Considerations for Video Scene Selection Margaret H. Pinson NTIA/ITS
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Transcript of Considerations for Video Scene Selection Margaret H. Pinson NTIA/ITS
Scene Complexity
Should evenly span a wide range of coding difficulty Major impact to quality
Why use an objective metric? Uneven distribution in available
scenes More easy-to-code scenes available
since they are easy-to-film
Complexity Algorithm #1
ITU-T P.910 section 6.3 “Two Criteria for Video Test Scene
Selection”, ITU-T Study Group 12, 1994 Spatial Information
SI = maxtime {stdspace [Sobel (Fn)]}
Temporal Information TI = maxtime {stdspace [Fn-Fn-1]}
Complexity Algorithm #2
“Perceptual Effects of Noise in Digitial Video Compression,” SMPTE 1998
o = log10 {meantime [SIn * TIn]} SIn = rmsspace [Sobel (Fn)] TIn = rmsspace [Fn-Fn-1]
Scene Complexity Criteria
One very difficult to code scene One very easy to code scene One high spatial detail scene Evenly span full range of complexity
Some low Some medium Some high
Wide Variety of Scene Content
Pro Relieves viewer boredom Prevents viewer overtraining Analysis results more general
Con More scene content required Less HRCs for given sized full-matrix
test Could use partial block design
Wider Quality Spread at Lower Bit Rates
2 6 10 14 18 OriginalBad
Poor
Fair
Good
Excellent
Bit-Rate (Mbps)
MO
S
Scene Content Selection Criteria
Avoid repetition of scene type e.g., only one basketball scene
Use each scene as few times as possible to allow desired HRC comparisons e.g., pair each scene with 4 HRCs
Divide experiment into 2 or more full matrixes (block design)
Scene Cuts Masking effect
Hides impairments Few frames before, ≈0.25 sec after
Philosophy No scene cuts Television ≈3 to 5 sec between scene cuts Opening credits rapid scene cuts
GOP structure interactions MPEG-2 GOP 15F for 30fps H.264 / MPEG-4 part 10 GOP 33F for 30fps
Scene Cuts Criteria
One scene with rapid scene cuts ≈½ source no scene cuts ≈½ source with scene cuts Avoid scene cuts at very beginning
or end of edited scene
Camera or Original Quality High quality camera recording
Many people don’t have Medium quality camera recording
Mild coding noise, mild analog noise Impacts HRC response
Low quality camera recording VQEG does not use Commonly available to end users
Impact of Scene Content
Despite viewer instructions “Please do not base your opinion on
the content of the scene or the quality of the acting.”
Ratings include opinion of content “Susie effect”
popular scene
Impact of Scene Content “Aspen” HDTV 50Mbps MOS=4.7
excellent (17 viewers) good (8 viewers) fair (0 viewer)
“ControlledBurn” 25 Mbps HDTV MOS=4.5
excellent (15 viewers) good (6 viewers) fair (3 viewer) coding artifacts
“TouchdownDay” 100 Mbps HDTV MOS=4.0
excellent (4 viewers) good (17 viewers) fair (3 viewers) professional cameraman, no scene cuts TouchdownDay
ControlledBurn
Aspen
Original Scene Content & Quality Criteria No objectionable or controversial
content No politics, violence, scantily clad people
Avoid scenes with technical issues Strong judder, awkward scene cuts, poor
focus, motion blur HDTV test – viewers more discriminating CIF test – viewers more tolerant
Include Animation
Coder/decoder response very different H.264 higher quality MPEG-2 lower quality
Animation overlay increasingly common
Scrolling text and edge noise Preferably, use at least one scene with
animation or animation overlay
Unusual Scene Characteristics for Coding Difficulty & Viewer Perception
Fine detail Gravel, grass, hair, rug texture,
pinstripes Sensitive to blurring, but viewers may
not notice or care Sharp black/white edges Blurred background, foreground in
focus Night scene or dim lighting
At least one
Unusual Scene Characteristics for Coding Difficulty & Viewer Perception
Ramped color with graduated change of color (e.g., sunset)
Water, fire & smoke contribute unusual shapes and shifting patterns
Picture jiggles or bounces significantly Hand-held camera
Flashing lights or other very fast events Emergency lights, camera flash, falling
snow, breaking glass
Unusual Scene Characteristics for Coding Difficulty & Viewer Perception
High motion E.g., object moves 20+ pixels per
frame at VGA resolution Action is in a small portion of the
total picture Attention focus
Colorful scene Important
Unusual Scene Characteristics for Coding Difficulty & Viewer Perception
Small amounts of analog noise Multiple objects moving in a
random, unpredictable manner
Include Close-up of People Popular Skin tones Knowledge of how people ought to
appear & move Internal reference
Internal Reference No Internal Reference
Close-up People Criteria
Filming Privacy issues Releases
Faces large enough to be easily seen Several scenes with close-up people
Close-up Crowd Scene
Contrast and Brightness One scene with low contrast
Soft edges One scene with high contrast
Hard edges One scene with low brightness
Dim One scene with high brightness
Mostly white
Obtaining Content
TV & movie content strictly controlled Purchase for own use
Typically cannot redistribute Hire someone to make content for you Shoot it yourself!
Royalty-free distribution More flexible usage No time expiration