Transcript The EYE and the Television Display

The EYE and the Television
Display
A brief consideration of the eye’s viewing potential
and the relationship to a Television display is given.
Discussion is encouraged on this complex subject
which can only have a subjectively based
conclusion.
Compiled by Wayne Dickson
SMIREE MIEAust. CPEng. Member SMPTE
in consultation with Bryan Powell of the ABC
27-May-16
13 October 98
WTD
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The Normal EYE
• What is “20/20 Vision” ?
– Being able to, at a distance of 20 feet, read a
character, eg the letter E, which is meant to be read
at a distance of 20 feet.
– The size of the letter E for example which can be
read by the eye with 20/20 vision is :
1
1
1
1
1
5 minutes of arc
1
5
• 20/15 vision is better than 20/30 vision.
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The size of the characters
to test 20/20 vision ?
• 1 minute equals 1/60 of a degree
• This is the “normal” minimum discernible resolution for a human eye
when tested for character recognition.
O
D
20 feet
O = 1 minute
D = 2 x 20 feet x Tan (O/2)
= 0.07 inches ( 1.8mm)
Hence the letter E will be 9 mm x 9 mm if intended to be read by
a person with 20/20 vision at a distance of 20 feet or 6 metres.
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Maximum resolving power
• The eye under some conditions may provide :
– “Vernier Acuity” of 8 seconds of arc.
8 sec.
Eg. Offset of two lines placed end to end.
– “Detection” can go down to 1 second, maybe 0.5 second
Eg. single power lines in the sky.
• With more complex patterns like a matrix of pixels in a
colour television display, a probable best resolving
power of around 30 seconds is thought to be typical.
– Note that the eye can discriminate down to 1 % in intensity between
overlapping light sources.
– The eye has a greater resolution for vertical separated lines compared to
horizontal separated lines.
Hence approx. 1mm differences between “objects” maybe detectable,
at a viewing distance 6 metres from a display, by a typical eye.
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Maximum resolving power
related to a Display size
• With a viewing distance of 6 H (6 x height of picture) for SDTV
and 4H for HDTV, and a typical best resolving power of the eye
for a complex pattern of pixels of 30 sec. of arc, the minimum
discernible object separation is :
Display
Viewing
Minimum discernible
Display
height
Distance
object separation
diagonal dim.
76 mm
0.5 m
5”
0.07 mm
183 mm
1.1 m
12”
0.16 mm The minimum
274 mm
1.6 m
18”
0.24 mm pixel separation
@ 6H
a television
335 mm
2m
22”
0.29 mm on
display is currently
412 mm
2.5 m
27”
0.36 mm 0.21 mm for
“Professional”
488 mm
2.9 m
32”
0.43 mm aMonitor
0.35 mm for
640 mm
2.6 m
42” (16:9)
0.38 mm to
a “consumer”
7.3 m @ 4H 1.1 mm display.
10ft (16:9) 1830 mm
14.6 m
20ft (16:9) 3658 mm
2.1 mm
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“Pixel” separation in a display
4 (P)
D
16 (P)
D
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3 (L)
Horizontal pixel separation
= 4*D/(P*(4^2 +3^2)^0.5)
= 4*D/(P*5)
Vertical line separation
= 3*D/(L*5)
Where P = horizontal Pixels & L = vertical Lines
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Horizontal pixel separation
= 16*D/(P*(16^2 +9^2)^0.5)
=16*D/(P*(337)^0.5)
Vertical line separation
=9*D/(L*(337)^0.5)
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4:3 Display
“pixel” size
4 (720)
18”
Horizontal pixel separation
= 0.51 mm
Vertical line separation
= 0.48 mm
The “eye” discernability is
possibly 0.24 mm @ 6H
3 (576)
4 (720)
27”
Horizontal pixel separation
= 0.76 mm
Vertical line separation
3 (576) = 0.71 mm
The “eye” discernability is
possibly 0.36 mm @ 6H
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16:9 Display
“pixel” size
16 (720)
42”
9 (576)
Horizontal pixel separation
= 1.2 mm
Vertical line separation
= 1.1 mm
16 (1920)
42”
Horizontal pixel separation
= 0 .48 mm
9 (1080)
Vertical line separation
= 0.48 mm
For robustness, variable pitch is sometimes used.
The “eye” discernability for a 42” display is possibly 0.4 mm @ 4H
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Large 16:9 Display
“pixel” size
16 (1920)
10 foot
9 (1080)
Note pixel count is :
2,073.600 pixels and
“dot” count is :
6,220,800 dots.
Horizontal pixel separation
= 1.4 mm
Vertical line separation
= 1.4 mm
The “eye”discernability for a 10ft display is possibly 1 mm @ 4H
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Pixel separation
versus
Picture resolution
Horizontal
Pitch of the “Resolution” lines
(some examples)
Mask
pattern
B
R
G
Pixel
A
G
R
R
B
Pixel
B
R GB
B
G
Pixel
C
“Dot”
Pixel separation
R G B or R G B R G B R G B
or R G B
R GB
Pixel
A
Pixel
B
Pixel separation
Pixel
C
Pixel
A
Pixel
B
Pixel
C
“Trinitron”
or Plasma
“Slot”
Pixel separation
That is 1920 pixels horizontally gives 960 lines resolution
and 720 pixels horizontally gives 360 lines resolution
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Pixel separation
versus
Picture resolution
Vertical
Pitch of the “Resolution” lines
(some examples)
Pixel
A
Pixel
B
Line & Pixel separation
Pixel
C
R
B
on
on
G
B
R
off
G
or
off R G B
B
R
G
Pixel
A
R GB
on
on
R GB
Pixel
B
Line & Pixel separation
Pixel
C
Note stripes are continuous
for a Trinitron
That is 1080 pixels vertically gives 540 lines resolution
and 576 pixels vertically gives 288 lines resolution
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Other Considerations
• The other dominant factors which may influence
whether the line structures or the increased resolutions
can actually be seen are :
– “Kel factor” associated with interlace scans. (works to decrease the observed resolution both
vertically and horizontally by 0.7 to 0.8)
– Interlace artefacts such as “pairing” in displays (H to V xtalk)
– Room lighting conditions.
– Programme material type.
– Programme production and coding artefacts
– Display structures - dot, line, rectangular, black matrix, tube, plasma etc.
– Display dynamics, persistence, dynamic focus, and shading correction.
– Viewing distance - this analysis is based on 6H for SDTV and 4H for HDTV.
– Variability of the human observer from the typical normal vision for a young observer.
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Concluding analysis
• By analysing the eye’s potential and the display’s
“mechanics” to see if :
–
–
–
–
the number of vertical lines is too low and hence is observable
or the number of vertical lines is too high and is wasted
the displayed horizontal resolution can be seen
or the displayed horizontal resolution is below what could be resolved by
the observer
• Is the “eye” able to see the separation between the
pixels or is the eye only able to detect the separation
between alternate pixels, that is the resolution lines ?
– I suspect the answer is dependent upon the “other considerations”, in
particular the display structure and technology used.
– If the perception of the eye is 30 sec. of arc and if the variation between
adjacent pixels can be detected the followings conclusions are reached :
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Conclusions
• The following conclusions can generally be made at a
viewing distance of 6H for SDTV and 4H for HDTV
from the display:
– A SDTV (720 x 576) display’s line structure can
potentially be observed and the resolving power of
the eye is not reached with the displayed horizontal
resolution. ( possibly half the eye’s potential)
– A HDTV (1920 x 1080) display’s line structure is
probably not observable and the resolving power of
the eye is probably matched with the displayed
horizontal resolution.
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