Lecture 5 Computer Graphics PDF

Lecture -5 Computer Graphics Dr Ahmed Al-Shammari Plotting Points Plotting a point in computer graphics refers to marking a specific location in a coordinate system (usually in 2D or 3D space). To draw a pi...

Lecture -5 Computer Graphics Dr Ahmed Al-Shammari Plotting Points Plotting a point in computer graphics refers to marking a specific location in a coordinate system (usually in 2D or 3D space). To draw a picture on a raster display, it is important to determine the corresponding points in the frame buffer that make up the picture. - To perform this task , scan conversion point-plotting algorithm should be applied. - Both the frame buffer and the display screen are given a two-dimensional coordinate system with the origin at the lower-left corner. 2D Coordinates: In 2D graphics, a point is represented as a pair of coordinates (x, y). o The x-coordinate defines the horizontal position. o The y-coordinate defines the vertical position. Example: Plotting the point (3, 4) means moving 3 units along the x-axis and 4 units along the y- axis. Algorithm for plotting points: 1. Start at the origin (0, 0). 2. Move to the point (x, y) on the screen. 3. Place a marker at the specified coordinates. In many graphic systems, plotting a point simply involves setting a pixel on the screen. 3. Line Drawing Algorithms Drawing lines is a core operation in computer graphics. Many computer-generated pictures are composed of straight-line segments. - A line segment is displayed by turning on a string of adjacent pixels. - The accuracy and quality of the displayed line depend on the resolution of the display device. - Drawing lines with arbitrary slope creates several problems, because the display screen can eliminate only at pixel locations. 4. Simple Digital Differentiator Analyzer (Simple DDA) A Digital Differentiator is used to approximate the derivative of a digital signal or sequence. In the context of computer graphics, it can be used to analyze the changes in pixel values or color intensities. For instance, a simple digital differentiator could analyze how the pixel color changes across an image, which is useful for detecting edges or transitions in graphics. Lecture -5 Computer Graphics Dr Ahmed Al-Shammari Draw a line with endpoints (xstart, ystart) and (xend, yend) having slope: Any two consecutive points (x1, y1), (x2, y2) lying on this line satisfies the equation:- For abs(m) < 1 and xstart < xend increment x by one unit until xend is reached. - If xstart > xend swap the two endpoints x2 = x1 + 1 If abs(m) > 1 and ystart > yend , generate line by reversing this procedure. - Increment the y value by one unit until yend reached and solve for x. - If (ystart > yend) , swap the two endpoints. Y2=y1+1 or y2-y1=1 Use round function to convert the increment to integer. Summary Point Plotting: Essential in rendering individual pixels or basic shapes. Line Drawing: Used in vector graphics, wireframe models, and more advanced rendering techniques. Differentiator Analyzer: Crucial for detecting edges, contours, and transitions in images, used in applications like edge detection in computer vision or creating sharp images.