cadcampart3-1 docx

For color displays, each pixel is represented by three closely dots with red, green and blue colors. The electron beam selects the color elements and the intensity of each color elements. The resolution of the monitor is determined by the number of pixels displayable on the screen i.e. 640 X 480 and 1024 X 1024. A rasterization process is needed in order to display either a shaded area or graphics entities. The area or entities are converted into their corresponding pixels whose intensity and color are controlled by the image display system. COLOR GRAPHICS COLOR GRAPHICS Sơ đồ ống phóng tia Cathode (CRT) Màn hình màu CRT dùng 3 chùm điện tử với ba màu đỏ, xanh da trời và xanh cây để tạo màu cho mỗi điểm trên màn hình phosphor. Bằng cách phối hợp 3 màu với mức độ khác nhau, có thể tạo ra nhiều màu. Sản xuất màn hình với kỹ thuật vạch nét để tạo ảnh đủ chính xác là rất khó. Vấn đề kỹ thuật ở đây là khó đảm bảo 3 chùm tia trộn vào nhau sao cho chính xác trên màn hình. ĐỒ HOẠ MÀU Phối hợp màu trên màn hình kiểu quét mành COLOR GRAPHICS • A rasterizer is mainly a set of scan-conversion algorithms which are used to draw an entity by generating pixels to approximate an entity. • Bit map stores the scan conversion process. (each pixel value determines its brightness (grey level) or most often its colour on the screen). Every cell in the bit map is related to every pixel in the screen. • The bit map memory is arranged conceptually as a series of planes, one for each bit in the pixel value. For example, an eight- plane memory provides 8 bits/pixel, this provides different gray levels or different colours • The display process maps every cell into its corresponding screen pixel brightness or colour. • In order to maintain a flicker-free image the screen must be refreshed at the rate 30 or 60 Hz. COLOR GRAPHICS The value of a pixel in the bit map memory is translated to a Gray level or a colour through a look up table ( colour table, or color map). The pixel values is used as an index for this look up table to find the corresponding table entry value which is then used by the display system (processor and beam deflection system) to control the gray level or colour. COLOR GRAPHICS Color Raster Display With Eight Planes Relationship between pixel value and look up table COLOR GRAPHICS Relationship between pixel value and look up table COLOR GRAPHICS If cell P in the bit map corresponds to pixel P at the location P(x,y) on the screen, then the grey level of this pixel is 50 (00110010) or its corresponding colour is 50. The colour or grey-scale resolution is determined by the number of different colours or grey scales displayable at each pixel, usually measured in bits. Usually, displays are 4 bits (16 colours) 8 bits (256 colours) 16 bits (thousands of colours) 24 bits (millions of colours). Typically 4 to 8 bit/pixel are adequate for both monochrome and colour displays utilised in most engineering applications. COLOR GRAPHICS