Lecture 6Lecture 6

Graphics, Number Systems

7.2

Bit-map Graphics

• Similar to real painting on the canvas, there is no way to change something but paint over it.

• Bit-mapped graphics become ragged when you shrink or enlarge them.

7.3

• Paint pixels on the screen with a pointing device– Select painting tools from a tools palette– Create bit-mapped graphics– Realism of the images is

determined by the amount ofmemory allocation per pixel

– Resolution is determinedby the density of pixels

Painting: Bit-Mapped Graphics

7.4

• The outlinedareas can befilled with acolor or witha pattern

Painting: Bit-Mapped Graphics

7.5

• You can edit high-resolution bit-mapped images– Select editing tools

from a palette– Alter digitized

photographs andgraphics from paintprograms

Digital Image Processing:Photographic Editing by Computer

7.6

Image Formats

• BMP – The bit-mapped file format used by

Microsoft Windows.

• TIFF (Tagged Image File  Format) – A standard file format for storing images

as bit maps. It is used especially for scanned images because it can support any size, resolution, and color depth

7.7

Image Formats (cont)

• GIF (Graphics Interchange Format)– A standard for digitized images

compressed with the LZW algorithm (not image-specific, can be used for any data, in Unix a command compress). Allows for features such a transparent background, animation. Used in the Internet for small icon-like images.

7.8

Image Formats (cont)

• JPEG (Joint Photographic Experts Group)– JPEG is designed for compressing either full-color

or gray-scale digital images of "natural", real-world scenes. It does not work so well on non-realistic images, such as cartoons or line drawings. JPEG does not handle compression of black-and-white (1 bit-per-pixel) images or moving pictures. Used in the Internet for photos.

7.9

Vector Graphics

• A vector image consist of objects such as lines, rectangles, circles, etc. that can be easily moved around and resized.

• An object is usually chosen by a mouse click, and could be resized by dragging its borders.

• Objects stay separate from each other all the time.

7.10

Vector Graphics

• Such properties of an object as line thickness, color, fill pattern can be easily changed after the object was created.

• Several objects may be grouped in on composed object.

• A composed object can be broken down to the original objects it was made from.

• Objects can be arranged in several layers, so that they overlap in a defined manner.

7.11

Drawing: Object-Oriented Graphics

• Draw the shapesof objects with apointing device– The palette

of drawingsoftware differsfrom that ofpainting software

7.12

Drawing: Object-Oriented Graphics

• Shapes:– Are stored as formulas (text) describing

how to draw that shape the allows infinite resolution and requires less memory

– The shape formulas allow for infinite resolution of the image

– The shape formulas alsomean fewer memory demands

7.13

Image Formats

• Formats of drawing programs (e.g. xfig)

• PostScript, PDF– Graphics file format developed by Adobe

Systems. Postscript is widely used on Unix for distributing and printing documents. Portable Document Format (PDF) is de-facto standard for documents in the Internet

7.14

Painting Pixels vs.Drawing Object Shapes

• Painting pixels:– More control over textures,

shading and fine detail– Used to create screen

displays (for videogames, multimediapresentations, andWeb pages)

7.15

Painting Pixels vs.Drawing Object Shapes

• Painting pixels:– Used for simulating

natural paint media– Used to embellish

photographic images

7.16

Painting Pixels vs.Drawing Object Shapes

• Drawing object shapes:– Better choice for creating printed graphs,

charts, and illustrations with clean lines and smooth shapes

7.17

CAD/CAM: From Picturesto Products

• Engineers,architect, and designersuse (computer-aided design) CADsoftware to designor manufactureproducts

• AutoCAD

7.18

Screen shot

• In Linux it is possible to save an image of whole display, a fragment of the display or a window using Grab-feature in the xv-program.

• In Windows it is possible to take save an image of the currently active window by pressing <Alt>-<PrintScreen>, or of the whole display by pressing just <PrintScreen>. The image is then place into clipboard, and can be pasted for example into a WordPerfect document or into Paint program.

7.19

Number and Character Representation in Computers

7.20

A Bit About Bits

A bit (binary digit)– is the smallest unit of

information– can have two values

- 1 and 0.

Binary digits, or bits, can represent numbers, codes, or instructions.

On Off

7.21

Bits as Numbers

Binary number system - a system that denotes all numbers and combinations of two digits.

The binary system uses two digits to represent the numbers 0 and 1.

7.22

Bits, Bytes, and Buzzwords

Common terms might describe file size or memory size:

Bit: smallest unit of informationByte: a grouping of eight bits of

informationK: (kilobyte); about 1,000 bytes of

information - technically 1024 bytes equals 1K of storage.

7.23

Bits, Bytes, and Buzzwords

MB: (megabyte); about 1 million bytes of information

GB: (gigabyte); about 1 billion bytes of information

TB: (terabyte); about 1 million megabytes of information

7.24

Decimal System

• Humans have 10 fingers: count in DECIMAL  

• Numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, ...

• Use 10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9   • We know that 5304 =

5*103+3*102+0*101+4*100 • Base 10

7.25

Binary System

• BINARY numbers: – 0, 1, 10, 11, 100, 101, 110, 111, 1000, 1001,

1010, 1011, ....

• Written with only 2 digits: "0" and "1" • In the same way as for decimal, 1011 (binary)

= 1*23+0*22+1*21+1*20= 11 (decimal) • Base 2 • Converting from binary to decimal is simple,

just as for 1011 above.

7.26

Binary System (contd.)

• How to know if 1011 is in binary or in decimal? Subscripts are used to show the base: 10112 (binary number), 101110 (decimal

number) • Converting from decimal to binary a little bit

more tricky, we skip this, check some book if you are interested.

• Large binary numbers are cumbersome to write

7.27

Hexadecimal System

• Heavily used in modern computers to represent binary data

• Numbers: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1A, 1B, ...

• Base 16 • Again the same idea:

– 1A16 =1*161+10*160 = 2610

7.28

Hex (cont.)

• Groups of 4 bits

• 4 bits: 24 = 16 combinations... ... use digits 0-9 and A, B, C, D, E, F

• Converting between binary and hex is straightforward:

• 10111101112 => 10  1111  0111 =>

10(=2)  1111(=F)  0111(=7) => 2F716

7.29

Octal System

• Octal was used in computers with byte length of 6 bits

• Numbers: 0, 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 20, ...

• Base 8 • Groups of 3 bits • 3 bits: 23 = 8 combinations... use digits

0-7

7.30

Octal (cont.)

• Converting between binary and octal is straightforward: 10111101112 => 1 011 110 111 =>

1(=1) 011(=3) 110(=6) 111(=7) =>13678

• In UNIX chmod command takes absolute mode for file access rights in octal

7.31

Example Decimal            Binary      Octal           Hex

  (base 10)          (base 2)    (base 8)       (base 16)       0                0000        0              0       1                0001        1              1       2                0010        2              2       3                0011        3              3       4                0100        4              4       5                0101        5              5       6                0110        6              6       7                0111        7              7       8                1000       10              8       9                1001       11              9       10               1010       12              A       11               1011       13              B       12               1100       14              C       13               1101       15              D       14               1110       16              E       15               1111       17              F

35            10 0011       43              23     100          110 0100      144              64      255        1111 1111      377              FF

7.32

Bits as Codes

ASCII - American Standard Code for Information Interchange - most widely used code, represents each character as a unique 7-bit code.

7.33

Character Tables

• ISO Latin1– 8-bit code – Extension to ASCII (ASCII is compatible) – Has characters for European languages

• Cyrillic– A dozen of different encodings – Mostly used:

• KOI8 for UNIX • Windows-1251

• Unicode (16 bits) includes ALL characters from ALL languages (!)

• Character Sets in browsers