Digital Images

1
Digital Images

• A CS Introduction

2
What is a computer scientist?

• Computer user?
• Designs computers (hardware)?
• Designs algorithms (software)?

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Computer Vision andComputer Graphics

• Pictures
• Non-pictorial descriptions

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Digital Images

• Pixels
• http//www.library.cornell.edu/preservation/tutori
  al/intro/intro-01.html

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Color Information

• Black and white 1 bit
• Grayscale 2 bits
• http//developer.apple.com/techpubs/mac/ACI/ACI-48
  .html

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Color 8 bits

• RGB
• Red
• Green
• Blue

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HSV, HLS

• Hue, Saturation, Value

• Hue, Light, Saturation

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Additive vs Subtractive Colors
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CIE Chromaticity Diagrams

• 2D
• Human Vision

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File sizes of images

• Assume a 512 x 512 image
• Black and white
• How many bits in the file?
• Color - 8 bits
• How many bits in the file? Bytes?
• Color 24 bits
• How many bits in the file? Bytes?

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Time to download an image

• 24 bit color image
• 0.75 MB image file size
• 28K modem 28.8 K bps
• How long to download?
• Video
• 640 x 480 pixels, 30 frames a second
• Problem?

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Image Compression

• Compression Algorithms
• JPEG, a lossy algorithm
• http//www.mic-d.com/java/digitalimaging/jpegcompr
  ession

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Hardware

• Digital Cameras
• http//www.howstuffworks.com/digital-camera5.htm
• What color space?

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CRT Monitors

• http//www.pctechguide.com/06crtmon.htm
• What color space?

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Laptop Screen

• http//www.colorado.edu/physics/2000/laptops/
• Color Space?

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LCD Liquid Crystal Display

• Phosphors?
• http//www.colorado.edu/physics/2000/laptops/calcu
  lator.html

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Printers

• Inkjet
• http//www.kodak.com/US/en/digital/dlc/book2/chapt
  er2/index.shtml
• Color Space?

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What colors can we generate?

• Colors humans can see but cant be displayed on a
  CRT or a printer

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Will the photo from the printer look like the
photo on the screen?

• What extra colors on printer?

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• http//www.extremetech.com/article2/0,3973,92300,0
  0.asp

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How do we see color?

• What property of light conveys color information?

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The backwards retina

• The world is an illusion

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The backwards retinaThe world is an illusion
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Rod Sensitivity

• http//www.photo.net/photo/edscott/vis00010.htm

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Digital versus Analog Images

• Are digital images as high quality as film
  images?
• Resolution?
• Film grain size is larger
• Display devises can be limiting
• Is human vision digital?

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CG and CV

• For both CG and CV, we first need to understand
  digital images
• How to display them
• How to generate them
• How to interpret them
• Now youre ready to become a computer scientist.