1、 Rec. ITU-R BT.1438 1 RECOMMENDATION ITU-R BT.1438 SUBJECTIVE ASSESSMENT OF STEREOSCOPIC TELEVISION PICTURES (Question ITU-R 234/11) (2000) Rec. ITU-R BT.1438 The ITU Radiocommunication Assembly, considering a) that studies are in progress to develop stereoscopic television as a potential future bro
2、adcast service; b) that Recommendation ITU-R BT.1198 has been established for stereoscopic television based on R- and L-eye two channel signals; c) that subjective assessments are a vital element in the design and introduction of stereoscopic television systems; d) that shooting conditions, viewing
3、conditions and type of display may influence observer fatigue; e) that common assessment conditions appropriate for stereoscopic television systems should be established; these conditions should include evaluation methods, shooting conditions, viewing conditions, test materials to be used in the ass
4、essment and screening methods to ensure that observers have normal depth perception, recommends that the conditions described below should be used for the subjective assessment of stereoscopic television systems. 1 Assessment factors Assessment factors generally applied to monoscopic television pict
5、ures, such as resolution, colour rendition, motion portrayal, overall quality, sharpness, depth, etc., could be applied to stereoscopic television systems. In addition, there would be many factors peculiar to stereoscopic television systems. Some of them are listed below, and further studies are req
6、uired to identify others and to establish physical definitions. Depth resolution Spatial resolution in depth direction. Coarse resolution in depth direction may reduce picture quality in stereoscopic television. Depth motion A factor related to whether motion or movement along depth direction is rep
7、roduced smoothly. Puppet theatre effect This describes one type of distortion in reproduced 3-D images. Stereoscopic objects are sometimes perceived as unnaturally large or small. Cardboard effect This describes another type of distortion in reproduced 3-D images. The 3-D positions of stereoscopic o
8、bjects are perceived stereoscopically but they appear unnaturally thin. 2 Assessment methods The methods described in Recommendation ITU-R BT.500 could be applied for the evaluation of the general picture quality of stereoscopic systems as well as sharpness and depth (see Annex 2). When a reference
9、image is available, double-stimulus continuous quality-scale or double-stimulus impairment scale methods can be used. Examples include 2 Rec. ITU-R BT.1438 comparison of display systems, quality assessment of coding systems, and so on. When no reference is available, the categorical judgement method
10、 can be used, for example, to identify the merits of stereoscopic systems. Evaluation methods for the assessment of particular factors of stereoscopic television systems require further study. 3 Viewing conditions Two major factors peculiar to stereoscopic display should be taken into consideration,
11、 namely the display frame effect and inconsistency between accommodation and convergence. Stereoscopic pictures appear highly unnatural when objects positioned in front of the screen approach the screen frame. This unnatural effect is called “the frame effect”. The effect is generally reduced with a
12、 larger screen, because observers are less conscious of the existence of the frame when the screen is larger. The human eye focuses on an object according to the distance to that object. At the same time, we also control the convergence point (gaze point) on the object. Therefore, there is no incons
13、istency between accommodation and convergence in our everyday life. However when viewing stereoscopic images, the focus point (accommodation) must always be fixed on the screen, independent of the convergence point which is derived from the disparity of the signals. Otherwise, the observer cannot fo
14、cus clearly. Thus, an inconsistency between accommodation and convergence is introduced in stereoscopic systems. It is generally said that the minimum value for depth of field of the human eye is 0.3 D (Diopter: reciprocal value of distance (m) Hiruma and Fukuda, 1990. This means that we can perceiv
15、e the image without defocusing when the object is located within 0.3 D. When viewing stereoscopic television, the accommodation point is fixed on the screen, and therefore stereoscopic pictures should preferably be displayed within this range. Since ordinary television programmes include images at i
16、nfinite distance (that is D = 0), the desirable range of depth to be displayed with stereoscopic systems is considered to be within 0 to 0.6 D. Therefore, 0.3 D, i.e. 3.3 m, is considered to be the optimum viewing distance. Camera parameters (camera separation, camera convergence angle, focal length
17、 of lens), resolution of the system and the frame effect should be taken into account in determining viewing conditions (screen size). In the case of HDTV when watching at the standard viewing distance of 3 H (H denotes picture height), the viewing distance of 3.3 m corresponds to a 90-inch screen.
18、In the case of standard definition television (SDTV) when watching at the standard viewing distance of 6 H, this distance corresponds to a 36-inch screen. A subjective assessment of the relationship between screen size and depth perception was carried out with stereoscopic HDTV system, and the resul
19、ts showed that the most natural depth perception was obtained with a screen size of 120 inches, which corresponds to viewing distance of 2.2 H Yamanoue et al., 1997. 4 Observers Observers should have normal acuity (see Recommendation ITU-R BT.500). In addition, they should have normal stereopsis. In
20、 order to check their stereopsis, vision test materials listed in Annex 1 can be used. 5 Test materials Test materials for screening observers and still and motion sequences of natural scenes are listed in Annex. 1. The 3-D effects obtained from stereoscopic pictures depend largely on the shooting c
21、onditions, such as camera separation, camera convergence angle and focal length of the lens. The motion sequences were shot under the condition of camera separation of 65 mm, corresponding to average eye separation, and most of them were produced with the uncrossed camera layout, which gives an orth
22、ostereoscopic condition Yamanoue et al., 1998. Rec. ITU-R BT.1438 3 REFERENCES HIRUMA, N. and FUKUDA, T. December, 1990 Accommodation response to binocular stereoscopic TV images and their viewing conditions. J. SMPTE, 102, 12, p. 2047-2054. YAMANOUE, H. et al. October, 1997 Subjective study on the
23、orthostereoscopic conditions for 3D-HDTV. ITE Tech. Report, Vol. 21, 63, p. 7-12. YAMANOUE, H. et al. 1998 Orthostereoscopic conditions for 3-D HDTV. Proc. SPIE, 3295, Stereoscopic displays and Applications IV. ANNEX 1 Test materials for subjective assessment of stereoscopic television pictures 1 Vi
24、sion test Table 2 lists the test charts for the vision test. These 12 tests are selected according to the hierarchy of the human visual system from lower to higher levels. Eight main vision tests (VTs) are described below, and the other four are for the clinical test. Observers must have normal ster
25、eopsis, meaning that they must pass test VT-04 for fine stereopsis and test VT-07 for dynamic stereopsis. The remaining six tests are for more detailed characterization. The test charts should be viewed from three times the height of the display screen (3 H). Below, right and left thumbnail images a
26、re put side by side for crossed free fusion for explanatory purposes. a) VT-01 : Simultaneous perception (lion test) Tests the ability to perceive dichoptically presented images simultaneously and in the correct position. A cage image is presented to one eye and a lion image to the other eye, with i
27、ts position moving by 12/s. The size of each image is fixed at 10 so that the observers can capture the images within their paramacula. Observers with normal vision can see the lion in the cage at a certain time within the presentation period. 1438-01FIGURE 1Test chart for VT-01Right image Left imag
28、eFIGURE 1/BT.1438.D01 = 3 CM 4 Rec. ITU-R BT.1438 b) VT-02 : Binocular fusion (worth 4-dot test) Tests the ability to perceive two dichoptic images in left and right eyes as one image. The image for one eye has two dots, and the image for the other eye has three dots, with one dot in common. Observe
29、rs with normal vision can see four dots. 1438-02FIGURE 2Test chart for VT-02Right image Left imageFIGURE 2/BT.1438.D02 = 3 CM c) VT-03 : Coarse stereopsis (dragonfly test) Tests the ability to perceive dichoptically presented images with a parallax as one image with a coarse depth. The images for th
30、e two eyes are a stereopair of images of a dragonfly with its wings spreading. Observers with normal vision can perceive the wings in front of the display screen. 1438-03FIGURE 3Test chart for VT-03Right image Left imageFIGURE 3/BT.1438.D03 = 3 CM d) VT-04 : Fine stereopsis (circle test) Tests the a
31、bility to perceive dichoptically presented images with a parallax as one image with a fine depth. Nine test lozenge patches are provided and each of them has four circles in which only one circle has a small parallax. Observers with normal vision can perceive the circle with a small parallax in fron
32、t of the display screen. Table 1 shows the test number, correct answers, and angle of stereopsis at 3 H. Rec. ITU-R BT.1438 5 TABLE 1 Correct answers and parallax 1438-04FIGURE 4Test chart for VT-04Right image Left imageFIGURE 4/BT.1438.D04 = 3 CM e) VT-05 : Crossed fusional limit (bar test) Tests t
33、he ability to perceive dichoptically presented images with crossed disparities as one image. A stereopair of bars is presented with its parallax changing by 10/s. The fusional limits for the ascending and the descending series can be measured. Observers are instructed to report their fusional break
34、as soon as they perceive double images in the ascending series, and their recovery of fusion as soon as they perceive the dichoptic images as a single image in the descending series. FIGURE 5/BT.1438.D05 = 3 CM 1438-05FIGURE 5Test chart for VT-05Right image Left imageTest No. Correct answers Angle o
35、f stereopsis at 3 H (“) 1 Bottom 480 2 Left 420 3 Bottom 360 4 Top 300 5 Top 240 6 Left 180 7 Right 120 8 Left 60 9 0 6 Rec. ITU-R BT.1438 f) VT-06 : Uncrossed fusional limit (bar test) Tests the ability to perceive dichoptically presented images with uncrossed disparities as one image. Presented im
36、ages are the same as in the crossed case above, but right and left images are swapped. 1438-06FIGURE 6Test chart for VT-06Right image Left imageFIGURE 6/BT.1438.D06 = 3 CM g) VT-07 : Dynamic stereopsis (dynamic random dot stereogram test) Tests the ability to perceive depth in moving random dot ster
37、eogram images. Observers with normal vision can perceive a rectangular shape and a sinsoidal depth motion in the dynamic random dot stereogram. 1438-07FIGURE 7Test chart for VT-07Right image Left imageFIGURE 7/BT.1438.D07 = 3 CM h) VT-08 : Binocular acuity (acuity test) Tests the binocular acuity wi
38、th binocular fusion, including any imbalance of monocular acuity which might prevent good stereopsis. The images have four columns and five lines which consists of E characters with a variety of orientation and size. The centre two columns can be seen with both eyes; the left two columns can be seen
39、 only with the left eye; and the right two columns can be seen only with the right eye. Observers with normal vision can tell the orientation of the E characters correctly. The character sizes correspond to acuities of about 1.0, 0.5, 0.33, 0.25, and 0.125 at 3 H. Rec. ITU-R BT.1438 7 1438-08FIGURE
40、8Test chart for VT-08Right image Left imageFIGURE 8/BT.1438.D01 = 3 CM 2 Natural images The natural images consist of 15 still pictures and 15 motion sequences, as listed in Tables 3 and 4. Some of them are illustrated in Appendix 1. Each image is printed from left to right as left image, right imag
41、e, left image: the 3-D image can be obtained by fusing the leftmost pair (eyes uncrossed) or the rightmost pair (eyes crossed). 3 Status of usage of the stereoscopic test material Use of the test material is restricted to the following purposes only: Technical evaluation, including: research and dev
42、elopment of equipment and systems, testing of equipment in development and production process, testing of transmission condition for broadcasting and telecommunication, maintenance of equipment. Demonstration, including: presentation at technical conference and workshop, presentation of performance
43、and functionality of equipment, excluding commercial promotion. NOTE 1 Presentation of the motion sequence No. 10 Football, is allowed ONLY at research facilities such as universities, research institutes, and manufacturers laboratories, not in public. 8 Rec. ITU-RBT.1438TABLE 2 Stereoscopic test ma
44、terials VT No. Item Test for Content 1 Simultaneous perception The ability to perceive dichoptically presented images simultaneously and in the correct position A cage image is presented to one eye and a lion image to the other eye 2 Binocular fusion The ability to perceive two dichoptic images in l
45、eft and right eyes as one image The image for one eye has two dots, and the image for the other eye has three dots, with one dot in common 3 Coarse stereopsis The ability to perceive dichoptically presented images with a parallax as one image with a coarse depth The image for two eyes are a stereopa
46、ir of images of a dragonfly with its wings spreading 4 Fine stereopsis The ability to perceive dichoptically presented images with a parallax as one image with a fine depth Nine test lozenge patches are provided and each of them has four circles in which one circle has a small parallax 5 Crossed fus
47、ion limit The ability to perceive dichoptically presented images with crossed disparities as one image A stereopair of bars is presented with its crossed parallax changing by 10/s 6 Uncrossed fusional limit The ability to perceive dichoptically presented images with uncrossed disparities as one imag
48、e A stereopair of bars is presented with its uncrossed parallax changing by 11/s 7 Dynamic stereopsis The ability to perceive depth in moving random dot stereogram images Dynamic random dot stereogram 8 Binocular acuity The binocular acuity, including any imbalance of monocular acuity which might pr
49、event good stereopsis E characters with a variety of orientation and size 9 Horizontal strabismus The horizontal deviation of the eye which the patient cannot overcome Vertical and horizontal lines 10 Vertical strabismus The vertical deviation of the eye which the patient cannot overcome Vertical and horizontal lines 11 Aniseikonia A condition in which the ocular image of an object as seen by one eye differs in size and shape from that seen by the other The left image consists of the characters “o” and the right consists of
