEPTION EXPERIMENT

The main objective was to compare the three differentlenticular/panel designs by means of the emulator addressed inSection II-B.

A. Stimuli

Four images were used and are depicted in Fig. 5; Balls,Pipes, Apple and Boat respectively. The stimuli differed in de-sign and stereoscopic depths. The three considered designs havebeen discussed in Section II-B. For designs A and B, 9 viewswere rendered each with a view cone of 1.1 (for geometryparameters see Section II-D). Since design C had intermediateviews (visible along the lenticular slant in Fig. 3(c), the camerabase distance in the rendering was set to 3.15 cm, resulting in17 views. Hence, for all three designs the eye base distance be-tween a left- and right eye view was 6.3 cm, yet only design Ccontained a view in between.

The variation in stereoscopic depth was introduced byvarying the object distance in the Povray scenes relative to theintersection of the optical axes of the cameras. For more detailson the rendering, see Section II-D. The variation in stereoscopicdepth was chosen such that 1) the maximum screen disparity( – in Fig. 4) did not exceed the zone of comfort-able viewing (ZCV), which is one degree of screen disparity[21], and 2) realistic stereoscopic depth similar to conventionalautostereoscopic multi-view displays was displayed.

Fig. 4 depicts the resulting stereoscopic depth in object dis-tance (5, 10, 20, 30, and 40 cm) and the angular distances as aproportion of the ZCV (0.03, 0.06, 0.13, 0.19, and 0.25).

The reduction in perceived resolution of an autostereoscopiclenticular interleaved image depends on the lens slant andcannot be exactly described by a separable 2D filter [4], [23], itwas approximated by a factor 3 down scaling in both horizontaland vertical direction for all three designs to avoid image


Fig. 5. Original images: Balls (left top), Pipes (right top), Boat (right bottom)and Apple (left bottom). The images Pipe, Apple and Boat were altered scenesof existing Povray renderings by [22].

Fig. 6. Screen shot of a stimulus in the training mode. The red lines indicateview transitions, the green lines cone transitions and the two dots the eyes. Inthe top left corner, the number of the stimulus and the head-tracked image werevisualized.

quality issues due to differences between input images perdesign. Hence, all Povray renderings were resized twice withMatlab; from 1920 1080 to 640 360 and back to 1920 1080.This filtering also removes high-frequency details from indi-vidual views since otherwise sub-sampling, an inherent step inview multiplexing, would lead to aliasing perceived as colorfringing at sharp object boundaries, Moire patterns, granularnoise, etc. [4].

B. Participants

Twenty participants that had experience with stereoscopiccontent, with an average age of 44 years, ranging from 23 to70, participated. Participants could participate after signing theinformed consent with information about possible occurrenceof visual discomfort and successfully completing the Landolt-C(visual acuity of ) and Randot stereo test (stereo acuity of

30 sec. of arc) [24].

C. Procedure

The experiment was conducted at the Philips High Techcampus in a laboratory room, in which light settings were heldconstant: 30 lux measured vertically at the display surfacewhile the detector was pointing towards the observer and 77 luxmeasured horizontally at 1 m height at the viewing position ofthe observer. The experiment included three parts all performed

at a viewing distance of 3.3 m: a training, a ranking and a directassessment.

The training was incorporated to get acquainted with the em-ulation system and the stimuli. Information was provided aboutthe display (that the display renders multiple views throughwhich the observer could move his/her head), the head tracker(participants were instructed not to move their head too fastotherwise the head tracker looses tracking) and the evaluationconcepts of interest. Next, the image Balls was displayed threetimes; for the three designs all with a stereoscopic depth of30 cm. To clarify the functionality of the emulator, the nineviews (red lines), cone transitions (green lines) and the positionof the eyes in these views were superimposed over the stimulias depicted in Fig. 6. Since we were not interested in theperceptual impact of pseudoscopy at the cone transitions andthe system latency (the latter of which was barely perceptible),participants were instructed not to incorporate these aspects intheir evaluation.

In the first part, participants were asked to rank the threedesigns in terms of viewing comfort, 3D depth impression, andimage quality. The stimuli varied in content (Boat, Apple andPipes) and stereoscopic depth (5 levels, see Section III-A),which resulted in 15 ranks per evaluation concept. The order ofthe stimuli was randomized across participants.

In the second part, participants were asked to find a goodviewing position and assess 15 stimuli in terms of ease of findinga good viewing position, percept during head movement, 3Ddepth impression, image quality, and overall viewing experienceon a scale labeled with the adjective terms [bad]-[poor]-[fair]-[good]-[excellent] according to the ITU recommended method-ology for the subjective assessment of the quality of televisionpictures [12]. The image Apple was used and varied in designand stereoscopic depth. The order of the stimuli was random-ized across participants.

D. Results

The results of the first part, i.e., the ranking of the designs,are depicted in Fig. 7. Due to the ordinal character of the dataset, means and standard deviations cannot be extracted and sig-nificance testing is based on medians and frequency distribu-tions. The Friedman’s test statistic for the analysis of variance ofnon-parametric dependent data showed that the ranking was sig-nificant for all three evaluation concepts at all depthlevels, except for depth impression and image quality at a depthlevel of 5 cm. Fig. 7 depicts per depth amount the percentagea certain design was ranked number 1 (the best), and the ’ ’symbols outline the designs that significantly differed from theothers, e.g., design A had significantly the best image quality,except for a depth of 5 cm.

Though ranking elicited which design is perceived better thanthe other, the results were relative (all three designs can stillhave low image quality). In the second part, participants as-sessed the stimuli on a scale labeled with the adjective terms[bad]-[poor]-[fair]-[good]-[excellent]. To verify whether the or-dinal categorical scale was a parametric one, i.e., with perceivedequal distances between the adjectives, Thurstone’s law of cate-gorical judgement was applied to the data [25]. The assessmentscale was transformed to a numerical one in such a way that


Fig. 7. The results of experiment part 1: the ranking in percentages for the three evaluation concepts (different panels), per amount of depth (top of graph) andper design (x-axis). The ’�’ indicates the designs that significantly differed from the other design.

Fig. 8. The results of experiment part 2: the direct assessment averaged over participants and stimuli with their error bars (representing the 95% confidenceintervals) of the different evaluation concepts (different panels), per design (different lines) and per for different amounts of depth (along the x-axis).

the adjective [bad] corresponds to a rating of 1 and the adjec-tive [excellent] to a rating of 5. The raw data were transformedwith the software program ThurcatD [26] to a Thurstone scale.Two types of measures indicated the quality of the model fit;1) the probability stress that equals the weighted average abso-lute discrepancy between observed cumulative proportions andmodel cumulative probabilities, and 2) a -test for the devi-ation of the probability model from the observed proportion.The resulting data indicated that the model conditions deviatesmaximally 2.4% from the experimental conditions and the per-ceived intervals between the adjectives were perceived as equalfor all evaluation concepts ( -test indicates no difference at

level), which allowed the raw to be used in furtherANOVA analysis.

Fig. 8 depicts the assessment scores averaged over partici-pants and stimuli per evaluation concept (different panels) fordifferent designs (different lines) and different amounts of depth(along the horizontal/ordinal z-axis). An ANOVA revealed thatall main and interaction effects were significant , ex-cept for the effect of design on viewing experienceand the interaction between design and depth level for ease offinding a viewing position and 3D depth impression

. Some noteworthy results were: 1) that for designB participants had difficulty finding a good viewing position,even though positions were possible without crosstalk (this dif-ficulty consequently decreased the scores of the other evaluationconcepts); 2) participants preferred smooth transitions betweenviews and disliked the discrete image flips of design A; 3) forsmall depths, design had little effect on 3D depth impression;4) all scores for overall viewing experience were below “good;”

and 5) increasing disparity decreases image quality for designsB and C.

IV. DISCUSSION

To our knowledge this is the first research that directlycompares the perceptual impact of distinctive lenticular designson different viewing aspects. The optimal performance is goodimage quality without annoying degrees of blur, ghosting orbanding and smooth transitions between views for all depthlevels. Since this is not possible (yet), depending on the criteriaone applies, different design choices are required.

It is noteworthy to emphasize that this emulator is an approx-imated model. As such, the emulator incorporated ’observerlateral position dependent selection of views’, ’observer lateralposition dependent introduction of cross-talk’, and ’occur-rence of cone transitions’. The emulator, however, ignored’interference of black matrix causing banding’, ’viewing-anglecross-talk dependence due to lens aberrations’, ’observer dis-tance from the screen’ and ’variating observer angle to thescreen’. The relevance of these ignored aspects was acknowl-edged, yet for the first version of the emulator these aspectswere too difficult to implement with sufficient low latency inreal-time. Though this research compared different lenticulardesign choices with respect to the balance of some perceptualcriteria (being image quality, depth impression and viewingcomfort), one should keep in mind that these neglected aspectsmight influence results. Note however, that the qualitativevalidation addressed in Section II, shows that this emulatoris already a good first approximation of an existing physicalprototype.


For conservative stereoscopic depth (up to 10 cm), cross-talkhas clear beneficial effects; a good viewing position is easier tofind, the transitions between the views is smooth and thus com-fortable and the image quality and 3D depth impression is sim-ilar to the case without cross-talk. Hence, the overall viewingexperience is higher for window functions with a slant thanwithout a slant. This preference is mainly due to the fact thatpeople strongly dislike the discrete transitions between viewsor “choppy” changes as they refer to it.

For stereoscopic depth larger than 10 cm the perceptualimpact of crosstalk in terms of viewing comfort becomes ad-verse; smooth transitions were redeemed for ghost images. Fora depth amount of 40 cm, there is no difference in preferenceof viewing comfort (Fig. 7) between the designs A and C,meaning that blur and ghosting had a similar impact as imageflipping. The image quality and viewing experience of designC, however, is largely decreased. Hence, for these amountsof depth the overall viewing experience is higher for windowfunctions without a slant than with a slant. These results indi-cate that the overall viewing experience is a balance betweenimage quality, 3D depth impression and viewing comfort.Hence, to optimize the overall viewing experience a lenticulardesign without crosstalk is required with smooth transitionsbetween the views only perceptible when viewers move. Toour knowledge with the conventional lenticular technologythis can only be approximated by multiple views per eye, i.e.,increasing resolution.

V. CONCLUSION

An emulator was build to evaluate the perceptual effects ofdifferent autostereoscopic lenticular design parameters suchas the width of views, screen disparity, and lenticular slant.Even though some characteristic parameters were not takeninto account, a direct comparison with an existing lenticulardisplay showed that the emulator was able to model positiondependent crosstalk, cone transitions and depth-dependent blur.Three fundamental lenticular design extremes were compared;a 9-view low crosstalk system, a 9-view intermediate crosstalksystem, and a 17-view high crosstalk system. Crosstalk has onlya beneficial effect at conservative stereoscopic depth levels.However, using designs with less crosstalk causes unwanted’choppy’ changes between views that are also not appreciatedby viewers. With current native display panels resolutions anoptimum viewing experience is obtained at a fair depth levelof 10 cm, with good image quality and freedom of movement,while it is easy to find a viewing position.

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Marc Lambooij received the B.A. degree in technical engineering, with an af-filiation in medical engineering, and the M.Sc. degree in Human-TechnologyInteraction, in 2005, and the Ph.D. degree in 2012, all from the Eindhoven Uni-versity of Technology, the Netherlands. His Ph.D. research focused on visualcomfort associated with 3D-display systems from a human and a technologicalperspective.

Currently he is a perception research scientist in the Viewing Experience In-novation Group of Philips BG TV Innovation Site Eindhoven, Eindhoven, TheNetherlands.

Karel Hinnen received the M.Sc. degree in applied physics (cum laude) fromthe University of Twente, the Netherlands, in 2002, and the Ph.D. degree (cumlaude) from the Delft University of Technology, the Netherlands, in 2007..

From 2007 till 2010 he has worked at Philips Research Laboratories Eind-hoven (the Netherlands) on topics related to display systems and video pro-cessing. Currently he is a senior scientist at Philips Consumer Lifestyle.

Chris Varekamp received the M.Sc. degree in forestry (with thesis subjects onthe topics remote sensing and geostatistics) and the Ph.D. degree for his thesis ti-tled: “Canopy reconstruction from interferometric SAR” from Wageningen Uni-versity, The Netherlands, in 1995 and 2001.

From 2001 to 2010, he worked as a senior scientist with Philips Research.Since August 2010 he works as a senior scientist at Philips Consumer Lifestyle.His research interests include: computer vision algorithms, image/video seg-mentation, information extraction from cameras and autostereoscopic 3D tele-vision principles.

emulating autostereoscopic lenticular designs

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