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Actual film contrast in movies

Discussion in 'Projectors, Screens & Video Processors' started by EN, Jun 1, 2004.

  1. EN

    EN
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    Do you know the max film contrast at image projected in theaters? (It is my job to know, but I don't. I only remember that there is no photo-film in the world that could handle more than 1:1000 contrast in lighting)
    I watched TROY and THE AFTER TOMMOROW and I observed the contrast radio on the screen. At no time there was real black, although contrast was superb.
    My point is that may be search for the contrast in home pj or plasmas may be shouldn't be so absolute, because in the original movies there no such black.
     
  2. buns

    buns
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    I have tried arguing this point before.... I didnt get so far. Very reliable sources have told me that cinema is in the hundreds:1 in a good cinema.... but no one here believed me! :p

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  3. EN

    EN
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    I will make experiment this weekend.
    I will project non-exposured film vis slide projector on the same screen for movies and I will take mesuraments: first light falling to the screen and then light reflecting from the screen with exposure meter Minolta VI, for example. Second I will project fil with absolutly white (You know that film has Dmin, for it is not transperent) and take mesuraments in the same fashion.
    Then I will calculate the contrast ratio. Any suggestions/improvments on the mesuring scheme?
     
  4. RTFM

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    EN, as i'm sure you are aware there are so many different types of film stock for shooting and printing ( and internegs ) that vary so much in their own properties, ie. some are high contrast stock, some are low, some are grainy etc.
    It won't be easy to draw conclusions from your experiments but I will be very interested to hear the results. Good luck.

    Jeff
     
  5. EN

    EN
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    Yes, because I'm usind different types of films. So, I'll get the one with most contrant and deep black, not technical film, just regular slide one.
     
  6. Mr.D

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    Ok.

    Negative motion film stock is reffered to as having a low contrast. Print film is regarded as being high contrast. Does this mean negative has less contrast than print film....No and this is where we get to the fact that the term "contrast" is used incorrectly a lot.

    Negative records more intensity variation than print stock.
    If I were to refer to a 10 bit code value scale neg stock would range from 0 code values to 1023 code values. Print would range from 0 code values to 685. However because of the non-linear distribution of intensities on film and because of the higher "contrast" of film the 685 represents the white clip point of print stock relative to the "superwhite" region of neg stock which is said to extend to 1023.

    The point?

    When its printed film can be stopped down ( I forget exactly how much but 2.5 stops rings a bell) a certain amount without compromising the peak/specular whites ( they stay white up to a certain point: as long as you haven't brought them down below 685).

    This is useful for a number of reasons: on exposure film stock can be overexposed to make the lower intensities register above the end toe of the film. This gives you more intensity detail , however the film may look milky as a result. Printing it down restores the low intensities to nicer level but retains that extra intensity resolution you originally captured in the neg.

    And you haven't compromised the peak whites region so you end up with an image that appears contrastier and cleaner compared with a normal exposure.

    Anyway:
    Film based on cineon 10 bit log format has 2.048 density range with a quantization step size of 0.002D which gives you an intensity step size of 1024 within this film normally doesn't register any intensity variation below 95 code values ( the Dmin of the film...this isn't actually set in stone any more as filmstocks and scanners have improved) and values above 685 are only percieved if the film is printed down as discussed ( this is still totally valid and is essential to modern film exposure practice).

    so say 590 discernable intensity changes from black to white in each channel (RGB) In practice probably about 1-500

    video I don't have the figures close to hand but from memory I think its about 100 intensity variations between black and white at best ( The whole IRE pattern system is based around this I think someone else look it up) and of course its downsampled from that a fair bit when you take the old 4:2:0 colorspace into account...too tired to work it out.

    Blacks...

    Film doesn't necessarily need "pristine" blacks as there is a lot of discernable intensity variation detail down in the lower end . There is no nasty sharp fall off into black unlike with video. The clip into white is also a lot less visually severe with film compared with video

    Whilst video material itself doesn't have a very large intensity range it needs to make the most of it to give a pleasing image so the blacks have to be ideally as black as you can go and the whites have to be way up there relative to black even though there is a lot less intensity variation in between.

    Imagine a sheet of white paper with black text on it : looks nice and contrasty but it only has an intensity range of 2. Print grey ink on darker paper and the writing is a lot less easy on the eye but the intensity range is still the same.
     

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