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Horizontal Resolution (NTSC video)
 

(Editor's disclaimer, 2008 : this article is very OLD and possibly outdated !!!)


[tech]
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A PC screen may have a resolution of 800 x 600 which means 800 pixels (dots) going across horizontally (width) and 600 pixels going down vertically (height)*.

TV's engineers, however, only speak about TV resolutions in terms of the number of lines going across (resolution width) not down vertically (resolution height)! Why? Because all TV's have exactly the same amount of lines going down (resolution height), but not all TV's have the same amount of discernable dots going across. For example, an American TV picture will always scan (project) 480 lines horizontally (resolution height), but the number of lines going across (resolution width) will always depend on the quality of the TV and the signal broadcast to it.
A VHS video will only offer about 210 dots across while a TV station may offer about 330 dots across!

TV engineers use a test pattern to determine a TV's resolution. This test pattern has lots of vertical lines like this:

The engineer increases the lines until it is impossible to see any lines because they have all blurred into each other. When the lines cannot be seen any more the maximum resolution of the TV has been reached. These test lines are stacked from left to right as seen in the picture above. Because the lines are stacked from left to right, the number of discernable lines across on the TV screen is called the horizontal resolution!

So when we say a TV has 485 lines we mean it has a maximum resolution of 487 dots across. But to say a TV has 487 dots across is never correct since it will always be less unless the signal quality is perfect . . . If we take into account signal loss and low broadcast quality we are looking at something like 330 lines.

           

TV screens have an aspect ratio of 1.33:1 and are slightly oblong.

Video Format.............................. Horizontal Resolution (resolution width)
Standard VHS............................. 210 Vertical "Lines"
Hi8...............................................400 Lines
Laserdisc......................................425 Lines
DV...............................................500 Lines
DVD............................................540 Lines(?) [some actual DIGITAL sizes: 720(w)x480(h), 704(w)x480 or 352(w)x480 ]

Typically, for actual NTSC signals, 485 lines are used for displaying the picture (because real NTSC signals are interlaced, that equals 242.5 lines for each of the two fields making up the frame).

Note: NTSC has a reported horizontal resolution width of 525 lines; not all of these are _visible_!

"We suggest capturing at a resolution that most closely matches the resolution of the video source.
For video sources from VHS, Hi8, or Laserdisc, SIF resolution of 352x240 will give good results.
For better sources such as a direct broadcast feed, DV, or DVD video, Half D1 resolution of 352x480**is fine."

*Note that PC resolutions are typically expressed in "pixel-width by pixel-height"; sometimes abbreviated as (w) x (h) ...
**352 matches the actual visual resolution width of about 330 for TVs; 480 provides that max theoretical visual resolution height.

 

 
Links: (new)
The following article helps clear this up better than I did above:
http://www.hometheaterhifi.com/volume_6_3/essay-video-resolution-july-99.html
   
  
Comments:

Name: John Love-Jensen
Comment Date: Wednesday, May 16th 2007
Regarding (subject or URL)::
http://lyberty.com/encyc/articles/tech/vid_horizontal_resolution.html

Comments:
NTSC has 486 visible scan lines.
The "485 visible scan lines" is only if one prefers to count the two half-wide scan lines
(line 263 at the bottom of field 1, and line 283 at the top of field 2) as 0.5
instead of counting them integrally as a scan line (albeit ones that are only half-wide).


"Private" writes:
Comment Date: Wednesday, June 11th 2008

Comments: "You list VHS as '210 Horizontal Lines' for the Horizontal Resolution. I think it should be 210 Vertical 'lines'. "
[Corrected. Thanks. -Editor]
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