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

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 WTD

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 WTD

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 WTD

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

“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 WTD

4:3 Display “pixel” size 4 (720) Horizontal pixel separation = 0.51 mm Vertical line separation = 0.48 mm 18” 3 (576) The “eye” discernability is possibly 0.24 mm @ 6H 4 (720) Horizontal pixel separation = 0.76 mm Vertical line separation = 0.71 mm 3 (576) 27” The “eye” discernability is possibly 0.36 mm @ 6H 17-Jan-19 WTD

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 = 0 .48 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 mm @ 4H 17-Jan-19 WTD

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 Vertical line separation = 1.4 mm = 1.4 mm The “eye”discernability for a 10ft display is possibly 1 mm @ 4H 17-Jan-19 WTD

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 WTD

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 WTD

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 WTD

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 WTD

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