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Author Topic: Your Curves  (Read 149276 times)
Mark D Segal
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« Reply #80 on: July 28, 2007, 03:13:43 PM »
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Good point.

..............what do you think?

1. Keep saturation when increasing bright may lead to clipping, that is why saturation is reduced in the pixels where the curve increases Bright. To compensate the overall effect, saturation is increased in the pixels where our curve is applying Bright reduction.

2. Human eye behaviour: since it is more difficult to recognize colours in dark areas than bright ones, saturation is increased in pixels that get darker, and reduced in the ones getting brighter.
[a href=\"index.php?act=findpost&pid=130312\"][{POST_SNAPBACK}][/a]

Guillermo, something strange is going on - of course you have the curve in Luminosity mode which may be producing an opposite effect from what happens in Normal Mode, but in Normal mode the normal expectation is that saturation of the brighter colours increases with increasing contrast. When time permits I should try some saturation measurements before and after a curve shift in Luminosity mode to see whether I replicate your results.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
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« Reply #81 on: July 29, 2007, 07:12:57 AM »
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here seems to have been an overall saturation loss, but I am looking at the images together again now, and I don't think it is too noticeable, what do you think?

(from post #75)

First, Guillermo, thanks for your illustrated response!  Well, I think the corrected image looks less saturated. Mark (thank you Mark) cited Bruse Fraser in response to my question about saturation:

Quote
<<Saturation: The property of a color that makes it appear strongly colored. Black, white, and gray have no saturation. A red tomato has high saturation. Pastel colors have low saturation. Also known as Chroma. (This attribute of color is used in the HLS (Hue, Lightness, Saturation) and HSB (Hue, Saturation, Brightness) color models. >>


For example, the blue shirts/sweaters behind the woman in the red dress both look less saturated to me. Is this just a function of their being brighter? If they were mesured with the eyedropper, I certainly hope they wouldn't show up as more saturated in the second image. But now I don't know, thus am questioning my understanding of saturation.

Do you base it on your perception, or a color sampler reading?
Upon closer examination, the sample you took from the lip, Guillermo, even appears (by my eye) to become slghtly more saturated in your target area. I hope this is the case. It would explain a lot
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laughfta
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« Reply #82 on: July 29, 2007, 07:26:11 AM »
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What we've observed (to varying extent between Guillermo and me) is that curves have much more impact on saturation than they do on hue, but this is how the authors of the program intended it to be.


Thank you, Mark. My lingering question is what does a curve do to a bunch of pixels to make them "saturated"? It seems that lightening pixels makes them less saturated, darkening them makes them more saturated. Lightening and darkening can be seen in a histogram; where do you see saturation? What is the color sampler tool actually reading?

Does hue impact this in any way?
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Guillermo Luijk
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« Reply #83 on: July 29, 2007, 07:50:19 AM »
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(from post #75)

First, Guillermo, thanks for your illustrated response!  Well, I think the corrected image looks less saturated. Mark (thank you Mark) cited Bruse Fraser in response to my question about saturation:
For example, the blue shirts/sweaters behind the woman in the red dress both look less saturated to me. Is this just a function of their being brighter? If they were mesured with the eyedropper, I certainly hope they wouldn't show up as more saturated in the second image. But now I don't know, thus am questioning my understanding of saturation.

Do you base it on your perception, or a color sampler reading?
Upon closer examination, the sample you took from the lip, Guillermo, even appears (by my eye) to become slghtly more saturated in your target area. I hope this is the case. It would explain a lot
[a href=\"index.php?act=findpost&pid=130396\"][{POST_SNAPBACK}][/a]

Gloria, the lips get lighter, and less saturated. I showed you the values in the info palette:



Look at the 'S' value, is Saturation.
Original: 23%
PS curves Lum mode: 15%
ACR curves: 12%

Both curves mean desaturation on those areas affected by a bright increase.

Regarding the blue T-Shirt, I have checked with the eyedropper (all checks I do in this thread I am using it): and we have both, Saturation increase (in the dark parts, that get darker because of the curve) and reduction (in the light areas, that get lighter because of the curve):



Probe 1 (dark blue area):
Original S: 29%
PS curves Lum mode S: 32%
ACR curves S: 53%

Probe 2 (light blue area):
Original S: 31%
PS curves Lum mode S: 23%
ACR curves S: 27%


Your understanding of saturation is right, I think simply saturation is much more noticeable in bright areas than in dark ones, so the saturation correction in the brigter areas will provide the final overall saturation perception.
As increasing contrast means increase bright in brighter areas, and this means reduce saturation on them, you have a feeling of an overall saturation loss.

This is just my hypothesis, I am investigating at the same time as you all.

Regards.
« Last Edit: July 29, 2007, 07:52:49 AM by GLuijk » Logged

laughfta
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« Reply #84 on: July 29, 2007, 08:24:30 AM »
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Gloria, the lips get lighter, and less saturated. I showed you the values in the info palette:

Of course. Sorry, Guillermo, I was looking at a printout of the thread, and got them turned around. Now the logic is once more in place.

In my previous post, the quote from Bruce Fraser didn't show up:

Quote
<Saturation: The property of a color that makes it appear strongly colored. Black, white, and gray have no saturation. A red tomato has high saturation. Pastel colors have low saturation. Also known as Chroma. (This attribute of color is used in the HLS (Hue, Lightness, Saturation) and HSB (Hue, Saturation, Brightness) color models. >>


Thanks again.
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Mark D Segal
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« Reply #85 on: July 29, 2007, 09:23:28 AM »
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(from post #75)

For example, the blue shirts/sweaters behind the woman in the red dress both look less saturated to me. Is this just a function of their being brighter? If they were mesured with the eyedropper, I certainly hope they wouldn't show up as more saturated in the second image. But now I don't know, thus am questioning my understanding of saturation.

Do you base it on your perception, or a color sampler reading?
Upon closer examination, the sample you took from the lip, Guillermo, even appears (by my eye) to become slghtly more saturated in your target area. I hope this is the case. It would explain a lot
[a href=\"index.php?act=findpost&pid=130396\"][{POST_SNAPBACK}][/a]

Gloria, thinking about saturation and brightness, I believe we can be fooled trying to distinguish them unaided by measurements. For example, it is well known that if you add Black to any other colour, it will make that colour look "stronger". Is this because the colour has become darker or because it has become more saturated? I think the former, but we often think that stronger-looking colours are more saturated. Formally however, colours gain saturation as they extend from the center to the edge of a colour wheel or gamut frame.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
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« Reply #86 on: July 29, 2007, 09:39:59 AM »
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Thank you, Mark. My lingering question is what does a curve do to a bunch of pixels to make them "saturated"? It seems that lightening pixels makes them less saturated, darkening them makes them more saturated. Lightening and darkening can be seen in a histogram; where do you see saturation? What is the color sampler tool actually reading?

Does hue impact this in any way?
[a href=\"index.php?act=findpost&pid=130399\"][{POST_SNAPBACK}][/a]

The fact is you don't see saturation in a histogram. A histogram is a representation of brightness levels either in aggregate or for each channel of the colour space being represented.

When we manipulate a tone curve we are remapping the relationships between lighter and darker pixels. The answer to your lingering question is that by design, saturation is adjusted to match with contrast changes because the developers' evaluation of working these contrast adjustments purely in luminosity mode, where constrast and saturation are not moving in sync, causes the results to look odd.

The colour sampler tool reads what you instruct it to read when you select your options for the read-out of the Info Palette. The tool itself has options to read 1 pixel, or averaged grids of 3*3 or 5*5 pixels. I normally leave mine set to 5*5, because I fear a 1 pixel read-out can be misleading if that one pixel is somehow not representative of the normally visible tone we are trying to understand through the measurement.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
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« Reply #87 on: July 29, 2007, 09:48:09 AM »
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Your understanding of saturation is right, I think simply saturation is much more noticeable in bright areas than in dark ones, so the saturation correction in the brigter areas will provide the final overall saturation perception.
As increasing contrast means increase bright in brighter areas, and this means reduce saturation on them, you have a feeling of an overall saturation loss.

This is just my hypothesis, I am investigating at the same time as you all.

Regards.
[a href=\"index.php?act=findpost&pid=130403\"][{POST_SNAPBACK}][/a]

Guillermo, we aren't converged on this matter yet. If you go back to my paper and look at the results in Figure 26 reported for the readings done on Figures 24 and 25, you will see that brightness and saturation are positively correlated - not to the same extent for each sample, but same positive direction of association nonetheless. You seem to be getting negative correlation, so there is something different going on here that I don't understand. One thing I do understand, however, is that the results I got do reflect what I am given to understand the program writers intended to achieve.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
Guillermo Luijk
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« Reply #88 on: July 29, 2007, 11:29:57 AM »
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Guillermo, we aren't converged on this matter yet. If you go back to my paper and look at the results in Figure 26 reported for the readings done on Figures 24 and 25, you will see that brightness and saturation are positively correlated - not to the same extent for each sample, but same positive direction of association nonetheless. You seem to be getting negative correlation, so there is something different going on here that I don't understand. One thing I do understand, however, is that the results I got do reflect what I am given to understand the program writers intended to achieve.
[{POST_SNAPBACK}][/a]

Yes, this bright up-saturation down & bright down-saturation up trend is found only in curves in PS with blending mode Luminance. In ACR and Normal blending mode curves, saturation simply increases at every pixel.

I have uploaded a cut of the flag in the sample picture, with 2 probes:
- Probe 1 located at a point where curves increases bright (all curves but PS Lum increase saturation, PS Lum reduces saturation).
(H, S, B ) values:
Original=(50º, 64%, 63%)
PS Lum cur=(50º, 48%, 84%)
PS Norm cur=(58º, 95%, 86%)
ACR cur=(52º, 100%, 95%)

- Probe 2 located at a point where curve reduces bright (all curves increase saturation).
(H, S, B ) values:
Original=(50º, 60%, 34%)
PS Lum cur=(50º, 97%, 21%)
PS Norm cur=(33º, 93%, 26%)
ACR cur=(53º, 100%, 21%)

Please download a portion of the flag picture from: [a href=\"http://www.guillermoluijk.com/download/flag_cut.zip]Sample image[/url]

« Last Edit: July 29, 2007, 11:40:09 AM by GLuijk » Logged

PeterLange
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« Reply #89 on: July 29, 2007, 11:30:37 AM »
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Mark wrote
>> No math here – I wouldn’t know where to start.<<

If of interest:

One simplified approach is to look at RGB curves is in terms of adjacent tangents – means to approximate a curve section by section by a straight line which represents the “local” slope and offset.  As common with linear equations, the term Offset refers to the crossing point of a straight line with the vertical “y” axis:

Slope > 1: increase of contrast
Slope < 1: decrease of contrast
Offset > 0: decrease of HSB-Saturation
Offset < 0: increase of HSB-Saturation
---

RGB-Levels’-whitepoint setting
or a respective "curve" which is already a straight line,
or +EV with the Exposure slider in ACR (from an empirical point of view):

Slope > 1: increase of contrast (difference between lighter and darker pixel)
Offset = 0: Color integrity is perfectly maintained. Linear scaling of RGB data does not change the intensity ratios of R:G:B per pixel, which is synonymous to unchanged HSB hue & saturation.
---

RGB-Levels’-blackpoint setting
or a respective "curve" which is already a straight line,
or the Shadows slider in ACR:

Slope > 1: increase of contrast
Offset < 0: increase of HSB-Saturation, mainly for the shadows with decreasing significance towards the highlights.

Note that the saturation boost and damage of color integrity is the more severe the higher the underlying gamma of the working space is: http://www.c-f-systems.com/Docs/ColorIntegrityCFS-243.pdf
---

Increasing brightness w/the RGB-Levels’-midtone slider,
or a respective solely right-curved curve
or the Brightness slider in ACR:

From the shadows to the mids:
Slope > 1: increase of contrast
Offset > 0: decrease of HSB-Saturation

From the mids to the highlights:
Slope < 1: decrease of contrast
Offset > 0: decrease of HSB-Saturation
---

Reducing brightness w/the RGB-Levels’-midtone slider,
or a respective solely left-curved curve:

From the shadows to the mids:
Slope < 1: decrease of contrast
Offset < 0: increase of HSB-Saturation

From the mids to the highlights:
Slope > 1: increase of contrast
Offset < 0: increase of HSB-Saturation
---

Before addressing more complex sigmoidal curves, it should be mentioned that analogous Lab lightness settings or changing to Luminosity blend mode are by far NOT always superior. It depends.

Peter

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« Last Edit: July 29, 2007, 11:41:43 AM by PeterLange » Logged
Mark D Segal
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« Reply #90 on: July 29, 2007, 12:02:51 PM »
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Yes, this bright up-saturation down & bright down-saturation up trend is found only in curves in PS with blending mode Luminance. In ACR and Normal blending mode curves, saturation simply increases at every pixel.
[a href=\"index.php?act=findpost&pid=130436\"][{POST_SNAPBACK}][/a]

OK, that's a relief. You've just saved me some time.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
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« Reply #91 on: July 29, 2007, 12:09:41 PM »
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Mark wrote
>> No math here – I wouldn’t know where to start.<<.
If of interest:.....................................

............................................
Before addressing more complex sigmoidal curves, it should be mentioned that analogous Lab lightness settings or changing to Luminosity blend mode are by far NOT always superior. It depends.

Peter

--
[a href=\"index.php?act=findpost&pid=130437\"][{POST_SNAPBACK}][/a]

Peter, thanks for all that and for the reference document. I have downloaded it.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
laughfta
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« Reply #92 on: July 29, 2007, 12:14:19 PM »
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Yes, this bright up-saturation down & bright down-saturation up trend is found only in curves in PS with blending mode Luminance. In ACR and Normal blending mode curves, saturation simply increases at every pixel.


Well...
It is also found if a point is raised or lowered without added contrast—I downloaded your flag file, Guillermo, turned off the curve layer and added a new curve layer. I Control clicked on your yellow target, and used the arrow key to lighten the resulting point on the curve. When checked, the saturation was lower on the lightened image.

I could do this with the target adjustment tool in LR, as well. I don't have CS3, so I have to export from LR into PS2. Nevertheless, I got the same result; less saturation.

From Mark:
Quote
The answer to your lingering question is that by design, saturation is adjusted to match with contrast changes because the developers' evaluation of working these contrast adjustments purely in luminosity mode, where constrast and saturation are not moving in sync, causes the results to look odd.


From Dan:
Quote
When one lightens an image in CR, saturation increases. The operator can not modify or turn off this effect."


Sounds like when CR dynamic range adjustments are used as they are meant to be used they add contrast, and increase saturation. It appears to me that the operator can modify this effect, but not turn it off.

Is this accurate?
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Guillermo Luijk
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« Reply #93 on: July 29, 2007, 12:33:14 PM »
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Oops, I am talking about the picture with the flag, and I have just realised I used it in another forum. I show you here the results with that picture, which confirm all we are discussing:

Original


Result of applying curve in ACR / Result of applying curve in PS (Luminosity blending mode)

 .  

Curves:


Comparision of tone histograms (animated GIFs: 'original' corresponds to the Original image):

Original vs curve in ACR / Original vs curve in PS (Luminosity blending mode)
 .  

ACR generates new blue tones that did not exist in the original image.
On the other hand PS Luminosity curves accurately replicate tones in such a way that is really difficult to find the differences (look closely at some blinking pixels in the histogram).
« Last Edit: July 29, 2007, 12:36:29 PM by GLuijk » Logged

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« Reply #94 on: July 29, 2007, 01:51:44 PM »
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Personally, the Luminance Curve image looks dead to me...
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Mark D Segal
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« Reply #95 on: July 29, 2007, 02:28:28 PM »
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Personally, the Luminance Curve image looks dead to me...
[a href=\"index.php?act=findpost&pid=130470\"][{POST_SNAPBACK}][/a]

Of course it does - that's exactly what Thomas said would happen (and I saw it over and over again as I played with the images for my essay), so they developed the synchronous adjustment of contrast and saturation.
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Mark D Segal (formerly MarkDS)
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« Reply #96 on: July 29, 2007, 02:31:18 PM »
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ACR generates new blue tones that did not exist in the original image.
On the other hand PS Luminosity curves accurately replicate tones in such a way that is really difficult to find the differences (look closely at some blinking pixels in the histogram).
[a href=\"index.php?act=findpost&pid=130455\"][{POST_SNAPBACK}][/a]

Guillermo, it would surprise me if CR were generating "new blue tones" (whatever that means) that didn;t exist before. For sure it generates much more saturated blue given the hugely pronounced S curve you put into that rendition, and the brightnesses will be very different, so yes it can look like "new blue" but is it really? - have the hue values shifted at all or by more than a couple of degrees?
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Mark D Segal (formerly MarkDS)
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« Reply #97 on: July 29, 2007, 02:40:58 PM »
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From Dan:

Sounds like when CR dynamic range adjustments are used as they are meant to be used they add contrast, and increase saturation. It appears to me that the operator can modify this effect, but not turn it off.

Is this accurate?
[a href=\"index.php?act=findpost&pid=130450\"][{POST_SNAPBACK}][/a]

Firstly, what does Dan mean when he says "when dynamic range adjustments are used as they are meant to be used" - they are meant to be used in any way you the user wants to use them to achieve whatever effects you think the image needs. This may be to increase contrast, but there are times when one may wish to downplay contrast. So the quote starts out being a bit vague. That's a quibble. Let's assume he means increasing contrast. I believe he is correct that the effect can be modified but not "turned off". There are at least three ways to modify it:

(1) reduce Vibrance, (2) reduce Saturation, (3) in the HSL tab alter the luminance and/or saturation of specific colour ranges that may be problematic. Because all this is happening simultaneously in meta-data before rendering it should be non-destructive, and more often than not it should give you the result you want, or very close thereto. This is where we want to end-up isn't it? If we get there, does it matter whether the effect can be "turned-off" or not? I would think not; at the same time however, I can see some merit to the idea of a pure luminance-based contrast tool in CR. That said, not clear to me how much priority Adobe would assign to its development given the other ways available there to do the needful.
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Mark D Segal (formerly MarkDS)
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« Reply #98 on: July 29, 2007, 02:42:34 PM »
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Of course it does - that's exactly what Thomas said would happen (and I saw it over and over again as I played with the images for my essay), so they developed the synchronous adjustment of contrast and saturation.

I read it's all sloppy math. That the product isn't suitable for professional users. Are you suggesting that the guys who wrote the math and looked at the final color appearance (that historically have pleased its users) are right?
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Andrew Rodney
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« Reply #99 on: July 29, 2007, 02:44:39 PM »
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Personally, the Luminance Curve image looks dead to me...
[a href=\"index.php?act=findpost&pid=130470\"][{POST_SNAPBACK}][/a]
Well, the shot on the left was by Jay Maisel, and the shot on the right... no, wait a minute...
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