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 05/04/06-10:51:39 AM Z