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Masking...what is it.?

Discussion in 'Projectors, Screens & Video Processors' started by museumsteve, Mar 11, 2002.

  1. museumsteve

    museumsteve
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    I keep reading about masking screens etc, but I assumed (stupidly) that is was just finishing the screen edge off. I guess it isn;t as the last post I saw mentioned light spill and 3D image (not real 3D obviously)..
    So can anyone simply explain it to me as I'm in the middle of my new project room right now and the screen is due to go this Thursday/Friday and I'd like to make changes if needed..Thanks as always.:)
     
  2. calibos

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    Masking is framing your projected image according to what ratio screen you have and what ratio image you are projecting. What this means is that:

    If you have a 4:3 ratio screen and you are watching a 4:3 image then you are using the whole screen area so you don't need masking. If you're watching 16:9 material then there will be small 'black' bars above and below the image. ie you wont be using the full area of your 4:3 screen. These 'black' bars aren't really black though. Although your projector isn't projecting light on these areas, there will be some light spillage from the projector and also reflected light back off your walls and ceilings etc. So these 'black' bars will actually be grey. This doesn't help the perceived contrast of the picture though so most people using masking on their screens which could be a piece of black velvet attached to the screen with velcro covering the 'black' bars This material soaks up the light and improves the percieved picture quality. In more expensive home cinema installs there would be motorised masking bars the move into position in front of your screen according to the ratio of the movie being watched. With a 2.35:1 ratio film the bars would be bigger and you have to mask more of the screen.

    On a 16:9 screen you wouldn't have to mask for 16:9 films but would have to mask a small portion of the screen top and bottom for 2.35:1 movies. For 4:3 material projected onto a 16:9 screen you would have to mask left and right of the image unless you used a mode on the projectoer to stretch the 4:3 to fill the 16:9 screen. Your PT AE100 has a mode called 'Just' that does this as does your new Sony VW11ht and most widescreen tvs for that matter.

    Hope this clears it up for you.
     
  3. jrwood

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    Well if you have a 4:3 projector and use it for a Home Cinema most people mask using Velvet/BlackOut Material ABOVE and BELOW their 16:9 projector screen. All this does is absorb the light of the 4:3 projected light around the 16:9 screen so the perceived contrast of the image is greater. I`m sure you would agree watching a film with a lot of light spilling at the top and bottom would distract you from the film!. People also do this for 16:9 projectors as if they are watching 4:3 content then obviously you will have light spill at the sides of the 16:9 screen.

    Although why anyone would want to watch 4:3 material who knows!, that is why a 16:9 projector is ideal. Although I must admit having black velvet above and below the screen makes it look really cool and cosy :)

    http://www.myhometheater.homestead.com/masking.html
    http://www.weavervale.co.uk/onscreen/screen.htm
    http://home.earthlink.net/~prometheus5/ !

    James
     
  4. gavan

    gavan
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    er, maybe because the source material happens to have been shot in 4:3, perhaps? The aspect ratio has nothing to do with the quality of the programming.

    There's a lot of 4:3 TV programming still out there, most videogames are 4:3 and camcorder footage will usually be 4:3 too. There's even quite a bit of stuff in 4:3 format on DVD, especially concerts/music material and back catalogue TV shows.


    Gav
     
  5. museumsteve

    museumsteve
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    thanks chaps..I'm on the case..:)
     
  6. museumsteve

    museumsteve
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    does it have to be black and will very very dark blue (and I mean very dark) suffice..It's all I can find locally..:(
     
  7. jrwood

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    Don't you have a John Lewis near you?, or some haberdashery which should sell that kind of stuff.

    Take a torch with you and shine it on the material and see if it soaks up the light!. Seriously its probably better to buy a small piece and take it home to see how it performs.

    James
     
  8. Guest

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    Hi guys;
    Will masking the lense (for example use a piece of cardboard with a hole in it) be an equal, better or worse solution?
     
  9. Chris Frost

    Chris Frost
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    Masking the lens only works if the vignette (mask) is at least a foot or more from the projector. Too close and you get a soft edge rather than a crisp clean line.

    If you have a projector try holding a DVD case over half the lens, you'll see how the edge softens and sharpens as you move the case nearer or further away.

    Regards
     
  10. jrwood

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    Yep I made some custom cardboard but like Chris says it creates a soft faded edge but it does help cut out most of the light spill from a 4:3 projector. However this soft faded edge starts to detract from the picture, plus the fact that a screen surrounded by soft black velvet makes the home cinema experience even cosier!.

    James
     

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