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Losing resolution when letterbxing?

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Eoin Ryan
Losing resolution when letterbxing?
on Nov 2, 2008 at 3:41:06 am

"Rescaling anamorphic video in order to see the entire wide screen frame on a standard definition 4:3 monitor is called "letterboxing," and results in the loss of the maximum resolution available in the source footage."

from: http://support.apple.com/kb/TA26788?viewlocale=en_US

Can someone explain to me why this action loses resolution? Thanks.


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Noah Kadner
Re: Losing resolution when letterbxing?
on Nov 2, 2008 at 4:23:50 am

Pretty simple- you are using less screen area. With 16:9 you fill the entire frame with anamorphic shaped pixels. With 4:3 letter box you only fill the area within the black bars. So that's all the black bar area wasted. This might help:

http://www.thedigitalbits.com/articles/anamorphic/anamorphic185demo.html

Noah

My FCP Blog. Unlock the secrets of the DVX100, HVX200 and Apple Color and Win a Free Letus Extreme.
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Eoin Ryan
Re: Losing resolution when letterbxing?
on Nov 12, 2008 at 10:54:12 pm

If there is less area used when letterboxing, does this not mean there'd just be the same if not HIGHER resolution? I mean, if you pack more pixels into a smaller space, usually, the resolution is higher...



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Johan Nordanfors
Re: Losing resolution when letterbxing?
on Nov 17, 2008 at 4:55:35 pm

The pixels don't scale with the image. The number of pixels per area (or more accurate: vertical lines per frame) is constant in the wonderful world of video. Therefore when you downsize an image within a video frame you are effectively reducing the number of pixels (lines) that make up the image. Thus achieving less resolution.

The key is to understand the relationship between the frame and the footage.



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Eoin Ryan
Re: Losing resolution when letterbxing?
on Nov 17, 2008 at 11:06:09 pm

Can you elaborate further or point me towards an article explaining this? I don't get it. Thanks.



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Johan Nordanfors
Re: Losing resolution when letterbxing?
on Nov 18, 2008 at 10:37:10 am

I haven't found an article that explains it in detail but these I found somewhat informative.

http://www.optomahometheater.com/howto/b5_2.asp

http://www.theprojectorpros.com/learn-s-learn-p-theater_anamorphic_dvd.htm

http://www.sandelinmedia.com/widescreen/index.html
(esp. the discussion on the bottom of the page)






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Eoin Ryan
Re: Losing resolution when letterbxing?
on Nov 19, 2008 at 2:30:55 pm

Thanks for the links.

I was a bit startled when reading the following from the "widescreen on video" link. I use a Canon XL2 and shoot 16:9 50i PAL footage and burn anamorphic DVDs. Does this mean I'm not getting widescreen? What does he/she mean by "standard formats use anamorphic techniques"?

"There is no true 16:9 resolution for standard video, including DV, even though some newer DV cameras are being marketed as "true" 16:9 (in reality, only their picture sensors have a 16:9 aspect ratio). Standard formats use anamorphic techniques to get a widescreen 16:9 picture - i.e the final displayed picture has a wider aspect ratio than the video frame."





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Johan Nordanfors
Re: Losing resolution when letterbxing?
on Nov 20, 2008 at 1:31:54 pm

I was a bit startled when reading the following from the "widescreen on video" link. I use a Canon XL2 and shoot 16:9 50i PAL footage and burn anamorphic DVDs. Does this mean I'm not getting widescreen? What does he/she mean by "standard formats use anamorphic techniques"?


It simply means that the only difference between 4:3 and 16:9 in the world of standard definition is how the frame is presented on screen. The formats are both stored in the 720x576(PAL) frame but will be stretched out differently when presented on your screen. There is no true widescreen frame format in that sense. A true widescreen format would be one where the information coming from the lens/ccd panels of your cam is stored in a 1:1 pixel aspect ratio frame. Ideally that would be 1024x576 in SD.

But to answer your first question: Yes you are getting as much widescreen as SD permits, though the correct technical term for "full" widescreen in SD is Anamorphic Widescreen. The term anamorphic has a long history in filmmaking and refers to the specific type of lens used to squeeze a wide picture onto a narrow chemical film. To get the wide picture stretched out again you just had to reverse the process in the playback projector.



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Eoin Ryan
Re: Losing resolution when letterbxing?
on Nov 22, 2008 at 4:32:50 am

I've been burning 16:9 SD DVDs the way I've been told in iDVD. It's anamorphic and fills the screen of my 42" inch plasma widescreen TV. However, when filling the screen it seems stretched vertically. This is in the 'Auto-Wide' setting on my TV. If I press a button on my remote and change the setting to 16:9, then the TV displays the image with black bars and this is a lot more pleasing to watch and doesn't look stretched. In fact, it's perfect. What gives here? I thought 16:9 footage is supposed to fill a 16:9 TV? Don't get me wrong - it's not that badly stretched - but I can notice that wheels on cars aren't perfectly round.



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Johan Nordanfors
Re: Losing resolution when letterbxing?
on Nov 22, 2008 at 12:06:13 pm

Obviously there is something wrong in your production flow because had you done everything right you would have had an image that filled your widescreen tv without looking stretched. If I were you I'd shoot some reference footage and run it through your normal production routines. Shoot something you know to be perfectly circular, and shoot it from the side in a straight angle. Center the object in your footage so that you can use it to judge if any sqeezing or stretching occurs later on in your process. If everything is correct you will see the same perfect circle in your footage on a widesreen screen without any bars.



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Eoin Ryan
Re: Losing resolution when letterbxing?
on Nov 28, 2008 at 3:03:46 am

I shot a wheel of a car. Tested it. I was seeing things. It wasn't stretched at all. All is good. Although, I still think the 16:9 TV setting is better for anamorphic footage (I guess it will differ from TV to TV), but the 16:9 setting on my 42" Samsung Plasma TV gives the footage black bars and it looks a lot better.



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