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B&W picture is bluish-green

Discussion in 'Electronic Design' started by [email protected], Aug 25, 2012.

  1. Guest

    When I watch the "oldies" tv channels, (This TV or Me-Tv) I noticed that
    all those old Black and white programs are actually black, white, and
    shades of gray. But when the Patti Duke show comes on every morning on
    This-Tv, it's bluish-green tinted. It's only that show, all the other
    B&W shows are really B&W. Some episodes of the Patti Duke show are more
    tinted than others. Why is this?

    Note, this is not just one tv set. I notice it on several tvs, and they
    are different brand tv sets and converter boxes. They is hooked to
    rooftop antennas.
     
  2. Jasen Betts

    Jasen Betts Guest

    possibly converted from film to digital and had the wrong lamp in the
    converter?
     
  3. Tim Williams

    Tim Williams Guest

    NTSC or digitalized?

    I don't know if DTV supports monochrome the same way NTSC did. When an
    NTSC signal doesn't contain a colorburst subcarrier, the chroma detection
    is turned off and the set reverts to B&W operation -- tint would be
    controlled by RGB balance and gain, but these will be correct in a
    properly adjusted set.

    I'd guess digital is always color and the actual color a B&W program has
    depends on how it was transcoded. It's very easy to apply a filter to a
    video stream these days, some may simply have different opinions of
    "white".

    Tim
     
  4. Phil Allison

    Phil Allison Guest

    ** You can always turn down the "color" saturation and get a B&W pic.

    Wot a whinger....


    ..... Phil
     
  5. Gib Bogle

    Gib Bogle Guest

    As far as I'm concerned b&w TVs were never b&w. I noticed this one
    night walking in the street - from the outside the flickering TVs in
    peoples' houses looked bluish.
     
  6. Phil Allison

    Phil Allison Guest

    "Gib Bogle"
    ** That is an optical illusion created by the differing "colour temps" of
    (1950s or 60s) incandescent street lighting and the daylight white of TV
    screens.



    ..... Phil
     
  7. Gib Bogle

    Gib Bogle Guest

    Interesting. Makes sense. I once had my mind blown by a talk given by
    a guy from Polaroid, about the determining influence of context on
    colour perception.
     
  8. Phil Allison

    Phil Allison Guest

    "Gib Bogle"

    ** Oh yeah - human eyes quickly correct for varying ambient lighting
    conditions, including the colour, so we see colours much the same as in
    daylight.

    OTOH a camera is a dumb animal and sees colour pretty much as it is.

    Take a pic of someone standing under a leafy tree and they look greenish.



    ..... Phil
     
  9. spamtrap1888

    spamtrap1888 Guest

    The P4 phosphor has a radiance peak at 450nm. See for example, Fig. 4
    here:

    research.opt.indiana.edu/Library/Fry91/Fry1991.pdf
     
  10. Gib Bogle

    Gib Bogle Guest

    On reflection ... some of the places where I observed TVs from outside
    had no street lights. It was quite dark. Hmm.
     
  11. Phil Allison

    Phil Allison Guest

    "Gib Bogle"

    ** But all the homes had incandescent lights on inside - so the same thing
    happens.



    ..... Phil
     
  12. Gib Bogle

    Gib Bogle Guest

    Maybe ... I can't remember.
     
  13. Gib Bogle

    Gib Bogle Guest

    Maybe they did, I can't remember. But if the TV looks blue in
    comparison with the incandescent lights from outside, why not from
    inside too?
     
  14. Gib Bogle

    Gib Bogle Guest

    I don't know enough about the subject to say for sure, but perhaps this
    is the reason.
     
  15. Nemo

    Nemo Guest

    This is not the answer to your question, but it is an interesting
    historical thing about the development of colour TV.

    Some 30 years ago a friend was watching old B&W reruns of The Outer
    Limits and thought he could see colour in the opening credit sequence -
    even though he was watching on a B&W TV. He wrote to the BBC techies to
    enquire what was going on. They replied that at the end of the B&W era
    TV / film techs had experimented with simulating colour by strobing the
    intensity at certain frequencies, which fooled the eye somehow. It
    worked, sort of, but then proper colour TV took off and it was not pursued.
     
  16. Guest

    All B&W (positive) film stock did not necessary have a completely
    neutral tint. The human eye will quickly adopt to this, but a film
    scanner will capture this tint if not properly compensated or closing
    the chrominance channels.

    I have also seen quite a few WW2 era B&W news films in TV
    programs/DVDs with a distinct brownish tint, apparently for artistic
    purposes. If the program also contained colour news clips, the use of
    some brown tint was even more common, apparently to reduce the
    difference between colour and B&W clips, a brownish B&W clip looks
    like some old colour clip that has lost the blue colour during the
    years :).
    In SD digital luminance signal is sampled at 13.5 MHz, while the two
    chrominance signals are sampled both at 6.75 MHz. The B&W material
    should be contained in the luminance channel, while the two
    chrominance channels should be empty, thus maximizing the luminance
    throughput.
     
  17. SoothSayer

    SoothSayer Guest

    It is called 'sepia' and I can't believe that you know so much about
    video re-construction, but have no clue about image capture roots.
     
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