Digital BW, The Print

----- Original Message -----
From: "Martin Wesley" <mwesley250@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Sunday, October 20, 2002 12:33 AM
Subject: Re: [Digital BW] Re: Reflective Densitometer Method


> Lloyd, Jeff, Paul, Antonis,
>
> Thank you for the feed back. I guess there is no standard for how to back
> semi-opaque samples for reading reflectance. Since almost all of our work
in
> this regard is to compare one process to another or "before & after"
> situations all that matters is that we be consistent as you say. When we
> post results we should note how the measurements were done, at least for
> paper white and the lighter tones which are the most effected.
>
> The white underneath to match mounted prints makes sense in one way but
not
> another. I speculate that the increase seen from light passing through the
> paper and being reflected back out is a result of a very intense light
> source for taking the reflected density light readings that may far exceed
> any normal level of illumination for print viewing. So using a black
backing
> for density readings might actually give a more accurate reading for
prints
> that will wind up mounted. Don't know for sure.
>
> I get the same result as Antonis, that is I get the same reading with no
> backing as I do with black backing. So I think that I will go with black
or
> no backing for my own measurements since this will be consistent to with
my
> Spectrocam which uses a black measuring plate.
>
> On the color readings the 811 has Tm for C-41 processed film, (I gather
that
> the instrument has circuits or programming to filter out the orange mask),
> Ta for E-6 processed slide film and R for prints. To answer Austin's
> question, the 810 and the 811 are identical except for the addition of the
> E-6 profile in the 811. These were designed for process monitoring for
> commercial film processing businesses. In each of the three modes you can
> measure in "VIS" or "RGB". A bit annoying that you can't get all 4 to
> display at once.
>
> Any precanned software to let you access the serial output on these units?
>
> Now that I know that R density = -C density I am wondering how you would
> calculate CMYK% and Lab values from the RGB density numbers.
>
> Did get new calibration plaques by the way and I was able to down load the
> manual from X-Rite. Just basic operational info though.
>
> For those interested I picked up the 811 on eBay for $325 including
shipping
> plus another $125 for new calibration plaques for a total of $450. The 811
> sells new for $4,250 and the 810 for $3,500. So this seems like a good
deal.
> Quite a bit of X-Rite equipment on eBay at similar cost reductions if you
> are interested.
>
> Thanks,
> Martin Wesley
>
> http://www.borderless-photos.de/guests.html

The consensus on the colorsync list was to add extra sheets of the same
paper you measure. The black at the back was only advised when there's
another print or text at the other side of the paper like it happens in the
printing industry. 'The same paper' as that will not influence the
measurements for colour readings like another white paper will do. The
amount of light doesn't influence the reflectancy, paper fibres will deflect
the rays enough to give a uniform reflectency percentage from any source.

Ernst