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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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Field of View

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Vignetting

• A gradual fading of the image away from the center

• Caused by lens optics

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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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Camera Display

• Small Screen

• Review of images

• Camera control

• Viewfinder

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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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CCD vs. CMOS

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Mosaic vs. Foveon

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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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Camera Speed

• Time to read sensor

• Time to write image to media

• Faster is better

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Compression

• JPEG

• JPEG2

• Is the image always compressed?

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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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Noise

• Statisitcal variations in the pixel values

• Noise obscures detail

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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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Flash

• Does camera use a flash?– Internal

– External

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Tripod

• Holds camera

• Useful for – long exposures

– Repeated shots

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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