<strong>IEEE</strong> COMSOC MMTC E-LetterKari Pulli received his Ph.D. in ComputerScience from University of Washington inSeattle, WA, USA and an MBA from Universityof Oulu, Finland. He is currently a ResearchFellow at Nokia Research Center in Palo Alto,CA http://research.nokia.com/people/kari_pulli/.He has been an active contributor to severalKhronos standards, Research Associate atStanford University, Adjunct Professor (Docent)at University of Oulu, Visiting Scientist at MIT,and briefly worked at Microsoft, SGI, andAlias|Wavefront.http://www.comsoc.org/~mmc/ 14/41 Vol.4, No.7, August 2009
<strong>IEEE</strong> COMSOC MMTC E-LetterAssessing 3D Displays: Naturalness as a Visual Quality MetricWijnand A. IJsselsteijn, Eindhoven University of Technology, The Netherlandsw.a.ijsselsteijn@tue.nlBinocular vision is based on the fact thatobjects and environments are seen from twoseparate vantage points, created by theinterocular distance between the two eyes. Thishorizontal separation causes an interoculardifference in the relative projections ofmonocular images onto the left and right retinas.When points from one eye's view are matched tocorresponding points in the other eye's view, theretinal disparity variation across the imageprovides information about the relative distancesand depth structure of objects. Stereopsis thusacts as a strong depth cue, particularly at shortdistances [1].Stereoscopic display techniques are based onthe principle of taking two images anddisplaying them in such a way that the left viewis seen only by the left eye, and the right viewseen only by the right eye. There are a number ofways of achieving this [2, 3, 4]. Stereoscopicdisplays can be categorized based on thetechnique used to channel the right and leftimages to the appropriate eyes. A distinguishingfeature in this regard is whether the displaymethod requires a viewing aid (e.g., polarizedglasses) to separate the right and left eye images.Stereoscopic displays that do not require such aviewing aid are known as autostereoscopicdisplays. They have the eye-addressingtechniques completely integrated into the displayitself. Other distinguishing features are whetherthe display is suitable for more than one viewer(i.e., allows for more than one geometricallycorrect viewpoint), and whether look-aroundcapabilities are supported, a feature inherent to anumber of autostereoscopic displays (e.g.,holographic or volumetric displays), but whichrequires some kind of head-tracking whenimplemented in most other stereoscopic andautostereoscopic displays.Potential benefits of stereoscopic displaysinclude an improvement of subjective imagequality, improved separation of an object ofinterest from its visual surrounding, and betterrelative depth judgment and surface detection.Such characteristics make the use of stereoscopicdisplays advantageous to a variety of fields,including camouflage detection (e.g.,stereoscopic aerial photography), precisionmanipulation in teleoperation or reduced visionenvironments (e.g., minimally invasivetelesurgery, underseas operations), as well ascommunication and entertainment environmentsthrough creating a greater sense of social orspatial presence [5].The effectiveness of stereoscopic displays insupporting certain tasks can be assessed in arelatively straightforward manner, by takingcertain quantitative outcome measures (e.g.,number of errors, time taken to successfullycomplete a task) and comparing monoscopic andstereoscopic modes of operation in terms of suchmeasures. Such a performance-oriented approachwill not be applicable, however, whenstereoscopic displays are being developed anddeployed for entertainment purposes, such astelevision or digital games. In an appreciationorientedcontext, the standard assessmentcriterion that is applied to assess the fidelity ofimage creation, transmission and display systemsis image quality [6].Engeldrum [7] has defined image quality as“the integrated set of perceptions of the overalldegree of the excellence of the image” (p.1).Image quality research has traditionally focusedon determining the subjective impact of imagedistortions and artifacts that may occur as aconsequence of errors in image capture, coding,transmission, rendering, or display. Instereoscopic imaging, image quality research hasfocused on effects of (i) stereoscopic imagecompression, (ii) commonly encountered opticalerrors (image shifts, magnification errors,rotation errors, keystone distortions), (iii)imperfect filter characteristics (luminanceasymmetry, color asymmetry, crosstalk), and (iv)stereoscopic disparities (in particular verticaldisparities as a consequence of toed-in cameraconfigurations). More recently, with the adventof the RGB+Z format [8], new image artifactshave been introduced that require more extensivequality evaluations.The International Telecommunication Union(ITU) offers a series of recommendations(standards) for the optimal assessment of picturequality of television images. Tworecommendations are of specific importance tous here. The first, ITU RecommendationBT.500-11, Methodology for the SubjectiveAssessment of the Quality of Television Pictures,http://www.comsoc.org/~mmc/ 15/41 Vol.4, No.7, August 2009
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