# Re: How to translate log density readings to percent?

From: Dave Soemarko ^lt;[email protected]>
Date: 09/08/04-06:57:18 AM Z
Message-id: <001501c495a3\$5fa62b70\$0a808080@wds>

Loris,

It is not "so wrong" to aim for 50% density relative to Dmax, but when you
achieve that, you will find that the image might not be right either.

The aim of calibration, in most cases, is that you can match the monitor
look to the look of final print. Well, there is always some mental
translation needed as monitor transmit light but prints reflect light, but
we aim for some ball park. Depending on what gamma you set for your monitor,
you can adjust your image on screen to look good and then generate a
negative; but this negative won't prnit right with simply each % prints
right.

The actual process is that you adjust the gamma, black point and white point
right, then you print the negative, then you make the print, then you adjust
the curve so that the print match the monitor. If the adjustment required is
very big, then you would adjust the gamma, black and white points and re-do
the process, etc.

But if want the density of 50% with Dmax of 1.33 (or different Dmax), I can
give you the formula later. I don't have it written somewhere, so I need to
write it out myself, but I need to go to work now, so I will write later.

Dave S

----- Original Message -----
From: "Loris Medici" <loris_medici@mynet.com>
Sent: Wednesday, September 08, 2004 6:55 AM
Subject: RE: How to translate log density readings to percent?

> Thanks for the long post Etienne,
>
> Shortly, you're saying that the formulas I used in my first message (to
> form the sample table) are correct (that was my original question -
> thanks for the confirmation). In the other hand, I understand that both
> you and Dave say that I shouldn't map dmax to 100% (and the remainder
> values accordingly). BUT, I don't aim for 50% "absolute" density in the
> print that was exposed under 50% negative - I aim for 50% "relative"
> density (relative to the dmax figure of the emulsion/paper combo). Is
> that so wrong? (I guess there's a point that I'm not able to grasp...)
>
> Thanks,
> Loris.
>
> > -----Original Message-----
> > From: Etienne Garbaux [mailto:photographeur@softhome.net]
> > Sent: Wednesday, September 08, 2004 2:24 AM
> > Subject: RE: How to translate log density readings to percent?
> >
> >
> > My apologies if this appears twice -- it is AWOL since this morning.
> >
> > The task is to map a logarithmic scale to a linear scale.
> > First, note that the log scale is ratiometric and the percent
> > scale is absolute. Therefore, there is no finite log value
> > for 100%. Zero transmission (100% density) would be
> > represented as log (1/0), or log density infinity.
> > ...
>
>
Received on Wed Sep 8 06:57:36 2004

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