ATTRIBUTES OF OUTPUT PRIMITIVES IN COMPUTER GRAPHICS

Filled Area Primitives
NEHRUREVATHY
DEPARTMENT OF BCA

Filled Area Primitives:
• Region filling is the process of filling image or
region.
• Filling can be of boundary or interior region.
• Boundary Fill algorithms are used to fill the
boundary.
• Flood-fill algorithm are used to fill the interior.

Filled Area Primitives-Example:

Boundary Filled Algorithm:
• This algorithm uses the recursive method.
• First of all, a starting pixel called as the seed is
considered.
• The algorithm checks boundary pixel or
adjacent pixels are colored or not.
• If the adjacent pixel is already filled or colored
then leave it, otherwise fill it.
• The filling is done using four connected or
eight connected approaches.

Boundary Filled Algorithm:
N
S
E WC
NNE
E
SE S SW
WC
NW

Boundary Filled Algorithm-Two
Approaches:
• 1.Four connected approaches: In this approach,
left, right, above, below pixels are tested.
• 2. Eight connected approaches: In this approach,
left, right, above, below and four diagonals are
selected.
• Boundary can be checked by seeing pixels from
left and right first.
• Then pixels are checked by seeing pixels from top
to bottom.
• The algorithm takes time and memory because
some recursive calls are needed.

Problem with recursive boundary fill
algorithm:
• It may not fill regions sometimes correctly when
some interior pixel is already filled with color.
• The algorithm will check this boundary pixel for
filling and will found already filled so recursive
process will terminate.
• This may vary because of another interior pixel
unfilled.
• So check all pixels color before applying the
algorithm.

Algorithm:
Procedure fill (x, y, color, color1: integer)
int c;
c=getpixel (x, y);
if (c!=color) (c!=color1)
{
setpixel (x, y, color)
fill (x+1, y, color, color 1);
fill (x-1, y, color, color 1);
fill (x, y+1, color, color 1);
fill (x, y-1, color, color 1);
}

Flood Fill Algorithm
• In this method, a point or seed which is inside region is
selected.
• This point is called a seed point.
• Then four connected approaches or eight connected
approaches is used to fill with specified color.
• The flood fill algorithm has many characters similar to
boundary fill.
• But this method is more suitable for filling multiple
colors boundary.
• When boundary is of many colors and interior is to be
filled with one color we use this algorithm.

Flood Fill Algorithm
• In fill algorithm, we start from a specified
interior point (x, y) and reassign all pixel
values are currently set to a given interior
color with the desired color.
• Using either a 4-connected or 8-connected
approaches, we then step through pixel
positions until all interior points have been
repainted.

Algorithm:
Procedure floodfill (x, y, fill_color, old_color: integer)
{
If (getpixel (x, y)=old_color)
{
setpixel (x, y, fill_color);
fill (x+1, y, fill_color, old_color); // Four-Connected
fill (x-1, y, fill_color, old_color);
fill (x, y+1, fill_color, old_color);
fill (x, y-1, fill_color, old_color);
}
}

8-Connected Flood Fill Algorithm
floodfill(x+1,y,old,newcol);
floodfill(x-1,y,old,newcol);
floodfill(x,y+1,old,newcol);
floodfill(x,y-1,old,newcol);
floodfill(x+1,y+1,old,newcol);
floodfill(x-1,y+1,old,newcol);
floodfill(x+1,y-1,old,newcol);
floodfill(x-1,y-1,old,newcol);

Disadvantage:
• Very slow algorithm
• May be fail for large polygons
• Initial pixel required more knowledge about
surrounding pixels.

ATTRIBUTES OF OUTPUT
PRIMITIVES

ATTRIBUTES OF OUTPUT PRIMITIVES
• Any parameter that affect the way a
parameter is to be displayed is referred to as
an attribute parameter.
• Example attribute parameter are color
specification,size,position,orientation and so
on.
• some attributes are:
1.Line Attributes

ATTRIBUTES OF OUTPUT PRIMITIVES
2.Curve Attributes
3.Color and Grayscale levels
4.Area Fill Attributes
5.Character Attributes
6.Marker Attributes

1.Line Attributes
• Basic attributes of a st. Line segment are:
1.Line Type
2.Line Width
3.Pen and Brush Options
4.Line Color

1.Line Type – Line Attributes:
• Four types:
# Solid Lines( )
# Dashed Lines (------------)
# Dotted Lines (.................)
# Dashed Dotted Lines(-.-.-.-.-.-.-.-)
• Syntax:
setlinetype(lt);
Where, lt - takes 4 values(positive integer numbers)

1.Line Type – Example:
• Parameter lt,
1- Solid Lines
2- Dashed Lines
3- Dotted Lines
4- Dashed Dotted Lines
• Example:
setlinetype(2);
setline(100,200,300,200);
------------------------

2.Line Width-Line Attributes:
• Thickness of the line.
• Syntax:
setlinewidthscalefactor(lw);
• Parameter lw indicates width of the line to be
displayed.
• Three values:
1 Standard line width
0.5 Half of the Standard line width
>1 Thicker than the Standard line width

Disadvantage- very thick line:
• Use Line Cap—to adjust the shape of the line
ends to give them a better appearance by
adding line caps.
• Three types of line cap:
1.Butt Cap
2.Round Cap
3.Projecting Square Cap

Line Cap – Types:
1.Butt Cap:
It is obtained by adjusting the end positions of
the components parallel lines so that the thick
line is displayed with square end.

Line Cap – Types:
2.Round Cap
It is obtained by adding semicircle to butt cap.

Line Cap – Types:
3.Projected Square Cap
It is us to extend the line and add the butt
cap.

Three Methods for smoothly joining
two line segments:
1.Miter Join: Join two segments by extending
outer boundaries.
2.Round Join: Joining two segment by circular
boundary.
3.Bevel Join: Joining two segments by butt cap.

1.Miter Join 2.Round Join 3.Bevel Join

3.Pen and Brush Options
# Lines can be displayed with pen or
brush selections.
#Options in this category include
shape,size and color

4.Line Color
• Number of color choices depends on the
number of bits.
• Syntax:
setcolor(lc);
• Example: setcolor(0); black

2.CURVE ATTRIBUTES
• Parameter for curve attributes are same as
those for line segments.
• Curves displayed with varying
colors,widths,dot-dashed pattern and pen or
brush options.

3.Color and Grayscale Levels
• Two types of system:
1.Raster Scan System(any number of color)
2.Random Scan System(limited color)
• Color Options:
# Color information is stored in the frame buffer in two ways:
1.Store the color code directly into the
frame buffer.
# Suitable only for high resoultion system.
# very expensive
Each time if we access the frame buffer for choosing the
colors,frame buffer cost will be increased.

Color and Grayscale Levels
2.maintains the color table
# suitable for low resolution system
# very cheap
# use the color code in a separate table and
use pixel as an index into this table.

# Color Codes:
• 3bit per pixel
• Ex: 0 0 0
leftmost middle control rightmost
Control red green control blue
INTENSITY LEVEL

• Each color codes has been controlled by RGB
mode.
• Color Table:
# The table which is used to store color values
in a color look up table.
# Also called as video lookup table.
# Frame buffer values are now used as an
index into color table.

• Color Representation:
To represent the colors use the following
syntax:
setcolorrepresentation(ws,c,colorpts)
where,
ws---workstation
c---colorindex
colorpts---3bits of colors

Advantages:
1.uses 256 or 512 different colors.
2.color table is unique
3.reduce the repeated colors
4.reduce the frame buffer storage

Gray Scale Levels
• Gray(2 bits)
• Grayscale(3 bits) black+white=gray
• No color capability
• Shaded gray or grayscale colors
• Values 0 to 1
• Intensity codes for a four level Gray scale
system:

Gray Scale Levels—3bits
FRAME BUFFER VALUE 3 BITS BINARY CODE COLORS
0 000 BLACK
1 001 DARK BLACK
2 010 LIGHT BLACK
3 011 DARK GRAY
4 100 LIGHT GRAY
5 101 DARK WHITE
6 110 LIGHT WHITE
7 111 WHITE

4.Character Attributes
• Character Attributes: The appearance of
displayed characters is controlled by attributes
such as font, size, colour and orientation.
• Attributes can be set both for entire character
strings and for individual characters, known as
Marker symbols.

Character Attributes-Text Attributes
1. Text Attributes:
• There are many text options available, such
as font, colour, size, spacing, and orientation.
• Text Style:
The characters in a selected font can also be
displayed in various underlining styles (solid,
dotted, dashed, double), in bold, in italics,
shadow style, etc.
Example: setTextFont(tf)

Character Attributes-Text Attributes
• Text Color:
Control of text color is managed with: Example:
setTextColorIndex(tc)
where tc specifies an allowable color code
• Text Size:
We can adjust text size by changing the overall
dimensions, i.e., width and height, of characters
or by changing only the width.
Example: setCharacterHeight(ch)

• The width of the text can be set by
setCharacterExpansionFactor(cw)
where,cw---scales the body width of a
character.

• Spacing between characters is controlled
separately with
• Ex: setCharacterSpacing(cs)

Ex:
setCharacterUpVector(upvector)
• Text Orientation: The
text can be displayed at
various angles, known
as orientation.
• Character strings can be
arranged vertically or
horizontally.
• A text orientated by 45
degrees in anticlockwise
and clockwise direction

Text Path:
#Character strings are arranged vertically or
horizontally.
#This is known as Text Path.
#Text path can be right, left, up or down.
• Ex:setTextPath(tp)

Ex:
setTextAlignment(h,v)
Text Alignment:
• This attribute
specifies how text is
to be positioned.
• Vertical alignment
can be top, cap,
half, base and
bottom.
• Similarly, horizontal
alignment can be
left, centre and
right.
------------------------TOP
-----------------------CAP
-----------------------HALF
-----------------------BASE
----------------------BOTTO
LEFT CENTRE RIGHT
ALIGNMENT VALUES FOR A STRING
PRINCE

5.Marker Attributes
• It is a single character that can be displayed in
different colors and in different sizes.
• To set the marker symbol,use:
setMarkerType(mt)
• It takes 5 values:
VALUE MARKERTYPE
1 Dot(.)
2 Vertical cross(+)
3 Asterisk(*)
4 Circle(0)
5 Diagonal cross(x)

Marker Attributes
• To set the marker size,use
setMarkerSizeScaleFactor(ms)
• Marker color is specified with
setPolyMarkerColorIndex(mc)
use the color code
VALUE MEANING
VALUE>1 Character Enlargement
VALUE<1 Reduce the marker size

ATTRIBUTES OF OUTPUT PRIMITIVES IN COMPUTER GRAPHICS

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ATTRIBUTES OF OUTPUT PRIMITIVES IN COMPUTER GRAPHICS