Quantcast Would Overscan Improve or Worsen Picture Quality for MPEG-1 ? - digitalFAQ.com Forums [Archives]
  #1  
06-30-2003, 04:57 AM
Sykes Sykes is offline
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1st question is ... Knowing that this feature can save space can someone tell me if using this would improove or worsin the picture quality for mpeg1 kvcd ?

2nd question ... say a movie without this feature goes at 75% CQ,
does this mean that if i enable tis option on the same movie will i be able to copy at a higher CQ lets say 80-85

Thankx in advance
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  #2  
06-30-2003, 06:10 AM
serrabastien serrabastien is offline
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With overscan you encode less pixels so for the same space your bitrate is higher and then the quality is improved.

In fact :
- if you keep the same bitrate (min, max, CQ), your final file will be smaller for the same quality,
- if you want to keep the same file size, your bitrate (CQ value) will be higher and so the final quality will be improved.

'Z
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  #3  
06-30-2003, 06:34 AM
Sykes Sykes is offline
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Thank u very much "Z"
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06-30-2003, 06:44 AM
Sykes Sykes is offline
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How come we cant see the " overscaned" Black bars on our tv's then?
Our our dvd players limited ta only showin vcd compliant picture ?
Or whats the logical explination for this
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06-30-2003, 07:17 AM
Dialhot Dialhot is offline
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Quote:
Originally Posted by Sykes
How come we cant see the " overscaned" Black bars on our tv's then?
Our our dvd players limited ta only showin vcd compliant picture ?
Or whats the logical explination for this
There's a technical reason : you TV is _always_ setted to "eat" a small part of the picture on all sides.

This is done to avoid to have people returning their TV set to the shop telling "there is some distort on the border on the picture, fix it !".
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06-30-2003, 07:43 AM
serrabastien serrabastien is offline
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That's right. Some TV eat more or less part of the picture.

With my TV (Thomson 19/9 63cm) I can use overscan=1 for 352x240(28 res and 2 for higher res (>352x480(576)).

Btw overscan doesn't cut/eat the picture but resize it. So if you make the comparaison with a dvd source you will finally have a smaller picture but with "all" the pixels.

'Z
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  #7  
06-30-2003, 08:16 AM
Sykes Sykes is offline
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So what u guys r saying is basicly the cuttoff point for all tv's is different?
Does that mean if i cant see no little black bars on this tv
(if i use overscan) But if i go buy a diff tv it could show the borders >?
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06-30-2003, 08:20 AM
serrabastien serrabastien is offline
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I've tried some KVCD on some different TV and yes sometimes this borders appears (Try it on you PC screen.... you'll see them )

But you'll usually not see them.

'Z
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06-30-2003, 08:30 AM
Sykes Sykes is offline
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Like i guess what i'm sayin is that i dont wanna use overscan if they are gonna show on tv sets i buy later on , On the tv i got now 27 inch it doesnt show, But on my computer it shows
What do u figure 1 should do ?

1 Stop using overscan period ... or

2 use it cause u think only older tv's would be dumb enough ta show it & that the newer ones should'nt show it
?
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  #10  
06-30-2003, 08:32 AM
audioslave audioslave is offline
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I believe I read somewhere (on this forum) that overscan loses pixels on the height. Is that correct or have I misunderstood the whole thing?
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  #11  
06-30-2003, 08:34 AM
Sykes Sykes is offline
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I dunno lets ask "Z" He seems ta know his tech stuff
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  #12  
06-30-2003, 08:37 AM
audioslave audioslave is offline
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Good idea, Sykes. So, Z, what do you say?
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  #13  
06-30-2003, 08:47 AM
serrabastien serrabastien is offline
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Maybe i'm wrong but I don't think overscan cut lines.
I've made some test on my TV and i thought all pixels were present, the picture was a bit smaller (test made with Star Wars Ep1, borders were biggers and details appeared on left and right side).

'Z
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  #14  
06-30-2003, 08:53 AM
Sykes Sykes is offline
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Hmmm maybe its not such a bright idea using overscan,
Maybe I should jus leave it without borders at 528x480
That way its smaller then dvd (which is at 704x480) BUT it will never show borders on any tv ... Depends on how u like it, Im a perfectionist lol
I use tmpeg & avi synth 2.52 for everything, (Only so i can cut the movie into a 2 cd movie & cut it where i want it to say change disc (not where tok decides) lol
Put together with all of avisynth2.52's filters the tmpeg sharp filter is wicked when u goto -64 (removes blocks & makes them rounder
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  #15  
06-30-2003, 08:56 AM
audioslave audioslave is offline
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No, you're absolutely right 'Z!
I found the post I was refering to. And I found out that "overlap" (letterbox) covers part of the video and "overscan" resizes the video. That's it!
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  #16  
06-30-2003, 10:58 AM
Jellygoose Jellygoose is offline
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However you were right audioslave. When you use overscan, the whole picture will be resized differently, so that the height will be reduced too.
If you want to avoid this I'd recommend using Letterbox filter.
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  #17  
06-30-2003, 11:48 AM
jorel jorel is offline
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excuse me friends,let me "jump" here.
tv was my job,write in english don't.
maybe i can help a little.


'Z post: "...on some different TV and yes sometimes this borders appears"
right,depend of the "internal" tv adjusts(not by the user).
the adjusts aren't perfects and some tvs show the borders, others none.
one model never show the same like other model,
you can adjust it with extreme precision but you got differents results.

Sykes post:"...Im a perfectionist lol..."
me too my friend, better is burn a sample with overscan1 and 2
to test your tv. i have 5 and only can use overscan1 in one model or
it show borders, the others i can use overscan2!

audioslave post:"...overscan loses pixels on the height. "
depend of the resizer.i see differences uing gripsize and bicubic.

Jell post:"...so that the height will be reduced too.."
yes,like i talk(talk?),depend of the resizer.

load one script with gripsize and another
with bicubic in vdubmod or ToK...
you will see the differences(in thin details)
and loose little size image in the height!




important:
why i call Jellygoose as Jell?
cos he's a friend of mine!

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  #18  
06-30-2003, 08:54 PM
Sykes Sykes is offline
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Thankz jorel ... I'm gonna try the 1, My tv can handle overscan 2 but I'd rather not loose to much pixels,
Thing is kvcd needs at least alil overscanning say at 1 with the sharp-blur feature for tmpg at -64 & i get great results
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