Question 8
A graphic display system has a frame buffer that is 640 pixels wide, 480 pixels high and 1 bit of color depth. If the access time for each pixel on the average is 200 nanoseconds, then the refresh rate of this frame buffer is approximately :
Answer : (1) 16 frames per second
Given Values:
Frame buffer width is 640 pixels = horizontal line on screen
Frame buffer height is 480 pixels = vertical line on screen
Color depth is 1 bit
Solution:
Framebuffer is the size of the maximum image that can be displayed.
Screen forms a Matrix of pixels with width of 640 and height of 480.
No of total pixels in the frame buffer = (width x height)= 640 x 480 px = 307200
Here, color depth is 1 bit.
Memory required by frame buffer = Memory required for total pixel =
Total pixels in the frame buffer x (Color depth) = 307200 x 1
If access time for each pixel on the average is 200 nanoseconds
Time requires to refresh the "whole screen" or "frame buffer" = Memory required by frame buffer x 200 ns = 61440000 nano second = 61440000 x 10−9 second
Then, refresh rate of frame buffer =
number of frame changes per second = 1 / 61440000 x 10−9 second = 100,00,00,000 / 61440000 = 100,000 / 6144 = 16.2760 = 16 (Approximately)
So, Option (1) is correct answer.
What is color depth?
Color depth, also known as bit depth, is either the number of bits used to indicate the color of a single pixel, in a bitmapped image or video framebuffer, or the number of bits used for each color component of a single pixel.
Reference: Color depth
Here Color depth is 1 bit. bit can either depict 0 or 1, i.e., the two colors used for a binary image are black and white. Image with 1 bit color depth is called 1-bit monochrome.