Wayde Allen (wallen@boulder.nist.gov)
Tue, 12 Jan 1999 12:01:30 -0700 (MST)
On Mon, 11 Jan 1999 FotoDave@aol.com wrote:
> I know some of you are probably thinking that this fotodave must be crazy
Nah, we already know this to be true <VERY BIG GRIN>.
> But I do understand the reason for confusion. One thing is people tend to
> think that as resolution gets higher and higher and higher to a point that you
> can't see the dots with naked eye or say with a 8x loupe, you get a continous-
> tone negative. Well, you don't. You still get a negative with all the dots,
> except that they are so fine that you cannot see them.
I think your basic premise is reasonable. However, you make several
seemingly significant assumptions:
1. The dots are in direct contact with the sensitized emulsion. If
not, the shadows cast by adjacent dots may overlap.
2. The dots themselves are perfectly uniform and opaque with no
overlap. If not you won't get the purely binary pattern you
describe, and the pattern will show some diffusive/dispersive
effects.
3. The dots are two dimensional rather than three dimensional. With
three dimensional structures there can be some shading generated by
light rays not striking normal to the surface.
4. The light used for exposing through these dots is highly
collimated. This is related to assumption number 3, since exposure
of three dimensional dots by highly diffuse light source would
cause overlapping shadows. Smaller dot sizes would accentuate this
effect.
5. You are ignoring diffraction effects.
In general doubt that all of these assumptions are met. I'm wondering if
in practice, you wouldn't get results that lie somewhere intermediate
between the purely binary structure you describe, and a true continuous
tone?
> Just think of a chess board with high Dmax and clear area. Now shrink the
> checker board into 1/2 its size. It still has the clear area and the Dmax
> area. Shrink it 100 times, it still has the clear area and the Dmax area. If
> it is 50% covered, it should have a density of 0.30, but it is NOT the same as
> a continous-tone negative with a density of 0.30. A clear understanding of
> this will help you a lot in succesfully printing a digital negative.
Like I said before, I think your initial premise is correct, but when the
checkerboard gets small enough, the thickness of the ink pattern as well
as optical interaction between the spots caused by diffraction and
diffusion probably need to be considered.
> And if you don't believe me, one day you will. :)
Or perhaps we need to refine your model <grin>.
- Wayde
(wallen@boulder.nist.gov)
This archive was generated by hypermail 2.0b3 on Sat Nov 06 1999 - 10:06:41