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Ideal characteristic curve for digital printing

 
 
Marc Wossner
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      04-12-2008

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
 
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Don Stauffer in Minnesota
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      04-12-2008
On Apr 12, 5:57 am, Marc Wossner <(E-Mail Removed)> 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

 
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Marc Wossner
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      04-12-2008
On 12 Apr., 16:14, Don Stauffer in Minnesota <(E-Mail Removed)>
wrote:
> On Apr 12, 5:57 am, Marc Wossner <(E-Mail Removed)> 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

 
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Don Stauffer in Minnesota
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      04-13-2008
On Apr 12, 11:52 am, Marc Wossner <(E-Mail Removed)> wrote:
> On 12 Apr., 16:14, Don Stauffer in Minnesota <(E-Mail Removed)>
> wrote:
>
>
>
> > On Apr 12, 5:57 am, Marc Wossner <(E-Mail Removed)> 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.

 
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