Explain the following with the help of a suitable diagram or an example.
Any two characteristics of video cards / adapters 5m Dec2005
FIVE CHARACTERISTICS OF VIDEO CARDS / ADAPTERS:
The purpose of your graphic display system is to display bitmapped graphics on your monitor. The image displayed on your system thus consists of small dots called pixels.
1. Resolution
Resolution is the parameter that defines the possible sharpness or clarity of a video image. Resolution is defined as the number of pixels that make up an image. These pixels are then spread across the width and height of monitor. Resolution is independent of physical characteristics of monitor. The image is generated without considering ultimate screen it is to be displayed upon. Hence, the unit of resolution is the number of pixels, not the number of pixels per inch.
2. Colour Depth
Colour Depth (or the number of Colour Planes) is the number of bits assigned to each pixel to code colour information in it. These are also called Colour Planes because each bit of a pixel represents a specific colour and the bit at the same position on every pixel represents the same colour. Hence, the bits at the same position can be thought of as forming a plane of a particular colour shade and these planes piled on top of each other give the final colour at each point. Thus, if each pixel is described by 3 bits, one each for red, green and blue colour, then, there are 3 Colour Planes (one each for red, green and blue) and 6 colour planes if there are 6 bits.
3. Video Memory
Video memory is also called framebuffer because it buffers video frames to be displayed. The quality of a video display depends a lot on how quickly can the framebuffer be accessed and be updated by the video system. In early video systems, video memory was just a fixed area of the system RAM. Later, there was video RAM which came with the video cards themselves and could be increased by putting additional video RAM under the UMA (Unified Memory Architecture). Video RAM is again part of the system RAM. UMA is what you get in the modern low-cost motherboards with on-board video and sound cards etc. The amount of video memory required is dependant on the resolution and colourdepth required of the system.
4. Refresh Rates
A special circuit called the Video Controller scans the video memory one row at a time and reads data value at each address sending the data out in a serial data stream. This data is displayed by a process called Scanning where the electron beam is swept across the screen one-line-at-a-time and left-to-right. This is controlled by a vertical and a horizontal field generated by electromagnets — one moving the beam horizontally and another vertically.
The rate at which horizontal sweeps take place is called horizontal frequency or horizontal refresh rate and the rate at which vertical sweeps take place are called vertical frequency or vertical refresh rate or simply refresh rate or frame rate.
5. Graphic Accelerators and 3-D Accelerators
A Graphic Accelerator is actually a chip, in fact the most important chip in your video card. The Graphic Accelerator is actually the modern development of a much older technology called the Graphic Co-Processor. The accelerator chip is actually a chip that has built-in video functions. These functions execute the algorithms for image construction and rendering. It does a lot of work which would otherwise have to be done by the microprocessor. Hence, the accelerator chip is actually optional but very important for good graphics performance.
The graphic accelerator determines whether your system can show 3-D graphics, how quickly your system displays a drop-down menu, how good is your video playback, etc. It determines the amount and kind of memory in the framebuffer and also the resolution your PC can display.