Chapter 2 Digital Data
- 2. CHAPTER HIGHLIGHTS • Elements of digital media. • Digital codes. • Digital files. • Digitization process. • Compression for digital media. • Advantages of digital media. • Challenges of digital media. Chapter 2 - Digital Data 2
- 3. CODING DIGITAL INFORMATION • Symbols represent something else. – Organized and understood by a conventional standard. • Data are the givens of experience. – Measurements, facts, observations. • Information is data made useful, interpreted, and applied to produce understanding. Chapter 2 - Digital Data 3
- 4. YOU DECIDE: DATA OR INFORMATION? Age = 30 yrs. Temperature = 30 degrees Distance = 30 mi. Cost = $30 People who are 30 years old, pay $30 to run 30 miles in 30 degree weather for a charity benefit. Chapter 2 - Digital Data 4
- 5. ANALOG vs. DIGITAL DATA • Analog data - varies continuously. • Digital data - consists of separate, discrete units. Chapter 2 - Digital Data 5 1, 2, 3, 4 Hour glass to tell time. Numbers Wind mill motion.
- 6. DIGITAL DATA • Digit = number. • Binary digit (bit) = 0 or 1. • Bits are the symbols to encode digital data. • Digital encoding assigns bits to data items. Chapter 2 - Digital Data 6 Data Binary Representation Letter A 0100 0001 Number 5 0011 0101 More bits in the code, means more distinct items to encode.
- 7. BUILDING DIGITAL CODES • Number of distinct bit combinations that can be produced is given by the formula 2n. – n = number of bits used in the code. • Adding 1 to the power doubles the number of distinct data items that can be encoded. Chapter 2 - Digital Data 7 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 items 4 items 8 items 16 items Complete the table to identify the number of distinct items represented by 2 5, 2 6, 2 7, and 2 8.
- 8. COMMON CODES • ASCII ( 7 bit code) - 128 letters, numbers, & symbols in English language. • ASCII-8 (8 bit code) - 256 letters, numbers, & symbols in English language. • Unicode (16 bit code) - Over 65,000 different characters. • 24-bit color - Displays the full range a human eye can perceive. • 16-bit sound - Plays the full decibel range the human ear can perceive. Chapter 2 - Digital Data 8
- 9. DIGITAL FILES • A container for binary codes. • File formats define how instructions and data are encoded in the file. – Sample formats that define data differently: • Word file format • Acrobat file format • Media player file format Chapter 2 - Digital Data 9
- 10. ALL ABOUT FILES • File size – Measured in units of bytes. • Kilo Bytes, Mega Bytes, Giga Bytes. • File extensions – Series of letters to designate the file format. • .fla, .exe, .rtf, .jpg • File compatibility – Ability to use the file in a different platform of hardware and software. Chapter 2 - Digital Data 10
- 11. FILE TYPES • Program files – Contain executable instructions. • Data files – Can hold text, images, sounds, video, animation. Chapter 2 - Digital Data 11
- 12. DATA FILE COMPATIBILITY • Cross-platform compatible files. – Open and use on any computer hardware and software configuration. • Files that are native or specialized to the application that created the data file. – Require source application to open the file. Chapter 2 - Digital Data 12
- 13. FILE MAINTENANCE • Data loss and destruction impacts multimedia project completion. • Effective file maintenance involves: – Identification – Categorization – Preservation Chapter 2 - Digital Data 13
- 14. DIGITIZATION Chapter 2 - Digital Data 14 ANALOG TO DIGITAL CONVERSION.
- 15. SAMPLING ANALOG DATA • Sampling analyzes a small portion of the analog source and converts it to digital code. Chapter 2 - Digital Data 15
- 16. SAMPLE QUALITY • Factors that influence sample quality – Sample Resolution. • Number of bits used to represent digital sample. • Quantization is process of rounding off the value of a sample to the nearest available digital code. – Sample Rate. • Number of samples taken in a given unit of time (sounds) or space (images). • Spatial resolution describes sample rate in image files. Chapter 2 - Digital Data 16
- 17. YOU DECIDE: SAMPLE RESOLUTION Which image and sound sample will have better quality? Which image uses fewer bits to describe the color sample? Chapter 2 - Digital Data 17 Image Sound 8 bits / sample 8 bits / sample 24 bits / sample 16 bits / sample
- 18. YOU DECIDE: SAMPLE RATE Which image and sound sample will have better quality? Which image has a higher spacial resolution? Chapter 2 - Digital Data 18 Image Sound 72 pixels/inch 11 kHz 300 pixels/inch 16 bits / sample 50ppi 300ppi
- 19. DIGITAL ENCODING • Description-based encoding – A detailed representation of the discrete elements that comprise the media. • Command-based encoding – A set of instructions the computer follows to produce the digital media. Chapter 2 - Digital Data 19
- 20. MEDIA ENCODING COMPARED Chapter 2 - Digital Data 20 Description Command Advantages Represent natural scenes and sounds. File sizes are small. Supports detailed editing. Scaled without distortion. Limitations Large file sizes. Not appropriate for detailed photographs and natural sounds. Lose quality if enlarged. Requires knowledge of music and vector image creation.
- 21. FILE COMPRESSION • Process of re-encoding digital data to reduce file size. • Codec: a program to compress a file into a smaller size and decompress it into a usable form. Chapter 2 - Digital Data 21
- 22. MAJOR TYPES OF COMPRESSION • Lossy – Number of bits is reduced and some data is lost. – Lossy strategies include MP3 and JPEG compression. • Lossless – Efficient encoding reduces file size without loss of original data. – Lossless strategies include RLE and GIF compression. Chapter 2 - Digital Data 22
- 23. YOU DECIDE… Lossy or Lossless • Choose a compression strategy best suited for: – Photograph of sailboat on ocean. – Journal article explaining nanotechnology. – 1812 Overture by New York Philharmonic Orchestra. – Database of student names and addresses. – Video of hot air balloon flying over a cornfield. Chapter 2 - Digital Data 23
- 24. ERROR DETECTION & CORRECTION • Digital bits may be lost during transmission or damaged on storage media. – CDs get scratched. – Communication lines have interference. • Strategies to preserve data vary. – Parity bits help detect an error during transmission. – CDs include redundant data to replace data when an error occurs. Chapter 2 - Digital Data 24
- 25. DIGITAL INFORMATION: ADVANTAGES • Reproduction without generation decay. • Editing and re-editing is much easier than with analog media. • Integration of media using cut, copy, paste is more efficient. • Distribution over Internet - nearly everyone can be reached by anyone else. Chapter 2 - Digital Data 25
- 26. DIGITAL INFORMATION: CHALLENGES • File sizes are large. • Digital media is processor intensive. • Absence of media standards renders data files incompatible. • Some media requires high bandwidth to distribute on networks. • Concern for longevity and future accessibility of digital data. Chapter 2 - Digital Data 26
- 27. WRAP UP • Analog vs. Digital data. • Symbols and binary code. • Data vs. Information. • Files as containers. • Digitization process. • Description- vs. Command-based media. • Compression strategies. • Error detection & correction. • Advantages & Challenges of digital data. Chapter 2 - Digital Data 27
Editor's Notes
- #4: Students should provide examples for each of these concepts.
- #5: Raw data at left, information garnered from that data on the right.
- #6: Which ones are analog and which could be considered digital? Hour Glass – analog Numbers – digital Wind Mill - analog
- #8: 25 = 32 26 = 64 27 = 128 28 = 256
- #10: Have students identify additional common data formats and program formats. What would happen if one tired to open a program file format such as Excel.exe as a data file in Word? Could students read the contents of a file that contains binary instructions in a Word program?
- #13: Have students identify file formats that are cross platform (PDF, JPG, TIFF for example) and Native to an application such as Word, Photoshop, Flash files (.docx, .psd, .fla for example).
- #14: Have students identify techniques to manage files effectively using meaningful file names, organized folders, backup data on routine basis.
- #18: Use this slide to discuss decisions developers must make to balance quality and file size. Higher sample resolutions lead to larger file sizes, but lower sample resolutions lead to lower quality representation of the analog data. Ask students where they expect to find higher levels of quantization and why?
- #19: Use this slide to discuss decisions developers must make to balance quality and file size. Higher sample rates lead to larger file sizes, but lower sample rates lead to lower quality representation of the analog data. Ask students to identify the spatial resolution setting for their digital camera. If they have a camera phone, have them locate the spatial resolution for the images they take on their camera phone.
- #20: Students should identify different forms of description and command based encoding. Bitmapped images = description Vector images = command Sampled sound = description Synthesized sound = command
- #21: Use this table to compare digital data from a photograph or recording of bird songs to understand the benefits of using descriptive encoding. Consider the benefits of creating MIDI sounds or PowerPoint clip media using command based encoding. Discuss the decision process developers must make when they chose the format to capture, edit and save media in each mode.
- #22: Class should identify why compression is necessary with digital media and two reasons why developers should have an understanding of compression. Example Program: Irfanview, which compresses image files.
- #24: Discussion should center on what types of data are best suited for lossy or lossless strategies. Photos and videos can lose data without compromising the content. A article would not be intelligible if some of the text were lost.
- #25: Have students research the error correction overhead on a CD and DVD.
- #26: Consider additional advantages not mentioned here.
- #27: Have students identify a specific example for one of the disadvantages. Examples might be to research the file size of a 40 minute uncompressed digital video, how many processors it takes to render a feature length animation, the bandwidth requirements for full motion video, the problem of preserving data on magnetic tape or disk cartridges.