| |
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?
|
|
... 64 posts hidden. Click here to view all posts....
|
| |
JackAsser
Registered: Jun 2002
Posts: 2014 |
"does the TV know anything about odd/even fields, or that is entirelly driven by the incoming signal?"
It's driven by the signal. The half PAL line you sometimes see on the bottom of one of the fields actually makes the next field jump down half a raster line. C64 never outputs this line, thus the fields never jump up and down => progressive display.
About chrominance, that's simply that the color data has half y-resolution (per field). The chrominance data is not "re-used" between different fields.
One field consist of 720/(576/2) luminance pixels and 720/(576/2/2) chrominance pixels.
On the C64, the same field is output twice without any half PAL line on the bottom, thus u effectivly get 720/576/2 resolution, progressive with 720/576/2/2 chrominance resolution.
|
| |
chatGPZ
Registered: Dec 2001
Posts: 11360 |
Quote:About chrominance, that's simply that the color data has half y-resolution (per field). The chrominance data is not "re-used" between different fields.
ah yes "re-used" is the wrong term. what happens (originally, in older, analog tv) is that the chrominance while beeing used for the current scanline it is also feed into a delay-line (in the simpliest case this is literally just a very long wire) and then in the next scanline (of the current field) the signal coming out of the delay line is used for chrominance.
confusion complete? =D |
| |
Oswald
Registered: Apr 2002
Posts: 5086 |
groppie:I've checked wiki, and it says the chrominance averaging/delaying stuff is done to eliminate errors (transmission bugs?) originally it was NOT used in the early tvs.
edit: thus the chrom data is not truly half reso, rather avged with prev line. |
| |
Oswald
Registered: Apr 2002
Posts: 5086 |
jack, how do I interpret all those magic numbers?:) |
| |
chatGPZ
Registered: Dec 2001
Posts: 11360 |
the wiki is wrong :) the chroma signal is half resolution to save bandwidth. the averaging thing is true however, the current scanline chroma will always be a mix of 1 third of the previous scanline chroma and 2/3 of the current scanline chroma. (no, its not like this, its more complicated, but i forgot =D) |
| |
MagerValp
Registered: Dec 2001
Posts: 1074 |
To understand how a CRT display works, stop thinking about pixels and lines. It's an analog display, and everything is driven by timing. Lines are not horizontal, but drawn in a zig-zag pattern. There are no pixels, but an electron cannon firing continuously at a phosphor layer that lights up for roughly 1/50th of a second. There are no dim 2/3rd lit up half scanlines inbetween, that's just how VICE approximates the effect of CRT dot pitch on high resolution PC displays.
Talking about odd or even fields on the VIC is also pointless, as you only have fields in interlaced video modes. The VIC outputs 50 frames per second, and no fields. Not odd, not even. The VIC does not output a spec conforming video signal, but it works because CRTs are not intelligent - they have no concept of odd and even fields. An interlacing video output device (Amiga's Denise, your TV receiver, whatever) "tricks" the CRT into moving every other field half a scanline down by delaying video signal 32 microseconds.
Please go read some articles on how CRTs, and especially interlaced video, works.
|
| |
MagerValp
Registered: Dec 2001
Posts: 1074 |
Quote: the wiki is wrong :) the chroma signal is half resolution to save bandwidth. the averaging thing is true however, the current scanline chroma will always be a mix of 1 third of the previous scanline chroma and 2/3 of the current scanline chroma. (no, its not like this, its more complicated, but i forgot =D)
Please don't bring chroma mixing into this already confused discussion :P
(and it's 50:50 mixing btw, though technically it varies from CRT to CRT, and it has half the *horizontal* resolution)
|
| |
Oswald
Registered: Apr 2002
Posts: 5086 |
alrighty its nor odd nor even scanlines still there must be in some (to me unknown) form every 2nd line skipped. isnt it? on some TV's you can stretch/shrink the screen horizontally / vertically. but neither of that messes up the display. so when adjusting the vertical size the half lines must be still there in some timed form. also the outside signal can tell the tv wether its an odd or even field how does that happen ? |
| |
chatGPZ
Registered: Dec 2001
Posts: 11360 |
Quote:also the outside signal can tell the tv wether its an odd or even field how does that happen ?
jackasser already said how that works, wether the next field is odd or even is determined by the length of the last scanline. (and again, this is why/how the "true" interlace on the c128 works - it manipulates the length of that very scanline) |
| |
Oswald
Registered: Apr 2002
Posts: 5086 |
why can then magervalp say that the vic's output is nor odd nor even ? it must be either this or that!! |
| Previous - 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 - Next |
