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Computer Graphics is the use of computers to show and handle information in graphical or pictorial form. The information is then displayed either on a visual-display unit or via a printer. Computer imagery has applications for film special effects, medical imagery, simulation and training, flying logos, games and many others. As computer graphics is a vast field that encompasses almost any graphical aspect, in this essay I am going to concentrate mainly on the generation of images of 3-dimensional scenes (3D). I will look at the processor, memory needed, speed and the software used.
3D computer graphics are special graphics that use a three dimensional representation of geometric data that is stored in the computer. The data is then used for performing calculations and rendering 2D images. 3D models are created by manipulating polygon meshes and moulding them into objects, characters and scenes. 3D art is used in everything from print ads, Web sites, television, movies, video games and beyond.
The Central Processing Unit (CPU) is the brain of computer systems. Its function is to execute programs stored in the main memory by fetching their instructions, examining them, and then executing them one after another. The CPU also contains a small, high speed memory used to store temporary results and certain control information. (Tanenbaum, 2006)This general purpose processor can handle any task. In 3D graphics this process is carried out by Graphics Processing Unit (GPU) which is a specialised processor. These processors handle complicated calculations related to 3D graphics. The GPU is a processor that offloads 3D graphics rendering from the microprocessor. It is used in mobile phones, personal computers, embedded systems, workstations, and game consoles. A GPU is attached to a graphics card and is there to calculate floating point operations. A graphics accelerator incorporates custom microchips which contain special mathematical operations commonly used in graphics rendering. The efficiency of the microchips therefore determines the effectiveness of the graphics accelerator. They are mainly in use in 3D games or high-end 3D rendering.
Modern GPUs are very efficient at manipulating computer graphics. Their highly parallel structure makes them more effective than general-purpose CPUs for a range of complex algorithms. In a personal computer, for example, a GPU can be present on a video card, or it can be on the motherboard. Nearly 90% of new desktop and notebook computers have integrated GPUs, which are usually far less powerful than those on a dedicated video card. 3D computer graphics need a lot of computer processing power and a large amount of memory. Until late 1995, 3D acceleration was only found in a small number of high end products.
The images we see on monitors are made of tiny dots called pixels. A typical screen displays over a million pixels and it's up to the computer to decide how to use them in order to create an image. To carry out these tasks the computer needs a translator. The translator takes the binary data (computers operate using base 2 number system also known as binary number system) from the GPU and turn it into a picture you can see. For a computer to be able to do this it must have graphics built into the motherboard otherwise the translation takes place on the graphics card. A typical example would be an art department in a company. When people in the company want a piece of artwork, they send a request to the art department. The art department decides how to create the image and then puts it on paper. The information is then sent for processing. A graphics card works along the same principles (Tyson et al, 2000).
The GPU works in conjunction with software applications to send information about the image to the graphics card. Every aspect of computing today, from creating animation to simple tasks such as word processing and e-mail, uses lots of graphics to create a more natural work environment for the user. The way this card connects to your computer is key in your computer's ability to render graphics. The graphics card's sole responsibility is to decide how to use the pixels on the screen to create the image. It then sends that information to the monitor through a cable. The graphics card accomplishes this task using four main components, a motherboard which connects for data and power, a processor to decide what to do with each pixel on the screen, memory to hold information about each pixel and to temporarily store completed pictures and a monitor which is used for connection so you can see the final result (Hill, 2001).
Most 3D graphics you see on your computer are built by a texture map. Texture maps are like wrapping paper. The computer takes a flat, 2D image and wraps it around a set of parameters dictated by the graphics card to create the appearance of a 3D image. The creation and storage of texture maps is the main thing that uses most of the memory from both the graphics card and the system overall. With a Peripheral Component Interconnect (PCI) based graphics card, every texture map has to be stored twice. First, the texture map is loaded from the hard drive to the system memory (RAM) until it has to be used. When needed, it is pulled from memory and sent to the CPU to be processed. Once processed, it is sent through the PCI bus to the graphics card, where it is stored again in the card's frame buffer. The frame buffer is where the graphics card holds the image in storage once it has been rendered so that it can be refreshed every time it is needed. All of this storing and sending between the system and the card is very draining to the overall performance of the computer (Tyson et al, 2000).
Memory is the section of the computer where information is stored. For the GPU to create images, it needs somewhere to hold information and completed pictures. It uses the card's RAM for this purpose, storing data about each pixel, its colour and its location on the screen. RAM is short for random access memory which is the best known form of computer memory. It is called random access because one can access any memory cell directly if you know the row and column that intersects the cell. Part of the RAM can also act as a frame buffer, meaning that it holds completed images until it is time to display them(Hill, 2001). Memory used to store image data that the computer displays is video random access memory (VRAM). It acts as a buffer between the CPU and the video card. For a picture to be displayed on the screen, the image is first read by the processor and then written to the VRAM. From there the data is converted by a RAM digital to analog converter called a RAMDAC into analog signals that are sent to the display. Contrary to most system RAM, VRAM chips are dual ported, which means that while the display is reading from VRAM to refresh the currently displayed image, the processor is writing a new image to the VRAM. This prevents the display from flickering between the redrawing of images. There are many different types of VRAM. The SGRAM (Synchronous Graphics RAM) is one type which can modify data into single operation rather than as a sequence of read, write, and update operations, it is expensive though. Other types are RDRAM (Rambus Dynamic RAM), WRAM (Window RAM) and MDRAM (Multibank Dynamic RAM).The VRAM connects directly to the digital-to-analogue converter, called the DAC. This converter (RAMDAC) translates the image into an analogue signal that the monitor can use. Some cards have multiple RAMDACs, which can improve performance and support more than one monitor. The RAMDAC sends the final picture to the monitor through a cable.
The Accelerated Graphics Port (AGP) interface is a new platform bus specification that enables high performance graphics capabilities, especially 3 dimensional, on PCs. It is a dedicated bus from the graphics subsystem to the core-logic chipset. The bus moves the memory requirements for the 3D portions of a graphics subsystem from the local frame buffer memory to main system memory. AGP improves the process of storing texture maps by allowing the operating system to allocate RAM for use by the graphics card. This type of memory is called AGP memory or non-local video memory. Using the much more abundant and faster RAM used by the operating system to store texture maps reduces the number of maps that have to be stored on the graphics card's memory. In addition, the size of the texture map your computer is capable of processing is no longer limited to the amount of RAM on the graphics card (Tyson et al, 2000).
The display is the most-used output device on a computer. It provides instant feedback by showing text and graphic images as you work or play. Most desktop displays use liquid crystal display (LCD) or cathode ray tube (CRT) technology. Nearly all portable computing devices such as laptops incorporate LCD technology. The hardware of computer graphics has progressed from random scan CRT via the direct view tube to high resolution colour raster graphics in a short time. Because of their slimmer design and lower energy consumption, monitors using LCD technology (also called flat panel or flat screen displays) are replacing the venerable CRT on most desktops. Resolution refers to the number of individual dots of color, known as pixels, contained on a display. Resolution is expressed by identifying the number of pixels on the horizontal axis (rows) and the number on the vertical axis (columns). Resolution is affected by a number of factors, including the size of the screen.
A computer image is represented as a discrete grid of picture elements called pixels. The number of pixels determines the resolution of the image. Typical resolutions range from 320x200 to 2000x1500. For a black and white image, a number describes the intensity of each pixel. It can be expressed between
0.0 (black) and 1.0 (white). However, for internal binary representation reasons, it is usually stored as an integer between 0 (black) and 255 (white). For a colour image, each pixel is described by a triple of numbers representing the intensity of red, green and blue (Tyson et al, 2000).
Accelerated Graphics Port (AGP) is a high point to point channel for attaching a video card to the computer's motherboard to accelerate 3D computer graphics. It enables the computer to have a dedicated way to communicate with the graphics card, enhancing both the look and speed of your computer's graphics. The most critical aspect of 3D graphics is the processing of texture maps, the bitmaps which describe in detail the surfaces of three-dimensional objects (Hill, 2001). Texture map processing consists of fetching one, two, four, or eight texture elements from a bitmap, averaging them together based on some mathematical approximation of the location in the bitmap (or multiple bitmaps) needed on the final image, and then writing the resulting pixel to the frame buffer. In pre-AGP PCI systems, there are five basic steps involved in processing textures:
1. Prior to their usage, texture maps are read from the hard drive and loaded into system memory. The data travels via the IDE bus and chipset before being loaded into memory.
2. When a texture map must be used for a scene, it is read from system memory into the processor. The processor performs point-of-view transformations upon the texture map then caches the results.
3. Lighting and viewpoint transforms are then applied to the cached data. The results of this operation are subsequently written back to system memory.
4. The graphics controller then reads the transformed textures from system memory and writes them in its local video memory (also called graphics controller memory, the frame buffer, or off-screen RAM). In present-day systems, this data must travel to the graphics controller over the PCI bus.
5. The graphics controller next reads the textures plus 2D colour information from its frame buffer. This data is used to render a frame which can be displayed on the 2-D monitor screen. The result is written back into the frame buffer. The system's digital-to-analogue convertor will read the frame and convert it to an analogue signal that drives the display (Hill, 2001).
Software comprises the formal procedures used to accomplish a task as well as the data these procedures evaluate. 3D computer graphics software refers to programs used to create 3D computer generated images. These computer graphics may be web graphics, clip art, headings, logos, digital photos or backgrounds.3D uses specialised applications like CAD (computer aided design) which is often used in architecture. Objects created by CAD software can be moved, rotated instantly and resized. There are several types of programs available to help you create 3D models. These programs are usually referred to as modelers. SolidWorks, Blender, SketchUp and 3D Cafe are all different kinds of software used for modelling, animation, rendering, post production and interactive creation. There are many uses for 3D models. The needs to experience objects visually are other important motivations that lead to a larger and broader context for studying object models. Below are some of uses for 3D models:
To show how a product looks before it is manufactured, best combination of shape, colour and layout.
To assess appearance: existing environment, does it need more or less lighting?
To observe part relationships: how things fit together, do parts touch or collide that should be separated?
To check whether the object meets the design specifications? Can it satisfy
constraints on stress, loading and heat transfer.
3D computer technology seems to be redefining entertainment, offering viewers a truly immersive, high definition experience. Industries such as automotive, aerospace, biotechnology, broadcasting, gaming, geophysical exploration, manufacturing, medical and applied engineering are all turning to 3D graphics. Recently football matches have been shown in 3D glasses leaving people wondering whether this is the next big thing on the market.