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Author Topic: Your Curves  (Read 144570 times)
PeterLange
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« Reply #180 on: August 02, 2007, 04:36:36 PM »
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Peter - I can live with "slope" and "offset" instead of "percentage" and "add" ! And as you say it does help one visualize a relationship between curve shape and impact on saturation. Your concern about adjusting Luminosity in Lab space rather than RGB space is mentioned in other words on page 3 of my essay, adapted from the referenced discussion with Thomas Knoll, who also referenced corroboration from Bruce Lindbloom - so there is consensus between the three of you on this point.
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Mark,

Could it be that there's some humor included with the last sentence. Anyway, it's fine with me .
 
 
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Gloria, In principle, in Luminosity mode neither the hue nor the saturation should be affected.
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Photoshop’s HSL blend modes including Luminosity blend mode are supposed to refer to a proprietary version of the HSL color model wherein Luminosity is computed as a weighted average of green, red and blue. This accounts for many similarities with CIE Lab even though these blend modes are a pure RGB derivative.

In other words, Luminosity blend mode and the HSL double cone are different from HSB brightness and the HSB cylinder.
[a href=\"http://en.wikipedia.org/wiki/HSV_color_space]http://en.wikipedia.org/wiki/HSV_color_space[/url]
http://en.wikipedia.org/wiki/HSL_color_space
http://www.fho-emden.de/~hoffmann/hlscone03052001.pdf

Hence the definitions for Saturation are different.
Definitions for the Hue angle are the same.

Peter

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laughfta
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« Reply #181 on: August 02, 2007, 06:48:53 PM »
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In other words, Luminosity blend mode and the HSL double cone are different from HSB brightness and the HSB cylinder.
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Hi Peter,

I am so glad you took the time to relay this info! I did look at the Wiki site at the beginning of this thread, due in part to trying to understand the data you provided. The HSL article said that the Adobe applications used the HSV color model. Maybe you could edit it—I suspect you could have written the article! Anyway, I appreciate you clearing the path.

Gloria
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PeterLange
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« Reply #182 on: August 03, 2007, 04:56:46 PM »
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... The HSL article said that the Adobe applications used the HSV color model. Maybe you could edit it—I suspect you could have written the article! Anyway, I appreciate you clearing the path.
Hello Gloria,

Many thanks for the kind words.

As far as I can tell, Photoshop likes to mix different color models under the hood. This may or may not always make sense. I’d like to hear the thoughts of the engineers, but obviously their marketing decided for a "looks good, is good" approach. Here are some examples from my files. I’d be more than happy if someone would like to check:

With the Shadow/Highlight-tool, the main Shadows and Highlights controls are already operating in Luminosity blend mode. That’s OK with regard to the curves (plus selections) standing behind. However, the black and white clipping settings refer to normal RGB mode and the RGB color model.  Too much saturation can be added depending on Black clip percentage if it is used at all.

With the Hue/Sat.-tool, the Hue slider is always HSB (alias HSV) which in this case is the same as HSL-hue anyway. OK with me. But the Saturation slider is a very different beast:
http://luminous-landscape.com/forum/index....opic=11074&hl=#

With the main Adjust tab in ACR, the main tonal controls such as Exposure, Shadows, Brightness and Contrast are referring to normal RGB mode and the RGB color model. – even though they’re acting on linear gamma data (and Exposure might be realized as the 9th degree of freedom during initial matrix conversion). Oh and yes, the resulting invisible curves were reported to be equipped with a hue lock. As agreed earlier there’s a competitive edge compared to Lab or Luminosity blend mode. But I’m not sure if I finally like this set-up because RGB or HSB curves are prone to effect yellow-green hues much more than other colors with regard to perception.  So let’s be tolerant by concluding that it is no Color appearance model yet. Anyway, the Saturation slider obviously acts in Saturation blend mode.  I think that’s OK.

HSB readings in Photoshop are however really HSB. And also the HSL blend modes are consistent in itself.

Hope this is of help.
Best regards, Peter

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« Last Edit: August 03, 2007, 04:59:21 PM by PeterLange » Logged
laughfta
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« Reply #183 on: August 13, 2007, 10:18:45 PM »
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Hi Mark,

I would like to thank you for part two of your Curves essay. You have brought up a lot of information in a very accessible presentation. Just as importantly for the readers who are trying to evaluate occasionally conflicting opinions, you have stated your beliefs and presented your results with great courtesy and respect, which I have come to understand is both your style and your preference.

I am trying to understand something about CR. I see that several other Raw converters have 3 channel curve functions. After your work on the files in part 2, do you feel that having access to 3 channels in CR would have made a noticeable difference in outcome?
I know this entails different ways of working, so perhaps I'm asking if 3 channels in CR would have made your adjustments any easier or offered any other advantage?

Also, are you evaluating these as prints? As I suspect you are, can you provide some details in that regard?

Again, congratulations and thank you!
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Mark D Segal
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« Reply #184 on: August 13, 2007, 11:08:20 PM »
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Hi Mark,

I would like to thank you for part two of your Curves essay. You have brought up a lot of information in a very accessible presentation. Just as importantly for the readers who are trying to evaluate occasionally conflicting opinions, you have stated your beliefs and presented your results with great courtesy and respect, which I have come to understand is both your style and your preference.

I am trying to understand something about CR. I see that several other Raw converters have 3 channel curve functions. After your work on the files in part 2, do you feel that having access to 3 channels in CR would have made a noticeable difference in outcome?
I know this entails different ways of working, so perhaps I'm asking if 3 channels in CR would have made your adjustments any easier or offered any other advantage?

Also, are you evaluating these as prints? As I suspect you are, can you provide some details in that regard?

Again, congratulations and thank you!
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Thanks Gloria, glad you enjoyed the article.

First, I think we need to recognize that Curves is a User Interface. The important thing is what the math does to individual pixel values behind the Curves. And in Camera Raw, before you get to the Curves there is the Basic Tab. What math underlies those functions? And after the Curves tab there is the HSL Tab, with three possible sets of operations on each of eight colour groups. The short answer to your question I can think of is that IF CR had individual tone curves for each of the primary colours, it may be helpful, but I haven't felt any compelling need for it. That said, I do not have experience using other raw converters that are said to have such "Curves". For sure, 3 channels wouldn't make life easier, because the more the options the more the work in selecting what is best. The real issue is whether they would improve quality, and that remains an open question. Based on what I've been doing, I'm skeptical. Anyone reading this who does have comparative experience with this should jump in and tell us.

When I evaluate images on the monitor, I do so in soft-proof mode, which is about as faithful as a print. I did not print all those variants because the soft-proof is a good indicator.
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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 #185 on: October 05, 2007, 07:09:43 AM »
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Those of you subscribed to this topic (and possibly others) may be interested to know that Martin Evening's latest essay was published on the Adobe Lightroom News site yesterday; it deals extensively with the subject of this thread. His findings are on the whole consistent with mine, but he derived his results in a different, and ingenious, manner. You will find his essay here: Martin Evening on LR and PS Curves
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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 #186 on: October 05, 2007, 07:51:52 AM »
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Thanks so much for pointing this out, Mark.  

I think Peter explains the saturation differences back a few posts, and goes into more detail here:  http://luminous-landscape.com/forum/index....opic=11074&hl=#

I don't pretend to fully understand, but it's nice to think the saturation behavior/inconsistency is explainable!

Gloria
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Guillermo Luijk
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« Reply #187 on: October 05, 2007, 01:28:52 PM »
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In brief my conclusions were:
- PS Luminosity curves preserve Hue in all cases, and increase saturation where luminance is reduced, and reduce saturation where luminance is increased.
- PS Normal and ACR curves do not preserve Hue, and increase saturation in all cases.

In Martin's parrot:



* Point A and B: reduce luminance because of the 'S' curve (and increase Saturation in PS Lum).
* Point C: remains approximately with the same luminance after 'S' curve (and preserves saturation as well in PS Lum).
* Point D: reduces luminance because of the 'S' curve (and reduces Saturation in PS Lum).

Regarding LR, the new one:
- Seems to preserve Hue much better than PS Normal, but still modifies Hue.
- Increases saturation nearly the same as PS Normal.

Again what can be more pleasant to our eyes because of the apparent PS Luminance desaturation, can be PS Normal or LR.
However numbers say PS Luminance preserve better the original parameters.

In fact I wonder, looking at the final parrot point D, if PS Normal and LR could be losing some information (texture) because of the heavy saturation, specially PS Normal. LR seems to keep texture better in that area however.
« Last Edit: October 05, 2007, 01:37:43 PM by GLuijk » Logged

Mark D Segal
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« Reply #188 on: October 05, 2007, 02:09:37 PM »
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In fact I wonder, looking at the final parrot point D, if PS Normal and LR could be losing some information (texture) because of the heavy saturation, specially PS Normal. LR seems to keep texture better in that area however.
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Guillermo, this was a good part of the basis for Dan Margulis's complaint about using an RGB curve: he says the saturation boost "hoses" image detail in bright colours. The problem with his argument is that if you implement the curve shift in CR or LR and you notice the saturation of certain colourts becoming excessive, it can be scaled back down to taste, and bingo, the so-called "hosed" detail comes back, because it was never truly lost in the first place - of course one can lose it by rendering into Photoshop an over-saturated image with smothered detail, but why do that when the application allows us to avoid this error? Especially when there is a limit to the saturation of any colour that a printer can handle.

Mark
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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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