Digital television systems (DTS) Lecture 1: Introduction, Information Human vision and television Photometry Lˇ. Maceková, 2017 Technical Univ. of Kosice Faculty of Electrical Engineering and Informatics

Information Technical Univ. of Kosice Faculty of Electrical Engineering and Informatics Department of Electronics an Multimedia Telecomunication (Katedra elektroniky a multimediálnych telekomunikácií – KEMT) ftp server of the KEMT subjects: https://data.kemt.fei.tuke.sk/ - materials for DTS: https://data.kemt.fei.tuke.sk/DigitalnaTelevizia/Digital_Television_Systems/ Ľudmila Maceková, ludmila.macekova@tuke.sk, Vysokoškolská 4, 1-st floor academic year 2017/18

Plan of lectures Human vision and raster imaging. Digitization. Lightness terminology and Photometry parameters. Colorimetry. Color Spacies. Image and Video Quality criteria. Cameras – principle, components, analogue/digital cameras. Digital projectors and displays. TV-signal – analogue/digital, TV-norms, color standards, video. standards, audio standards, modulations, coding. Video streaming. Digital TV and Video Broadcasting methods. (It can be modified.)

Human vision and television

test 20/20 (normal) vision (?) - at eye doctor 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 = 6.096 m 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).

Viewing Distance and angle (Spatial Domain) Fig. The astronomers rule of thumb (1 degree of arc) [2] ppi ... pixel per inch

Viewing Distance and angle (Spatial Domain) The result: The angle less then 1/60 of spatial degree (ergo 1 minute) is not visible for human eye  spatial constraint - advantage for TV system design

How it relates with TV system design SDTV: aspect ratio 4 : 3 (NTSC, USA)

Horizontal pixel separation = 0.51 mm Vertical line separation 4:3 Display “pixel” size (SDTV PAL, SECAM - Australia, Europe) for different screen diagonal. 4 (720 elements) Horizontal pixel separation = 0.51 mm Vertical line separation = 0.48 mm 18” 3 (576 rows) 4 (720) Horizontal pixel separation = 0.76 mm Vertical line separation = 0.71 mm 3 (576) 27” 1” = 2.54 cm)

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)

Examples for homework: How long is minimal distance (D1) of viewer from the screen of TV receiver, if its diagonal (D2) is 55” and 4/3 -format (SDTV)? What is the ratio D1/D2? How long is minimal distance of viewer from the screen of TV receiver, if its diagonal is 55” and 16/9 – format (HDTV)? What is the ratio D1/D2?

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. 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. [1]

Pixel separation versus Picture resolution [1] 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

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 [1]

Other Considerations [1] 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.

Spatiotemporal Domain) temporal lag of human eye  the advantage for the TV system design: temporal constraint: cca 50 frames per second for perception of fluent motion / imperceptible alternation of frames (in cinematography, 24 frames x 2 per second) - in TV, 25 frames x 2 interlieved fields (Europe) / 30 frames x 2 fields (USA) per second (frame frequency, frame rate, [Hz])

Aspect ratio [2]

[2]

Light Lightness terminology In grayscale imagination: only wavelength ... λ = c . T = c / f [m] c ... light velocity (about 3x108 m/s) f ... frequency or the radiation [Hz] T ... period = 1/f [s] Lightness terminology In grayscale imagination: Brightness - formally as the attribute of a visual sensation according to which an area appears to emit more or less light Intensity - radiant power in a particular direction Radiance - intensity per unit projected area

Lightness terminology In color imagination: also wavelength [nm] – from the spectral range 400 – 700 nm Luminance - radiance weighted by the spectral sensitivity associated with the brightness sensation of vision Illuminance - luminance integrated over a half-sphere Lightness – formally, CIE L* – is the standard approximation to the perceptual response to luminance (in grayscale imag.) tristimulus values – for color sensation and reproduction – their amplitudes are proportional to intensity but their spectral compositions are carefully chosen according to the principles of color science - set of 3 (mostly R, G, B) gamma correction – intensity correction of image signal (voltage, current ) because of nonlinear transfer characteristics of some imaging systems (CRT-screens and displays) – R’, G’, B’ Luma (Y’) is formed as a suitably weighted sum of R’G’B’; it is the basis of luma/color difference coding.

compressed color TV signal transmission, coding store Luma and color difference components – digital difference signals CR, CB (R’-Y’ , B’-Y’ respectively; PB, PR in analogue area) dedicated for: compressed color TV signal transmission, coding store Y = 0.2126 R + 0.7152 G + 0.0722 B U = 0.539 (B - Y) V = 0.635 (R - Y) Colour Difference Signals:

Photometry = the science of the measurement of light, in terms of its perceived brightness to the human eye Human eye is not equally sensitive to all wavelengths of visible light  the formula for TV system design: the composite color signal contains weighted (not equal) intensity R, G, B components Human sensitivity for different wavelength is different in dark conditions (scotopic vision) and in light condition (photopic vision) relative photopic/scotopic sensitivity [Fig. Wikipedia] λ [nm]

Table: SI photometry quantities [Wikipedia]

Contrast. K = LV max / LV min [-] Contrast ... K = LV max / LV min [-] .... Contrast is a measure of this relative variation of luminance. Reflex coefficient ... kR = Φ0 / Φc [-] Transparency coefficient ... kT = ΦT / Φc [-]

References: [1] W. Dickson, SMIREE MIEAust. CPEng.: The EYE and the Television Display. 1998. [2] Ch. Poynton: Digital Video and HDTV, Algorithms and Interfaces. 2003 by Elsevier Science (USA)