A Framework of Perceptual Quality Assessment on LCD-TV

A Framework of Perceptual Quality Assessment on LCD-TV

A Framework of Perceptual Quality
Assessment on LCD-TV
Journal of Displays
Vol. 28, No. 1, 2008
Wen-Hung Kuo, Po-Hung Lin, and Sheue-Ling Hwang
Presented by Euiwon Nam
School of Electrical Engineering and Computer Science
Kyungpook National Univ.
Abstract
 Evaluation framework
– Perceptual quality on liquid crystal display-television (LCD-TV)
• Analytical hierarchy process(AHP)
• Relationship between subjective assessment and physical measurement
• Providing useful information for improvement of industry
− Important factors for quality of LCD-TV
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Introduction
 Video display unit(VDU)
– Cathode ray tube(CRT)
– Liquid crystal display(LCD) monitors
• Smaller, lighter, lower power
– Plasma display panel (PDP)
– Digital light processing (DLP)
– liquid crystal on silicon (LCoS)
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 Image quality assessment of television
– Nishizawa
• Comparison of picture quality between CRT-TVs and LCD-TVs
− Contrast ratio, viewing angle, response speed, and color reproduction
– Heynderickx and Langendijk
• Comparison of image with PDP, LCD, CRT, and LCoS Projection
− Color rendering, brightness, contrast, display function, ambient illumination,
sharpness, and artifact
– Rajae-Joordens and heynderickx
• Depth impression and overall image quality for 2D-TV
− Resolution, sharpness, contrast, and luminance
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 Image quality assessment of human perception
– Display quality measurement
• User’s point of view
– Besuijen and Spenkelink
• Evaluation of essential factor in display quality measurement
– Bech
• Development of RaPID(Rapid Perceptual Image Description)
– Nyman
• Hybrid, qualitative/quantitative measurement
– Rajae-Joordens and Engel
• Perceived difference in field of visual perception experiment
• Applied to translate paired comparison data
− Heynderickx and Langendijk
» PDP, LCD, CRT, and LCoS projection
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– Satty
• Analytical hierarchy process(AHP) for subjective measurement
− One of the popular and powerful methods for decision-making
– Analytical hierarchy process(AHP)
• Development of intelligent material handling equipment selection system
− Chan
• Selection of most appropriate tool to support knowledge management
− Ngai and Chan
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 Proposed method
– Evaluation framework based on investigation of five LCD-TVs
• Important factors for affection of video or images quality
• Comparison between subjective assessment and physical measurement
− Improvement of quality of LCD-TVs
− Suitable LCD-TVs for consumer as user
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Evaluation framework
 Three stage for evaluation frame
– Obtaining ordinary users’ feelings or knowledge
• Requirements of high quality LCD-TV
– Analytical hierarchy process(AHP)
• subjective assessment of important factors
– Physical measurements by instruments
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– Framework of proposed
Fig. 1. Evaluation framework of LCD-TV perceptual quality assessment.
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Evaluation experiment
 Composition of experiment
– Subjects; 23 – 30 age(mean 27.2 and SD 2.28)
– Experimental LCD-TVs and test patterns
• BenQ DV3250, Polyview NLC30C2, Sampo LM-32HX, Sumsung LTP326W, and Sharp LC- 30HV6U
Fig. 2. Five LCD-TVs prepared in the experiment.
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• Test patterns
− Two still images and one motion picture
• Eight factors
Table 1. Eight factors considered in experiment
(a)
(b)
(c)
Fig. 3. (a) and (b) are two still images from ISO
12640; (c) is motion picture from movie ‘‘Mulan’’.
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– Instrumental measurements
• Notebook and displayed on LCD-TVs
Fig. 4. Set-up for measuring static image quality.
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• Test pattern
− Contrast and luminance
(a)
(b)
Fig. 5. (a)Test pattern for contrast and (b) is test pattern for luminance.
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• Calculating signal change of LCD-TVs from oscilloscope
(a)
(b)
Fig. 6. Set-up for measuring moving image quality.
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– Evaluation process
• General feeling or requirement from ordinary user’s point of view
− Suitable adjectives for high quality LCD-TV
− Specifications or functions for high quality LCD-TV.
» Color, response, viewing component
• Subjective assessment based on AHP method
− Evaluation of image quality of LCD-TV
− Explanation of eight factors
» Score for importance of factors
Table 4. Rotated component matrix with Varimax rotation method
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− Construction of four-level AHP model
Fig. 7. Set-up for measuring moving image quality.
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• physical measurements of some measurable factors
− Comparison for each factor
» Subjective assessment (second stage)
» physical measurement (third stage)
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Results and discussion
 The results through questionnaire
– Results of first stage
Table 2. Rank of factors from the questionnaire
Table 3. Rank of adjectives from the questionnaire
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 The results from AHP
– Judging importance of factor
• Weight of factor
m
Wn  m  (cin  ein )
(1)
i 1
where n is importance of factor.
cin and ein are local priorities of corresponding
elements of factor n in second and third levels obtained
from subject i (i  1,. . . , m).
− Example for weight of luminance based on image 1
Wlum 
10
10
 (c
i 1
i ,lum
 ei ,lum )
(2)
where ci ,lum is local priority of color component in second level.
ei ,lum is local priority of luminance in third level obtained from subject i
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» Result of example
Table 5. Local priority of luminance in still image 1
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– Result for eight factor
• Still image and motion picture
Table 6. Weight of eight factors in the still images
Table 7. weight of eight factors in the motion picture
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– Judging importance of factor
• Weight of factor on LCD-TV
m
W  m  cin  ein  link
k
n
(3)
i 1
where link is local priority of factor n on LCD-TV (k ) in fourth level obtained
from subject i (i  1,. . . , m).
Table 8. Weight of eight factors on each LCD-TV
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– Obtaining rank of these LCD-TVs
• Global weight
 m
W    m  cin  ein  link
 i 1
n 
k



(4)
where link is local priority of factor n on LCD-TV (k ) in fourth level obtained
from subject i (i  1,. . . , m).
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 ANOVA of different scenarios
– Investigation of subjective assessment of three scenarios
 Comparison between questionnaire’s and AHP’s results
– Three common important factors
• Contrast, luminance, and response time
Table 9. ANOVA table of different scenarios
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 Comparison between physical measurement and AHP result
Table 10. Comparison of measurements and weights of AHP
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Conclusion
 Evaluation framework
– Perceptual quality assessment
• Common user’s feeling or knowledge from the questionnaire
• Subjective assessments from AHP
• Physical measurements by instruments
– Found Importance factor for quality of LCD-TV
• Most important quality factors
− Contrast, luminance, and response time
• Most differentiable factor
− Sharpness
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