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Oswald
Registered: Apr 2002
Posts: 5086 |
VIC and the odd/even fields
okay this is getting confusing for me now. in another thread on lemon64 groepaz says that the vic does always display the same field, but it doesnt matter if its odd or even, and it lights up both the odd/even lines.
some1 can tell me:
- does vic use odd or even or dontcare lines?
- what does the term field mean from the tv electronics viewpoint?
- how does the vic only light up the odd (forex.) lines on the tv screen, and a little bit from the other ones?
- are there really 2 modes in the tv electronics for odd / even fields
- why does computer graphics flicker a hell more lot while "normal" tv screens looks as steady as my ass?
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chatGPZ
Registered: Dec 2001
Posts: 11360 |
Quote:why can then magervalp say that the vic's output is nor odd nor even ? it must be either this or that!!
no, since both fields are the *same*, there is no "odd" or "even" field technically :=) |
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Oswald
Registered: Apr 2002
Posts: 5086 |
sdglékjasflékgjsdfkljglasfjkglsdfkglsdfg
*pulls all hair out*
but its either all odd or all even no matter what. the last scanline clearly determines that. |
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chatGPZ
Registered: Dec 2001
Posts: 11360 |
Quote:but its either all odd or all even no matter what. the last scanline clearly determines that.
yes :=) |
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Oswald
Registered: Apr 2002
Posts: 5086 |
SIGH
then why do ppl always say it neither odd neither even when its clearly one of them. |
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chatGPZ
Registered: Dec 2001
Posts: 11360 |
its just terminology.... technicans only refer to odd and even fields when there is actually interlace taking place. |
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Oswald
Registered: Apr 2002
Posts: 5086 |
.. making something incredibly simple concept incredibly hard to understand. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
oswald. listen. the CRT is all about timing as magervalp says. Since one of the fields is delayed due to the last line is longer on the previous field, that effectivly moves down the display half a line.
Also, CRTs doesn't "skip" every 2nd line. see it like:
OE
DV
DE
_N
1
1
12
12
32
32
34
34
_4
_4
The CRT it self doesn't know about fields, it simply displays frames, a new one on each vertical sync. In PAL 50 per second and by altering the length of the last rasterline every 2nd frame you effectivly wiggle the display up and down half a pixel, thus get a preceived higher resolution to the cost of 25hz motion instead (u don't want the two fields to be separated in time because that leads to weaving artefacts when moving).
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Oswald
Registered: Apr 2002
Posts: 5086 |
jack, now that is starting to make sense, but brings up new questions: why is every "2nd" line darker when the vic drives the CRT if the CRT effectively scans every line ?
2ndly according to wikipedia the fields are indeed seperated in time.
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JackAsser
Registered: Jun 2002
Posts: 2014 |
@oswald, simply because the raster beam moves in a zig-zag pattern. During a horizontal sync the signal is ultra-black and when that happens the TV starts moving the beam back to the left + moves it down a bit. Hence, if your beam is narrow enough and your screen has a dense enough fosfor-thingie then you'll see the individual scanlines quite easy.
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: jack, now that is starting to make sense, but brings up new questions: why is every "2nd" line darker when the vic drives the CRT if the CRT effectively scans every line ?
2ndly according to wikipedia the fields are indeed seperated in time.
@oswald, the fields are NOT separated in time. Either u misunderstand the wiki OR the wiki is wrong. The fields CAN be separated in time, but TV-signals generally are NOT. Badly re-interlaced movies by lame-ass converter-kiddies usually have the fields separated though. ;D
Of course every other field is shown 20ms after the other one, but the content it displays belongs to the same time frame when the camera snapped them.
You CAN separate the fields in time so that each field effectivly has a strickly forward time-pointer, but that will yeild weiving artefacts (plz see my twister in LCP Memories). The upside is that motion gets 50hz, downside is that effective resolution is halved, conclusion bandwidth is the same.
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