Subjective Quality Assessment in Stereoscopic Video Based on

Analyzing Parallax and Disparity

Juan Pedro López Velasco, Juan Antonio Rodrigo, David Jiménez and José Manuel Menéndez

Universidad Politécnica de MadridLas Vegas NV, 10th January 2015

Index

• Problem description: Visual discomfort in 3D• Work methodology:

Characterization of individual sequences Description of pairs of sequences Subjective quality assessment

• Results and examples • Future work• Conclusions

Problem description (I)• The differences and variations in 3D Disparity

may cause visual discomfort.• What is disparity in 3D video?

• Disparity may offer an incredible experience.• The eye focus the objects. Accommodation of

the eyes needs enough time to adapt to changes for correct vision of 3D videos.

Problem description (II)

Problem description (III)

• If video sequences are not well controlled, especially in abrupt changes, which need fast converging process in the eye…

What happens??

Problem description (IV)• The eye has not enough time to focus

objects, discomfort, annoyance and, consequently, headache may occur.

• Because convergence in 3D sequences is more complex than when contemplating bidimmensional video.

Problem description (V)• But…

– How do we evaluate the reactions of human eye derived from abrupt changes when contemplating 3D video?

• Answer:

– With subjective assessment showing the spectator pairs of sequences and analyzing the abrupt changes among us.

– Knowing the variations between parallax diagrams is useful for this effect.

Problem description (VI)

Examples of 3D disparity (I)

Examples of 3D disparity (II)

Work methodologyCharacterization of individual video sequences

Sequence 1

Sequence 2

Combination of video pair sequences

Sequence

Motion

Parallax

Distribution

12

High variety of types of transitions

Subjective assessment with pairs of sequences for transition analysis

3

Analysis of when visual discomfort happens4

Characterization of individual video sequences

• Parallax diagrams– Ranges and variance of negative and

positive parallax• Distribution of parallax in the image.• Values of Temporal (TI) and Spatial (SI)

Information (also in 2D tests)– Motion (TI)– Spatial complexity and detail (SI)

Parallax and disparity diagram

Visual distributionof parallax

Parallax Histograms

With the use

of SAD

techniques

Combination of video pair sequences

– Analysis of types of changes or transitions between two 3D sequences.

– Types of sequences transitions:• Combination of sequences with positive and

negative parallax• Combination of sequences with higher or lower

variance of negative/positive parallax• Combination of sequences with objects located

in different / same regions of the image

Subjective assessment

• Battery of tests with 3D high-definition video sequences

• Annoyance 5-notes Scale for evaluating the transition between each pair of videos

MOS Scale

Annoyance derived from transition Quality of Experience

5 Very comfortable Excellent Experience4 Comfortable Good Experience3 Mildly uncomfortable No visual discomfort2 Uncomfortable Visual discomfort1 Extremely uncomfortable High visual discomfort

Device Philips 65PFL9708SResolution 3840 x 2160pBrightness 450 cd/m²

Size 65” WidescreenTechnology LED Ultra HD

3D Passive glasses

Example 1• Transition 12: “Angel” to “Ladder” 40% of the people give a score that manifests visual

discomfort

Example 2

• Transition 14: “Spaceship” to “Astronaut” Negative parallax in right side of first video to

negative/positive combination

Example 3• Transition 16: “Station” to “Itaca3d” This is the worst scored transition in the tests

↑↑Motion↑↑Motion

Hiperstereoscopy!

Example 4

• Transition 2: “Boxers” to “Dance” Negative parallax located in different areas, less

annoyance for observers.

Example 5

• Transition 4: “Hall” to “Laboratory” Both videos with negative parallax in both videos and

window violation → low scores. Window violation!

Conclusions (I)• Motion is a key element of production of

visual discomfort, but it is not the only one. When it is combined with sequences with high negative parallax may generate visual discomfort.

• If the negative parallax in hyperstereoscopy is located in different parts of the sequences in the transition, visual discomfort appears less than when located in same areas.

Conclusions (II)• Fast variation of negative parallax is usually

the main source of visual discomfort, especially when the transition is produced to a content with a completely different disparity diagram.

• Only hyperstereoscopy (i.e. pixels with negative parallax with disparities higher than 5) in the sequence is not enough for detecting visual discomfort, it is the transition what provokes the discomfort.

Future work

• After detecting the main sources of visual discomfort…

Developing recommendations and guidelines for 3D contents creators.

Generating tools for automatic detection of discomfort in 3D videos.

Thanks for your attention!!