Date post: | 27-Dec-2015 |
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Digital Cameras
• Consumer digital cameras have been around since 1995
• What features make a good camera?
• How do we optimize good features with a limited budget?
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Exposure
• How many photons contribute to each pixel?– More is better!
• Exposure is a combination of several factors– Aperature Size
– Shutter speed
– Lens size
– Sensor Sensitivity
– Sensor size (bigger is generally better)
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Lens
• The lens gathers light
• The lens focuses the image
• Sharpess of the image depends on the lens
• Larger lenses gather more light
• Smaller lenses allow for a smaller camera
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Lens Focal Length
• Focal length– Macro
• have short focal lengths
• Allow imaging small objects
– Normal • have intermediate focal lengths
• Most cameras have one
– Telephoto• have large focal lengths
• Allow imaging far away objects
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Optical Zoom
• Changes lens focal length
• More lenses can lead to glare and loss of sharpness
• Large zoom can benefit from image stabilization
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Digital Zoom
• Digital zoom extracts a region
• Similar to cropping
• Use optical zoom if possible
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Shutter Speed
• Controls how long the sensor is exposed
• Short– Need lots of light
– Good for moving objects
• Long– Good for stationary objects
– Need less light
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Aperture
• Controls amount of light entering camera
• Provides field of view– Small aperture
• acts like a pinhole
• Entire image in focus
– Large aperture• Narrow range in focus
• Provides emphasis on foreground objects
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Viewfinder
• Allows us to identify the content of the image
• Optical– Through the lens
– Off axis
• Electronic– Small
– Full-size
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Sensor
• Acquires the image
• Electronic equivalent of film
• CCD– Charge-coupled device
• CMOS– Complementary Metal
Oxide Semiconductor
http://www.shortcourses.com/how/sensors/ccdwaffer.jpg
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Analog to Digital Conversion
• Electronic cameras convert energy from an analog signal to digital– Discrete in time
– Discrete in amplitude
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Quantum Noise
• Based on the number of photons
• Variation is the square root of the number of photons
http://telin.rug.ac.be/~frooms/research/steer/www/
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Other Noise
• Electronic– Heat
– Cheap Electronics
– Design
• Senosor– Bad pixels
• Hot
• Cold
– Bad line
• See http://www.imatest.com/docs/tour_lightfall.html
http://www.starizona.com/ccd/software/biasframe.jpg
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Data Storage Media
• Physical device where images are stored
• Tradeoffs– Physical size (smaller is better)
– Speed (faster is better)
– Data size (larger is better)
– Cost per GB (more is better)
– Reliability• How permanent is the storage?
• What is the failure rate?
– Availability• What other devices can use the media?
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Battery Power
• Provides camera with power
• Disposable– Costly in long run
– Low power
• Rechargeable– Lithium
– NiMH
• Important question– How many pictures
can be taken on one charge?
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Camera Settings
• What special features does the camera provide?– Shutter priority
– Aperture priority
– Movies
– Red-eye reduction
– Delayed shutter
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Connectivity
• How does the camera interface with computers?– USB
– Firewire
– Serial
– Removable media
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Carrying Case
• Holds camera and other supplies– Tripod
– Batteries
– Recharger
– Manual
– Extra media
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Hybrid Cameras
• Digital camera that can directly print to polaroid film any desired photos
• Preview of film images before processing• Dual film/digital camera where one can
easily switch between the two modes• A 35 mm cassette that has the same form
factor as a film camera, yet acquires digital images
• Direct digital conversion of film during processing