Bandwidth for colour signal transmission.
The following section gives an overview about the Bandwidth for Color signal transmission.
Overview of the Signal transmission:
- The Y signal is transmitted with full frequency bandwidth of 5 MHz for maximum horizontal details in monochrome.
Such a large frequency spectrum is not necessary for colour video signals because:
- For very small details, the eye can perceive only the brightness but not the colour.
- Perception of colours by the human eye, which are produced by combinations of the three primary colours is limited to objects which have relatively large coloured areas (≈ 1/25th of the screen width or more).
- On scanning they generate video frequencies which do not exceed 0.5 MHz.
For medium size objects or areas which produce a video frequency spectrum between 0.5 and 1.5 MHz, only two primary colours are needed because:
- For finer details the eye fails to distinguish purple (magenta) and green-yellow hues from greys.
- As the coloured areas become very small in size (width), the red and cyan hues also become indistinguishable from greys.
- Thus for very fine colour details produced by frequencies from 1.5 MHz to 5 MHz, all persons with normal vision are colour bling and see only changes in brightness even for coloured areas.
Minimum and Maximum bandwidth:
- Therefore, maximum bandwidth necessary for colour signal transmission is around 3 MHz (± 1.5 MHz).