digital negatives, just a thought

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
Received on 05/04/06-10:20:25 AM Z