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contrast and amb light levels, trick of the eye?

Discussion in 'Projectors, Screens & Video Processors' started by stryker, Sep 10, 2005.

  1. stryker

    stryker
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    Maybe I'm just mad but.... has anyone noticed the following.

    I'll watch a movie in a dark room and the picture looks great. Then after I bring the room lights up to 50% on the dimmer so the wife can find her way out to make a coffee :D

    Now the picture looks eeuuww, blacks are greys and colours are bleached. However as I sit there watching the usual sky inter-movie adverts its like I adjust to the ambient light and the picture starts to look a little better, ie blacker blacks and richer colours.

    Is this a trick of the mind or maybe some kind of iris effect in my eyes, OR am I nuts?

    Thoughts.
     
  2. PJTX100

    PJTX100
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  3. KoThreads

    KoThreads
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    i hadn't seen that before PJ. cheers. It happens with me as well.
     
  4. Timbo21

    Timbo21
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    I suppose your pupils at first are open when you turn on the lights & then they contract a bit & normalise the light to your eyes?
     
  5. DEANO-B

    DEANO-B
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    WOW thats really really freaky :eek: :eek: - thought it was bo!!ocks until I cut and pasted it :confused: :confused:
     
  6. Gary Lightfoot

    Gary Lightfoot
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    Stryker,

    Timbo has the answer there, and the effect you saw is similar to bias lighting. With some ambient light in the room, your iris shuts down enough to prevent dark area detail from being seen because your eye is not open enough to allow that level of light to enter the eye in sufficient quantity to be visible. The effect you get is that the grey looks black.

    The negative effects are that you are probably not seeing some shadow detail, and your overall contrast ratio has been reduced - if you double black level, you halve the contrast ratio. With a digital projector and an elevated black level, it's possible to tweak the ambient to a level where you don't decrease the overall contrast because the room light is equal to the projectors light output when it is projecting black, but you may also bias the eye enough to make the blacks look blacker. This isn't really something you can do with CRT due to their better black levels, and it's probably not a good idea to have any light in the room in case it does compromise image reproduction (if image quality is you main aim).

    Gary.
     
  7. stryker

    stryker
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    Thanks for that guys. Big tip I found, watch something, anything for a little while before you start with the calibration test pics :)
     
  8. Gary Lightfoot

    Gary Lightfoot
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    Geting the eye accustomed to the rooms darkness is a good idea - I have heard it said that is why we have to sit and wait for the main feature in the Cinema - it's getting you used to the darkness.

    However, that won't work with test images such as Avias moving black and white bars though, because the bright white half of the screen will cause the iris to shut down and you won't see the black bars until you raise the black level. If you then go to the full black screen the brightness setting will be set too high.

    It can be a bit of a compromise to get the setting correct for best black level and contrast, against visible shadow detail under all conditions and a raised black level.

    Gary.
     
  9. PJTX100

    PJTX100
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    Yep, it's definitely not designed to make you eat all your scoff and prompt you to go and get some more...PJ ;)
     
  10. MacReady

    MacReady
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    You beat me to it....I love that optical illusion as people will swear blind that it is rubbish until they get it into something like Photoshop and look at the pantones of the colours :rotfl:
     

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