Lightbox - Screen Matches
Lightbox - Screen Matches
- Subject: Lightbox - Screen Matches
- From: "Fleisher, Ken" <email@hidden>
- Date: Mon, 18 Jun 2007 11:23:11 -0400
- Thread-topic: Lightbox - Screen Matches
Hi all. I¹d like to bring up a topic for discussion for which I¹ve never
really received a satisfactory answer-setting of light box luminance for
color matching to screen. In particular, I¹d like to discuss matching of a
screen image to a transparency. In ISO 12646, Annex A.1:
³NOTE 2 - If the displayed image is to be viewed as a simulation of the
printed reproduction, but is to be compared directly to a transparency, it
should be noted that the conditions for viewing a transparency image
specified in ISO 3664 are not practical because of the high level of
luminance specified for transparencies. For this application a nonstandard
transparency illumination condition is normally required,
typically of about 25% of the standard value. However, all other
attributes should conform to those specified in ISO 3664.²
1. Is there a difference if the displayed image is being compared to the
transparency, but not as a simulation of printed reproduction? I don¹t see
why there would beyou are still comparing the screen image directly to a
transparency.
2. I understand why the luminance of the light box needs to be lowered-so
that the luminance is a closer match to the luminance of the monitor. But
this is where I have difficulty understanding the logic of this
recommendation.
To elaborate, let¹s say the transparency is typically illuminated with a
source at 1270 cd/m^2. If comparing to a monitor, then it should be set to
~25% of 1270 which is 317.5 cd/m^2. If a monitor is producing 120 cd/m^2,
this is only about 1/3 of the light box. Even if the monitor is closer to
300 cd/m^2 (which is not always possible), that will not change my question.
The problem is this: When I achieve a visual match between transparency and
screen (and I AM able to achieve this match), I am matching the transparency
when viewed in non-standard conditions. In other words, the transparency
looks VERY dark and more importantly, so does the image on my screen that
matches it! For the transparency, this is fine because I can always crank up
my light box again to view it normally. But now I am left with an image on
my screen that is far too dark and does not even closely resemble the
appearance of the transparency under normal conditions (1270 cd/m^2).
It seems to me that what I really want is an appearance match between a
transparency viewed at 1270 cd/m^2 and a screen image with a monitor set at
120 cd/m^2. The complete solution would be to employ a color appearance
model. But short of that, how is this supposed to work? What can be done to
achieve this appearance match? Why is lowering the luminance of the light
box supposed to work in a practical way (besides the obvious result of
creating equivalent viewing conditions for the two different media)? From my
experience, this only results in digital images that are considered too
dark.
I look forward to all input on this topic!
--
Ken Fleisher
Photographer
Imaging & Visual Services
National Gallery of Art
Washington, D.C.
Phone: (202) 712-7471
email@hidden
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