Re: digital negatives, just a thought

Thanks,

I think it is possible to do it right away, by this I mean we don't need to
wait until there are special inks around, what is needed is a dedicated
profiling system that could get it's data directly from the source, the
inks. Another idea I have about this goes about like this, we print a
certain number of "step" such that only one ink source will be spit out by
the printer, say we manage to print some 20 values of only yellow ink, we
read this back with a UV densitometer and use some regression methods to
find out all values in between. We could do this for each ink but I think
only 3 would do fine. Next, the Beer-Lambert law says that all this should
be linear for a single ink source as per the concentration of the ink but
when you mix inks together, we may loose some more then you bargain for, I
know this is all chinese so let say I'll try this another way. If we think
of ink as neutral density filter you can use as many filters having 0.1 in
density as we need to create a 0.5 filter or whatever by simply putting 5 *
0.1 filters back to back but with colored filters the resulting density may
not be as easily predictable in practice. That's because colored filter
affect not only the amount of light but which colors will go through the
filter. Since you need only the UV part from the source of light to do our
prints this may not be as bad as it seems. The theory says it doesn't matter
for a single wavelength of light but this is not what is normaly used.

You are absolutely right the colors that appear on the neg, they are
irrelevant and the resulting negative may very well look hawful but it will
do the job just fine.

Regards
Yves

----- Original Message -----
From: "bsinger" <bsinger@sasktel.net>
To: <alt-photo-process-l@usask.ca>
Sent: Thursday, May 04, 2006 12:49 PM
Subject: Re: digital negatives, just a thought

> Yves Gauvreau wrote:
>
> >Hi,
> >
> >Lately, as you may be aware I have said and wrote many things about
digital
> >negatives and a new concept I came up with but now this message is about
> >putting all this in persective and explain in as simple terms as I can
what
> >I mean by all this.
> >
> >The premise of all this is, information lost, you may not be aware that
most
> >printer, at least those I have used, can only output 256 tones in B&W and
16
> >million plus colors which comes from the combinaison of 256 values of
red,
> >256 values of green and 256 values of blue or 24 bits if you prefer. I
think
> >most of you may print digi-negs in color but you use none the less only
256
> >colors what's worst is when you use a curve and here is why.
> >
> >I'll use only the 256 B&W tones in order to keep things simple but the
same
> >can be said about color. Mark told us the other day that it was possible
to
> >obtain a (UV) density as high as 4.0 from a printer and most process need
> >less then half this value to do the job right. What happens to the other
> >half you don't need? Well it is lost, another way to say this, is out of
the
> >256 tones or densities a printer can produce the process requires only a
> >(small) subset of that. The less exposure range a process needs the worst
> >this information lost becomes. In other words you are putting on your
> >digi-neg just a few distinct densities and it is bound to show on your
> >prints in some way.
> >
> >The concept I'm working on would use all the 256 tones present on your
> >original and translate them into 256 distinct densities that spread the
> >exposure range required by the process you intend to use and that's a
world
> >of difference. Like I said to Don Bryant, it would be like choosing
between
> >a bicycle ride and a F-18 ride. The concept resemble what we do when we
> >create a profile for a printer, when we do this we are interested in how
our
> >printer spits ink on the medium from the various input values basically
and
> >we adjust what we feed the printer such that the output meet our
> >expectations color wise, all this is done behind the scene with color
> >managment.
> >
> >With this new idea of mine, we would do something very similar, we want
to
> >know what UV densities each of the 2^24 possible colors can produce.
Knowing
> >all this we could choose only 256 from of all those colors that spreads
> >uniformaly the hole range of densities required for a particular process.
In
> >other words absolutely no information loss, better yet do you think out
of
> >these 16 million colors of which a printer can only print a subset but
still
> >a very large one, could there be enough distinct densities that we could
> >translate a 16 bit original B&W into 65k uniformly spread densities from
0
> >to whatever a particular process requires? I don't know yet but I just
know
> >any number larger then 256 would be an impressive improvement.
> >
> >I ear already voices saying how will you do this, is it practical to
measure
> >16 million colors, is it feasable, will it be easy to use, do we need
this
> >level of control, etc. At this time I would be more then satisfied to
reach
> >a one to one translation for an 8 bit original B&W or 256 tones to 256
> >densities if you prefer. I hope everyone knows that a specific value of
> >density on a negative translate to a specific value of exposure for the
> >print, just in case and the more distinct densities we can use the more
> >continuous the tonalies on the print will appear, think of what happen
when
> >you use a step tablet you get a very visible stair case effect in the
> >tonality gradation. Increasing the number of step to an as large number
as
> >possible will simply make the steps practically invisible to the naked
eye,
> >it is as simple as that.
> >
> >I don't think it would be reasonable to expect that someone would measure
16
> >million possibilities manually but a computer could. Ultimately what we
want
> >to know is how a particular process will translate the input we give it
in
> >the for of a negative and that's easy to find out. I could refine this
later
> >but for now let just say that I create an 8x10 color image with about
50000
> >1mm square each having a distinct color, I print this on a transparency
and
> >I use it to expose a particular emultion. I would only need to scan this
> >print, look at the histogram and I would know in a second if I have a
full
> >range of tones from 0 to 255 but it is most probable that I don't
actually
> >need the values to spreads from 0 to 255 because the paper is not
perfectly
> >white so I shouldn't get as high as 255 values and the Dmax of the
emultion
> >may very well not translate to a 0 black. What I'm looking for then is
that
> >the histogram as no empty bin sort of speak from the minimum to the
maximum
> >values I can read back from the print and the best way to know this is to
> >make a 16 bit scan and have a look at the data directly. Unfortunately,
> >photoshop and other similar programs won't be of much help for this but
this
> >may not be such an handicap, someone could write a little program to do
just
> >that and we would need one to translate our 8 bit original into the the
> >proper colors. I'm sure this is kid stuf.
> >
> >I have other and possibly better ideas to find out the net output of a
lot
> >of colors would have on a alt-process print but for now lets keep it as
> >simple as possible. Just like profiling a printer with the right tools is
> >relatively easy, this concept would require about the same amount of work
as
> >for a printer profile, print a large number colors on a transparency, use
it
> >to make an print, scan it back, feed this to a program that generate a
> >mapping for each 256 values an original can have, then every time you
want
> >to print something using the same process and parameters, feed this to
the
> >translater program with the appropriate "profile" or mapping et voila!
Just
> >like you would do for each printer, paper and inks combinaison you
profiled.
> >
> >If anything about this concept is still unclear to you do not hesitate to
> >ask me directly or through the list. To resume all this, I think the step
> >tablet idea is the easiest to understand, if there is not enough usable
> >steps on the step tablet or ultimately on the negative the results can be
> >far from an apparent continuous gradation of tonalities from the lightest
to
> >the darkest tones of the print, as shown quite visibly with just the few
> >step available on step tablet.
> >
> >Regards
> >Yves
> >
> >
> >
> >
> I think you are on the right track. UV light is not full spectrum
> light. What ever color appears on the printed negative is really
> irrelevant. What should count is the degree to which the ink allows UV
> light to pass though. I can see, someday a set on inks that would be
> used to print negatives, that would be soley based upon the inks ability
> to transmit UV light. No there is something to think about.
>
> Barry
>
Received on 05/04/06-11:50:44 AM Z