good new, not-so-good news, an sad news

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ACR 3.x supports linear curves. Finally. Good news.

Curve is limited to 16 points - not so good news, as the common scale is 20 points.

The curve in ACR acts in linear space, but is using logarithmic scale only. 3eV range from mid-gray to black in compressed in 1/4 range of the curve, another quarter is waisted, being below shadow level. Thus the whole range is shifted, and what should be shadows is represented by 3/4 tone on the curve. Sad news.
 
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Iliah - thanks for the analysis. Could you go iinto a bit more detail?

Btw, I've been using the curve tool in ACR, and I don't do anything in Photoshop now except blur, resize and sharpen. I love it!
 
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It's just that I am not clear on your last paragraph, the 'sad news' one. Especially where you say that a quarter of the curve is wasted, being below shadow level.

If that were the case, wouldn't changing the left most 1/4 of the curve have no effect?

See - I'm missing something. I'll be back online later tonight (`5, 6 hours from now.)
 
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It is waisted in the sense that you can't effectively manipulate it - first, because of compression of values, second, because of extremely fragile nature of this area - any sudden move :) can bring up noise, loss of shadow neutrality, posterization.

What I call for is giving more photographic meaning to that curve, basically - eV scale, gray scale under the curve - those highly useful visualization aids; and having a separate curve for common adjustments in gamma-corrected space - like Nikon wisely done, separating linear luminosity "camera" curve from Capture curves in gamma-corrected space. But unwisely separating those curves to two different applications - Camera Control and Capture :)
 
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I haven't used the ACR 3 Curves tab enough yet to make a judgement on it. Maybe the "abstraction" to gamma-corrected imposes some limitations (if Iliah says so who am I to disagree).

I will say this though. I understand the reason for wanting to adjust the curve in linear space before conversion, and I understand why a true linear curve behaves differently when adjusting the highlight side compared to the shadow side. But that doesn't mean that I like it; it's actually pretty non-intuitive and can make it really tedious to make precise adjustments. Maybe ACR's implementation leaves something to be desired but I think they had a good idea.
 
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JeffKohn said:
Maybe ACR's implementation leaves something to be desired but I think they had a good idea.
Jeff, I started saying "good news", and I actually mean that.

Now, trick is to make the abstraction layer for curve editing so that eV values are spaced evenly. That is not linear scale. But having 3 curve scale modes - linear, logarithmic, and eV-uniform may be too much.
 
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Dear Jeff,

Of course we will unlock it. It seems to us that this next step is logical, as users are ready. It will also be implemented in new release of CurveSurgery
 
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Iliah said:
What I call for is giving more photographic meaning to that curve, basically - eV scale, gray scale under the curve - those highly useful visualization aids; and having a separate curve for common adjustments in gamma-corrected space - like Nikon wisely done, separating linear luminosity "camera" curve from Capture curves in gamma-corrected space. But unwisely separating those curves to two different applications - Camera Control and Capture :)
Isn't that what Adobe has done as well? Linear curve in ACR and gamma corrected curve in Photoshop proper?

I don't know how useful I'd find a gray scale, I prefer the ability to click the image and see where the clicked sample falls on the curve (ala Photoshop's g.c. curve.)
 
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