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Motion blur : an explanation to subjective quality differences between CRT & LCD ? VQEG Boston meeting April 2006 S. Tourancheau, S. Péchard, P. Le Callet,

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Presentation on theme: "Motion blur : an explanation to subjective quality differences between CRT & LCD ? VQEG Boston meeting April 2006 S. Tourancheau, S. Péchard, P. Le Callet,"— Presentation transcript:

1 Motion blur : an explanation to subjective quality differences between CRT & LCD ? VQEG Boston meeting April 2006 S. Tourancheau, S. Péchard, P. Le Callet, M. Carnec, A. Tirel, D. Barba

2 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? - Uncompressed HDTV ( i) - 7 BITRATES H.264 (JM reference encoder) main profile - SAMVIQ Methodology (Random Access, explicit reference & hidden reference) - Room: Rec. ITU BT Observation distance : 3 H MOBCALPARKRUN SHIELDSSTOCKHOLM 4 CONTENTS from SVT (10s) – TEST SPECIFICATIONS

3 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT Studio Monitor JVC DTV1910CG 19’’ Interlaced scan Picture height : 20 cm DISPLAYS LCD Philips (prototype) 37’’ (native resolution 1920x1080) Progressive scan NO POST-PROCESSINGS  1 test per display with different observers (naïve)  15 valid observers for each test

4 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? VIDEO RENDERING CHAIN SDI : 1920x i YUV 4:2:2 8bits DVI-D : 1920x p RGB 8bits HD PLAYER DOREMI V1-UHD - real-time playback of uncompressed HDTV SDI/DVI converter DOREMI HDVI-20d - de-interlace - convert color spaces - top of the art quality conv CRT DISPLAY LCD DISPLAY  Full digital video rendering chain  No lossy scaling from source to display

5 Motion blur : an explanation to subjective quality differencies between CRT & LCD ?

6 TEST RESULTS Correlation between CRT and LCD MOS : 0,938

7 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? HDTV CONTENT MOBCALPARKRUNSHIELDSSTOCKHOLM  MOS (CRT-LCD) TEST RESULTS Mean IC on CRT 5.34 Mean IC on LCD 6.15

8 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? Motion blur is induced by the type of response of LC display which is different from CRT’s one: –Hold type display : LCD emitted light is sustained all the frame period (b) when CRT’s one consists in pulses (a) ; –Response time : LCD response time is long with regards to classic frame rate when CRT’s one can be considered almost instantaneous. MOTION BLUR

9 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? ISO : response time is the sum of rise time (from black to white) and fall time (from white to black). Manufacturers specify this response time or even only the rise time from black to white. But gray-to-gray transitions are very slowest. For the majority of displays sold before 2005, the average rise time (over gray-to-gray transitions) was superior to the frame period which leaded to annoying motion artifacts. LCD RESPONSE TIME

10 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? Results (rise + fall times) : Overdrive (OD) : RESPONSE TIME COMPENSATION without overdrive with overdrive (Xbit Labs, december 2005)

11 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? With overdrive, the rise time is less than the frame period … But even if response time was instantaneous, motion blur artifacts would be present LCD are therefore called « hold type » displays : emitted light is sustained on the screen during all the frame period … => when tracking the eyes anticipate the object motion while the image is sustained. Edges of the object are then spatially integrated on the retina during the whole frame period, resulting in a blur. HOLD TYPE DISPLAY

12 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD t = 0 MOTION BLUR PERCEPTION smooth pursuit eye movement eye image on the retina eye image on the retina

13 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? MOTION BLUR PERCEPTION t = T / 4 image on the retina CRT LCD smooth pursuit eye movement eye

14 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD MOTION BLUR PERCEPTION t = T / 2 smooth pursuit eye movement eye image on the retina eye image on the retina

15 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD MOTION BLUR PERCEPTION t = 3T / 4 smooth pursuit eye movement eye image on the retina eye image on the retina

16 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD MOTION BLUR PERCEPTION t = T smooth pursuit eye movement eye image on the retina eye image on the retina

17 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD MOTION BLUR PERCEPTION t = T + T / 4 smooth pursuit eye movement eye image on the retina eye image on the retina

18 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD MOTION BLUR PERCEPTION t = T + T / 2 smooth pursuit eye movement eye image on the retina eye image on the retina

19 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD MOTION BLUR PERCEPTION t = T + 3T / 4 smooth pursuit eye movement eye image on the retina eye image on the retina

20 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD MOTION BLUR PERCEPTION t = 2T smooth pursuit eye movement eye image on the retina eye image on the retina

21 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD t = 2T + T / 4 smooth pursuit eye movement eye image on the retina eye image on the retina MOTION BLUR PERCEPTION

22 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD MOTION BLUR PERCEPTION t = 2T + T / 2 smooth pursuit eye movement eye image on the retina eye image on the retina

23 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? CRT LCD MOTION BLUR PERCEPTION t = 2T + 3T / 4 smooth pursuit eye movement eye image on the retina eye image on the retina

24 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? We set an experiment in order to measure the blur width of a moving edge, changing its velocity. The stimuli used was a periodic structure of vertical (resp. horizontal) bars moving from left to right (resp. from down to up) on a black background. Displayed and perceived stimuli : BLUR WIDTH PERCEPTION

25 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? The scrolling of the bars was continuous. Using the arrow keys of a keyboard, the observer can increase or decrease, in real-time, the space between the bars. He can operate as many times as he wants, until he considers that the two blurred areas are just merging. When he is satisfied, he validates his measure and then the next presentation is displayed. EXPERIMENT : TASK

26 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? 7 observers : –all of them were familiar with the procedure and have a perfectly corrected sight. Protocol : –1 session consists in a set of 17 presentations, concerning four types of stimuli (vertical/horizontal and white/red) for different velocities, –the sequence is totally random, –each observers repeated the test twice, on a different day –average lenght of a session was between 10 and 15 minutes. EXPERIMENT : PROTOCOL

27 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? Mean Blur Width Curve fitting give us the following model : RESULTS with where : - w is the blur width in pixels - v is the velocity in pel / seconds - T is the frame period - V = vT is the velocity in pel / frames

28 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? Results and model for a white stimulus moving with an horizontal movement : RESULTS AND MODEL

29 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? Pan, H., Feng, X.-F. et Daly, S. (2005). LCD motion blur modeling and analysis. IEEE International Conference on Image Processing, II:21–24. Mathematical model to predict the blur width in function of velocity and in which the temporal response of LCD is a parameter. They studied for examples two types of response, linear and sinusoidal one, the model give the following results : As we can see, the sinusoidal response gives model wich are very close to our results. ( 1.047(vT) ) PAN’s MODEL

30 Motion blur : an explanation to subjective quality differencies between CRT & LCD ? When a ideal instant temporal response (a) of LCD is used, a blur width of 0.8vT is obtained, only 25% motion blur is caused by slow response on a standard LCD panel. Hold-type is responsible for 75% of motion blur. In the same way, reduction methods can be evaluated by modifying the temporal response of LCD : –Black data insertion (b) –Back light flashing (c) –Frame rate doubling method and motion compensated inverse filtering PAN’s MODEL

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