1. 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
13 October 98
17-Jan-19
WTD

2. 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 :
20/15 vision is better than 20/30 vision. 1 1 1
5 minutes of arc 1 1 1 5
17-Jan-19
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3. 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.
17-Jan-19
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4. Maximum resolving power
The eye under some conditions may provide :
“Vernier Acuity” of 8 seconds of arc. 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.
8 sec.
Hence approx. 1mm differences between “objects” maybe detectable,
at a viewing distance 6 metres from a display, by a typical eye.
17-Jan-19
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5. 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
diagonal dim.
Display
height
Viewing
Distance
Minimum discernible
object separation 5”
12”
18”
22”
27”
32”
42” (16:9)
10ft (16:9)
20ft (16:9)
76 mm
183 mm
274 mm
335 mm
412 mm
488 mm
640 mm
1830 mm
3658 mm
0.5 m
1.1 m
1.6 m
2 m
2.5 m
2.9 m
2.6 m
7.3 m
14.6 m
0.07 mm
0.16 mm
0.24 mm
0.29 mm
0.36 mm
0.43 mm
0.38 mm
1.1 mm
2.1 mm
The minimum
pixel separation
on a television
display is currently
0.21 mm for
a “Professional”
Monitor
to 0.35 mm for
a “consumer”
display.
@ 6H
@ 4H
17-Jan-19
WTD

6. “Pixel” separation in a display
Horizontal pixel separation
= 4*D/(P*(4^2 +3^2)^0.5)
= 4*D/(P*5)
Vertical line separation
= 3*D/(L*5) D
3 (L)
Where P = horizontal Pixels & L = vertical Lines
16 (P)
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) D
9 (L)
17-Jan-19
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7. 4:3 Display “pixel” size 4 (720) Horizontal pixel separation = 0.51 mm
Vertical line separation
= mm
18”
3 (576)
The “eye” discernability is
possibly H
4 (720)
Horizontal pixel separation
= mm
Vertical line separation
= mm
3 (576)
27”
The “eye” discernability is
possibly H
17-Jan-19
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8. 16:9 Display “pixel” size 16 (720) Horizontal pixel separation
= 1.2 mm
Vertical line separation
= 1.1 mm
42”
9 (576)
16 (1920)
Horizontal pixel separation
= mm
Vertical line separation
= 0.48 mm
42”
9 (1080)
For robustness, variable pitch is sometimes used.
The “eye” discernability for a 42” display is possibly 0.4 4H
17-Jan-19
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9. Large 16:9 Display “pixel” size
16 (1920)
10 foot
9 (1080)
Note pixel count is :
2, pixels and
“dot” count is :
6,220,800 dots.
Horizontal pixel separation Vertical line separation
= 1.4 mm = 1.4 mm
The “eye”discernability for a 10ft display is possibly 1 4H
17-Jan-19
WTD

10. Pixel separation versus Picture resolution
Horizontal
Pitch of the “Resolution” lines
(some examples)
Mask
pattern R G B R B G R B R G B R G B R G B R G B R G B or or G R B G R G B
Pixel A
Pixel B
Pixel C
Pixel A
Pixel C
Pixel A
Pixel B
Pixel C
Pixel B
“Dot”
“Slot”
“Trinitron”
or Plasma
Pixel separation
Pixel separation
Pixel separation
That is 1920 pixels horizontally gives 960 lines resolution
and 720 pixels horizontally gives 360 lines resolution
17-Jan-19
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11. Pixel separation versus Picture resolution
Vertical
Pitch of the “Resolution” lines
(some examples) on on
Pixel A R B R G B
Pixel A G
Pixel B R B R G B
Pixel B or
off
off G
Line & Pixel separation
Line & Pixel separation
Pixel C R B R G B
Pixel C G on on
Note stripes are continuous
for a Trinitron
That is 1080 pixels vertically gives 540 lines resolution
and 576 pixels vertically gives 288 lines resolution
17-Jan-19
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12. 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.
17-Jan-19
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13. 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 :
17-Jan-19
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14. 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.
17-Jan-19
WTD