CSI 421: Computer Graphics CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com 3
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com 10
MNE P=(xp, yp) is pixel chosen by the algorithm in previous step To calculate d incrementally we require dne w If d > 0 then choose NE If d < 0 then choose E ( x + 1, y + ) ( x + 2, y + 3 ) p 2 1 p 2 MNE NE M yp E P=(xp, yp) xp xp+1 xp+2 Previous Current Next CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
The most common side effects when working with raster devices are: Aliasing Unequal intensity Overstrike Picket fence problem CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
Consider equation y = mx + b For m = 0.5, b = 1 and x = 3 : y = 2.5 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 + b For m = 0.5, b = 1 and x = 3 : y = 2.5 So the point (3,2.5) is plotted at alias location (3,3) Remedy Apply 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 | saleh.sabbir.aiub@gmail.com
CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
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. Remedy If speed of scan conversion is main then ignore By increasing the number of pixels in diagonal lines By increasing the intensity of pixels on diagonal lines. CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
The same pixel is written more than once. This results in intensified pixels in case of photographic media, such as slide or transparency Remedy Check each pixel to see whether it has already been written to prior to writing a new point. CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
Occurs when a user attempts to scan-convert an object that will not fit exactly in the raster. Original Object Local aliasing Global aliasing Remedy Local Aliasing: the distances between pickets in the picket fence will be kept as close to their true relative distance as possible Global Aliasing: the overall length of the picket fence will be approximately correct by the spacing between pickets will be distorted. CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com
Must Read: Optional: References: •Ellipse: Scan conversion •Region filling algorithms •Point conversion •DDA algorithm •Bresenham’s Algorithm •Solved problems (3.1-3.7) References: Text book – chapter 3 Wikipedia and google with topic name http://classes.cec.wustl.edu/~cse452/lectures/lect02_ScanConvert_2pp.pdf CSI 421: Computer Graphics | saleh.sabbir.aiub@gmail.com