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IVY LAB Stereoscopic 3D image database for visual discomfort prediction

Automatic prediction of the degree of visual discomfort for stereoscopic 3D contents has increasingly gained its importance. The stereoscopic 3D image database provided below was generated to evaluate the performance of the proposed method for visual discomfort prediction. In addition to the stereoscopic images, we provide subjective comfort scores obtained by using the Single Stimulus (SS) method, mentioned in ITU-R BT.500-11. The mean opinion scores of visual comfort were used to evaluate the performance of visual discomfort prediction.

 

Stereoscopic 3D images

A total of 120 real scenes were captured using a 3D digital camera with dual lenses (Fujifilm FinePix 3D W3®). In summary, the database consists of various types of images with a resolution of 1920 × 1080 pixels. 62 of them are indoor scenes and the others are outdoor scenes (see Fig. 1). These images contain various types of object (humans, trees, structures, man-made objects, etc.). Twenty images include human objects. The magnitude of maximum crossed disparity of each scene ranges from 0.11 to 5.07 degrees in our experimental condition, corresponding to 0 to 285 pixels.

To download the stereoscopic images, please click here

 

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Fig. 1.  A total of 120 stereoscopic images used in our experiment.

 

Subjective assessment results

For subjective assessment experiments of visual comfort, we used a linearly polarized stereoscopic monitor manufactured by Redrover (true3Di®). It consisted of a half mirror and two 40" LCD displays. A spatial resolution of the monitor was set to 1920 x 1080 pixels. The viewing distance (1500mm) was fixed to about three times the height of the screen. The design of experimental environments was in line with the recommendation of ITU-R BT.500-11. A total of 20 subjects (non-experts) were recruited under approval of KAIST IRB (Institutional Review Board). However, two subjects had abnormal stereopsis according to the stereo fly test. A total of 18 subjects, aged between 20 and 29 years, involved in this subjective assessment. All 18 subjects had normal or corrected vision and a minimum stereopsis of 60 arcsec (in the stereo fly test).

In test sessions, subjects assessed all 120 images that were randomly arranged. Display duration of each image was 10 seconds and the resting time was 5 seconds using a mid-gray image. During the resting time, subjects were instructed to grade the overall level of subjective visual comfort for each image by considering physiological symptoms such as eye strain, general discomfort, headache, focusing difficulty, and nausea. The adjectival categorical method of the Single Stimulus (SS) method of ITU-R BT. 500-11 was used with a five-grading scale of visual comfort (5: very comfortable, 4: comfortable, 3: mildly uncomfortable, 2: uncomfortable, 1: extremely uncomfortable). After collecting all subjective scores, we performed a screening analysis recommended by ITU-R BT.500-11 (see Annex 2 in ITU-R BT.500-11). This screening process allows discarding observers who have produced votes significantly distant from the average scores. One subject was rejected after screening. Consequently, mean opinion score (MOS) for each image was obtained from 17 subjects.

As shown in Fig. 2, the subjective assessment results of visual comfort revealed that subjective scores of 6 images ranged from “extremely uncomfortable” to “uncomfortable”. 16 images induced from “uncomfortable” to “mildly uncomfortable”. 52 images induced from “mildly uncomfortable” to comfortable”. 46 images induced from “comfortable” to “very comfortable”.

To evaluate the reliability of the subjective assessment results, we computed the Cronbach’s alpha that has been commonly used to measure the internal consistency of a psychometric test score. With our subjective scores of visual comfort, the Cronbach’s alpha was computed as 0.98. Note that Cronbach’s alpha of 0.70 is considered acceptable. A correlation analysis was also conducted as an additional means to evaluate the consistency of the subjective assessment results. For the correlation analysis, participants were divided into two independent halves, and then the correlation between MOSs obtained from the two groups was measured by the Spearman rank order correlation coefficient (SROCC) for 100 random trials. This evaluated monotonic relation of MOSs between two groups. As a result, 89% of SROCC was obtained.

To download the subjective assessment results, please click here

 

Fig. 2.  Subjective assessment results for visual comfort of 120 stereoscopic images used in our experiment.

 

The functional parameters ( and ) used in the equation (4) in the paper [1] (Please click here).

 

[1] Y. J. Jung, H. Sohn, S. Lee, H. W. Park, and Y. M. Ro, “Predicting visual discomfort of stereoscopic images using human attention model,” IEEE Trans. Circuits and Systems for Video Technology (CSVT), 2013. (online publication)

Image and Video Systems Lab, Department of Electrical Engineering,
Korea Advanced Institute of Science and Technology (KAIST),
Daejeon, Korea

Contact: Hosik Sohn, sohnhosik@kaist.ac.kr; Yong Ju Jung, yj.jung@kaist.ac.kr;