lecture 6 graphics, number systems. 7.2 bit-map graphics similar to real painting on the canvas,...
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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
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