Since we have been bombarded with a bit too much Pro ACR evangelism lately, I decided to write down my crude thoughts on some of the ACR peculiarities. These are meant as constructive criticism and thought provokers, not as pure critique or putting down the product.
Suppose you're a photographer and see a beautiful scene with almost mystical colors worth capturing. For argument's sake we have the following 3 simplified possibilities:
1. The scene is perfect daylight D50 to which you also calibrated your monitor. White should become R=G=B=max (255) etc...
2. The scene has a mystical tint which is exactly reproduced compared to perfect daylight D50. White does not become R=G=B=max but some other combination which does depict the mystical tint correctly.
3. The scene has a mystical tint, but only because your vision has adapted to some non-standard white temperature. To capture the mystical color relative to D50 some corrections are necessary.
Suppose for argument's sake that the internal profile are correct, then how would you process this capture in ACR?
Case 1 & 2:
you should set the TEMP slider to D50 and the TINT slider to zero
Case 3:
you are completely on your own. There is no relevant TEMP value, the TEMP value in the camera RAW file bears no relation whatsoever to the captured RAW data (to begin with), and the TINT slider has no relation to the Mystical tint to be captured.
So what it the use of the TINT slider?
No photographer in this world is actual capable of "thinking" a colorbalance in terms of Temperature & TINT (as in correlated temp). Most people I know think in terms of tint as ColorCast. And most of the time the ColorCast is desirable and should not be completely corrected.
I would prefer a temperature and ColorCast correction slider.
But that would still be inadequate because the real question is: where and how do you neutralize the white-balance and correct or INTRODUCE a desirable colorcast?
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
But that would still be inadequate because the real question is: where and how do you neutralize the white-balance and correct or INTRODUCE a desirable colorcast?
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Simple answer? In Capture One. It has the Temp and Tint sliders, but after that it has also a colour wheel where you can simply by dragging the cursor from dead centre adjust any desired tint to your liking (or even more precisely using hue/saturation sliders).
Very nicely done.
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
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...I decided to write down my crude thoughts on some of the ACR peculiarities. These are meant as constructive criticism and thought provokers, not as pure critique or putting down the product. ...
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Good idea and two interesting posts/threads!
I should really check the Soap Box much more often.
Referring to ACR critique 1 :
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...I would prefer a temperature and ColorCast correction slider. But that would still be inadequate because the real question is: where and how do you neutralize the white-balance and correct or INTRODUCE a desirable colorcast?
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Oscar – you may be way beyond me here. Let me first try to clarify the nature of current Temperature & Tint sliders.
According to literature, Temperature control lets you specify the blue-yellow color balance, whereas Tint control lets you fine tune the color balance along the red-green axis. Camera Raw, B. Fraser, p.49-50.
To say it politely, this is only part of the story. The good news is that both controls, respectively, seem to be akin of coupled Highlights-slider for input/output (or vice versa), thus, executing a linear scaling along every single channel R/G/B. Same as R/G/B-Levels'-Highlights-sliders do in PS - just coupled. In other words, it’s not a R/G/B gamma setting. Appreciate this.
Temperature control lets you mainly specify the blue-yellow color balance (RG:B), but also changes R:G. Tint control lets you mainly fine tune the color balance along the magenta-green axis (RB:G), but also changes R:B.
In other words, both, Temperature as well as Tint change all ratios R:G:B, with different weighting. I assume that this has to do with this profile-to-profile interpolation story. Whereas the linear scaling may happen later on in a gamma 1.0 pRGB sphere (speculation # 1).
I'm not sure about the deeper sense. The Temp slider (sometimes) seems to allow to change the apparent color temperature within a certain range and without the need to rebalance the Tint. It could be that the Temp slider somehow tries to follow the Black body radiator curve (speculation # 2).
However, this architecture makes it very hard e.g. to change a gray point from its given RGB combo to certain target values. It can require balancing Temp, Tint + Exposure, altogether. Simple R/G/B Highlights-sliders such as given with PS Levels would be a gem – IMO.
Does this somehow meet your point?
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Referring to ACR critique 2 :
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... ACR 3 has introduced a new Curves tab. ... Whether this curve is combined with the conversion curve or simply a post-process is unclear to me, but if we are to believe Bruce Fraser, ...
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I'm still with CS1. However, just recently I came to a somehow similar question, but that was certainly within the wrong thread.
Referring to the ACR/camera default tone curve from Contrast & Brightness controls: application of this S-shape curve before gamma-encoding would probably damage the linear data due a compression of shadows’ levels. Application of this S-shape curve after gamma-encoding would probably be the same as working in PS – where I prefer to use adjustment layer.
So I just can hope (or rely to literature) that Adobe was wise enough to combine both. Gamma-encoding + this S-shape curve would add to very gentle rendering function.
I’m not sure if your conclusion is anything close to mine (could of course be completely different): I just want to see my data passing through ACR with minimum loss, thus, staying with image editing in standard PS.
Yes, I know about highlight recovery … and also CT should be treated at linear RAW … just my personal decision to stick to adjustment layer for everything else.
So I guess the core of my question is, if the default tone curve is safe to use for a standard capture (if there’s something like that)? Or, if certain (fix) deviations from default Contrast, Brightness & Shadows settings could benefit?
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Oscar – I'm sorry that I could not really reply to your points. Taking the occasion, I placed some of my own questions. Further, please don’t misunderstand my style; nothing is really settled wisdom, I’m just used to sell things as given facts ….
Looking forward to hearing from you.
Kind regards, Peter
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White Balance so easy, even our 5 year old can do it.- Melissa Strickland
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The Temp slider (sometimes) seems to allow to change the apparent color temperature within a certain range and without the need to rebalance the Tint. It could be that the Temp slider somehow tries to follow the Black body radiator curve (speculation # 2).
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I presume you mean the planckian locus. According to some early reports when ACR was first conceived, the TEMP slider follows the planckian locus, and the TINT slider follows the iso-temperature lines. But this is typically a "technical" approach. From a technical point-of-view you could control all possible colors this way. But this has two problems, one technical (see below) but first and foremost one practical:
Nobody really "thinks" in terms of planckian locus and iso-temperature lines. That's why you get the rather crude description of which colors the TEMP slider changes, and which colors the TINT slider changes. It has been said before: a camera is not a scanner. Trying to treat it that way, but disguising the treat behind controls more familiar to Photographers is not necessarily the most appropriate setup. That's not to say that scanner controls are not useful. But the question is: what control at what stage?
Or in other words, how does a photographer "think", even at the very first stages of actual preparing a shoot. How does he/she select a certain whitebalance? How does that translate to the controls found in ACR?
The temperature slider in itself is probably a useful feature. But the tint slider should probably be more like a color-cast correction slider. i.e. you click the gray-card and the TEMP slider goes to the closest correlated daylight-equivalent. Then you still might have a tint in the gray-card, but this is sometimes desirable, sometimes not, and mostly something in-betweenish; a color-cast correction slider would then correct the color from 100% color-cast to neutral gray or something in-betweenish...
GEEK TALK: Technically the iso-temperature lines give you the daylight-equivalent closest to an arbitrary tint. And it only is meant for colors that are close to the planckian locus. So it is not meant to do the inverse, especially across possibly large deviations. i.e. go from daylight-equivalent to an arbitrary tint which may not be close to the planckian locus at all...
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
But that would still be inadequate because the real question is: where and how do you neutralize the white-balance and correct or INTRODUCE a desirable colorcast?
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Simple answer? In Capture One. It has the Temp and Tint sliders, but after that it has also a colour wheel where you can simply by dragging the cursor from dead centre adjust any desired tint to your liking (or even more precisely using hue/saturation sliders).
Very nicely done.
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Is that equivalent to the DPP implementation?
It may be a solution, but why does one get to change the TEMP/TINT which have a colorspace independent equivalent and additionally select a Hue/Sat which you most likely judge by your monitor? Or is the Hue/Sat wheel actually converted between the monitor and whatever colorspace the app has designated to the data at that particular moment?
(I mean "you" in a general sense).
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
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I presume you mean the planckian locus. According to some early reports when ACR was first conceived, the TEMP slider follows the planckian locus, and the TINT slider follows the iso-temperature lines. But this is typically a "technical" approach.
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Oscar,
Thanks a lot for this clarification! That’s a really valuable insight.
Admittedly, I’m pleased that my simple analysis went in the right direction.
It may be seen as a nice side story that the Blackbody Radiator historically bookmarks the failing of classic physics. Hope this doesn’t include any prophecy.... Planck solved the matter by introduction of discrete energy quantums.
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... Nobody really "thinks" in terms of planckian locus and iso-temperature lines. ... Or in other words, how does a photographer "think", even at the very first stages of actual preparing a shoot. ...
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The basic two options I see are (1.) to push & wait until digital has largely adapted to “our” way of thinking. My best guess is that this will take another five to ten years. Or (2.), to try adapting the way of thinking to digital . I’m not sure if this goes faster - speaking for me only.
The latter is certainly not an easy task, i.e. to get the underlying principles of sw settings. In fact, my top wish for ACR would be a comprehensive flow chart with some nice illustrations to clarify “what happens in detail and when exactly - to the data”. And yes, the one or other basic equation would not be wrong, too … IMO.
As soon as such insights have become “public domain”, it might get easier to argue for certain changes / improvements.
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FWIW , let me try to summarize what I got from this thread, literature, plus some latest, own “crazy” thoughts:
> It is reported that ACR uses a gamma 1.0 version of pRGB as an intermediate working space. That’s the sphere where Temp and Tint follow the Planck radiator and “vertical” iso-temperature lines, respectively.
Temp and Tint act on the RGB data as akin of coupled Levels’-Highlights-sliders, thus, executing a linear scaling along each R/G/B channel. At least that’s given near the grayscale. And, at least that’s what apparently happens – there could be another, “”easier”” explanation.
> One step before this, Temp and Tint influence the famous interpolation between two input profiles (D65 daylight & A tungsten). Rendering from whatever the resulting input profile exactly is (linear-gamma camera space) -> to huge 1.0 pRGB could be AC , thus, superseding the need to play with imaginary highlight slider!? That’s what I meant with headache. The illuminants and interpolations follow the Plank radiator anyway.
> One step afterwards it’s time to think about Brightness & Contrast settings. Both controls “affect the rendering tone curve controlling the conversion from linear-gamma ProPhoto RGB to the final gamma-corrected output space” – Camera Raw, B. Fraser, p.33 -
English is not my mother tongue, but this seems to say that “gamma-encoding + B&C settings” are executed simultaneously. What a cool rendering curve, extremely gentle to the shadows by creating a local gamma < 1.8.
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IF this is at faintest true – what a nifty setup.
Oops … can’t believe it. Am I converting to ACR evangelism here?
O.k., this intermediate 1.0 pRGB is not my favorite (volume deltaE3 > Lab). But seeing it that way it would just be a transition state (like PCS Lab) with Temp & Tint being active before, and B&C being applied afterwards. No real movements in this linear-gamma pRGB???
Kind regards, Peter
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White Balance so easy, even our 5 year old can do it.- Melissa Strickland
Linear Mode
