Frame buffer

This presentation contains -
- Frame Buffer
- Digital-to-Analog ( DAC ) Converter
- Single bit plane frame buffer
- N-bit plane frame buffer
- 3-bit color frame buffer
- 24-bit color 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 2 20 (2 10 = 1024, 2 20 = 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 2 N entries. Each entry in the lookup table is W-bit wide. W may be greater than N. When this occurs, 2 W intensities are available, but only 2 N 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 Black 1 Blue 1 Green 1 1 Cyan 1 Red 1 1 Magenta 1 1 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