what's the difference between Exposure and Exposure?

Problems with HiRePP®, NegaFix or profiles

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Gregory C
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what's the difference between Exposure and Exposure?

Postby Gregory C » Thu Feb 05, 2004 5:46 pm

when working with Negafix, the Negafix palette has an Exposure slide with values from -3 to +3. in addition, the Auto-Tolerance slider affects the exposure indirectly.

there is also an Exposure slider in the Picture Settings palette with values from -2 to +2.

and finally, there is the L level in the Histogram.

do these controls all perform the same function? if not, how do they differ? which controls are preferable to use to adjust the exposure for maximum quality/detail? in what order should they be used?

regards
Gregory

theo
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Postby theo » Sat Feb 07, 2004 2:37 pm

Hi,

thats a very good question, quite a number of controls are not
documented in detail and one has to figure out how the influence
the results (gamma setting in SF HDR is one example).

The following what I say is guessing on observations:

I think Negafix works the following way:

- it analyses the histograms of the different color channes
and sets the black and white point on the individual channels

- The auto tolerance slider controls how sensitive this white/(black ?)
point setting is (means how much of the pixels are allowed to
be "whiter than white")

- The exposure slider in the negafix control seems to switch between
different Negafix profiles. I get the feeling that there is a profile for
-3, 0 and +3 and the profiles between are interpolated (just a guess).

- The L level in the Histogramm seems to be like a gamma control, but
with much less impact than the gamma control in PS histogramm.
I would appreciate if the control works more similar to the PS control.

- I did not use the Exposure slider in the picture setting because it
is not available in all SF versions. (I know it just from HDR)

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Gregory C
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Postby Gregory C » Thu Feb 12, 2004 4:42 pm

after using HDR a little more, I've come to the conclusion that:

1. Negafix Exposure should be used when processing negative images.

2. Picture Settings Exposure should be used when processing positive images.

it *feels* right this way.


regards
Gregory

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Exposure Settings In SilverFast

Postby President_LSI » Thu Feb 19, 2004 6:06 am

Exposure Settings In SilverFast

Dear Theo, dear Gregory,

you have basically both figured it out alright:

NegaFix Exposure for "negative image data" is interpolating values between 3 different NegaFix profiles (-3 ) (0) (+3).
The Tolerance slider is defining how many pixels in the NegaFix histogram trigger the NegaFix white amd black point position, i.e. how much highlights and shadow points move "inside" the histogram.

Exposure in SF DCPro or HDR for "positive image data" is re-mapping values in 16 bit colour space (kind of a gamma change). You can see the effect in the "Resultant Histogram" by pressing the "option"-key when in the histogram. You can see how the histogram on the right (exposure value increased) shows its values are shifted to the left (more brightness).

?histogram

The "L" (Logarithmic) or "N" (Normal) triangle control in the histogram is the same function as the mid-tone slider in the gradation dialog.

?
If you think some of the controls should work differently, we are always grateful to receive your proposals!

best regards

Karl-Heinz Zahorsky

degrub
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Postby degrub » Thu Feb 19, 2004 3:36 pm

Suggestion for improving the manual:

Add a section specific glossary to clarify how functions/tools operate, or at least expand what is in the section text. For example:

"The Tolerance slider is defining how many pixels in the NegaFix histogram trigger the NegaFix white amd black point position"

i searched the manual in detail, but could not find this clear explanation. i only found a reference to "mask recognition strength" . Once we understand what a tool or adjustment is actually doing to the image data, we are better prepared to use to tool effectively and efficiently. And we can experiment more intelligently.

Regards,
Frank

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SilverFast Manual

Postby President_LSI » Thu Feb 19, 2004 4:01 pm

SilverFast Manual

We will certainly add more explanations on how to use the tools!

regards

Karl-Heinz Zahorsky


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