1080i vs 720p (not picture quality)

james.miller said:
there are 30 full frames displayed per second. with interlaced material these frames are split in to fields. all the odd numbered lines are drawn in the first field, all the even numbered lines are drawn in the second field. each two fields = 1 frame.

yes, the screen is 'updated' 60 times a second. it wouldnt matter if it were updated 1000 times a second, there's still only 30 frames to display.
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It's not the same as something being updated at 30fps progressive.

The game is still rendered at 60 fps, but only alternate lines are displayed every 1/60th of a second.

30fps: Whole image changes every 1/30th of a second
60fps interlaced: Half of the image changes every 1/60th of a second

Sure, 30 full fps are drawn each second with both methods but with interlaced you get some of the information quicker, and more up to date since the engine driving this method must refresh at 60fps.

It's a fact that 30fps and 60fps interlaced are not interchangeable terms. 60fps interlaced requires the same resources to render but requires half of the bandwidth to display compared to 1080p.

I apologise for the "even you" comment :)

Edit: I'm strictly talking in terms of consoles so the 1080i60 vs 1080p30 using the same bandwidth is irrevant as they both require different sources for the data, providing a trade off between data and refresh rate.

Edit 2: I have put in bold the most important part that separates the two from a gaming perspective.
 
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Kreeeee said:
Sure, 30 full fps are drawn each second with both methods but with interlaced you get some of the information quicker, and more up to date since the engine driving this method must refresh at 60fps.
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thats where your going wrong, the engine (or at least the image output) doesnt run at 60fps. if it did half of the information would be disgarded anyway. The clue is in that half the bandwidth being needed.

while you do techincally get half a frame quicker, that also means the other field (other half of the frame) is 1/30th second behind the first. if the render engine is chucking out 60fps, that means on the second field the frame being diplays wont actually be the same as the first field (because the engine woul dhave advanced to the next frame) and the end result is the same as running without vsync on a montitor - tearing and other related artifacts.

obviously that isnt desired which is why the engine runs at 30fps. and thats why half the bandwidth is needed:)

I apologise for the "even you" comment
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apology accept:)
 
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james.miller said:
apology accept:)
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I'm cranky from working 7 days a week :(

james.miller said:
thats where your going wrong, the engine doesnt run at 60fps. if it did half of the information would be disgarded anyway. The clue is in that half the bandwidth being needed.

while you do techincally get half a frame quicker, that also means the other field (other half of the frame) is 1/30th second behind the first. if the render engine is chucking out 60fps, that means on the second field the frame being diplays wont actually be the same as the first field (because the engine woul dhave advanced to the next frame) and the end result is the same as running without vsync on a montitor - tearing and other related artifacts.

obviously that isnt desired which is why the engine runs at 30fps. and thats why half the bandwidth is needed:)
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I believe that is why hard vertical lines appear soft during horizontal panning on 360 games (a well documented artifact of 1080i on the 360), because the engine is running at 60fps and the 2 fields are not perfectly in sync as a result.
 
lol so is it 30fps or not?! :)

I can't tell any difference even if it is so meh :p

I will test out 720p again tonight to see whether I still get the crash after 10 mins or not (this has happened pretty much constantly in the past but a quick reset and the console works fine for hours (something I found out after accidently leaving it on overnight lol))
 
Kreeeee said:
I say not truely, james says yes. Eitherway it really doesn't matter at all :p
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lol I was getting confused from both of your posts. :p

For forza 2 though I couldn't care less if it was at 30fps or 60fps in 1080i as the game just looks better.
 
Kreeeee said:
I believe that is why hard vertical lines appear soft during horizontal panning on 360 games (a well documented artifact of 1080i on the 360), because the engine is running at 60fps and the 2 fields are not perfectly in sync as a result.
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thats a possiblilty. ive not seen an xbox360 running 1080i so i couldnt confirm that, but it would go some way to explain that. soft lines when panning are a problem with interlaced signals in general though. imaging in its simpliest form, a straight vertical line pannign to the right on an interlaced display. remember than every other line is refreshed in each field

Code: 
    frame one            frame two
field 1   field 2      field 1   field 2
 :           :            :          :
 :          :             :         :
 :           :            :          :
.:...      .:...        ..:...    ..:...

you can see where each other line is updated the image changes. on any line that pans, you wont have a pin sharp line, you have a 'fuzzy' line as half of it is updated behind the other half.

for clarification, 1080i isnt 60fps as a rule. however, if the xbox 360 is still outputting at 60fps, thats another situation:)
 
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james.miller said:
for clarification, 1080i isnt 60fps as a rule. however, if the xbox 360 is still outputting at 60fps, thats another situation:)
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My arguement was that 1080i60 wasn't the same as 1080p30 (even if my arguement was poorly formulated :p)

It appears we've reached a middle ground :)
 
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