Frame buffer
- 1. Frame Buffer Presented by Asst. Prof. Aparna Joshi
- 2. Frame Buffer / Refresh Buffer: • It is a digital memory where the image is stored as a matrix of intensity values of pixels. Or • The portion of the memory used to hold the pixels is called “frame buffer”. Or • The Intensity values for all pixels are stored into an array. It is used to raster-scan display. A 1024 x 1024 element square raster requires 220 (210 = 1024, 220 = 1024 x 1024) or 1,048,576 memory bits in a single bit plane
- 3. Digital-to-Analog (DAC) Converter • The frame-buffer is a digital device, while CRT is an analog device, conversion from a digital representation to an analog signal must take place when information is read from the frame buffer and displayed on the raster CRT graphics device. This is accomplished by a digital-to-analog converter (DAC). • Each pixel in the frame buffer must be accessed and converted by DAC before it is visible on the raster CRT.
- 4. A Single Bit-Plane Black-and-White Frame Buffer Raster CRT Graphics Device
- 5. N-Bit-Plane Gray Level Frame Buffer Color or gray levels are incorporated into a frame-buffer raster graphics device by using additional bit planes. Following Fig. schematically shows an N-bit-plane gray level frame buffer.
- 6. An N Bit Plane Gray Level Frame Buffer with W-bit Wide Lookup Table • An increase in the number of available intensity levels is achieved for a modest increase in required memory by using a lookup table, as shown in following fig.
- 7. • Upon reading the bit-planes in the frame buffer, the resulting number is used as an index into lookup table. • The lookup table must contain 2N entries. Each entry in the lookup table is W-bit wide. W may be greater than N. When this occurs, 2W intensities are available, but only 2N different intensities are available at one time. • To get additional intensities, the lookup table must be changed (reloaded).
- 8. Simple 3-Bit Plane Color Frame Buffer • If there are three primary colors, a simple color frame buffer is implemented with 3 bit planes, one for each primary color. • Each bit plane drives an individual color gun for each of the three primary colors used in color video. • These three primaries (red, green & blue) are combined at the CRT to yield eight colors, as shown in table.
- 9. Red Green Blue Color 0 0 0 Black 0 0 1 Blue 0 1 0 Green 0 1 1 Cyan 1 0 0 Red 1 0 1 Magenta 1 1 0 Yellow 1 1 1 White
- 10. Simple 3-Bit Plane Color Frame Buffer
- 11. A 24 Bit-plane Color Frame Buffer • Additional bit planes can be used for each of the three color guns. • A schematic of a multiple-bit-plane color frame buffer, with 8 – bit planes per color, i.e. a 24-bit-plane frame buffer as shown in fig.
- 12. A 24 Bit-plane Color Frame Buffer
- 13. Thank You