High Definition VideoIn The Real World

by: Don Schultz

Technical Principal

The Boeing Company

Proliferation of High Definition (HD)

• SDTV sales have nearly disappeared• LCD HDTV sales in 2010 expected to exceed 170

million (over 200 million HDTVs total?)• HD programming exceeds 50% of total

broadcasts in some areas– There are HD alternatives for almost every channel– Content quality not always consistent with true HD

• HD Technology becoming nearly ubiquitous• 3D building momentum & UHD on horizon

HD’s Market Hype vs True Value

• Had HDTV in our home for almost 5 years

• Were finding HDTV in more hotels, restaurants, bars, etc. every day (love it!)

• However, market pressure is also pushing the technology into other environments like aircraft where weight, power and space are critical factors and where HD could place a greater demands on limited resources

High Definition (HD) 101

• 3 basic HD formats – 720p, 1080i & 1080p– 480p = 480 vertical lines progressive scan

• Not HD – but the standard DVD format in the US.– 720p = 720 vertical lines progressive scan– 1080i = 1080 vertical lines interlaced– 1080p = 1080 vertical lines progressive scan

• 720p & 1080i are the most common formats for HDTV broadcasting

• 1080p is currently the highest quality format– used on Blu-Ray discs and some cable networks– Not yet commonly used for HDTV broadcasting

HD Aspect Ratio• High definition video formats 720 & 1080

conform to a 16:9 aspect ratio– 1280 pixels horizontal x 720 pixels vertical– 1920 pixels horizontal x 1080 pixels vertical

16:9

HD Pixel Count• 1920x1080 refers to pixel dimensions – not resolution• Total number of pixels per each format are fixed

– 480: 720 x 480 = 345,600 pixels– 720: 1280 x 720 = 921,600 pixels– 1080: 1920 x 1080 = 2,073,600 pixels

16:9 1080720

1280

1920

Pixel Density

Dp = # of pixelsDi = Distance in inches

• Pixel Density Determines Resolution & Is Not Fixed• Varies With Display Size And Is Measured in Pixels Per

Inch (PPI)• PPI = # Diagonal Pixels / Diagonal of Display in Inches

Note: Can use the PythagoreanTheorem to find both

Sample Pixel Densities (Dp/Di = PPI)

• Sample Calculations For 720p– 9 In: 1469 Pixels / 9 Inches = ~ 163 PPI– 11 In: 1469 Pixels / 11 Inches = ~ 134 PPI– 15 In: 1469 Pixels / 15 Inches = ~ 98 PPI– 23 In: 1469 Pixels / 23 Inches = ~ 64 PPI

• Sample Calculations For 1080p– 9 In: 2203 Pixels / 9 Inches = ~ 245 PPI– 11 In: 2203 Pixels / 11 Inches = ~ 200 PPI– 15 In: 2203 Pixels / 15 Inches = ~ 147 PPI– 23 In: 2203 Pixels / 23 Inches = ~ 96 PPI

Human Vision• In Ophthalmology, normal “20/20” visual

acuity is the ability to recognize letters on the Snellen chart when they subtend 5 minutes of arc.

• Under ideal test conditions, a person may be capable of resolving two pixels separated by as little as .5 arc-minutes (~.008 deg) of angle.

• The human eye does even better with lines.

Human Vision (cont.)

Resolving Video Images• The human eye’s ability to resolve detail in an

image (visual acuity) is directly proportional to the size of the elements of the image and inversely proportional to distance from those elements.

• The objective is to find the optimum viewing distance for maximum image resolution without revealing pixel detail

Viewing DistanceS

cre

en

Wid

th (

SW

)

Viewing Distance (VD) = SW x 2 ViewingAngle

Rule of thumb for distance is twice the width of display

Determining Viewing Angle

Example viewing numbers using a 23 inch display:• Screen width (sw) = ~19.5 inches• Viewing distance (vd) = ~39 inches• Viewing angle = ~28 degrees

• Compare Viewing Distance With Graphic Display Tool – Next Slide

Equivalent View – Display Size vs Distance

Video Quality in the Real World

Real world image quality is highly subjective and depends upon many factors including:

– Pixel Count or Dimensions (HD or SD)– Pixel Density– Dot Pitch of Display– Gate to gate display response time– Quality of Processing & Filters (codecs, deblocking, deinterlace, etc)– Displays Spatial & Spectral Resolution– Contrast (fragile)– Color calibration– Brightness (Luminance)– Visual Acuity of Viewer– Ambient Light– Viewing distance– Resolution & Quality of Original Video

HD on Smaller Displays?• This is a key question with no easy answer• Evaluating the quality of HD video on smaller

displays is difficult, subjective and leads to more questions for some…– In what HD format is the visible quality lost on smaller

displays?– Is most of the HD quality lost on highly compressed,

low bit rate video?– Is the trade-off between the quantity of SD titles on

the server and a marginal improvement in quality from HD content worthwhile?

– If there is no perceived visual benefit, is the marketing value of HD enough?

HD Video Demonstration & Q&AObjective: compare HD formats and bit rates side by side• Videos encoded with SMPTE VC-1

– Encoded in 420p, 720p and 1080p formats at 24fps– Continuous Bit Rate – 2 Pass - Main Profile– Available in bit rates from 500kbps to 6mbps

• 3 Display Sizes – 11 inch, 15 inch and 23 inch– 11 inch – 1280x768 LCD (industrial display)– 15 inch – 1920x1200 LCD (Dell laptop)– 23 inch – 1920x1200 LCD (Sony SDM-P234)

• Note: Video quality is EXTREMELY subjective and affected by many factors including viewing conditions.

– Bottom Line…You’re The Judge!