SansGrip Filters: How To Use "Overscan" together with Letterbox
 

Hi all!

Ok here's my idea:

When using Blocks TV Overscan with the KVCDx3 Template, I usually use the value 2, as recommended.
however with very letterboxed movies, the height of the movie will decrease also a lot, which sometimes really sucks as the borders just get too big for my taste... :wink:
So for these movies I usually use Letterbox(0,0,16,16) which cuts off 16 pixels at each side...
Now I tried to combine these two methods, in order to get a compromise between maximum height AND maximum width (because Letterbox just cuts off pixel, which Overscan doesn't...).
I therefor had the idea to use let's say overscan=1 + Letterbox(0,0,8,8 ).
Anyone can tell me if this works, because for me it didn't... Where do I have to put the Letterbox Line if I want to use both, letterbox and overscan?

Btw: I think Letterbox can also handle values like (0,0,10,10), which makes it a good choice if you want maximum compression by only displaying as much as your TV shows... you can test how many pixel you can cut off the edges, without getting visible borders on your TV!

Re: How To Use "Overscan" together with Letterbox.
 

Yep! I totally agree with you.
I use it in the same way... When I want to preserve the same height of the source, I use NO Overscan and use Letterbox(0,0,16,16). That's for widescreen sources, If your source is fullscreen, then you can use Letterbox(16,16,16,16).


Yes, but it will cut off pixels that you would not see with the source either (in the same TV).


If you want to preserve more width information then you have to sacrifice a little height view. That's what you do if you use overscan=1. But you can still use letterbox=16, because you still want to have the 16 less lines to encode.
Put the letterbox at the end of your script, just before the sampler().


Well, with my TV I can go as far as 20 (with 544x480), but I stay with 16 because it's the size of the macro blocks. And I like to have this 4 pixel safety margin. :wink:

I'm not sure if I understood you the right way muadibb :wink: ...

So Letterbox in fact does the exact same job that Overscan is doing :?:

Because when I use Letterbox(0,0,16,16) on a widescreen movie, of course the height is preserved... But it seems to me that there are pixel missing on the sides which ARE visible in the source... (does that make sense to you) ?
I could see this very clearly, viewing Austin Powers 3 , when there were some letters missing in the beginning of the movie, where the credits were shown...

however If I understood you correctly If I wanted to cut 2 more lines on each side (18 instead of 16) AND use overscan, I would use Overscan set to 2 PLUS Letterbox(0,0,18,18) :?:
or would that mean that I only cut pixel from the sides?

sorry for being a pain in the rear buddy :wink:

LetterBox doesn't add borders, it just creates a black area over the existing film pixels. AddBorders doesn't cover any existing film pixels, that's why it's used as overscan blocks.

Edit: LetterBox is very handy if you capture from a VHS tape as there's often some garbage at the bottom of the screen.

that's what I thought...

So putting the line Letterbox(0,0,2,2) after the Gripborders() line would give me 2 pixel of additional border (blackened out video) on each side right?

@muadibb: I know the size of a macroblock is 16 and therefor the borders should be a multiple of this but, do you really see a difference? Well I guess I just try for myself, but my encode of A Beautiful Mind w/ FaeryDust and C3d is taking forever :wink: ... sometimes I just get too crazy about all this I guess...

No! When you use overscan, you are resizing the full frame smaller than the desired size and then ADDING black borders to compensate the small resize and "fill" the space that was missing to reach the desired resolution. That's why you end up with a small height then your source.
Letterbox, as Boulder said, just overlap the frame with black borders.


Well, when talking about overscan or letterbox all depends on what resolution you are using, because placing a 16 pixel border over a 740x480 frame is totally different then placing a 16 pixel border over a 352x480. In the last case, the 16 pixel will be stretched much more.

When you say that there are pixels missing on the sides, are you watching it on your monitor or on your TV?
I'm asking it because of course there are missing pixel on the sides. Using Letterbox(0,0,16,16) you are blacking 16 pixel columns of the left side and 16 pixel columns of the right side. But in a normal TV you would not see these pixels anyway. Got it? :D

I think that using the "resize" method of overscan or using the "overlap" method of letterbox is a matter of taste.
The first you preserve the full visible width and get a smaller height.
The second you maintain the full visible height, but cut some side pixels.
I prefer the second one... :wink:


Yes, that's it.
If you use overscan, you will get the smaller height (and width). Then you will be letterboxing the overscan's side borders + 2 pixels.


You are not! :mrgreen: :mrgreen:
I'm happy if I can help. :D

NO!
Well, at leats if you use some overscan in the GripSize...
Gripborders will add the overscan borders, then you will place 2 pixel black border over the already black border from overscan.


NO. :mrgreen: :mrgreen:
But I use it... just for the hell of it. :mrgreen:

Ok thanks muadibb and boulder! you helped a lot!

:)