Friday 31 March 2017

Video Quality Vs. Data Rate

       Public are groomed to have insatiable appetite for high resolution,  vivid colour images and videos. This unending desire in one end helps the consumer durable manufacturers to have market for new model televisions and cameras.  In other end the engineers have to burn their mid night oil to find ways and means to solve the challenges posed by high resolution images. 

            Increase in image resolution has a direct bearing on generated volume of data. Few examples are presented to substantiate the claim. Next, reasons for the inability of conventional CMOS interfaces to transport digital data pertaining to high resolution images are discussed.
         

Case I: Digital TV

            In Television (TV) series of frames (images) are shown in succession to create a illusion of motion or continuity. In American system 30 frames are shown per second and European systems use 25 frames per second. In olden day televisions, picture resolution is measured by number of lines and not by number of pixels. They use interlaced scanning with an aspect ratio of 4:3 (Width Vs. Height) is employed. In a digital (Standard Definition or High Definition) TV picture resolution is measured by pixels . Each colour pixel have red, green and blue channel with 8 bit width. So, each colour pixel takes up 24 bits. 

            Net data generated by conventional digital TV titled 480i (suffix i denotes interlaced scanning mode) is
 
480 (V) x 640 (H) x 30 (fps) x 24 (bits) = 0.22 
Gbps (Giga bits per second)             (1)

where V = Resolution in Vertical direction, H= Horizontal direction, fps = frames per second