[Tig] Neophyte with calibration questions

Mark Jaszberenyi mark
Tue Apr 29 01:18:45 BST 2003

Re: [Tig] Neophyte with calibration questionsRichard,

The reason for the "just visible" definition for setting the black with the pluge
is  that the human eye is usually more responsive in detecting slight differences
between two very dark patches than most available measurement devices,
at least the inexpensive ones.

Experience shows that "just visible differences" gets the job done more
precisely than using the measurement devices, and it is usually much faster,
due to the device needs a long measurement time because of the very low
light levels.

Humans have highly advanced vision that is 'tuned' to detect these edges
of two very dark patches, like in the pluge. I guess this ability added a lot
to the survival rate and hunting success during the night.


Mark Jaszberenyi
CEO and Founder
  ----- Original Message ----- 
  From: Richard Simon 
  To: tig at tig.colorist.org 
  Sent: Monday, April 28, 2003 3:46 PM
  Subject: RE: [Tig] Neophyte with calibration questions

  To me this begs a question:  How is this really defined?  That is, whats the real definition of "just visible" in the case of these two bars?  What is the difference in their origin signal and how (quantitatively) should that be represented by the display?
  Why shouldnt I just try to generate a full screen of the "blacker than black" bar, measure that, then generate the "merely black" bar and measure that, then define the specific signal difference I'm looking for?
  Pardon me if I'm posing naive questions, but I'm really chasing, perhaps in vain, quantitative definitions for "that monitor looks too dark"

  Richard Simon 
  Giant Killer Robots 
  576 Natoma St. 
  San Francisco, CA 94103 
  (415) 863-9119 

    -----Original Message-----
    From: Dave Corbitt [mailto:david.corbitt at verizon.net]
    Sent: Monday, April 28, 2003 3:38 PM
    To: Graham Collett; tig at tig.colorist.org
    Subject: Re: [Tig] Neophyte with calibration questions

    At 11:16 PM +0100 4/28/03, Graham Collett wrote:
      I think I recently read an article that explains some of this effect; I believe it said that with some bright signals like color bars, the energy on the CRT's screen at the brighter areas of a picture will bounce around inside the tube, raising the level of some darker areas (like the pluge?).  That sounds possible, I guess. 

      Isn't that a good reason for not using SMPTE bars and use a proper pluge generator!!!

    I couldn't agree more. The SMPTE Pluge in the lower right corner of Color Bars is all wrong. But we discussed that just recently.

Dave Corbitt
    Madison, NJ
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