csi 421: computer graphics csi 421: computer graphics | [email protected]
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2CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
P=(xp, yp) is pixel chosen by the algorithm in previous step
To calculate d incrementally we require dne w 1
If d > 0 then choose NE If d < 0 then choose E ( x + 1, y
+ )p 2
( x + 2, y +
3 )p
2
P=(xp, yp)
Exp
xp+1xp+2
Pre
vio
us Curr
ent N
ex
t
yp
MNE
NE
M
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
The most common side effects when
working with raster devices are:
1. Aliasing
2. Unequal intensity
3. Overstrike
4. Picket fence problem
CSI 421: Computer Graphics | [email protected]
Refers to the plotting of a point in a location other than its true location in order to fit the point into the raster.
Consider equation y = mx + bFor m = 0.5, b = 1 and x = 3 :
y = 2.5
So the point (3,2.5) is plotted at alias
location (3,3) RemedyApply anti-aliasing algorithms. Most of these algorithms introduce extra pixels and pixels are intensified proportional to the area of that pixel covered by the object.
CSI 421: Computer Graphics | [email protected]
CSI 421: Computer Graphics | [email protected]
Human perception of light is dependent on Density and Intensity of light
source. 1
Thus, on a raster display with perfect squareness, a diagonal line of pixels will appear dimmer that a horizontal or vertical line.
Remedy1. If speed of scan conversion is main then ignore2. By increasing the number of pixels in diagonal
lines3. By increasing the intensity of pixels on
diagonal lines.CSI 421: Computer Graphics | [email protected]
The same pixel is written more than once.
This results in intensified pixels in case of photographic media, such as slide or transparency
RemedyCheck each pixel to see whether it has already been written to prior to writing a new point.
CSI 421: Computer Graphics | [email protected]
Occurs when a user attempts to scan-convert an object that will not fit exactly in the raster.
CSI 421: Computer Graphics | [email protected]
RemedyLocal Aliasing: the distances between pickets in the picket fence will be kept as close to their true relative distance as possibleGlobal Aliasing: the overall length of the picket fence will be approximately correct by the spacing between pickets will be distorted.
Original Object Local aliasing Global aliasing
Must Read:•Point conversion•DDA algorithm•Bresenham’s Algorithm•Solved problems (3.1-3.7)
Optional:
•Ellipse: Scan conversion
•Region filling algorithms
References:1. Text book – chapter 32. Wikipedia and google with topic name3. http://classes.cec.
wustl.edu/~cse452/lectures/lect02_ScanConvert_2pp.pdf
CSI 421: Computer Graphics | [email protected]