08_HADWARE.pptVIP

Computer Graphics Hardware Conceptual Framework for Interactive Graphics Vector and Raster Displays Examples of raster and vector device pictures Basic Definitions Basic Definitions Hard Copy Devices Display Technologies Cross-section of a CRT Color CRT A Shadow Mask Colour CRT Raster Scan Let the electron beam constantly loop through individual pixels (one at a time) 2. The electron gun will either light up a pixel or leave it dark when it passes by The electron gun has to move very fast 4. Why? Refresh Refresh – the electron gun needs to come back to hit the pixel again before it goes out, otherwise the picture will disappear from the screen, after about 10-60 microseconds. A right refresh rate depends on the property of phosphor coating Phosphor persistence: the time it takes for the emitted light to decay to 1/10 of the original intensity Relies on the persistence of vision phenomenon of the human visual system (Critical Fusion Frequency - CFF). A good refresh rate must be maintained to avoid flicker. Typical refresh rate: 60 – 80 times per second (Hz) (What will happen if refreshing is too slow or too fast?) Scanning Process Non-Interlace vs. Interlace Non-Interlace: Scan every scan line Interlace: Scan only every other scan line (even - odd - even - odd …) - so the refresh rate becomes twice as fast Raster Scan Control Scan Controller (video adaptor/controller) and frame buffer Frame Buffer Frame buffer: the memory to hold the pixel intensity values Properties of a frame buffer that affect the graphics performance: Size: screen resolution Depth: color level 1 bit/pixel: black and white 8 bits/pixel: 256 levels of gray 24 bits/pixel: 16 million colors Speed: refresh speed Color is expensive … At least used to be The more color you want, the more bits you will need for each pixel Exercise: 1024 x 1280 screen with 24 bits per pixel, how large is the frame buffer?