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Author Topic: Today's DSLR should have another exposure mode  (Read 27498 times)
John Sheehy
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« Reply #60 on: June 03, 2006, 11:38:26 AM »
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Bill,
I use this technique quite often but not to recover highlight detail, which one can do with a single conversion and a negative EC, but to reduce noise and improve image quality in the shadows. For example, I'll often blend 2 conversions, one of which has a -2EC setting and the other a +2EC. However, the improvements are fairly marginal and this technique is no substitute for 2 separate exposures.
[a href=\"index.php?act=findpost&pid=67279\"][{POST_SNAPBACK}][/a]

I've always felt that the fact that people need to do this, to get results, is only a reflection on the primitive state of RAW converters or the post-processing software.  There is absolutely no reason why a 16-bit TIFF can't carry all the DR of the RAW file.  The amount of shadow DR potential in a 16-bit TIFF gamma-adjusted is astronomical, compared to what is in a RAW file, and a linear 16-bit TIFF (a full conversion but without tone re-mapping) is sufficient.

Post-processing could do any kind of s-curve or zone-based contrast boosts/enhancements.

Blending is awkward, and full of artifacts, and really should only be necessary for multiple shutter events.  Even with multiple shutter events, the HDR process should be done to the data in a totally linear state.  I don't know why PS CS2 doesn't merge the data in a RAW state, at a higher bit depth, and then convert it.  That would make so much more sense, as the linear data is mathematically simple.  If you shoot a grey step card at 1/100, and then again at the same ISO and aperture at 1/1000, the ratio of the average level of each square, minus the blackpoint for that image, is *EXACTLY* the same ratio between the two images in the RAW data.  The only thing that differs, other than the scaling difference between the two images, is the S/N ratio.  There are minor exceptions, of course; the Canon 20D, for instance, is not linear at ISO 100 in the top half stop or so of RAW highlights, due to some kind of data manipulation (the opposite of what you'd expect from saturation).
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Ray
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« Reply #61 on: June 03, 2006, 12:26:20 PM »
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I've always felt that the fact that people need to do this, to get results, is only a reflection on the primitive state of RAW converters or the post-processing software.  There is absolutely no reason why a 16-bit TIFF can't carry all the DR of the RAW file.  The amount of shadow DR potential in a 16-bit TIFF gamma-adjusted is astronomical, compared to what is in a RAW file, and a linear 16-bit TIFF (a full conversion but without tone re-mapping) is sufficient.

John,
That might be true. There is more than one way to skin a cat. I imagine that anyone more skilled in PS than I am could do an equal or better job with a single conversion into 16 bit tif than I can do with a dual conversion.

I use the layer mask method described in an LL tutorial here . I adjust the levels of the individual layers before flattening and find the whole process very quick and easy. The only problem is a tendency to getting halos if the EC gap is too extreme between the 2 conversions. But this problem can usually be fixed with the gamma slider in levels with one or both of the layers and/or a greater degree of Gausiian blurring of the B&W mask. If not, then the whole process has to be repeated with less extreme differences in EC.

I've always assumed that a +2EC (for example) conversion will provide more bits for the shadows and provide better quantization, which in turn translates to better tonality in the shadows and marginally better S/N.
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Dennis
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« Reply #62 on: June 04, 2006, 11:50:20 AM »
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I've always felt that the fact that people need to do this, to get results, is only a reflection on the primitive state of RAW converters or the post-processing software.  There is absolutely no reason why a 16-bit TIFF can't carry all the DR of the RAW file.
You're right, but a 16bit TIFF is much bigger than a Raw file. Further, you have already interpolated RGB triples in a TIFF, so the real deal is still the raw format. It's the smallest file, containing the most information.
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Dennis
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« Reply #63 on: June 04, 2006, 11:51:44 AM »
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When dealing with very high DR situations, one should not overlook the possibility of doing a double conversion, one for highlights and another for shadows, and then blending them digitally.
Yes, if the raw converter is able to produce a good highlight conversion.
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Ray
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« Reply #64 on: June 04, 2006, 08:41:45 PM »
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Yes, if the raw converter is able to produce a good highlight conversion.
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I don't see the dual conversion method relating directly to recovering highlights. Recovering highlights is dependent upon the converter, as you mention. ACR and C1 appear to be best in this regard. The problem is, after applying the negative EC to recover highlights (-2 EC or whatever), it's then difficult to recover the vibrancy and general tonality of the lower mid-tones and shadows from the converted TIF, even if it's in 16 bit.

Dual conversion is the best technique I happen to know which can improve the tonality of the darker parts of an image with recovered highlights.
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Dennis
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« Reply #65 on: June 05, 2006, 05:44:25 AM »
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I don't see the dual conversion method relating directly to recovering highlights.
For the dual conversion method, you need one conversion with good highlights, right? See my picture above. With dcraw, there's not much in the highlights worth a dual conversion.
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Dennis.
Ray
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« Reply #66 on: June 05, 2006, 08:05:42 AM »
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For the dual conversion method, you need one conversion with good highlights, right? [a href=\"index.php?act=findpost&pid=67420\"][{POST_SNAPBACK}][/a]

I need one conversion with good highlights, period. If I think the shadows are slightly degraded as a consequence of a negative EC applied to a wide DR subject, I might think it worthwhile to blend the image with a second conversion which brings out the shadows and improves tonality.
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PeterLange
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« Reply #67 on: June 05, 2006, 03:40:12 PM »
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.... The problem is, after applying the negative EC to recover highlights (-2 EC or whatever), it's then difficult to recover the vibrancy and general tonality of the lower mid-tones and shadows from the converted TIF, even if it's in 16 bit.

Dual conversion is the best technique I happen to know which can improve the tonality of the darker parts of an image with recovered highlights.

Coincidently, I’ve been gone through some respective tests this weekend.

First, a ‘virgin conversion’ was accomplished by setting Brightness & Contrast to zero (curve tab linear).  Thus, blocking any tone curve (as far as I can tell).  Everything referring to ACR, ProPhoto RGB @ 16 bit.  Exposure was set to max possible without clipping textured highlights.

Then in Photoshop, a Curves’ adjust layer (i.e. an all-brightening sigmoidal curve) + Contrast mask were applied.

Now after comparing with diverse techniques which require blending of multi-Raw-conversions (+/- EC), I don’t see a competitive edge with these procedures.

So it seems that all ‘bit information’ silently lies in said ‘virgin conversion’, which can look quite dark at first. Things just have to be pulled-out, while preventing any damage ofthe highlights.

Peter

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Ray
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« Reply #68 on: June 05, 2006, 11:21:48 PM »
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So it seems that all ‘bit information’ silently lies in said ‘virgin conversion’, which can look quite dark at first. Things just have to be pulled-out, while preventing any damage ofthe highlights.
[a href=\"index.php?act=findpost&pid=67474\"][{POST_SNAPBACK}][/a]

Peter,
I think you are probably right. As I wrote before, there's more than one way to skin a cat. Photoshop is a complex program and one can achieve a similar end result through different processes.

Whenever I sit down at my computer to process some images, I have a choice of spending the time learning about Photoshop, or processing my images. I have that choice because I'm an amateur, but I generally prefer to spend the time processing my images with the few trusted techniques I'm familiar with.

I see dual conversion as one such technique of achieving a particular, desired end result. The technique seems to be beneficial with some images, but not with others, and it may well not have any advantage at all for someone more aware of the processing options Photoshop has to offer.

Geez! Posting on this site is certainly an exercise in humility   .
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Dennis
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« Reply #69 on: June 06, 2006, 06:40:03 AM »
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I need one conversion with good highlights
That's, what I am saying. The quality of the highlights depends on the raw conversion software, period.

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Everything referring to ACR, ProPhoto RGB @ 16 bit.
...
So it seems that all ‘bit information’ silently lies in said ‘virgin conversion’, which can look quite dark at first.
Of course, that's true. There's is no loss in tonalities converting a 12 bit raw into a linear 16 bit .psd file, especially, if you do not convert the gamut. If this is the goal, dcraw is your tool.
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PeterLange
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« Reply #70 on: June 06, 2006, 02:03:55 PM »
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Whenever I sit down at my computer to process some images, I have a choice of spending the time learning about Photoshop, or processing my images. I have that choice because I'm an amateur, but I generally prefer to spend the time processing my images with the few trusted techniques I'm familiar with.

OK.

Cheers! Peter

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jani
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« Reply #71 on: June 07, 2006, 04:45:55 AM »
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Just FYI, Lightroom appears to do a much better job at this than the default ACR interface.

I've played a bit around with it to extract shadow details and pull down highlights from a family shoot last weekend, and it seems to be working very well.

I only wish that the 20D's metering system wouldn't overexpose so often (maybe I need to get the meter cleaned up ...).
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Jan
Ray
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« Reply #72 on: June 07, 2006, 05:47:16 AM »
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Well, I can't let this be. I've been under the delusion all this time that doing a +EC conversion will provide more bits to describe whatever data is in the RAW image and consequently provide better tonality in the shadows.

I've just spent some time revisiting some conversions I did a while ago using the dual conversion method, which I thought was serving some useful purpose.

I now find that it was serving no purpose whatsoever. What's really surprising is that a -4EC conversion into 16 bit tif and ProPhoto RGB still seems to retain the full tonality of the RAW image. This leaves me a bit dumbfounded because the implication is, one could convert all images with a -4EC just to make sure one had retained all available highlight detail. There's no disadvantage except the additional time taken making curves adjustments.

The following images have had no sharpness, contrast or saturation adjustments outside of a simple RGB curves' adjustment or blending procedure. They are not finished, processed images. I'm just looking for any qualities that the blended image might have that can't be easily duplicated with curves applied to the very dark -4EC conversion. I can't find any. The slightly greater contrast noticeable in the small crop of the 'curves' adjusted' image can be changed either way. I just think the images are close enough to demonstrate the point and haven't bothered to get them more closely matched.

[attachment=663:attachment]                                               [attachment=664:attachment]



[attachment=665:attachment]                                              [attachment=666:attachment]


I don't why the curves preview image looks like that.
« Last Edit: June 07, 2006, 06:00:28 AM by Ray » Logged
John Sheehy
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« Reply #73 on: June 07, 2006, 10:27:17 AM »
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I only wish that the 20D's metering system wouldn't overexpose so often (maybe I need to get the meter cleaned up ...).
[a href=\"index.php?act=findpost&pid=67600\"][{POST_SNAPBACK}][/a]

My 20D is usually set to +2/3 EC by default.  The lowest I generally go is -2/3 for Great Egrets (bright white birds) small in the frame.  For ultra-low-contrast scenes, I find that the 20D limit of +2 EC is insufficient.  My 20D agrees with my Sekonic L-558 on a white wall.
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PeterLange
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« Reply #74 on: June 07, 2006, 01:51:18 PM »
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Well, I can't let this be. ...
Seems to be the same with me   .


Ray,

IF I may add a proposal … with all humility; being well aware that the following schematic approach can’t be ideal for every scene / image:


/>  In ACR, all tonal controls: Exposure, Shadows, Brightness and Contrast are initially set to 0 (- zero -; curve tab linear).

/>  Alt/click on the Exposure slider, move it left or right, to find this sweet spot of maximum Exposure which does not produce any relevant additional clipping.  I mean, some pixel of the sky seem to be already irrevocably clipped and obviously can’t be recovered.  So the task is to find the max Exposure setting which does not *significantly* enlarge these areas.
Admittedly, this step is a little bit a matter of feeling and in general the main ‘rule’ is not to clip any textured highlights. Most typically this ends in a +/- 0.75EC range, but that's of course just a my 'single'-experience.

/>  Set the Shadows slider somewhere reasonably towards the commencement of the histogram.  Leave Brightness & Contrast at zero.  Click OK to process the file from ACR to Photoshop (ProPhoto RGB, 16 bit).

The following three steps can be easily recorded as an Action:
/>  Ctrl/click on the RGB composite channel to select everything visible
/>  Ctrl + Shift + I to invert the selection
/>  Add a Curves’ adjust layer (80% Opacity and Normal blend mode) which then will carry the inverted selection as a layer mask.  The curve itself is a quite special one; it is defined by the following 6 anchor points for Input/Output = 31/40, 56/78, 83/124, 114/172, 147/212 and 180/240.

Then, manually operated again:
/>  Alt/click on the layer mask
/>  Apply an appropriate Theshold to cover & protect only the brightest regions by pure black, while the rest of the mask gets white.
/>  Apply a crude Gaussian Blur of some pixel width (maybe 10 or so)
/>  Change back to normal view to fine-tune Opacity


Frankly, I’m using this technique since some weeks, it’s simple in essence and I’m surprised how often it works without further effort (referring to respective ‘HDR’ cases which can’t be adequately treated by the ACR global controls only).  So at the risk that it doesn’t work here and it’s finally me looking   – I’d like to invite you to give it a try.

Peter

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Ray
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« Reply #75 on: June 07, 2006, 08:46:57 PM »
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Seems to be the same with me   .
Ray,

IF I may add a proposal … with all humility; being well aware that the following schematic approach can’t be ideal for every scene / image:
/>  In ACR, all tonal controls: Exposure, Shadows, Brightness and Contrast are initially set to 0 (- zero -; curve tab linear).

/>  Alt/click on the Exposure slider, move it left or right, to find this sweet spot of maximum Exposure which does not produce any relevant additional clipping.  I mean, some pixel of the sky seem to be already irrevocably clipped and obviously can’t be recovered.  So the task is to find the max Exposure setting which does not *significantly* enlarge these areas.
Admittedly, this step is a little bit a matter of feeling and in general the main ‘rule’ is not to clip any textured highlights. Most typically this ends in a +/- 0.75EC range, but that's of course just a my 'single'-experience.

/>  Set the Shadows slider somewhere reasonably towards the commencement of the histogram.  Leave Brightness & Contrast at zero.  Click OK to process the file from ACR to Photoshop (ProPhoto RGB, 16 bit).

The following three steps can be easily recorded as an Action:
/>  Ctrl/click on the RGB composite channel to select everything visible
/>  Ctrl + Shift + I to invert the selection
/>  Add a Curves’ adjust layer (80% Opacity and Normal blend mode) which then will carry the inverted selection as a layer mask.  The curve itself is a quite special one; it is defined by the following 6 anchor points for Input/Output = 31/40, 56/78, 83/124, 114/172, 147/212 and 180/240.

Then, manually operated again:
/>  Alt/click on the layer mask
/>  Apply an appropriate Theshold to cover & protect only the brightest regions by pure black, while the rest of the mask gets white.
/>  Apply a crude Gaussian Blur of some pixel width (maybe 10 or so)
/>  Change back to normal view to fine-tune Opacity
Frankly, I’m using this technique since some weeks, it’s simple in essence and I’m surprised how often it works without further effort (referring to respective ‘HDR’ cases which can’t be adequately treated by the ACR global controls only).  So at the risk that it doesn’t work here and it’s finally me looking   – I’d like to invite you to give it a try.

Peter

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Peter,
Thanks for the advice. I'll give it a try. You are quite right, the brightest part of the sky with the sun trying to burst through the clouds, is totally blown. At a 750th sec at f8 and ISO 100, there was no way I could have reduced exposure significantly without introducing unacceptable (and difficult to remove) noise in the shadows. This is the typical shot where autobracketing would have been useful. It so happened I did have a tripod in the back of the car, but by the time I got it out and set it up and searched for the remote cord, the mist has lifted and the scene was no longer as interesting. Nevertheless, I should have taken a series of handheld autobracketed shots. The bunglings of an amateur I'm afraid.
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Ray
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« Reply #76 on: June 09, 2006, 12:46:29 AM »
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Add a Curves’ adjust layer (80% Opacity and Normal blend mode) which then will carry the inverted selection as a layer mask.  The curve itself is a quite special one; it is defined by the following 6 anchor points for Input/Output = 31/40, 56/78, 83/124, 114/172, 147/212 and 180/240.
[a href=\"index.php?act=findpost&pid=67636\"][{POST_SNAPBACK}][/a]

Well, I followed some of your advice. Couldn't find that special curve with input/output anchor points of 31/40 etc. Where's that hidden   ?

The finished image (finished at this stage, anyway) looks like this. This is a screen grab of the 'proof cololors' image in relation to Epson Premium Lustre (paper color on) and K2 inks on the 7600, perceptual rendering intent.

[attachment=672:attachment]


On the other hand, a saturation rendering intent might be more appropriate   . What do you think?

[attachment=673:attachment]
« Last Edit: June 09, 2006, 01:04:02 AM by Ray » Logged
Ray
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« Reply #77 on: June 09, 2006, 02:28:00 AM »
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Just to get things into perspective, here's the monitor image with no proof colors, but same adjustments. Satuaration intent seems to be closer to the 'non-proof color' image to my eyes.

[attachment=674:attachment]
« Last Edit: June 09, 2006, 02:45:07 AM by Ray » Logged
PeterLange
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« Reply #78 on: June 09, 2006, 01:59:30 PM »
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Just to get things into perspective, here's the monitor image with no proof colors, but same adjustments. Satuaration intent seems to be closer to the 'non-proof color' image to my eyes.

[attachment=674:attachment]
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Ray,

I’m sincerely glad that clipping (due to exposure) does not only happen to me.  And in particular I’m glad that my remote proposal obviously did not went so wrong. As a pure amateur, I find that the last rendition communicates the mood of the scene very well.  For example, I could imagine that if your family shared this moment, they’ll love it.  My eldest daughter would probably suggest to try to crop & isolate the left half (x 0 to 505 or so); but, that’s definitively not the point with an image that was selected and generously offered for HDR test purposes.

Out of interest, at which settings did you finally arrive in ACR and in Photoshop?

IF of interest at your side:
/>  I had outlined some thoughts on tonal settings in ACR [a href=\"http://www.outbackphoto.com/tforum/viewtopic.php?TopicID=1991]here[/url]. Though I have to admit that I left discussion for some reasons.  Anyway, above text could be seen as a supplement, in case that the global tonal controls cannot compensate enough for dyn. range compression (scene to monitor) without causing damage.

/>  Referring to this special tone curve (31/40, etc.), in fact it comes from ACR’s presets.  It was just extracted to use it Photoshop; it’s an all-brightening slightly S-shaped curve -  a very nifty thing (as suggested here) and it has become a key part of my toolbox.

Peter

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« Last Edit: June 09, 2006, 02:01:55 PM by PeterLange » Logged
Ray
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« Reply #79 on: June 10, 2006, 11:16:31 AM »
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Out of interest, at which settings did you finally arrive in ACR and in Photoshop?
[a href=\"index.php?act=findpost&pid=67787\"][{POST_SNAPBACK}][/a]

Peter,
I can't remember precisely. This is the sort of image which can be reworked many ways, but approximately the ACR settings were, for the latest version above; minus 2EC, zero brightness, shadows and contrast (but maybe contrast was -50) and I might have used an ACR preset linear curve. I then ctrl clicked on the RGB channel, inverted selection and applied an adjustment curve with 80% opacity. The curve would have been similar to the one pictured above. I then selected the lower part of the image, to the base of the tree and including the cows, with the lasso tool and 40 pixel feather. Used levels to brighten the lower part as though it were a separate picture, applied a bit of 'local contrast enhancement' with unsharp mask to the selected part only and bumped up general saturation to +7 with the hue/sat control.

I wouldn't say this is the final image. There's a slight blocking of shadows in the foreground which can be avoided. It's a good image to play around with though. I'm not keen on cropping it but I wish I could soften the abruptness of the blown part of the sky.

The curve you've described with specific anchor points doesn't seem to work for this image.
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