[filmscanners] Re: Vuescan upper histogram

["Dana Trout" <dana@troutcom.com>]

PhotoShop uses the following values:
  Red: 30%
  Green: 59%
  Blue: 11%

You can easily test this for yourself by creating a small image and
filling it with pure red, then look at the Histogram Luminosity
reading
-- it says Mean: 30.00. Then fill the image with pure green, and you
will find the mean luminosity is 59.00. Finally, fill the image with
pure blue and the mean luminosity is shown as 11.00.

  --Dana

----------
From: Bob Shomler <bob@shomler.com>
To: dana@troutcom.com
Subject: [filmscanners] Re: Vuescan upper histogram
Date: Thursday, January 10, 2002 4:09 PM

> Weighted green is the most common method for evaluating lightness
..
>however, since Vuescan's histogram is most commonly used for
evaluating the
>endpoints, black & white, I wonder if equal weighting is more
appropriate(?)

Equal -- probably not.  There are some comments on this in Charles
Poynton's "ColorFAQ -- FREQUENTLY ASKED QUESTIONS ABOUT COLOR" at

  www.inforamp.net/~poynton/notes/colour_and_gamma/ColorFAQ.txt

According to Poynton's text, the contribution of green to luminance is
more than two thirds of the total while red and blue contribute about
21 and 7 percent respectively.  I think this is what Photoshop uses to
compute its luminosity histogram, though I cannot find a reference for
that right now.

<snip>

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