USB issues and black and white target point
USB issues and black and white target point
- Subject: USB issues and black and white target point
- From: "tlianza" <email@hidden>
- Date: Tue, 30 Sep 2003 07:55:18 -0400
>
Anyone know why the USB ports on a contemporary motherboard might be
>
considered inappropriate for using hardware calibration devices?
There are a number of issues that affect all manufacturers of USB devices.
The specification is very complex and like so many specs (the ICC
specification, for instance,) leads to a number of interpretations. The
REQUIRED compliance test configuration is not necessarily representative of
every motherboard that is out there. Keep in mind that Intel basically
"owns" USB. Many of the more modern machines are using SOC architectures
(System on a Chip) that employ highly integrated chipsets to perform IO. If
you would like to get a sense of the magnitude of the problem do a google
search using the following words: <USB via chipset problem>. This will give
you some idea of the level of the problems. It is not a problem that just
affects hardware calibration devices. You can view the manufacturer of
your chipset by looking in the device manager under heading "Universal
Serial Bus Controllers". Via is just one of a number of manufacturers that
share the same problem. Investigation into the Via problem indicated that
Intel supplies the basic driver set to the industry. The impression that I
was left with is that Intel is rather reluctant to look into potential
driver issues with non-Intel chip providers.....Who would have thought they
would react like that? There is NOTHING that we can do in a situation like
this other than to recommend users use separate card or a hub. The failure
is occuring before any of our software is invoked....
Another Colorsync user wrote
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The white point setting info (contrast) still seems a bit less scientific
than I would like. Sounds like "anything over 80 is good, higher is better
if that's what you prefer". Should it be set higher in a brighter work area
the achieve the "luminance ratio that is a least 100:1" as quoted in Roger
Breton's reply?
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If you refer the description of the Profile Connection Space (Annex D,
particularl D.1.5) of the latest published specification the dynamic range
of the reference medium is specified at 287.9 : 1. In my opinion, one
should set the display to roughly this range, if you are anticipating using
perceptual transforms.... For a display of 80 cd/mm2 the dark value would be
approximately .28 cd/mm2 . There are a number of good reasons to keep
display luminances within the 80-120 cd/mm2. The first reason is that some
monitors can actually hit those values when set to D50 with the contrast
ratio set to the nominal 290:1. The optimum setpoints of a display are very
display specific and require a great deal of characterization. I've written
some white papers in this area that I will make available to those who
contact me OFF LIST. Please note that these are in draft form and have not
yet been published to the web site....
Thanks for your time...
Tom Lianza
Technical Director
Sequel Imaging Inc.- A GretagMacbeth Company
25 Nashua Rd.
Londonderry, NH 03053
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