Understanding Interlaced and Non-Interlaced VideoWith the introduction of Computers in the home domestic market thus came the arrival of de-interlaced video via the VGA connector. Add to this the development of the flat screen within the home market (i.e. monitor, plasma, projector & LCD) this type of video signal has been brought into the Home Theatre set-ups.
What is Interlaced and de-interlaced video?
To get a picture on any screen, one picture (frame) is made up of two identical pictures merged together. Whether it is interlaced or not, depends how the signal is sent out from the playing device and how it is decoded by the monitoring screen (i.e. TV or Plasma etc.,).
Interlaced Video scans from top to bottom twice to produce one picture (frame) but uses only half of its resolution per scan.
De-Interlaced uses the full resolutions of each scan, therefore improving the picture quality.
What Equipment Uses De-Interlaced Video?
High Definition Televisions (know as HDTV), which are now being introduced to the Home Theatre market, together with Plasma's, LCD's and Projectors.
Plasma's normally have a bank of five phono or BNC's marked R,G,B,H & V when this connection is used it is De-Interlaced Video.
Is De-Interlaced Video known by any other name?
Yes, it is referred to as Progressive Scan.
Progressive Scan is now found on many DVD Players when playing Region 1 discs (NTSC); This is due to the US methods of production, when the actual film is shot, the film has 24 frames per second - but NTSC requires 30 frames per second, therefore 5 static video frames are inserted - without progressive scan these 5 static frames are inserted all at once, which causes jumpy motions experienced with fast moving action. Using Progressive scan these five frames are inserted one at a time across the 25 frames, which is then unnoticeable to the eye.
However, PAL (Region 2) requires 25 frames per second, therefore only 1 static frame per second is inserted, thus eliminating the need for Progressive Scan for this purpose.
What equipment uses Interlaced Video?
All your devices that have either Scart, Phono's, BNC's or SVHS connectors.
What equipment is compatible with De-Interlaced Video (Progressive Scan)?
Only those devices that offer the HDTV or 15-pin D-sub (VGA) connector (that is set for 31.2Khz)
Composite Video, S-Video and Component (YUV) can now be converted to Progressive Scan via a small converter box. See Converting SD to Analogue HD for Lektropacks full range.
Points to Consider when Purchasing a HDTV?
If you are currently using an amplifier for controlling all your AV equipment for both picture and sound, check to see whether your amp can actually handle de-interlaced video or Progressive Scan.
"Out of Range" what does that mean?
When this message appears on your screen it normally means that the screen cannot decode the signal from the playing device.
i.e. An interlaced video signal is being sent to a de-interlaced connection.
What are the Ranges for Interlaced & De-Interlaced Video?
15.6 Khz = Interlaced Video
31.2 Khz = De-Interlaced Video (Progressive Scan)
These are the either/or settings found in your device handbook for the 15pin D-Sub Connector (VGA).
Explanation for the More Technical
Interlaced Video
Interlaced video refers to video that is divided into two fields (upper and lower). Video standards that use interlacing are NTSC, PAL, and SECAM. In interlaced video, an image is drawn on the screen in two separate passes - in the first pass, the first field of information is drawn; the second pass fills in the remaining information for the second field. Non-interlaced video (also called progressive scan) displays video by drawing it on the screen in a single pass from top to bottom.
PAL and SECAM standards both draw images at 25 frames per second (50 fields per second). The field rate will be double the frames per second, since two passes are made to draw each frame on the screen (25 frames per second = 50 fields per second). So, using this standard, interlaced video draws 50 fields of information on a video screen every second. The United States standard is 30 frames per second video thus 60 fields per second.
If you're working strictly with digital video (for computer displays), then you won't have to worry about field settings. Computers display video on a monitor as a sequence of complete frames (non-interlaced). So, video formats designed for computers don't use fields.
Fields
Half of an interlaced video frame containing either all the odd or all the even numbered horizontal lines. The frame is the entire image consisting of two fields. An interlaced image such as the PAL analogue television standard draws all the odd lines of an image followed by all the even lines of an image (first drawing lines 1, 3, 5, 7, and so on then coming back to draw lines 2, 4, 6, 8, and so on). A field consists of all the odd or even lines that combine to create a complete image.
Non-Interlaced (De-Interlaced)
Also known as progressive, this term refers to the way a video image is displayed on screen where each line of a frame (one complete video image) is drawn on screen one after the other (one, two, three, four, five, and so on). This method of displaying a video image is in contrast to interlaced images that draw all the odd lines and then all the even lines in two separate fields to create the final frame or complete image.
However, progressive or non-interlaced video produces a higher quality image. Interlaced video suffers from flicker problems due to the full image not being displayed and from alignment problems where the odd lines do not exactly line up with the even lines. Alignment problems can be particularly bad in video containing fast moving images. Additionally, since fewer lines are projected at any given time using the interlaced format, there is a subjective degradation of picture quality and resolution compared to non-interlaced video.
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