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

2. TEST SPECIFICATIONS Uncompressed HDTV (1080 50i)
Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
TEST SPECIFICATIONS
4 CONTENTS from SVT (10s)
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
MOBCAL
PARKRUN –
SHIELDS
STOCKHOLM

3. DISPLAYS 1 test per display with different observers (naïve)
Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
DISPLAYS
CRT
Studio Monitor JVC DTV1910CG 19’’
Interlaced scan
Picture height : 20 cm
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. VIDEO RENDERING CHAIN SDI/DVI converter
Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
VIDEO RENDERING CHAIN
SDI/DVI converter
DOREMI HDVI-20d
de-interlace
convert color spaces
top of the art quality conv
Full digital video rendering chain
No lossy scaling from source to display
HD PLAYER
DOREMI V1-UHD
- real-time playback of uncompressed HDTV
SDI :
1920x i
YUV 4:2:2 8bits
DVI-D :
1920x p
RGB 8bits
CRT DISPLAY
LCD DISPLAY

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

6. TEST RESULTS Correlation between CRT and LCD MOS : 0,938
Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
TEST RESULTS
Correlation between CRT and LCD MOS : 0,938

7. Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
TEST RESULTS
HDTV
CONTENT
MOBCAL
PARKRUN
SHIELDS
STOCKHOLM
MOS
(CRT-LCD)
14.56
11.68
15.99
10.28
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.

9. Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
LCD RESPONSE TIME
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.

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

11. Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
HOLD TYPE DISPLAY
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.

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

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

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

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

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

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

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

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

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

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

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

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

24. Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
BLUR WIDTH PERCEPTION
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 :

25. EXPERIMENT : TASK The scrolling of the bars was continuous.
Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
EXPERIMENT : TASK
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.

26. EXPERIMENT : PROTOCOL 7 observers : Protocol :
Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
EXPERIMENT : PROTOCOL
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.

27. RESULTS Mean Blur Width Curve fitting give us the following model :
Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
RESULTS
Mean Blur Width
Curve fitting give us the following model :
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
Results and model for a white stimulus moving with an horizontal movement :

29. Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
PAN’s MODEL
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) )

30. Motion blur : an explanation to subjective quality differencies between CRT & LCD ?
PAN’s MODEL
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

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

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

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

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