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Author Topic: Combining RAW + JPEG  (Read 13733 times)
Peter_DL
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« on: March 20, 2008, 01:13:07 PM »
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IF of interest and maybe for discussion.
I’ve placed this as an ACR feature request:
http://www.adobeforums.com/webx?14@@.3bb6a85c.3bbc8060/357

>>
The merits of Raw are well documented and have been broadly discussed.  Compared to JPGs from in-camera conversion, Raw data can easily bear up to approx. 1-stop more of dynamic range.  Raw processing allows to recover these highlights e.g. via the Exposure slider in ACR.  Also, Raw features a better correction and ex post adjustment of White-balance via Temperature and Tint controls.
Further, Raw data can be processed and released into a large gamut such as ProPhoto RGB (pRGB), thus preserving a major part of scene-referred color saturation.  Many of such saturated colors are already within the reach of today’s printer; others may require particular attention to avoid posterization.
Image details and sharpening are another aspect. In-camera sharpening is not known to be particularly advanced and therefore prone to amplify noise or to cause artifacts if overdone.

Now referring to JPGs from in-camera conversion, and in consideration of all limitations including tiny sRGB gamut, we have to admit that their “look” can be surprisingly good if not even preferred.  Speaking for myself only and some experience with Canon gear, impression is that image rendition and color appearance with JPGs have much improved in the course of technological progress.  Same may apply to other brands.
Many user seem to feel the same and often enough a generic Raw converter such as DPP is preferred to access said “look”, even at the cost of workflow speed and convenience vs ACR. It’s sometimes claimed that any of such “look” can be mimicked in ACR, however, I’d like to disagree with this.  Even simple in-camera settings such as Contrast or Saturation are apparently following complex and different definitions than commonly known, and also single hues are shifted away from colorimetric accuracy to whatever camera engineers have identified as “pleasing”.
Further, it can be assumed that in-camera conversions feature a perceptual gamut compression, so there’s less channel clipping with saturated colors compared to a straight Raw -> pRGB –(RelCol)–> sRGB pathway.

Coming to the point:
Many of today’s cameras allow to capture Raw + JPG simultaneously.
ACR since version 4.x (iirc) allows to process Raw or JPG.

Wouldn’t it be possible to combine and blend both images at the level of linear-gamma ProPhoto RGB (1.0 pRGB) which ACR was reported to use as an intermediate working space ?

All controls which are applied before or during the conversion Raw -> 1.0 pRGB would still act on this transform only.  While the JPG is converted to same 1.0 pRGB at 16 bpc, all controls which are applied after arrival in 1.0 pRGB would act on a blend of both images.  This is of course just meant as rough description, hoping that Adobe engineers would get the gist while being much more familiar with ACR mechanics.

Basically I’ve tried what I suggest by doing such blends in Photoshop, then going back to ACR again.  Results seem to confirm the idea and intention in principle i.e. to enhance JPGs by insertion of Raw data information, or the other way round, to enhance the ACR processing chain by inserting a touch of “JPG look” as conceived by camera manufacturers.

Finally it should be mentioned that the idea is not really new (see Link and White Paper), but maybe today’s RAW + JPEG combo could offer an up to date implementation with ACR.
http://www.kodak.com/global/en/professiona...erit/erit.jhtml
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Peter

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sniper
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« Reply #1 on: March 20, 2008, 01:59:02 PM »
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While the idea has merit, I can see many problems to overcome, first most cameras have options for setting saturation etc, and conversion would have to take this into account. Another point is cameras vary, one eos 5d will probably be slightly different from the next and so on, all this has to be "designed in" so to speak.
Perhaps the biggest issue is how many people want their RAW to look like their jpeg, I for example ajust all my images before printing (jpeg or raw) so it makes little difference to me if they match.  A lot of people only use raw or jpeg, not both anyway, so they probably wouldn't care if they match.  Wayne
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Panopeeper
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« Reply #2 on: March 20, 2008, 02:20:14 PM »
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Basically I’ve tried what I suggest by doing such blends in Photoshop, then going back to ACR again.  Results seem to confirm the idea and intention in principle i.e. to enhance JPGs by insertion of Raw data information, or the other way round, to enhance the ACR processing chain by inserting a touch of “JPG look” as conceived by camera manufacturers.

I don't understand the point. What should the JPEG image contribute to the result? Whatever that "JPEG look" is, it has been achieved from the same basis, namely from the raw data; the rest is adjustment parameters, which can be achieved by ACR adjustments. Such sets of adjustments can be saved and treated as for example Picture Styles, so that they can be easily applied to other images.
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« Reply #3 on: March 20, 2008, 04:11:14 PM »
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I don't understand the point. What should the JPEG image contribute to the result? Whatever that "JPEG look" is, it has been achieved from the same basis, namely from the raw data; the rest is adjustment parameters, which can be achieved by ACR adjustments. Such sets of adjustments can be saved and treated as for example Picture Styles, so that they can be easily applied to other images.
[a href=\"index.php?act=findpost&pid=183045\"][{POST_SNAPBACK}][/a]

In terms of in camera processing, the JPEGs are as you say, getting built from the same Raw data we have in ACR, but the processing is highly proprietary. This is one reason I don't see much use in Raw+JPEG because the two rarely match (or I have to jump though hoops to make the Raw match the JPEG). I find it easier to just render the Raw as I prefer and save out a JPEG. Very fast and efficient in Lightroom.

That said, there has been talk of having a default Raw rendering that could somehow automatically match (closely) the JPEG which I suspect would require we actually shoot said JPEG (not sure). That might be a useful capability, at least as a starting point in the Raw rendering.
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Andrew Rodney
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« Reply #4 on: March 20, 2008, 04:58:48 PM »
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That said, there has been talk of having a default Raw rendering that could somehow automatically match (closely) the JPEG

There is no "the" JPEG. My camera offers the selection of seven sharpness levels, nine contrast, nine saturation and nine tone variations. All these together constitute a picture style, and all are involved (with the white balance) in the in-camera conversion of the raw in JPEG.

Consequently, one would have to have 5100 images as basis (with the combinations of the the settings) to select from. It would be simpler to record raw + JPEG and use that JPEG as template - but then why recording the raw at all?

I don' see any sense in the original suggestion.
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Gabor
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« Reply #5 on: March 20, 2008, 06:15:41 PM »
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There is no "the" JPEG. My camera offers the selection of seven sharpness levels, nine contrast, nine saturation and nine tone variations. All these together constitute a picture style, and all are involved (with the white balance) in the in-camera conversion of the raw in JPEG.

Consequently, one would have to have 5100 images as basis (with the combinations of the the settings) to select from. It would be simpler to record raw + JPEG and use that JPEG as template - but then why recording the raw at all?
[a href=\"index.php?act=findpost&pid=183073\"][{POST_SNAPBACK}][/a]

A picture style is a preset. We have them in say LR or ACR. The idea here would be an auto preset built based upon the color appearance of the JPEG (or some way to shoot a JPEG target, build a preset automatically).
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Andrew Rodney
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« Reply #6 on: March 20, 2008, 08:50:48 PM »
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A picture style is a preset. We have them in say LR or ACR

Picture Style is a feature of Canon cameras, Nikons too have it under a different name. They are combinations of the settings sharpness, contrast,....

Users are regularly venting their dissatisfaction on the Adobe ACR forum about ACR not being able to automatically reproduce their in-camera settings, the best as complete picture styles. That is, what people miss (those, who regard raw as a last resort in case they blew the shot). It is a joke to believe that the way to achieve that is through reverse-engineering a JPEG image.

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The idea here would be an auto preset built based upon the color appearance of the JPEG (or some way to shoot a JPEG target, build a preset automatically

The color is a different issue, but again, it is not the issue of reverse-engineering of a JPEG image. Btw, the new version of ACR (which has been aborted almost sooner than released) is supposed to have new camera profiles. I wonder if this helps on the omnipresent problem of ACR with color rendering.

The barrier of ACR is the DNG specification, preventing ACR from honouring in-camera settings. The new version is accompanied with a new DNG specification, containing at least 13 new tags. The documentation is not published yet. I wonder if Adobe had finally the courage to extent the specification with elements accomodating in-camera settings for governing the raw conversion.
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Peter_DL
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« Reply #7 on: March 21, 2008, 05:05:30 AM »
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I don't understand the point. What should the JPEG image contribute to the result? Whatever that "JPEG look" is, it has been achieved from the same basis, namely from the raw data; the rest is adjustment parameters, which can be achieved by ACR adjustments. Such sets of adjustments can be saved and treated as for example Picture Styles, so that they can be easily applied to other images.
[{POST_SNAPBACK}][/a]
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Picture Style is a feature of Canon cameras, Nikons too have it under a different name. They are combinations of the settings sharpness, contrast,....

Users are regularly venting their dissatisfaction on the Adobe ACR forum about ACR not being able to automatically reproduce their in-camera settings, the best as complete picture styles. That is, what people miss (those, who regard raw as a last resort in case they blew the shot). It is a joke to believe that the way to achieve that is through reverse-engineering a JPEG image.
The color is a different issue, but again, it is not the issue of reverse-engineering of a JPEG image. Btw, the new version of ACR (which has been aborted almost sooner than released) is supposed to have new camera profiles. I wonder if this helps on the omnipresent problem of ACR with color rendering.

The barrier of ACR is the DNG specification, preventing ACR from honouring in-camera settings. The new version is accompanied with a new DNG specification, containing at least 13 new tags. The documentation is not published yet. I wonder if Adobe had finally the courage to extent the specification with elements accomodating in-camera settings for governing the raw conversion.
[a href=\"index.php?act=findpost&pid=183122\"][{POST_SNAPBACK}][/a]

Panopeeper,

Your point that in-camera conversion also starts from the same basis, namely from the raw data, is well understood.
However, with the conversion it’s a matter of different math … and how to bring things together again:

In-camera conversions are, as Andrew says, highly proprietary.  Even if all of your settings such as Contrast or Saturation would be communicated to ACR, the question is about the underlying definition:
Is in-camera Contrast the same as the respective slider in ACR? I doubt. As far as I can tell, Canon likes to mix it with something like Clarity.  What is the definition i.e. the underlying color model for in-camera Saturation. With ACR it can be shown that the Saturation slider behaves like with the Hue/Sat.-tool but in HSL saturation blend mode and applied on a 1.0 pRGB basis. Now with in-camera Saturation … good luck with reverse-engineering. There are only quite few in-camera controls, however, these can be beasts if you want to dig down to their mechanics.

In addition, many in-camera moves and processing parameter might not be directly accessible. Have a look at this Canon brochure, page 44 (page 2 in the pdf; sorry it’s in German).  The chart illustrates how single hues are shifted for a more “accurate” rendition of memory colors; e.g. the deep blue sky etc.  A similar approach is described in Kodak patent US 679174.  Finally, every picture style might have its own agenda and maybe rendering table to get this accomplished.  That said, it’s even unclear (for me), if and to what extent such transforms could already be scene adaptive.
[a href=\"http://www.canon.de/Images/dsc_tcm83-282974.pdf]http://www.canon.de/Images/dsc_tcm83-282974.pdf[/url]
http://www.freepatentsonline.com/6791716.html


Sure, you can resort to ACR’s Calibrate tab in order to obtain a somewhat similar “look”. Eric Chan has described such color matching approach. But with all due respect, tweaking the matrix primaries is a quite coarse method with regard to the intended purpose.
http://people.csail.mit.edu/ericchan/dp/acr-color-match/

No, working with presets in ACR is certainly a good idea to create a specific look.  However, to claim that this approach would be suited to copy the specific look of another converter such as in-camera conversion, which in all probability utilizes different math, is not realistic … imo.

This at least is my experience and was the starting point of the initial proposal.
Perhaps a kind of: don’t fight against or try to copy, just blend it in.

Peter

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madmanchan
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« Reply #8 on: March 24, 2008, 05:54:31 PM »
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The problem of ACR (or any other RAW converter) not being able to match a known Picture Style (or whatever you call it) has nothing to do with limitations of the DNG specification.

Even if you know exactly what the in-camera parameters are (e.g., Picture Style = Faithful, Contrast -1, Saturation +1, Sharpening = -2), that by itself is relatively little information. There are an infinite # of ways to interpret that metadata, but only 1 of those ways will reproduce the vendor look. This is the vendors' secret sauce, and AFAIK they aren't divulging the recipes.
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Panopeeper
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« Reply #9 on: March 25, 2008, 12:30:53 PM »
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The lack of respective tags in the specification excludes the *communication* of such settings. It would be relatively easy to "map" the actions a given raw processor takes in response to such settings, though that would not be an absolute requirement.

I don't think Adobe or any other camera manufacture independent raw processor would try to imitate how all CNX or DPP or other "proprietory" raw processor is sharpening; that's quite nonsense. The point is, that users of a given raw processor are expecting, that their settings will be honoured. This does not need to be identical to DPP or CNX, and if a photographer uses consistently a given raw processor, than this is very normal: the camera setting should correspond to the actions of that raw processor.

This is what lots of photographers are missing in ACR, according to their complaints.

The *color reproduction* is a separate issue. Not only that mimicking another raw processor's color reproduction is more difficult than mimicking sharpness or contrast settings, but IMO mimicking an other reproduction is not the solution. One should be able to choose between many different reproductions.

The thread "ACR 4.4 and Clarity" picked up this subject, with Edmund complaining about the lack of interface for independent profiles. My opinion is, that that is the way to go, although I don't know, if the way Adobe selected is suitable for that. I mean I don't know, if the color conversion governed by matrix operations can fully utilize what a given sensor delivers. I wonder if there is a publically available analysis showing, how much of the gamut of the sensor can be transformed this way in CIE relating to a specific camera
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« Reply #10 on: March 25, 2008, 01:28:00 PM »
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The thread "ACR 4.4 and Clarity" picked up this subject, with Edmund complaining about the lack of interface for independent profiles. My opinion is, that that is the way to go, although I don't know, if the way Adobe selected is suitable for that. I mean I don't know, if the color conversion governed by matrix operations can fully utilize what a given sensor delivers. I wonder if there is a publically available analysis showing, how much of the gamut of the sensor can be transformed this way in CIE relating to a specific camera
[a href=\"index.php?act=findpost&pid=184180\"][{POST_SNAPBACK}][/a]

And as yet, no answer from Edmund (or you if you wish) about how this would ensure any desired color rendering nor if Edmund (or you) are unable to produce a desired color rendering without a custom ICC profile.
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Andrew Rodney
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« Reply #11 on: March 25, 2008, 02:08:00 PM »
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And as yet, no answer from Edmund (or you if you wish) about how this would ensure any desired color rendering nor if Edmund (or you) are unable to produce a desired color rendering without a custom ICC profile.
[a href=\"index.php?act=findpost&pid=184192\"][{POST_SNAPBACK}][/a]
I certainly can't state that this can be done, for I am not sure if the method chosen by Adobe is a viable one at all.

As to achieving the desired result without a custom profile: I am not complaining about the color rendition from my perspective, but I don't dismiss others' concerns with semantic arguments. The opening post of this thread by Peter too reflects the opinion, that the camera profiling capability of ACR is not the right way to solve the issues.
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Gabor
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« Reply #12 on: March 25, 2008, 02:18:58 PM »
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The opening post of this thread by Peter too reflects the opinion, that the camera profiling capability of ACR is not the right way to solve the issues.
[a href=\"index.php?act=findpost&pid=184205\"][{POST_SNAPBACK}][/a]

Solve what issues? All goes back to the original and simple question.
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Andrew Rodney
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« Reply #13 on: March 25, 2008, 02:34:47 PM »
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Solve what issues? All goes back to the original and simple question.

My answer was that the "expected" color reproduction can not always be achieved. I am not prepared to discuss about semantics. You may call it "desired color reproduction"; it is in fact whatever a user wants to achieve.

From the opening post:

Many user seem to feel the same and often enough a generic Raw converter such as DPP is preferred to access said “look”, even at the cost of workflow speed and convenience vs ACR. It’s sometimes claimed that any of such “look” can be mimicked in ACR, however, I’d like to disagree with this

I go a step further, for I don't want to restrict the achievable "looks" to those delivered by the native raw processor of a given camera.
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« Reply #14 on: March 25, 2008, 02:45:58 PM »
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My answer was that the "expected" color reproduction can not always be achieved.

Expected as a default or after using the various dials and sliders provided?

Looks are nothing more than a preset of rendering instructions. Every Raw converter I've ever seen can make looks (renderings). The question is, does the rendering provide the color appearance you want? If not is it close? If not is it a mile away and you can get to the look you want?

Getting something from the get go versus never being able to get what you want is a pretty significant difference.
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Andrew Rodney
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madmanchan
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« Reply #15 on: March 25, 2008, 06:38:34 PM »
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The point is, that users of a given raw processor are expecting, that their settings will be honoured. This does not need to be identical to DPP or CNX, and if a photographer uses consistently a given raw processor, than this is very normal: the camera setting should correspond to the actions of that raw processor.

I am not sure what you mean here. When you say "their settings" do you mean things that go in the raw file's maker note such as "Picture Style" and "Contrast" and "Saturation" settings?

If so, if a user selects Picture Style = Standard for a Canon 5D on the camera (using the camera's menus) and another user selects Picture Style = Faithful on his, how should a non-Canon raw converter interpret raw files from these two different cameras?  How should this "Picture Style" setting be honored?

Also, the camera vendors' image quality settings aren't standardized (how do Canon Picture Styles translate to Nikon Color Modes? they don't). Wouldn't it make more sense (and be easier) to just create a preferred style using the settings of the raw converter and save it as a preset for your camera? For example, if you prefer to have less contrast on your camera, couldn't you reduce the contrast in the raw converter and save that as the default for your camera?
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Peter_DL
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« Reply #16 on: March 26, 2008, 06:00:24 PM »
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The problem of ACR (or any other RAW converter) not being able to match a known Picture Style (or whatever you call it) has nothing to do with limitations of the DNG specification.

Even if you know exactly what the in-camera parameters are (e.g., Picture Style = Faithful, Contrast -1, Saturation +1, Sharpening = -2), that by itself is relatively little information. There are an infinite # of ways to interpret that metadata, but only 1 of those ways will reproduce the vendor look. This is the vendors' secret sauce, and AFAIK they aren't divulging the recipes. [{POST_SNAPBACK}][/a]
Thanks for confirmation on this part.


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... Wouldn't it make more sense (and be easier) to just create a preferred style using the settings of the raw converter and save it as a preset for your camera?  For example, if you prefer to have less contrast on your camera, couldn't you reduce the contrast in the raw converter and save that as the default for your camera? [a href=\"index.php?act=findpost&pid=184281\"][{POST_SNAPBACK}][/a]
Contrast is certainly an interesting example, because:  what’s the definition of “Contrast” ?

With ACR, the Contrast slider was reported to apply an S-curve around the midpoint set by Brightness (applied on 1.0 pRGB basis).  Thinking about the slope of such curve, this inevitably makes Brightness part of the definition of Contrast and vice versa. Also, Blacks and Exposure could be moved inwards to increase Contrast like with the legacy definition of Contrast as with the Brightness/Contrast tool in earlier PS versions.  Further, contrast can be altered via the Curve tab which might be based on a different color model and RGB separation, thus, introducing a different look.  And finally we have [a href=\"http://luminous-landscape.com/forum/index.php?showtopic=24097]Clarity[/url] to facilitate a perceived contrast i.e. midtone contrast via a totally different approach.

So what’s Canon’s definition for Contrast: something different or maybe a bit of everything from above?  Can’t answer; but a 1:1 match in ACR (if it makes sense at all to bother with such single parameter) might be quite hard to achieve.

Anyway, it seems we are going a bit in circles.
So will try to reconcile:

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Peter_DL
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« Reply #17 on: March 26, 2008, 07:25:20 PM »
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... to continue:
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My answer was that the "expected" color reproduction can not always be achieved. I am not prepared to discuss about semantics. You may call it "desired color reproduction"; it is in fact whatever a user wants to achieve. From the opening post: Many user seem to feel the same and often enough a generic Raw converter such as DPP is preferred to access said “look”, even at the cost of workflow speed and convenience vs ACR. It’s sometimes claimed that any of such “look” can be mimicked in ACR, however, I’d like to disagree with this [{POST_SNAPBACK}][/a]
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Expected as a default or after using the various dials and sliders provided? [a href=\"index.php?act=findpost&pid=184216\"][{POST_SNAPBACK}][/a]
Following comment, btw by Jeff Schewe, is from in an [a href=\"http://luminous-landscape.com/forum/index.php?showtopic=17588&st=8]earlier discussion[/url]: “Camera Raw supports (I think) over 130 cameras at present (over 10 camera makers-and a few that are no longer supported by the companies)...DPP supports only their Canon cameras.

So, at "default" which do you suppose will have better defaults?
”...

First question:  what are the reasons why a generic Raw converter such as DPP is (accordingly) often perceived to offer a better “default“ - in some aspects at least? Is it just because DPP honors the in-camera settings, or, does Canon somehow know their cameras better than anyone else, or, did they invest more man-years in the development of their proprietary recipe for a pleasing rendition, maybe a color appearance model or whatever? Perhaps impossible to answer here, so let’s ignore the question for the moment.

Second question:  can the DPP conversion be precisely copied by means of given ACR controls? I doubt.  And we seem to agree on this. Maybe somewhat close with reference to single aspects such as Contrast due to the variety of options in ACR, but all in all and particularly when it comes to Color - I’m quite sure that some very color-range-selective shifts in ACR would be needed; in 3D so to speak.

Third question: can ACR achieve and equal or more pleasing reproduction by utilizing the various dials and sliders provided? Maybe - depending on image and user skills. So perhaps I should leave it to more dedicated people to answer this, however, the burden seems to be on the user to do all settings necessary to accomplish this. OK, some folks may call it fun. Anyway. Another problem is “visual adaptation”. Within the closed sphere of one Raw converter, I tend to like “everything” I do. But then, cross-comparison with the results from another sphere i.e. Raw converter (and including in-camera conversion) is not so clear across different aspects.


Fourth question (and perhaps the key one): would it be easier to start with the DPP default "look", or at least some aspects thereof, whether from DPP itself or from in-camera conversion, but then having all the Raw rendering controls offered with ACR?  Clear YES from my side, even though it imposes a mechanistic contradiction which I wanted to address with initial proposal.

Or:
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... there has been talk of having a default Raw rendering that could somehow automatically match (closely) the JPEG which I suspect would require we actually shoot said JPEG (not sure). That might be a useful capability, at least as a starting point in the Raw rendering. [a href=\"index.php?act=findpost&pid=183069\"][{POST_SNAPBACK}][/a]

Peter

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madmanchan
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« Reply #18 on: March 26, 2008, 11:10:07 PM »
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Contrast is certainly an interesting example, because:  what’s the definition of “Contrast” ?

[snip]

So what’s Canon’s definition for Contrast: something different or maybe a bit of everything from above?  Can’t answer; but a 1:1 match in ACR (if it makes sense at all to bother with such single parameter) might be quite hard to achieve.

As you point out, there isn't a single definition of contrast. Intuitively all the reasonable definitions out there obey certain properties, such as that increasing "contrast" will make dark tones darker and light tones lighter. But there are an infinite number of ways to implement that.

Just to point out a common example, editing contrast in a photograph in a standard image editing application such as Photoshop usually means editing contrast in a gamma-encoded space (e.g., sRGB, Adobe RGB, or ProPhoto RGB). However, contrast editing in a raw converter may be implemented in a very different color space (with consequently different results). To add to the confusion, some raw converters allow editing contrast twice.

For example, in Canon's DPP you can apply a contrast curve which operates in camera coordinates (i.e., before colorimetric interpretation of those camera coordinates). That's in the RAW tab. You can then go to the RGB tab and also edit contrast, but this contrast curve is applied using whatever working space you have chosen (e.g., Adobe RGB or Wide Gamut RGB). And neither of these contrast curves have any direct correspondence to how Camera Raw's contrast curves work!

I am getting into technicalities here, but the main point is that a piece of camera metadata that says "Contrast +1" is meaningless in the same way that an 8-bit RGB value of (80, 100, 70) is meaningless. Without knowing the actual RGB color space (e.g., Adobe RGB), the latter gives us no colorimetric context. We can reasonably assume that (80, 100, 70) will likely be brighter than, say, (70, 90, 60), of course, in the same way that we can assume that Contrast +1 implies more contrast than Contrast -1.
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madmanchan
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« Reply #19 on: March 26, 2008, 11:29:38 PM »
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First question:  what are the reasons why a generic Raw converter such as DPP is (accordingly) often perceived to offer a better “default“ - in some aspects at least? Is it just because DPP honors the in-camera settings, or, does Canon somehow know their cameras better than anyone else, or, did they invest more man-years in the development of their proprietary recipe for a pleasing rendition, maybe a color appearance model or whatever? Perhaps impossible to answer here, so let’s ignore the question for the moment.

I don't think this is impossible to answer. As you are aware, there are many aspects of raw conversion image quality. One of them that is often discussed between ACR and Canon's DPP is color, and it is often suggested that Canon -- being the maker of the sensors of their DSLRs and of their cameras -- ought to have more info than anybody else on the spectral response of their color filters, the behaviors of their chips, etc. and therefore be able to produce more accurate color than anybody else.

Ironically, it's fairly easy to convince oneself that their out-of-the-box color isn't any more accurate than, say, Camera Raw's color. (It is actually less accurate from a colorimetric standpoint.) But some prefer DPP's default color because it has more pop and appears more 'pleasing' to the eye. My experience has been that most users do not want accurate color, despite making that claim. In fact, Canon's Picture Styles (with the exception of Faithful) do various color distortions which are clearly carefully designed to produce pleasing color, rather than accurate color (from a colorimetric standpoint).

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Second question:  can the DPP conversion be precisely copied by means of given ACR controls? I doubt.  And we seem to agree on this.

Not in general. In some cases it can be done on an image-by-image basis, but it is not possible to create a single preset that will, say, mimic the "Portrait" Picture Style across all images.  

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Maybe somewhat close with reference to single aspects such as Contrast due to the variety of options in ACR

The tone curve is pretty easy to match. Color is a different story.

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, but all in all and particularly when it comes to Color - I’m quite sure that some very color-range-selective shifts in ACR would be needed; in 3D so to speak.

Agreed.

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Third question: can ACR achieve and equal or more pleasing reproduction by utilizing the various dials and sliders provided?

I certainly believe this to be the case.

However, there's certainly an argument in favor of getting better starting points to help users improve their workflow. .

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Fourth question (and perhaps the key one): would it be easier to start with the DPP default "look", or at least some aspects thereof, whether from DPP itself or from in-camera conversion, but then having all the Raw rendering controls offered with ACR?  Clear YES from my side, even though it imposes a mechanistic contradiction which I wanted to address with initial proposal.

I don't know about 'easier'. I guess it would depend on how easy that 'look' information is to access. The problem if you just treat DPP as a black box and grab the final image as a starting point is that, well, you're no longer starting from a raw file! You're editing beginning with an output-referred image in which case some of the raw benefits would be lost.
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