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zx screen 2

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  • Catalin
    ... No. -- ... I didn t understand at first, so I plugged my Spectrum and PS1 into my TV and looked closely at the screen. There are faint black gaps between
    Message 1 of 1 , Jan 7, 2011
      > So basically the spectrum generates only F1 frames, 50 times a second.

      > But what happens with lines that are contained in F2 frames, are those

      > updated?


      No.


      --


      > I don't understand, if I only generate F1 frames, I should have

      > black lines in F2 frames because those are not updated.


      I didn't understand at first, so I plugged my Spectrum and PS1 into my TV and looked closely at the screen. There are faint black gaps between the F1 scan lines, but they're not really noticable.

      Then I realised I was thinking "digital" and not "analogue". The TV screen contains a sheet of phosphor with RGB spots arranged into little triangles along a scan line. However, the triangles of odd and even scan lines overlap slightly, so there is a slight blurring between lines 1 and 2, 3 and 4 etc:

      ----- ----- -----

      \R|G/ \R|G/ \R|G/ Line 1

      \\B//R\\B//R\\B//

       \ /B|G\ /B|G\ /  Line 2

      -- ----- ----- --

       / \R|G/ \R|G/ \  Line 3

      //R\\B//R\\B//R\\

      /B|G\ /B|G\ /B|G\ Line 4

      ----- ----- -----

      Therefore, the effect of not supplying every other scan line does not produce such a noticeable blank line. The downside of the blurring is that it reduces the perceived vertical resolution by about 30%.

      An odd line frame is known as Field 1, even line frame as Field 2.

      Most LCD televisions on the other hand have a regular and square pixel matrix, where pairs of odd and even scan lines do not overlap:

      +-----+-----+-----+-----+

      | RGB | RGB | RGB | RGB | ... Line 1

      +-----+-----+-----+-----+

      | RGB | RGB | RGB | RGB | ... Line 2

      +-----+-----+-----+-----+

      | RGB | RGB | RGB | RGB | ... Line 3

      +-----+-----+-----+-----+

      | RGB | RGB | RGB | RGB | ... Line 4

      +-----+-----+-----+-----+

      In this case, blank lines would be visible. However, I believe that these televisions and displays know when single field frames are being displayed (F1 or F2) and digitally fill-in the missing lines by duplicating the previous line.



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