Difference between revisions of "240p video"

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(Created page with 'Taken from http://retrogaming.hazard-city.de/ as a stub Most of the classic systems use a non-interlaced 15kHz output which is compatible to the classic TVs we all had at home i...')
 
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Taken from http://retrogaming.hazard-city.de/ as a stub
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In order to save costs and also to present a stable image on [[interlaced]] displays most games developed before the year 2000, and hence all the consoles and arcade games that played them, are rendered in a resolution around 320 pixels wide by 240 pixels high, commonly referred as 240p. This video mode is actually a hack on top of the NTSC standard, but it works on all SD displays without issues. The trick is to paint only even lines, and instead of painting the odd ones paint the even lines again. This is what causes our beloved scanlines on CRTs; they are actually part of the image.  
  
Most of the classic systems use a non-interlaced 15kHz output which is compatible to the classic TVs we all had at home in the 80s and 90s. That's usually between 220 and 240 lines of visible video, along with 280 to 330 pixels of horizontal resolution. In the 90s 480i output became popular. It provides 480 lines of resolution (but only 240 lines per field = at a time) at 640 to 720 pixels of horizontal resolution. A handful of SNES games used this mode (Ranma 1/2), some Saturn games (Columns Collection), quite some PSOne games (Tobal 2) and actually most of the PS2 games out there. While in theory 240p games don't have to be deinterlaced, 480i can be converted to 480p in a lot of different ways, providing different qualities in the result. 240p games run at 15khz as well and have still to be "upconverted" to 480p (31khz). Many newer TVs won't accept 240p on their component inputs. That's why it's often not an alternative to use a RGB Scart to Component (available for $50 to $100, e.g. from CYP) on those new TV sets.
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Why does all this matter? Simple, this 240p video mode is not considered by displays, and they process it as if it were 480i video, generating even more problems and delay in the process.  
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* [[240p test suite]]
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* [[XRGB-3]]

Revision as of 16:42, 10 May 2011

In order to save costs and also to present a stable image on interlaced displays most games developed before the year 2000, and hence all the consoles and arcade games that played them, are rendered in a resolution around 320 pixels wide by 240 pixels high, commonly referred as 240p. This video mode is actually a hack on top of the NTSC standard, but it works on all SD displays without issues. The trick is to paint only even lines, and instead of painting the odd ones paint the even lines again. This is what causes our beloved scanlines on CRTs; they are actually part of the image.

Why does all this matter? Simple, this 240p video mode is not considered by displays, and they process it as if it were 480i video, generating even more problems and delay in the process.