Matching Visual Elements
CS4340 Digital Special Effects
Leow Wee Kheng & Terence Sim
Department of Computer Science
School of Computing
National University of Singapore
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Introduction
Introduction
What’s wrong with this special effect?
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Introduction
To blend real/CG visual elements seamlessly, need to match these:
Scale
Visual elements should have the same scale.
Apparent size is related to scale and distance from camera.
Can be handled during live shooting and compositing.
Camera View
Visual elements should be viewed from the same angle.
Match camera’s internal parameters, position, orientation.
If camera moves, then need to perform matchmoving.
Object Motion
Visual elements should interact seamlessly.
Need to match objects’ motion.
Need to perform object tracking of real objects.
Poor example: Looney Tune 2
Good example: The Lord of the Ring: The Two Towers
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Introduction
Illumination
Visual elements should be illuminated by the same light.
Visual elements should cast similar shadows.
Match light source’s type, intensity, position, orientation.
If light moves (e.g., car’s head light), need to match light’s motion.
Color
Visual elements should have matching color tone.
Can be handled as part of illumination matching.
Can also be handled by color grading.
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Matching Scale
Matching Scale
Scale matching is used
to match size of CG and real objects,
to give the illusion of difference in size.
Example: Jurassic Park (1993): T-rex is larger than cars.
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Matching Scale
King Kong (2005): King Kong is much larger than human.
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Matching Scale
The Lord of the Rings: Different races have difference sizes.
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Matching Scale
Many techniques are available:
big rigs
scale double
scale compositing
forced perspective
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Matching Scale
Big Rigs
Put stunt person on stilts.
Dress them up with over-sized costume, false hands, etc.
Good for interacting with real actors of different size.
Example: From [3]
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Matching Scale
From [3]
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Matching Scale
Scale Doubles
Get very short or tall actors as doubles.
Dress them up with face masks and wigs.
Good when facial features are not clearly seen.
Example: From [3]
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Matching Scale
Scale Compositing
Shoot two actors at different scales.
Then, composite them into one footage.
Good when there is no intricate interations between actors.
Example: From [3]
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Matching Scale
Example: From [3]
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Matching Scale
Forced Perspective
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Matching Scale
Forced Perspective
Put actor of smaller height further from camera.
Good when there is no intricate interations between actors.
Example: From [3]
Past students’s work: Bunny Ears, Ricola
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Matching Scale
Forced Perspective with Moving Camera
Forced perspective is easy with stationary camera.
With moving camera, need to move camera and set to get consistent
perspective.
Demo: Forced perspective [3]
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Matching Illumination
Matching Illumination
Illumination matching
Match virtual light source to real light source.
Match light source’s type, intensity, position, orientation.
Illuminate CG objects in the same way as real objects.
Produce virtual shadows consistent with real shadows.
If light moves (e.g., car’s head light), need to match light’s motion.
If camera moves, need to match camera’s motion.
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Matching Illumination
Basic ideas:
Place reference object in scene.
Shoot live footage with reference object.
Use images of reference object as guide to configure virtual lights.
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Matching Illumination
Demo: Matching illumination [3]
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Color Grading
Color Grading
Color is a powerful tool for conveying mood [1, 2]:
hot, unbearable
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calm, peaceful
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Color Grading
bright, lively
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dark, gloomy
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Color Grading
Can depict different mood by changing color/tone of image:
bright sunny day
dark gloomy day
So, color manipulation is very important.
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Color Grading
Digital color grading
Use digital hardware/software tool to enhance images.
Can change intensity, color, contrast.
Can change highlight part of image, change shadow.
Digital color grading is used to
provide consistency across multiple live footages,
match intensity and color of live footages and CG elements,
depict emotional mood.
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Color Grading
Example: From [3]: Enhance color saturation.
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Color Grading
Example: From [3]: Depict fairy-like quality.
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Color Grading
Example: From [3]: Depict ancient/historical look.
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Color Grading
Example: From [3]: Depict warm feeling.
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Color Grading
Example: From Hunter Hunted (2007): Depict eerie look of Matrix.
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Color Grading
Example: From [3]: Highlight local region.
Demo [3]
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Summary
Summary
To blend real and CG visual elements seamlessly, need to
match scale
matchmove (match camera motion)
track object motion
match illumination
match color
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References
References
Colors and Moods, iit.bloomu.edu/vthc/design/psychology.htm.
Color 101, www.keidel.com/resource/wellness/color101.htm.
The Lord of the Rings DVD, The Appendices, Part 2: From Vision to
Reality.
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