Natural Tone Curve

Hi
I try to find a "Natural Tone Curve", meaning a tone curve which accounts for the non-linearity of human vision, but no pleasant tweaks added. I wonder in how far the interacting tone curve combo of PE/CR is such curve.
1-in the PE:
In
Eric Chan, "Starting profile for ColorChecker calibration in PE" #1, 24 Oct 2008 6:01 am
you (Eric) state that
"The Chart Wizard is designed to produce a reasonably accurate scene-referred color profile (within the technical limits of the input data)."
I wonder if this includes the little indent to the right at the base of the base curve? Or should I flatten this out, setting the starting point to 0/0? The indent seems to correspond to the Blacks +5 setting in CR.
2-in CR:
Is the Medium Contrast S-curve really part of the difference between human vision and linearity? Or should I set it to linear to be most natural?
In particular, again, the part reflecting the deepest shadows seems to be quite deliberately tweaked.
Thank you for your input.

Hi Eric,
thank you for a VERY fast reply! -
I learn that perceptual linearity is handled by ICC profiles, not by tone curves in the PE or in ACR. -
The advice you give to avoid pleasant tweaks is the recipe for a linear image, as you have given it to Brent Townshend
http://www.adobeforums.com/webx/.59b71da3/0
This was not what I had in mind. I am aware of that a linear image will not look natural.
In terms of the scene referred workflow as described by Tindemans
http://21stcenturyshoebox.com/essays/scenereferredworkflow.html
what I search for might be described as a subdivision of step 2 (called creative processing). There must be an area between linear and purely arbitrary, we might call it natural. The fact that this area can not be easily defined let alone measured objectively ought not to preclude us from at least identifying and naming it. As it is now, we can not even in terms separate between natural, and beautified ad libitum. Arbitrariness is being presented as unavoidable.
So my question aimed at: (How) can I make a base curve that is natural, but not beautified (by exaggerating the contrast)?
"The Chart Wizard is designed to produce a reasonably accurate *scene-referred* color profile" - but how is the "rendering intent" of the Base Curve?
I tried your advice with the linear curve in the PE + lightening in ACR on both the ColorChecker image and a real scene. The CC could be made look reasonable. But this is an image where the histogram has headroom on either side. So I experienced it like you said: this may work with an image whose DR matches that of the medium. With the real scene, whose histogram stretched end-to-end in the first place, using the Exposure slider led to highlight clipping at once, as exspected; instead, I had to use the Brightness slider - that is increase the contrast, if I understand it correctly.
So it looks like-:
1-The task of the Base Curve is to map the DR of an image to that of the screen
2-If there is any answer to my question, it is image-dependent. On the other hand: the PE uses ONE Base Curve. So the question may be allowed: What is the "rendering intent" of that curve?
Kind regards - Hening.

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Edward Allen wrote:
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I use a Nikon D7100 in camera RAW. In camera my images are always in balance. In LR, if I select Auto Tone in Basics invariably it will adjust the exposure. I tend to adjust exposure near last in my workflow because I assume my camera had the exposure setting right. When I feel I need to adjust the exposure my first stop is the Tone Curve. I'm wondering a couple of things:
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My recommendation:
(note: I am interpreting "exposure", in your question, to mean "dynamic range at right wall of histogram", i.e. white point)
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Most of my normal photos end up with:
+exposure (to fully brighten)
+whites (for full dynamic range without excessive exposure setting)
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(for abnormal photos or when desiring abnormal results - anything goes..).
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trying to recover highlights via -whites. try -highlights (and maybe +whites) before -whites.
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You already know this, but for the sake of completeness (and other readers): you can learn by clicking 'Auto Tone' "button". You may need to dial back the exposure afterward etc. but it can be very educational none-the-less..
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often, adjustment of whites is considered optional/fine-tuning, but sometimes optimal toning can only be had by using a large whites value adjustment, which dramatically impacts contrast, and exposure..
cteavin wrote:
I tend to adjust exposure near last in my workflow because I assume my camera had the exposure setting right.
In case not clear yet, adjusting exposure and/or whites (and/or white point on curve) and all the rest is often done to turn an image "with potential" into a very nice image, not just to compensate for in-camera exposure imperfection. I have lots of under-exposed images that end with -exposure (granted, usually +whites), and vice-versas.. That said, if you don't know whether to crank it up or down, there is something to be said for passing until you do..
Lastly, for emphasis: exposure slider is an intelligent slider. It behaves more like normal exposure adjusters at lower values, and more like brightness adjusters at higher values (has clipping protection and highlight roll-off logic which kicks in as you crank it up..). So, it's a mistake to think of adjusting it just to make up for non-optimal camera exposure setting.
Sorry for verbose answer, but there is really no short answer which doesn't run the risk of being bad advice: best way to adjust "exposure" depends...
Cheers,
Rob

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SO
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Am I missing something? Willing to be schooled always!
Many thanks if you made it this far.
(Note: I have posted this in LuLa too, so apologies to those who may frequent both)

Here's a Lightroom tone curve (saved):
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.5-c002 1.148022, 2012/07/15-18:06:45
">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about=""
xmlns:crs="http://ns.adobe.com/camera-raw-settings/1.0/"
   crs:Version="8.1"
   crs:ToneCurveName="Custom">
   <crs:ToneCurve>
<rdf:Seq>
<rdf:li>0, 0</rdf:li>
<rdf:li>99, 92</rdf:li>
<rdf:li>166, 156</rdf:li>
<rdf:li>231, 223</rdf:li>
<rdf:li>255, 255</rdf:li>
</rdf:Seq>
   </crs:ToneCurve>
</rdf:Description>
</rdf:RDF>
</x:xmpmeta>
and here's the same tone curve in a .dcpr file:
<dngclr:ToneCurve rdf:parseType="Resource">
    <dngclr:Edit0 rdf:parseType="Resource">
       <dngclr:X>0</dngclr:X>
       <dngclr:Y>0</dngclr:Y>
    </dngclr:Edit0>
    <dngclr:Edit1 rdf:parseType="Resource">
       <dngclr:X>99</dngclr:X>
       <dngclr:Y>92</dngclr:Y>
    </dngclr:Edit1>
    <dngclr:Edit2 rdf:parseType="Resource">
       <dngclr:X>166</dngclr:X>
       <dngclr:Y>156</dngclr:Y>
    </dngclr:Edit2>
    <dngclr:Edit3 rdf:parseType="Resource">
       <dngclr:X>231</dngclr:X>
       <dngclr:Y>223</dngclr:Y>
    </dngclr:Edit3>
    <dngclr:Edit4 rdf:parseType="Resource">
       <dngclr:X>255</dngclr:X>
       <dngclr:Y>255</dngclr:Y>
    </dngclr:Edit4>
</dngclr:ToneCurve>
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That's it! You just saved my day.
Thank you very much.

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