pctechguide.com

  • Home
  • Guides
  • Tutorials
  • Articles
  • Reviews
  • Glossary
  • Contact

Monitor Interlacing

Back in the 1930s, TV broadcast engineers had to design a transmission and reception system that satisfied a number of criteria:

  • that functioned in harmony with the electricity supply system
  • was economic with broadcast radio wave bandwidth
  • could produce an acceptable image on the CRT displays of the time without undue flicker.

The mains electricity supply in Europe and the USA was 50 Hz and 60Hz respectively and an acceptable image frame rate for portraying motion in cinemas had already been established at 24fps. At the time it was not practical to design a TV system that operated at either of the main electricity rates at the receiver end and, in any case, the large amount of broadcast bandwidth required would have been uneconomical. Rates of 25fps and 30fps would reduce the broadcast space needed to within acceptable bounds but updating images at those rates on a phosphor type CRT display would produce an unacceptable level of flickering.

The solution the engineers came up with was to split each TV frame into two parts, or fields, each of which would contain half the scan lines from each frame. The first field – referred to as either the top or odd field – would contain all the odd numbered scan lines, while the bottom or even field would contain all the even numbered scan lines. The electron gun in the TV’s CRT would scan through all the odd rows from top to bottom, then start again with the even rows, each pass taking 1/50th or 1/60th of a second in Europe or the USA respectively.

This interlaced scanning system proved to be an effective compromise. In Europe it amounted to an effective update frequency of 50Hz, reducing the perception of flicker to within acceptable bounds whilst at the same time using no more broadcast bandwidth than a 25fps (50 fields per second) system. The reason it works so well is due to a combination of the psycho-visual characteristics of the Human Visual System (HVS) and the properties of the phosphors used in a CRT display. Flicker perceptibility depends on many factors including image size, brightness, colour, viewing angle and background illumination and, in general, the HVS is far less sensitive to flickering detail than to large area flicker. The effect of this, in combination with the fact that phosphors continue to glow for a period of time after they have been excited by an electron beam, is what creates the illusion of the two fields of each TV frame merging together to create the appearance of complete frames.

There was a time when whether or not a PC’s CRT monitor was interlaced was as important an aspect of its specification as its refresh rate. However, for a number of years now these displays have been designed for high resolution computer graphics and text and with shorter persistence phosphors, making operation in interlaced mode completely impractical. Moreover, by the new millennium display many alternative display technologies had emerged – LCD, PDP, LEP, DLP etc. – that were wholly incompatible with the concept of interlaced video signals.

  • The Anatomy of a CRT Monitor (and CRT TVs)
  • CRT Monitor Resolution and Refresh Rates (VSF)
  • Monitor Interlacing
  • What is the Dot Pitch of a Computer Monitor
  • Dot Trio Monitors
  • Grill Aperture Monitors
  • Monitor Technologies: Slotted Mask
  • Enhanced Dot Pitch Monitors
  • Electron Beam Monitors
  • Monitor Controls
  • The Different Types of CRT Monitors – From ShortNeck to FST
  • What is a Digital CRT Monitor and How Does It Work
  • What is LightFrame Technology?
  • Safety Standards For Computer Monitors
  • TCO Monitor Standards
  • Monitor Ergonomics

Share this:

  • Click to share on Twitter (Opens in new window)
  • Click to share on Facebook (Opens in new window)

Related

Filed Under: CRT Monitors

Latest Articles

ISO 9660 Data Format for CDs, CD-ROMs, CD-Rs and CD-RWs

ISO 9660 is a data format designed by the International Standards Organisation in 1984. It's the accepted cross-platform protocol for filenames and directory structures. Filenames are restricted to uppercase letters, the digits 0 to 9 and the underscore character, _. Nothing else is … [Read More...]

How To Get Two Monitors On One Computer

Sometimes while attending to multiple tasks on your computer you feel the need for more monitor space to get all your work done at the same time. So, instead of getting a new, bigger and  more expensive monitor, you can actually purchase another cheap monitor. Having two monitors on one computer can … [Read More...]

Apple Quicktime

Recognizing the drawback of requiring a costly playback adapter, Apple developed a video format that can be played without special add-on hardware. The result, QuickTime, represents a major milestone for digital video. It provides a multimedia … [Read More...]

2021 PC Hardware Releases to Bolster Your Gaming

If you are a PC gamer, then chances are you are looking to upgrade your kit over the coming year. However, a lot of money can go into building the … [Read More...]

New Transfer Feature in Dropbox Enable Sharing files with Third Parties

Dropbox has been a popular P2P sharing platform for many years. They don't announce new features as often as other applications, since they have a … [Read More...]

Ransomware Operators Find Data Theft Profitable

How valuable is your data? That’s not a question that organizations or individuals have to ask themselves all that often. You might know the market … [Read More...]

Engineers Encounter the Quantum Challenge with Computers Running a Hundred Million Times Faster

Quantum computers have been a subject of discussion for many years. They have probably been something that philosophers and technology pundits have … [Read More...]

Transferring Image Files from Your Cell Phone Without Cables or Email

You don't have a cable available to transfer the photos from your cell phone to your computer? You don't feel comfortable sending them through your … [Read More...]

Why Drupal Accessibility is Vital for Your Website

Drupal may not be as popular as WordPress, but it is still used in over 1 million websites. The Internet might be more conducive to our needs if more … [Read More...]

Guides

  • Computer Communications
  • Mobile Computing
  • PC Components
  • PC Data Storage
  • PC Input-Output
  • PC Multimedia
  • Processors (CPUs)

Recent Posts

HAD Flat Panels

All of the displays discussed hitherto - whether they're made of liquid crystal, phosphors or plastic - have one thing in … [Read More...]

How Does a Virus Impact my Computer?

One of the most dreaded nightmares for any computer owner is viruses, spyware or malware. A computer virus is an executable file or program that has … [Read More...]

Transfer VHS to DVD Method

Transferring  a VHS tape  to a DVD sounds like something hard to do but in reality it's not.  It's basically taking what is on tape and converting it … [Read More...]

[footer_backtotop]

Copyright © 2021 About | Privacy | Contact Information | Wrtie For Us | Disclaimer | Copyright License | Authors