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1. Introduction of Computer Graphics
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- 2. Introduction Computer Graphics:- • Def. :- Computer graphics (CG) is the creation, representation, manipulation and display of picture with the help of computer. • Graphics is the ability for giving computer to express its data in pictorial form. • Computer graphics may be interactive or non- interactive.
- 3. Components of ComputerGraphics 1. Modeling 2. Storing/Representation: 3. Manipulation/Transformation 4. Rendering 5. Interaction 6. Viewing / Presentation
- 4. Components of ComputerGraphics 1. Modeling :- It deals with the definition of the object in terms of the primitives, coordinates and characteristics. In computer graphics, an object is made up by pixels so it deals with the object definition in terms of pixels, their address and intensity values. 2. Storing/Representation :- It deals with the storing scenes and images in memory and on disk. It is used to know how the picture is internally stored in computer. Objects, images or scenes are stored in computer in binary representation. So it deals with binary representation of pixels to define the object, scenes and images. 3. Manipulation/Transformation :- It deals with the changing the shape, position and characteristics of objects. It also includes various operations such as translation, rotation, scaling and clipping.
- 5. Components of ComputerGraphics 4. Rendering :- It deals with the applying physically based procedures to generate (photorealistic) images from scenes (using lighting and shading) 5. Interaction :- Interaction of the user can be achieved by hardware and software combination. It helps user to select or pick an object with the help of input devices such as mouse, light pen. 6. Viewing / Presentation: It deals with the displaying images. We can display the object in two-dimensional and three-dimensional form on two-dimensional devices.
- 6. Applications of ComputerGraphics • CAD (Computer Aided Design): • Presentation Graphics • Computer Art • Education and Training • Entertainment • Visualization • Image Processing • GUI (Graphical User Interface )
- 7. Concepts in ComputerGraphics • Pixel • Resolution • Aspect Ratio • Raster Vs Vector
- 8. Pixel / Pel/ Picture Element • Graphics images on the screen are built-up from tiny dots or points called “pixels”. • It is also called as “pixel” or “pel” i.e. Picture element. The pixel is smallest possible screen elements. • Each pixel has a name and address. This address corresponds to the co-ordinates points on the screen which identify points. • Each point must have some size. • We can also set the intensity and color of the pixel.
- 9. Resolution • Def. :- a)The maximum number of points that can be display without overlap on a CRT is called, “resolution” . or b) The number of points per cm that can be plotted horizontally and vertically are the, “resolution.” or c) The number of points in each direction is called, “resolution”. • The display resolution is define by the number of rows from top to bottom and number of columns from left to right on each scan light. • Higher resolution means more sharp and clear picture. Greater the number of points, the higher resolution. • Eg. :- Typical resolution of the screen is 1280 x 1024 , it means 1280 pixels in each row and 1024 in each column. • Other screen resolutions are - 640 x 480 - 800 x 600 - 1024 x 768 - 1152 x 864 - 1280 x 1024
- 10. Aspect Ratio It isa ratio of vertical points to the horizontal points, necessary to produce equal length lines in both directions on screen. In the above example, aspect ratio of 3 by 4 means that a vertical line plotted with 3 points has same length as a horizontal line plotted with 4 points. Aspect ratio is a property of video monitor. If a picture has aspect ratio of 2:1, it means width is twice as large as the height of that picture. While resizing picture, it is important to obtain the aspect ratio otherwise the picture may get stretched and gets distorted.
- 11. Raster Display • Inraster form, intensity values of the pixels of the picture are stored in the memory area, called frame buffer. • Here, picture is stored as a rectangular array or grid with intensity values of the all the pixels of picture part. • It uses bitmap method of character generation. • It requires higher refresh rate, because it refreshes all pixels whether it is a part of not a part of picture. • It can display the realistic and shaded scene.
- 12. Vector / RandomDisplay • In vector form, picture is stored with only end points and line drawing commands in memory area called, display file. • It uses stroke method of character generation. • It requires lower refresh rate than raster form, because it refreshes only picture part and endpoints of that picture element. • It cannot display realistic and shaded scene. • Here, order of refreshing is random and it has high clarity because it retains appearance regardless of size of image.
- 13. Character Generation Methods 1.Stroke Method ( Vector Method ) 2. Dot-Matrix Method ( Bit-Map Method ) 3. Starbust Method
- 14. Stroke Method (Vector Method ) This method creates characters out of a series of line segments, like strokes of a pen, as shown in fig. Fig. :- Stroke method for character ‘A’ We can decide which line segments needed for each character that we want to draw. To produce a character , we give a sequence of commands that defines the start point and end points of the straight lines.
- 15. Dot-Matrix Method (Bit-Map Method ) This method is called as, “Bitmap method”. In this method, characters are represented by an array of dots, as shown in fig. (a) and (b) Fig. (a) - Bit map method for character ‘A’
- 16. Fig. (b) –Bitmap method for character ‘B’ • A bitmap font uses a rectangular pattern of pixels to define each character. • It requires more space, because each variation (size or format) must be stored in memory.
- 17. Starbust Method • Inthis method a fix pattern of line segments are used to generate characters. • There are 24 line segments and out of these 24 line segments, segments required to display for particular character are highlighted. This method of character generation is called, “Starbust method” because of its characteristics appearance. • In this pattern of particular character is stored in the form of 24 bit code. Each bit representing one line segment. The bit is set to one to highlight the line segment. Otherwise it is set to zero.
- 18. • Eg. :-The starbust patterns for characters A and M • 24-bit code for Character ‘A’ is 0011 0000 0011 1100 1110 0001 and • 24-bit code for character ‘M’ is 0000 0011 0000 1100 1111 0011
- 19. Disadvantages of starbustmethod • It requires more memory. • It requires additional code conversion programs to display characters from the 24 bit code. • Requires code conversion software to display character from its 24-bit code • Character quality is poor. It is worst for curve shaped characters. • This method is not used now-a-days.
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