Ideal characteristic curve for digital printing

Dear ng,

the combination of the negative and positive charakteristik curves in
analog photography leads to the well known s-shaped curve of the final
print. The main reason for this characteristic is to compensate for
flare light. Camera flare and viewing flare lowers gamma mostly in the
dark tones and printer flare mostly in the light tones. So the gamma
of the photographic system must be raised a lot at the high desities
and a bit less at the low densities.
As there is no optical enlarging step in digital printing an ideal
characteristic curve for an image prepared to be printed on an inkjet
should have a different characteristic than this. - Of course it must
still care not to blow out the highlights, so ist should still be
somewhat rounded. Any thoughts or references about that?

Best regards!
Marc Wossner

On Sat, 12 Apr 2008 03:57:46 -0700 (PDT), Marc Wossner
wrote:


Dear ng,

the combination of the negative and positive charakteristik curves in
analog photography leads to the well known s-shaped curve of the final
print. The main reason for this characteristic is to compensate for
flare light. Camera flare and viewing flare lowers gamma mostly in the
dark tones and printer flare mostly in the light tones. So the gamma
of the photographic system must be raised a lot at the high desities
and a bit less at the low densities.
As there is no optical enlarging step in digital printing an ideal
characteristic curve for an image prepared to be printed on an inkjet
should have a different characteristic than this. - Of course it must
still care not to blow out the highlights, so ist should still be
somewhat rounded. Any thoughts or references about that?

Best regards!
Marc Wossner

In the days of silver halide, the rule of thumb was: expose for the
shadows, develop for the highlights. The process was exploited in
Ansel Adam's Zone System, which kept shadow detail in the final print,
and detail in the highlights without blowing them out, allowing
specular reflections to go full white.

In color, it was always expose for the highlights. Let the shadows
fall where they may.

In reality, having worked in film processing for over 30 years, as a
profession at a Major Industrial level, computers *scanned* the
negative and chose the best algorithm for the exposure of the
negative, at a very very high rate of speed.

Everything in *commercial* photo, not to be confused with advertising
photo, was processed by a *lab* and the *lab* was automated, except
for professionals who paid extra for "hand processing" which delivered
better than the normal. By that I mean, hand cropping, enhancement,
and so forth.

But for 99.99% of the photographing public, when they brought their
film to a lab, it went through an automated process. Only outliers
went back for a reprint. And they were few and far between.

Now with digital, the film isn't there anymore, but the principles
remain the same. A light meter is an AVERAGING device. If you
photograph a white piece of paper, a light meter will give you a
reading to render it a neutral gray with time and aperture.

If you photograph a black piece of paper, a light meter will give you
a reading to render it a neutral gray with time and aperture.

You have to know at some level, how the instrumentation is going to
*see* the subject material, and interpret it for proper gamma.

I most instances, I let the camera behave as it will withing
parameters I program into it (Nikon D80), those being minimum shutter
speed and preferred aperture, letting the ISO go wherever it must to
stay within my parameters. From there I post process for sharpness,
noise reduction, gamma/color balance, and even _this_ is now automated
now that I have set up my computer to do this without my attention to
each and every exposure.

Later, if I want to *tweak* for some special effect, I can still do
that. But for the majority of my photos, the software in-camera and
in-computer (quad-core 4 gigs ram) 2.4 GHz, takes care of the great
majority of the *issues* with the touch of a few buttons.

So to get back to your question: Program the parameters you want to
produce the results you need. This most likely will be adjustments to
software both in-camera and in your computer post-processing software.

Has this helped?

Lg

On Apr 12, 5:57 am, Marc Wossner wrote:
Dear ng,

the combination of the negative and positive charakteristik curves in
analog photography leads to the well known s-shaped curve of the final
print. The main reason for this characteristic is to compensate for
flare light. Camera flare and viewing flare lowers gamma mostly in the
dark tones and printer flare mostly in the light tones. So the gamma
of the photographic system must be raised a lot at the high desities
and a bit less at the low densities.
As there is no optical enlarging step in digital printing an ideal
characteristic curve for an image prepared to be printed on an inkjet
should have a different characteristic than this. - Of course it must
still care not to blow out the highlights, so ist should still be
somewhat rounded. Any thoughts or references about that?

Best regards!
Marc Wossner

I don't believe the main reason for the bends in the curve were to do
with flare. There were films with a quite straight curve, and ones
that were very S shaped. I believe the rounding of the ends (either a
lot or a little) were somewhat inherent in the chemical processes.

One could modify the curves by chemistry. The curve published in the
mfg's catalog was with a certain developer and concentration and time.
One could use a different developer, a different dilution, or a
different developing time. Of course, you also could use a modified
curve again when printing.

One of the first things I marveled at in digital processing was how I
could take an existing image and bend the curve around on the
computer, and put it back if I made a mistake. In the olden days to
change the curve on a negative after the fact meant reshooting :-(

On 12 Apr., 16:14, Don Stauffer in Minnesota
wrote:
On Apr 12, 5:57 am, Marc Wossner wrote:



Dear ng,

the combination of the negative and positive charakteristik curves in
analog photography leads to the well known s-shaped curve of the final
print. The main reason for this characteristic is to compensate for
flare light. Camera flare and viewing flare lowers gamma mostly in the
dark tones and printer flare mostly in the light tones. So the gamma
of the photographic system must be raised a lot at the high desities
and a bit less at the low densities.
As there is no optical enlarging step in digital printing an ideal
characteristic curve for an image prepared to be printed on an inkjet
should have a different characteristic than this. - Of course it must
still care not to blow out the highlights, so ist should still be
somewhat rounded. Any thoughts or references about that?

Best regards!
Marc Wossner

I don't believe the main reason for the bends in the curve were to do
with flare. *There were films with a quite straight curve, and ones
that were very S shaped. I believe the rounding of the ends (either a
lot or a little) were somewhat inherent in the chemical processes.

You are of course right, I should have written that the characteristic
of the final print must be somewhat curved or bent to accomodate the
different gammas required to compensate for the different amounts of
flare in the highlights and in the shadows as can be seen in the The
Focal Encyclopedia of Photography (http://books.google.de/books?
id=CU7-2ZLGFpYC&pg=PA148&lpg=PA148&dq=%22viewing+flare
%22+gamma&source=web&ots=d8tQGLXtfr&sig=8sI7ELK8w9 megD7pGtnm6qvt7FY&hl=de
page 146 top left).

But anyway, what about the fact that there is no optical enlarging
stage in digital imaging. How should that affect the characteristic of
the final print as far as the highlight part is concerned?

Marc Wossner

On Apr 12, 11:52 am, Marc Wossner wrote:
On 12 Apr., 16:14, Don Stauffer in Minnesota
wrote:



On Apr 12, 5:57 am, Marc Wossner wrote:

Dear ng,

the combination of the negative and positive charakteristik curves in
analog photography leads to the well known s-shaped curve of the final
print. The main reason for this characteristic is to compensate for
flare light. Camera flare and viewing flare lowers gamma mostly in the
dark tones and printer flare mostly in the light tones. So the gamma
of the photographic system must be raised a lot at the high desities
and a bit less at the low densities.
As there is no optical enlarging step in digital printing an ideal
characteristic curve for an image prepared to be printed on an inkjet
should have a different characteristic than this. - Of course it must
still care not to blow out the highlights, so ist should still be
somewhat rounded. Any thoughts or references about that?

Best regards!
Marc Wossner

I don't believe the main reason for the bends in the curve were to do
with flare. There were films with a quite straight curve, and ones
that were very S shaped. I believe the rounding of the ends (either a
lot or a little) were somewhat inherent in the chemical processes.

You are of course right, I should have written that the characteristic
of the final print must be somewhat curved or bent to accomodate the
different gammas required to compensate for the different amounts of
flare in the highlights and in the shadows as can be seen in the The
Focal Encyclopedia of Photography (http://books.google.de/books?
id=CU7-2ZLGFpYC&pg=PA148&lpg=PA148&dq=%22viewing+flare
%22+gamma&source=web&ots=d8tQGLXtfr&sig=8sI7ELK8w9 megD7pGtnm6qvt7FY&hl=de
page 146 top left).

But anyway, what about the fact that there is no optical enlarging
stage in digital imaging. How should that affect the characteristic of
the final print as far as the highlight part is concerned?

Marc Wossner

Fortunately, the dynamic range of digital cameras far exceeds the
dynamic range of printing papers. Thus using the curve tool in a good
image editor works fine. But there IS no rule about the preferred
shape. Each image is unique. If the original scene has a wide dynamic
range you must compensate somehow. However, it if is a flat, low key
scene you can use quite a linear shape.

One of the neatest aids recently has been the HDR software, either
special program or built into things like PS CS2 and 3, or the latest
version of PSP. This GREATLY eases the computer work for high range
scenes, though at the expense of needing to shoot multiple exposures.