"Monica Schulz" <monica.schulz@[EMAIL PROTECTED]
> wrote in message
news:55c237f9-dc18-4ff2-8f02-5a00f838164a@[EMAIL PROTECTED]
22 Feb., 10:57, "Richard Knoppow"
<dickb...@[EMAIL PROTECTED]
> wrote:
<snip>
> You are right that the overall contrast of aprint
> should be on the order of 1 but reflection prints are
> limited in the range of brightness they can reproduce so
> the
> unity contrastis usually true only of a range of mid
> tones,
> the shadows and highlights generally being compressed or
> simply going out of the range the paper can reproduce.
<snip>
> While there
> is some choice in contrast of colorprinting materials it
> is
> much less than for B&W. This is because the eye is much
> more
> sensitive to variations in the contrast of color. If color
> is too low or too hight in contrast the effect is quite
> obvious. So, the contrast of color recording and printing
> materials is much more highly standardized than for B&W.
On the risk of beeing pu****ng I must still insist on the
relation****p
between neg contrast and paper contrast.
As we agree that both must balance to about 1 and color
negative film
is normally developd to about 0,6, the paper should show
gamma of 1,7.
But almost all color printing papers have gamma values far
in excess
of 2. So how does the steeply raised contrast of the print
fit into
your above statement? Does the contrast have to be raised
that much so
offset the unavoidable flare? If thatīs true paper contrast
cannot be
calculated by simply using the reciprocal of the neg. Maybe
thatīs all
what blocked me from recognizing the true connection?!
Best regards!
Monica Schulz
I may be going over territory I covered in private
e-mail but want to answer it here if possible.
First of all I am not sure about your numbers for
negative and paper contrast. 0.6 is probably about right for
B&W negatives but I think color negs are somewhat lower,
perhaps around 0.4. In any case gamma can be misleading
because it applies only to the straight line ****tion of the
film or paper characteristic. More modern methods of stating
"effective" contrast are to use an average. This is done by
drawing a straight line between the shadow density and
highlight density and stating its slope. Average contrast,
or G bar, does not have a fixed interval between highlights
and shadows, the Kodak method called Conrtast Index does.
G-bar and CI can be the same. In general gamma will not
always agree with either.
The idea is that multiplying negative contrast and
positive contrast will give the contrast of the final print.
Target contrast is usually somewhere around 1.0 but can be
varied for a special effect or to compensate for something
such as flare.
Because the range of brightness that can be reproduced
by a reflection print under normal illumination is, in
general, less than the original scene some compression must
take place. Compression means some part of the image is
reproduced with lower contrast than the original. Since the
eye tends to judge the "correctness" of an image based on
its mid gray values or equivalent in color, the compression
is typically in the shadows and highlights. Since the eye
tends to compress these values in direct viewing the results
are acceptable. If the mid tone contrast is too little, in
an attempt to compress the entire tone scale, the results
will look "flat" even though details are visible in shadows
and highlights that are not in a more "normal" looking
print. If the print is made to have higher contrast than the
original scene it will still not look natural but may be
acceptable if the original scene was very low in contrast.
Since they eye is constantly compensating for brightness
variations our impressions of original scene contast may not
be too accurate. For instance, on a brightly lighted day
with deep shadows the eye will adjust somewhat when looking
into the shadows and see detail there that is not visible
when looking at bright objects, but, because one's attention
is not concentrated in the shadows then we are not generally
aware of it. Film, OTOH, is fixed in its sensitivity. It can
record a wide range of brightness but that range is centered
according to the exposure its given. Then, when a reflection
print is made, there is a further reduction of range since
the reproducing medium is not capable of reproducing the
full range of original scene brighnesses. Note that I am
talking about the presentation to the eye. If one prints a
long scale negative will onto a low contrast paper its
possible to reproduce the full range of tones on the
negative, but, the print will look very flat to the eye
because the original brightness scale will be compressed.
There are times when such prints are desirable, for instance
for scientific or evidentiary purposes but, in general, they
are not acceptable for pictorial purposes.
Where there is not a clear reference for the eye
distortion of contrast is acceptable. This is very true of
B&W but somewhat less for color. If there is no
psychological expectation the eye simply accepts what is
presented.
There is a great deal more to this and I have
oversimplified to some extent but I think the main answer is
that I think the gamma numbers you have are somewhat off.
--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@[EMAIL PROTECTED]
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