Transcript Lecture 6 - Helsingin yliopisto

Lecture 6
Graphics, Number Systems
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.
7.2
Painting: Bit-Mapped Graphics
• 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 of
memory allocation per pixel
– Resolution is determined
by the density of pixels
7.3
Painting: Bit-Mapped Graphics
• The outlined
areas can be
filled with a
color or with
a pattern
7.4
Digital Image Processing:
Photographic Editing by Computer
• You can edit highresolution bit-mapped
images
– Select editing tools
from a palette
– Alter digitized
photographs and
graphics from paint
programs
7.5
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
7.6
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.
7.7
Image Formats (cont)
• JPEG (Joint Photographic Experts Group)
– JPEG is designed for compressing either fullcolor or gray-scale digital images of "natural", realworld scenes. It does not work so well on nonrealistic 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.
7.8
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.
7.9
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.
7.10
Drawing: Object-Oriented
Graphics
• Draw the shapes
of objects with a
pointing device
– The palette
of drawing
software differs
from that of
painting software
7.11
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 also
mean fewer memory demands
7.12
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 defacto standard for documents in the
Internet
7.13
Painting Pixels vs.
Drawing Object Shapes
• Painting pixels:
– More control over textures,
shading and fine detail
– Used to create screen
displays (for video
games, multimedia
presentations, and
Web pages)
7.14
Painting Pixels vs.
Drawing Object Shapes
• Painting pixels:
– Used for simulating
natural paint media
– Used to embellish
photographic images
7.15
Painting Pixels vs.
Drawing Object Shapes
• Drawing object shapes:
– Better choice for creating printed graphs,
charts, and illustrations with clean lines
and smooth shapes
7.16
CAD/CAM: From Pictures
to Products
• Engineers,architect,
and designers
use (computer-aided
design) CAD
software to design
or manufacture
products
• AutoCAD
7.17
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.
7.18
Number and Character
Representation in Computers
7.19
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
7.20
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.
7.21
Bits, Bytes, and Buzzwords
Common terms might describe file size or
memory size:
Bit: smallest unit of information
Byte: a grouping of eight bits of
information
K: (kilobyte); about 1,000 bytes of
information - technically 1024 bytes
equals 1K of storage.
7.22
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
7.23
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
7.24
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.
7.25
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
7.26
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
7.27
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
7.28
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
7.29
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
7.30
Example
Decimal
(base 10)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
35
100
255
Binary
(base 2)
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
10 0011
110 0100
1111 1111
Octal
(base 8)
0
1
2
3
4
5
6
7
10
11
12
13
14
15
16
17
43
144
377
Hex
(base 16)
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
23
64
FF
7.31
Bits as Codes
ASCII - American
Standard Code for
Information
Interchange - most
widely used code,
represents each
character as a
unique 7-bit code.
7.32
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
7.33