Imaging Techniques in Digital Cameras

Presented by Jinyun RenJan. 29 2004

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Goals

Understand the basic operation of digital cameras

Tell the differences between digital cameras and film cameras

Study some terminologies related to digital cameras

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Confused Market

Price( Canada $) vs. Megapixels

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200

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<=2.9 3.0-3.9 4.0-4.9 >=5.0

Price(H)Price(L)

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Components

Similar to 35mm film camera Including lens, aperture and shutter

Already included: digital film Digital negative Digital development

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Digital film--Image sensor CCD or CMOS

charge-couple device Complementary Metal Oxide

Semiconductor Usually CCD Made of millions of

photosensitive diodes photosite

Each photosite captures a single pixel in final image

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Black and White Image sensor can only capture brightness Resulting a gray scale image Where are all colors from?

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What is color?

RGB CYM

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Color Filter Array (CFA) between CCD and lens cover each photosite

by one color in terms of certain pattern

Filter out all but the chosen color for that pixel

Obtain an image containing intensity values of basic colors

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Digital Negative--RAW

Data directly from image sensor Without any in-camera process contains the full range of tone and

color information captured by image sensor

Camera related– You can’t change! Final image depends on how you

digitally “develop” it

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Developing --true color

True color comes from interpolation based on neighboring pixels "I'm bright green and the red and blue

pixels around me are also bright so that must mean I'm really a white pixel."

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Developing --true color (cont)

Operation demosaicing algorithm

+ + =

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Resolution

Defined as X pixels times Y pixels of an image 1024X768

Equal to total pixels of CCD

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Resolution example Different

resolution The same

quality Determine

the size of images

Has nothing to do with image quality

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Image Quality On a basis of the same resolution A subjective term

Good quality poor quality

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Why Compression?

24 bits color 3 bytes per pixel File size is huge without compression

1024x768=786,432 2.4M 2592x1944=5,034,960 15M

Requiring to reduce file size in order to convenient operation

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Image compression

Lossless TIFF or RAW Files remain quite large

Lossy JPEG Control file size by choosing compression

levels A process to degrade the image quality

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What is “Megapixels”?

A marketing term to resolution 1-megapixel - 1024x768=786,432 2-megapixel - 1600x1200=1,920,000 3-megapixel - 2048x1536=3,145,728 4-megapixel - 2464x1632=4,021,248 5-megapixel - 2592x1944=5,034,960

Larger megapixel larger image size larger file size more storage

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Digital Pictures Usage Displaying on computer monitor

Resolution: 1600x1200=1,920,000 Print on 6”x4” paper with top quality

Resolution: 1280x960=1,228,800 Email to your friends

Around 600K (after compression) daily use 2 megapixel is enough Don’t burn too much money on

Megapixel!!

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Summary—how to choose

Lens, aperture and shutter are very important

Pay more attention to “digital film”, “digital negative” and “digital development methods”

Don’t get confused by “Megapixel”

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Time is up!

Q&A

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References

http://www.shortcourses.com/choosing/contents.htm

http://www.xilinx.com/esp/dvt/cdv/collateral/digital_camera.pdf

http://www.dpreview.com/learn/glossary/