1. Computer Graphics.pdf

Computer Graphics Unit-1. Introduction Basic elements of Computer graphics, Applications of Computer Graphics. Unit-2. Graphics Hardware Architecture of Raster and Random scan display devices, input/output devices. Basic elements of Computer graphics PIXEL - T...

Computer Graphics Unit-1. Introduction Basic elements of Computer graphics, Applications of Computer Graphics. Unit-2. Graphics Hardware Architecture of Raster and Random scan display devices, input/output devices. Basic elements of Computer graphics PIXEL - The full form of the pixel is "Picture Element" (pix = picture, el = element). It is also known as "PEL" - Pixel is the smallest element of an image on a computer display, whether they are LCD or CRT monitors. A pixel is represented with a dot or a square on a computer screen. - Any digital image that is displayed on the monitor is made up of thousands or millions of such small pixels. When these groups of pixels are viewed as a whole, we see the entire image. - The closely spaced pixels divide the image area into a compact and uniform two-dimensional grid of pixel lines and columns. - Each pixel-has a particular color and brightness value. - Though the size of a pixel depends mostly on the size of the electron beam within the CRT, they are too fine and close to each other to be perceptible by the human eye. MEGAPIXEL - A megapixel (MP) is a million pixels or a unit of measurement equivalent to 1,000,000 pixels. - Megapixels are commonly used to describe the resolution of a digital camera, still images, digital video, display monitors and screens. - In digital photography, the number of megapixels in an image refers to the total number of pixels that make up the image. This number is determined by multiplying the number of pixels in the width by the number of pixels in the height of the image. - When a video’s resolution described as 1080p, which really means that the video’s pixel count is 1920 × 1080. Total pixel count is 2,073,600 in each frame, this would be rounded down to 2MP. It is important to note that the “p” in 1080p does NOT stand for “pixels. PPI and DPI - Screen image sharpness is sometimes expressed as pixels per inch (PPI). - PPI is the number of pixels contained in one inch of a digital image. - DPI is the number of printed dots within one inch of a printed image. - The main difference between the two terms is that PPI is the quality of a digital image displayed on- screen, while DPI is the quality of a physical, printed image. The dots in DPI refer to the number of printed dots of ink. - Note : Although DPI is technically a term used for printing physical images. RESOLUTION The number of horizontal and vertical pixels on a display screen is called Resolution.  In Computer Graphics, there are two types of resolution exists: 1. Image Resolution 2. Screen Resolution Image Resolution: Image resolution refers to the pixel spacing, i.e. the distance from one pixel to the next pixel. In other words, the resolution of an image is the total number of pixels along with the entire height and width of the image. For example a full-screen image with resolution 800 x 600 means that there are 800 columns of pixels, each column comprising 600 pixels, i.e. a total of 800 x 600 = 480000 pixels in the image area. Screen Resolution: Screen resolution is the number of pixels on a screen, both horizontally and vertically. So, a screen that has a resolution of 3840 x 2160 (It is also known as 4k UHD), it can display 2160 pixels vertically, and 3840 pixels horizontally. DOT PITCH - The internal surface of the monitor screen is coated with red, green and blue phosphor material that glows when struck by a stream of electrons. - The dot pitch is the distance between adjacent sets (triads) of red, green and blue dots. This is also same as the shortest distance between any two dots of the same color, i.e. from red-to-red, or, green- to-green like that. - Usually monitors are available with a dot pitch specification 0.25 mm to 0.40 mm. - The smaller the dot pitch, the higher the resolution, sharpness. - Each dot glow with a single pure color (red, green or blue) and each glowing triad appears to our eye as a small spot of color (a mixture of red, green and blue). What is dot and pixel pitch? - The dot pitch is the distance between the centers of two adjacent dots of the same color on a computer display. The pixel pitch is the distance between the centers of two adjacent pixels. Image Resolution versus Dot Pitch - The dot pitch is the distance between the centers of two adjacent dots of the same color on a computer display. Resolution is the number of pixels in the horizontal and vertical dimension. Examples would be a 24 inch monitor with a 1920 x 1080 resolution has a dot pitch of 277 micrometers. - The smaller the dot pitch, the higher the resolution. ASPECT RATIO - The aspect ratio of the image is the ratio of the number of X pixels to the number of Y pixels, and is expressed with two numbers separated by a colon. - For the X:Y aspect ratio, the image is X units wide and Y units high. The standard aspect ratio for PCs is 4:3, means 4 units wide to 3 units high. - The term is also used to describe the dimensions of a display resolution. Resolution No. of pixels Aspect ratio 640 × 480 3,07,200 4:3 1024 × 768 7,86,432 4:3 1280 × 1024 13,10,720 5:4 1920 ×1080 20,73,600 16 : 9 Display Devices in Computer Graphics The display device is an output device used to represent the information in the form of images (visual form). Display systems are mostly called a video monitor or Video display unit (VDU). Display devices are designed to model, display, view, or display information. The purpose of display technology is to simplify information sharing. Today the demand for high-quality display is increasing. There are some display devices given below : 1. Cathode Ray Tube (CRT) 2. Color CRT Monitor 3. Liquid Crystal Display(CRT) 4. Light Emitting Diode(LED) 5. Direct view Storage Tubes (DVST) 6. Plasma Display 7. 3D Display 1. CATHODE RAY TUBE (CRT) CRT stands for Cathode Ray Tube. CRT is a technology used in traditional computer monitors and televisions. The image on CRT display is created by firing electrons from the back of the tube of phosphorus located towards the front of the screen. Component of CRT Electron Gun: The electron gun is made up of several elements, mainly a heating filament (heater) and a cathode. The electron gun is a source of electrons focused on a narrow beam facing the CRT. Control Electrode: It is used to turn the electron beam on and off. Focusing system: It is used to create a clear picture by focusing the electrons into a narrow beam. Focusing & Accelerating Anodes: These anodes are used to produce a narrow and sharply focused beam of electrons. Horizontal & Vertical Deflection Plates: These plates are used to guide the path of the electron the beam. The plates produce an electromagnetic field that bends the electron beam through the area as it travels. Phosphorus-coated Screen: The phosphorus coated screen is used to produce bright spots when the high- velocity electron beam hits it. The operation of CRT is very simple – - The electron gun emits a beam of electrons - The electron beam passes through focusing and deflection systems that direct it towards specified positions on the phosphor-coated screen. - When the beam hits the screen, the phosphor emits a small spot of light at each position contacted by the electron beam. - It redraws the picture by directing the electron beam back over the same screen points quickly There are two ways to represent an object on the screen: a) RASTER SCAN DISPLAY - Raster Scan Display basically employs a Cathode Ray Tube (CRT) or an LCD panel for display. - Its viewing surface is coated with a layer of arrayed phosphor dots. - At the back of the CRT is a set of electron guns (cathodes) that produce a controlled stream of electrons that says electron beam. - The phosphor material emits light when struck by these high-energy electrons. - The frequency and intensity of the emitting light depend on the type of phosphor material uses and the energy of the electrons. - To produce a picture on the screen, these directed electron beams start at the top of the screen. It scans rapidly from left to right along Figure : Schematic diagram of Raster scan display the row of phosphor dots. They return to the leftmost position one line down. It scans again and repeats this to cover the entire screen. The return of the beam direction to the leftmost position is one line down that says Horizontal Retrace. - As a particular frame ends, the beam of electron moves to the left top corner of the screen to move to another frame. This motion is referred to as Vertical Retrace. - The picture is then stored in an area of memory which is referred to as the frame buffer or refresh buffer. REFRESH RATE - When a dot of phosphor material is struck by the electron beam, it glows for a fraction of second and then fades. The screen image becomes unstable and gradually fades out. - To maintain a stable image, the electron beam must sweep the entire surface of the screen and then return to redraw it several times per second. This process says Refreshing. Refresh Rate is the number of times per second that the screen refreshes. It measures in Hertz (Hz). FRAME BUFFER - The frame buffer is the special area of memory (RAM) in raster displays which is dedicated to graphics. - This is used to hold or map the set of intensity values of the image displayed on the screen. - The stored intensity values are retrieved from frame buffer and displayed on the screen one row (scanline) at the time. - The amount of memory require to hold the image depends primarily on the resolution of the screen image and also the color depth used per pixel. - The formula to calculate how much memory is required is given below : Memory in MB = (X-resolution × Y-resolution × Bit-per-pixel) / (8 × 1024 × 1024) b) RANDOM SCAN DISPLAY: - In Random Scan Display, the electron beam direct straightway to the particular points of the screen where the image is to be produced. - It generates the image by drawing a set of random straight lines. It is like one might move a pencil over a piece of paper to draw an image. - Picture definition is stored as a set of line-drawing commands in an area of memory referred to as the refresh display file. - The drawing strikes from one point to another, one line at a time. That’s why this technique also says Vector Scan Display, strokewriting display, orcalligraphic display. RADOM SCAN VS RASTER SCAN DISPLAY Difference Raster scan displays Random scan displays Electron Electron Beam is directed from top to Electron Beam is directed to only that beam bottom and one row at a time on screen, part of screen where picture is required but electron beam is directed to whole to be drawn, one line at a time so also screen. called Vector Display. Resolution It has poor or less resolution because It has High Resolution because it stores picture definition is stored as an picture definition as a set of line intensity value. commands. Cost It is less expensive It is Costlier than Raster Scan System. Refresh rate Refresh rate is 60 to 80 frame per second. Refresh Rate depends on the number of lines to be displayed i.e. 30 to 60/sec Picture It Stores picture definition in Refresh It Stores picture definition as a set of line definition Buffer also called Frame Butter. commands called Refresh Display File.  Line drawing Zig - Zag line Is produced because Smooth line is produced because direct plotted value are discrete. the line path is followed by electron beam Draw an It uses Pixels along scan lines for It uses various mathematical function to image drawing an image. draw an image. 2. COLOR CRT MONITOR It is similar to a CRT monitor. The basic idea behind the color CRT monitor is to combine three basic colors- Red, Green, and Blue. By using these three colors, we can produce millions of different colors. The two basic color display producing techniques are: a) Beam Penetration Method b) Shadow-Mask Method a) Beam Penetration Method: - The Beam-Penetration method has been used with random-scan monitors. - In this method, a powerful electron beam penetrates the CRT, the CRT screen is coated with two layers of phosphor, red and green and the displayed color depends on how far the electron beam penetrates the phosphor layers. - This method produces four colors only, red, green, orange and yellow. - A beam of slow electrons excites the outer red layer only; hence screen shows red color only. - A beam of high-speed electrons excites the inner green layer. Thus screen shows a green color. - A beam with the medium speed of electrons, a mixture of red and green light is emitted to display two more colors- orange and yellow. Advantages : - It is a cheaper method. - This method provides high resolution. - It uses only one electron gun whereas the other method uses three or more electron guns. - Easily identifies the type of electron i.e., high, low, or medium potential. - A reliable method for producing colors. Disadvantages : - Produces only four colors. - Not suitable for producing realistic views. - Only suitable for the random scan. - Color changing process takes time. - The picture quality is quite poor. b) Shadow-Mask Method - It is used with a raster scan monitor for displaying pictures. - It has more range of color than the beam penetration method.  - It is used in television sets and monitors. - A Shadow Mask can display a wider range of pictures than beam penetration. Construction: A shadow mask CRT has 3 phosphor color dots at each pixel position. First Dot: Red color Second Dot: Green color Third Dot: Blue color 1. It has three different guns, one for each color dot. 2. It has a metal screen or plate just before the phosphorus screen, named “Shadow-Mask.” 3. It also has a shadow grid just behind the phosphorus coated screen with tiny holes in a triangular shape. Working: A Shadow Mask is a metal plate with tiny holes present inside a color monitor. A Shadow Mask directs the beam by consuming the electrons so that the beam hits only the desired point and displays a resulting picture. It has three different guns. When the three beams pass through a hole in the shadow mask, they activate a dotted triangle, which occurs as a small color spot on the screen. It is a task of a shadow mask to direct the beam on its particular dot on the screen and produce a picture on the screen. Difference between Beam Penetration and Shadow Mask method. Basis Beam Penetration method Shadow Mask method It is used with Random Scan System to It is Used With Raster Scan System to Where Used display color. display color. Number of Three electron guns are used; i.e., red, electron guns Only one electron gun is used. green and blue. used. It can displays Only four colors i.e. Red, Colors It can display Millions of colors. Green, Orange and Yellow. Less colors are available because the colors Millions of colors are available because the Color in Beam Penetration depends on the speed colors in Shadow Mask depends on the Dependency of the electron beam. type of the ray.  It is Less Expensive as compared to Cost It is More Expensive than other methods. Shadow Mask. Picture Quality of picture is not so good i.e. Poor Shadow Mask gives realism in picture with Quality with Beam Penetration Method. shadow effect and millions of color. Resolution It gives High Resolution. It gives Low Resolution. In Beam Penetration method, Color display In Shadow Mask Method, there are no such Criteria depends on how far electron excites outer criteria for producing colors. It is used in Red layer and then Green layer. computers, in color TV etc. APPLICATIONS OF COMPUTER GRAPHICS. Computer Graphics has numerous applications, some of which are listed below − 1. Computer Art: Using computer graphics we can create fine and commercial art like, Cartoon drawing, paintings, logo design can also be done. 2. Computer Aided Drawing: Designing of buildings, automobile, aircraft is done with the help of computer aided drawing. 3. Presentation Graphics: Presentation Graphics is commonly used to summarize the Financial, Statistical, Mathematical, Scientific, Economic Data for research, Managerial and other reports. Creation of bar graphs, pie charts, time chart, can be done using the tools present in computer graphics. 4. Entertainment: Used for creating motion pictures, music video, television shows, cartoon animation films, game industry. 5. Education: Using computer graphics many educational models can be created through which more interest can be generated among the students regarding the subject. 6. Training: Specialized system for training like simulators can be used for training the candidates in a short span of time with better understanding. Creation of training modules using computer graphics is simple and very useful. 7. Visualization: It is used for visualization of scientists, engineers, medical personnel, business analysts for the study of a large amount of information. 8. Image Processing: Processing of existing images into refined ones for better interpretation is one of the many applications of computer graphics. 9. Medical imaging − MRIs, CAT scans, etc. - Non-invasive internal examination. Etc.