1. Chapter 7 Digital Images and Video
Information Technology in Theory
By Pelin Aksoy and Laura DeNardis
Chapter 7 Digital Images and Video

2. Information Technology in Theory
Objectives
Learn how images are digitized
Understand the technical features and mathematical calculations that determine the bit size of a digital image
Understand the process by which digital video is made
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3. Objectives (continued)
Identify the factors that affect the quality of digital images
Learn about popular digital image and video file formats
Understand the technical attributes of different types of display technologies
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4. Information Technology in Theory
Imaging Technologies
Traditional camera
Invented more than a century ago
Captures images with a few simple components:
Lens
Shutter system
Photographic medium such as film
Light from the object is focused by the lens, the quick shutter action exposes the film to light, and the image is permanently captured on film
The film is then developed and printed on photographic paper
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5. Digitizing Images and Video
A digital image is an electronic file made up of a string of 1s and 0s when stored on a medium
When the image file is accessed and shown on a display screen or monitor, it is called a pixelized image
Composed of many elementary units called pixels (short for picture elements), each containing a single unit of color information
A pixelized image is similar to a mosaic
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6. Information Technology in Theory
Mosaic Image
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7. Information Technology in Theory
Pixelized Images
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8. Information Technology in Theory
A Bitmap Image
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9. Information Technology in Theory
Vector Graphics
Images are represented in the form of mathematical expressions
Parameters can include attributes such as orientation, length, width, and color
Takes up less storage space than bitmap images
Can be easily scaled without degradation in quality and resolution
Useful for representing geometric shapes but not effective for photographs
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10. Capturing Color Images Using Digital Cameras
Lens system
Sensor array
Filter system
Memory
Processor
Software
Viewing screen
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11. Capturing Color Images Using Digital Cameras
Lens system is used to focus the image onto a small sensor array called a CCD (charge-coupled device) array
These sensors detect light and produce electricity proportional to the intensity of that light
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12. Information Technology in Theory
The CCD Array
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13. The Additive Color Model
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14. The Additive Color Model
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15. Information Technology in Theory
Spinning Disk Filter
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16. Image Resolved Into Basic Color Components
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17. Color Palette and Corresponding Binary Codes
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18. Information Technology in Theory
Color Gamut
The color gamut is directly related to the number of bits assigned per pixel
The number of bits allocated to each pixel is called the bit depth
Commercial cameras usually have a bit depth of 24, meaning that 224, or roughly 16.7 million, colors can be captured by the camera; “true color”
This number of bits is necessary because our eyes are sensitive enough to detect approximately 10 million colors
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19. Spinning Disk Filter vs. Bayer Filter
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20. Calculating Digital Camera Image Sizes
Calculate the number of megabytes in a color image captured by a digital camera that can produce images with 2272 x 1704 pixels with a bit depth of 24
Calculate the total number of pixels:
Number of pixels = 2272 x 1704 = 3,871,488
Calculate the number of bits:
3,871,488 x 24 = 92,915,712
Convert bits to bytes (8 bits = 1 byte):
92,915,712 bits / 8 = 11,614,464
Convert bytes to megabytes (1MB = 220 bytes = 1,048,576):
11,614,464 bytes / 1,048,576 = 11.07MB
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21. Information Technology in Theory
Scanning Color Images
Scanner
Lens system
Sensor array
Filter system
Processor
Mirrors
High-intensity lamp
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22. Scanning Color Images (continued)
Object to be scanned is placed on a glass plate
The object is illuminated with a high-intensity light
A scanning head that carries the CCD array is positioned on the object and slides over it as scanning takes place
The image is filtered through RGB filters and focused on the CCD array by way of mirrors and lenses
The image is quantized and converted to a binary number, then stored as an electronic file
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23. The CCD Array of a Scanner
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24. CCD Array Positioned on a Scanner
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25. Calculating Scanned Image Sizes
Calculate the number of megabytes produced at the output of a 1200 x 2400 dpi scanner that has scanned an 8.5 x 11-inch photograph in true color
Calculate the total number of pixels:
Number of pixels = (1200 x 8.5) x (2400 x 11) = 269,280,000
Calculate the number of bits (true color corresponds to 24 bits):
269,280,000 x 24 = 6,462,720,000
Convert bits to bytes (8 bits = 1 byte):
6,462,720,000 bits / 8 = 807,840,000
Convert bytes to megabytes (1MB = 220 bytes = 1,048,576):
807,840,000 bytes / 1,048,576 = 770.4MB
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26. Some Facts on Resolution
Two characteristics determine the quality of digital images:
Spatial resolution
Brightness resolution
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27. Information Technology in Theory
Spatial Resolution
Spatial resolution
An indicator of the number of pixels per unit length
The more pixels per unit length, the higher the spatial resolution
The higher the spatial resolution, the better the image quality
Affected by image size, viewing distance
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28. Images with Different Spatial Resolutions
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29. Brightness Resolution
Related to bit depth and thus the number of colors present in the image
Low brightness resolution = fewer colors
Changing the brightness resolution changes the number of colors visible in the image
Human eye can discern about 24 bits worth of information
Dependent upon the device used to capture the image
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30. Information Technology in Theory
Monochrome Image
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31. Images with Different Brightness Resolutions
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32. Information Technology in Theory
Digital Video
Motion is emulated by showing images in rapid succession
Visual persistence causes us to see an image for a split second after closing our eyes
Human eyes can process approximately 20 images per second before losing the ability to distinguish the transition of one image to another
Motion picture industry standard uses 24 frames per second (fps) to create a continuous motion effect
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33. Digital Video (continued)
A stick figure drawn in different positions can be brought to life by flipping the pages in rapid succession
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34. Digital Image and Video Formats
Digital images and videos could not be captured, stored, and disseminated without the existence of standard formats for compression
These formats provide the sets of rules, or protocols, required to compress and view images on display devices such as televisions, computer screens, cellular phones, and PDAs
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35. Information Technology in Theory
Image Formats
JPEG: Joint Photographic Experts Group
GIF: Graphics Interchange Format
PNG: Portable Network Graphics
BMP: Bitmap Picture
TIFF: Tagged Image File Format
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36. Information Technology in Theory
Video Formats
MPEG: Moving Pictures Experts Group
AVI: Audio Video Interleaved
WMV: Windows Media Video
MOV: Apple (Quicktime)
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37. Information Technology in Theory
Display Technologies
CRT: Cathode Ray Tube
LCD: Liquid Crystal Display
LED: Light Emitting Diode
Plasma Display
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38. Information Technology in Theory
CRT Displays
CRT
Some computer monitors
Traditional television sets
Cathode ray tube emits three electron beams
Strength and direction of travel is controlled electromagnetically by a beam deflection mechanism
Follows a raster scan format
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39. Components of a CRT Display
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40. Information Technology in Theory
LCD Displays
LCD displays
Laptop computers
Digital camcorders
Gaming devices
Cellular phone
Use liquid crystal materials, whose properties can be varied by electrical signals
An LCD system contains two glass plates that sandwich a liquid with tiny crystals filled in small cells, two polarizing filters on each side of the glass plates, a color filter, and backlighting for illumination from one face of the plates
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41. Components of an LCD Display
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42. Information Technology in Theory
LED Displays
LED displays
Present both still and time-varying digital images
Large billboards, concert hall marquees, and sports events
An array of tiny light emitting diodes, similar to small bulbs, which emit light of a certain color
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43. Components of an LED Display
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44. Information Technology in Theory
Plasma Displays
Use an ionized gas that is trapped inside cells between two glass plates
Each cell acts like a miniature fluorescent bulb
The intensity of light emitted by each cell is controlled with electrical signals, and various phosphors that glow as red, green, and blue painted on one of the glass plates as light from the cells impinges on them
The combination of red, green, and blue phosphors forms the color of each pixel in the display
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45. Technical Characteristics of Display Devices
Spatial resolution
Screen size
Pixel/dot pitch
Brightness resolution (bit depth)
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46. Measurement of Screen Size
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47. Information Technology in Theory
Pixel/Dot Pitch
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48. Information Technology in Theory
Projection Systems
Film-based projectors
LCD-based projectors
Digital light processing (DLP) based projectors
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49. Components of a DLP Projector
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50. Information Technology in Theory
Summary
A digital image file is made up of a string of ones and zeros that represent the pixelized image
A pixelized image is made up of rows and columns of pixels, each with a unique color associated with it; a binary code expresses each pixel color
Two characteristics that determine the quality of images are spatial resolution and brightness resolution
Spatial resolution indicates the number of pixels per unit length (such as inches or centimeters) contained in an image
Brightness resolution describes the bit depth, and is the number of different colors inherently present in an image
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51. Information Technology in Theory
Summary (continued)
Digital video is based on the principle of motion emulation
Because the human eye can distinguish at most 20 images per second, the frame rate standard used in the motion picture industry is at least 24 frames per second (fps), which creates the illusion of a perfect continuous-motion effect
Formats such as JPEG, GIF, BMP, PNG, TIFF, MPEG, AVI, WMV, and MOV provide the rules for structuring and compressing files that allow us to share and display images and video
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52. Information Technology in Theory
Summary (continued)
The most common devices for displaying digital images are plasma displays, LCDs, CRT displays, and LED displays
The design features that contribute to the quality of display devices are spatial resolution, screen size, pixel pitch, and brightness resolution (also called bit depth)
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