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Fundamentals of CS Lecture3 Representing Text and image Dr Dalia Sayed

Fundamentals of CS Lecture3 Representing Text and image Dr Dalia Sayed. Outline. Representing Textual Data * ASCII * UNICODE Representing Images. DECIMAL TO OCTAL CONVERSION Conversion of 125 10 to octal. 8 125. r em a in der. 5 7 1. 8 15. 1. 8. 0. 125 10 = 175 8.

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Fundamentals of CS Lecture3 Representing Text and image Dr Dalia Sayed

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  1. Fundamentals of CSLecture3Representing Text and image Dr Dalia Sayed

  2. Outline • Representing Textual Data * ASCII * UNICODE • Representing Images

  3. DECIMAL TO OCTALCONVERSION • Conversion of 12510 tooctal 8125 remainder 5 7 1 8 15 1 8 0 12510 =1758 22

  4. DECIMAL TO HEXACONVERSION • Conversion of 45010 tohexadecimal 16450 remainder 2 12 1 1628 16 1 0 45010 =1C216 22

  5. CONVERSIONOFRATIONALNUMBERS BINARY Example1: DECIMAL 0.812510 =?2 =0.11012 24 Stop when the fraction becomes 0

  6. FractionPart BINARY Example2: DECIMAL .14579 x 2 0.29158 x 2 0.58316 x 2 1.16632 x 2 0.33264 x 2 0.66528 0.1457910 =?2 x 2 1.33056 etc. =0.001001... • This process is continued until the number of digits have sufficient accuracy. 25

  7. FractionPart OCTAL Example3: DECIMAL

  8. SO, ( Integer part . Fraction part)10 =(?)r =( Integer part conversion. conversion)r Fractionpart Example: 41.687510 =101001.10112 153.51310 =231.4065178

  9. CONVERSIONBETWEENNUMBERSYSTEMS Decimal Octal Binary Hexadecimal

  10. EXAMPLE1:BINARY OCTAL • 23=8 Octal digit = 3 binarydigits 10110001101011.1111000001102 =?8 101 001 11010011 . 111 100 000110 2 6 1 5 3 7 4 0 6 =26153.74068

  11. EXAMPLE2:BINARY HEXA • 24 =16 Hexa digit = 4 binarydigits =10110001101011.111100102 16? 0110 1100 101011. 11110010 2 C 6 B F 2 =2C6B.F216

  12. EXAMPLE 3: OCTAL BINARY 7058 =?2 =1110001012

  13. EXAMPLE 4:HEXA BINARY  10AF16 =?2 1 0 A F 0001 0000 10101111 = 00010000101011112

  14. EXAMPLE 6:OCTAL HEXA 10768 =?16 1 0 7 6 001 000 111 110 E 2 3 =23E16

  15. EXAMPLE 7:HEXA OCTAL 1F0C16 =?8 1 F 0 C 0001 1111 0000 1100 1 7 4 1 4 =174148

  16. IV. Binary Fractions

  17. Decoding the binary representation of 101.101

  18. V. Hexadecimal (base 16) • Binary code is too long in representation. Hex is much shorter. • Converting a binary number to a Hex number is relatively easy • Every 4 bit can convert to a Hex • Problem: we are short of numbers • A-10 B-11 C-12 D-13 E-14 F-15

  19. Lookup table

  20. Example

  21. Reading for this lecture • Computer Science: An Overview Section 1.4 2. External links and sources to help you understand the materials.

  22. How to represent text inside the computer? • “I love computer science” • “I was born on 5 Jan. 1998” • “sqrt (9) = 3” • “لا يؤمن أحدكم حتى يحب لأخيه ما يحب لنفسه”

  23. You are right  • Each character (letter, punctuation, etc.) is assigned a unique bit pattern. • ‘a’ , ‘b’ , ‘c’, etc. • ‘+’, ‘-’ , ‘(‘, ‘)’, ‘%’ , ‘$’ , etc. • ‘1’ , ‘2’ , ‘3’ , ‘4’ , etc. (“5 Ahmed Zewail St.) • But what do we do if every company decided to give its own bit patterns?

  24. You are right again   • ASCII (American Standard Code for Information Interchange) • It is the scheme used to represent characters. • ASCII: Uses patterns of 7-bits to represent most symbols used in written English text • If 8-bits are used, the first bit is always set to 0

  25. ASCII Code • ASCII was first proposed by the American National Standards Institute or ANSI in 1963, and finalized in 1968 as ANSI Standard X3.4. • The purpose of ASCII was to provide a standard to code various symbols ( visible and invisible symbols)

  26. ASCII Table Symbol decimal Binary 7 55 00110111 8 56 00111000 9 57 00111001 : 58 00111010 ; 59 00111011 < 60 00111100 = 61 00111101 > 62 00111110 ? 63 00111111 @ 64 01000000 A 65 01000001 B 66 01000010 C 67 01000011

  27. “Hello.” in ASCII 28

  28. How would I know ? If this is letter H ? Or it is Hexa 48 = Decimal 72 ? They both look the same in memory !! 29

  29. How many characters can ASCII represent? • ASCII code can represent only 128 = 27 characters. • It only represents the English Alphabet plus some control characters. • From (00000000)2 (00)16 • To (01111111)2 (7F)16

  30. Exercise • Use the ASCII table to write the ASCII code for the following: • CS111 • 6=2*3

  31. What do we do with other languages? • ISO developed a number of 8 bit extensions to ASCII, each designed to accommodate a major language group • Each defines a “code page” that uses the undefined space from 128-255 in ASCII, mapping it to various characters. • What is the problem with this approach?

  32. What do we do with other languages? • Unicode is designed to represent the world commonly used languages. • It uses 16 bits or more (or less). • It can encode all characters of live languages. • For compatibility, the first 128 Unicode are the same as the ASCII. • Unicode is a family of encoding methods. There is UTF-8, UTF-16, etc.

  33. https://betterexplained.com/articles/unicode

  34. Exercise • Open a file in notepad • Type “ABC” • Store the file with different encoding each time • ANSI • Unicode (UTF-16 Little Endian) • Unicode Big Endian • UTF-8 • Every time, open it in a hexa editor and see the hexa content.

  35. What happens when I type? • When you type the letter A, the hardware logic built into the keyboard automatically translates that character into the ASCII code 65. • Which is then sent to the computer. • Similarly, when the computer sends the ASCII code 65 to output devices, the output hardware instead draw letter “A” on your screen or your computer.

  36. What happens when I type? Screen W E B Memory RAM Keyboard 42 42 W E B 45 45 57 57 Central Processing Unit

  37. Storage Measures • 1 bit • 1 byte = 8 bits • 1 kb = 210 bytes = 1024 bytes !=1000 • 1 Mb = 1 k k bytes = 210 * 210 bytes • 1 G b = 210 * 210 * 210 bytes • 1 Terab = 210 * 210 * 210 * 210 bytes

  38. Storage Measures • 1 petabyte = 210 * 210 * 210 * 210 * 210 bytes (2 to the 50th power ) • 1 exabyte= 260 • 1 zettabyte = 270 • 1 yottabyte = 280

  39. What do these figures mean? • 1 bit: a binarydecision • 1 byte: a character • 5 Megabytes: The complete works of Shakespeare • 2 Gigabytes: 20 meters of shelved books • 10 Terabytes: The printed collection of the US Library of Congress • 200 Petabytes: All printed material in the whole word. • 5 Exabytes: All words ever spoken by human beings

  40. How can we represent Images? • ?? https://mostafanageeb.com/ https://www.youtube.com/watch?v=OHZyrFlpMVE

  41. How can we represent Images? • We can break it into pixels • The simplest form is black/white • We can represent a pixel by one bit

  42. 2. Image representation • An image can be divided into many tiny squares, called pixels. • Each pixel has a particular colour. • The quality of the picture depends on two factors: • the density of pixels. • The length of the word representing colours. • The resolution of an image is the pixels density. • The higher the resolution the more information the image contains. • 600 x 800 is better than 400 x 600

  43. 2. Image representation • Black and white images • Gray images • Colored images • Bitmap images • Vector images

  44. B&W - Gray – Colored Pictures

  45. Black & White Bitmap Images

  46. Black & White Bitmap Images 111111110000000000000000000000000000000000000000000000000000000000000 000000001110000000000000000000000000000000000000000000000000000000110 000111111111100000000000000000000000000000000000000000000000000000110 001111111111110000000011111000000000000000000000000000000000000000000 000011111111100000000111110000000000000000000000000000000000000000000 000000000000000000001111110000000000000000111110000000000000000000000 000000000000000000001111110000000000000000111111000000000000000000000 000000000000000000001111100000000000000000111111100000000000000000000 000011111110000000001111100000000000000000011110000000000000000000000 000001111111100000001111100000000000000000000000000000000000010000000 000011111111110000001111110000000000000000000000000000000011111110000 000011111111110000001111110000000000000000000000000000000011111110000 000011100011110000001111110000000000000000000000000000000011111111000 000111100001111100001111110000000111100000000011110000000111000111110 000111100000111100001111110000001111100000000111110000000111000111110 001111100001111100001111110000001111100000000011111000001111000011110 001111110000111110000111110000000111110000000011111100001111000011110 001111111111111100000111100000000011110000000001111100001111111111110 000111111111111100000111100000000001111000000001111100001111111111110 001111111111111000000111000000000001111000000000111100011111111111110 000011111111111000001110000000000001111000000000111100000111111111110 000000000000000000001110000000000001111000000000111100000011111111110 000000000000000000000000000000000111110000000001111000000000000011110 000000000000000000000000000000000111100000000111111000000000000111110 000000000000000000000000010000011111100000011111110000000000011111100 000000000000000000000000011111111111001111111111100000011111111111000 000000000000000000000000001111111110000011111111000000001111111110000 000000000000000000000000001111111100000001111110000000000011111110000 000000000000000000000000000000111000000000111000000000000001111000000

  47. Gray Bitmap Images • Each individual pixel (pi(x)ctureelement) in a graphic stored as a binary number • Pixel: A small area with associated coordinate location • Example: each point below is represented by a 4-bit code corresponding to 1 of 16 shades of gray

  48. 4=22 choices 00 (off, off)=white 01 (off, on)=light grey 10 (on, off)=dark grey 11 (on, on)=black = (white) 0 0 = (light grey) 0 1 = (dark grey) 1 0 = (black) 1 1 Example: 2-bit per pixel

  49. Colour representation • Colours are represented with a sequence of bits. • 256 colours – how many bits? • Hint for calculating • To figure out how many bits are needed to represent a range of values, figure out the smallest power of 2 that is equal to or bigger than the size of the range. • That is, find xfor 2 x => 256 • 24-bit colour – how many possible colors? • Hints • 16 million possible colours

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