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Author Topic: LAB COLOR  (Read 25155 times)
Mark D Segal
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« Reply #80 on: December 04, 2007, 05:17:24 PM »
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I've tried out editing in Lab space white balancing the blue cast out of sunset lit limestone rock while not affecting the blue in other elements in the scene such as flowers. Far more intuitive and smoother than using selective color in RGB.

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 An overall inconsistancy in hue and saturation levels permiates through different areas of the image giving it an odd look.

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[a href=\"index.php?act=findpost&pid=158216\"][{POST_SNAPBACK}][/a]

I'm having some trouble understanding what's happening here. If limestone is lit by the setting sun, one would not normally expect it to have a blue cast. If anything, the stone should be rather yellow/orange. This raises a question about the quality of colour balance in the scan itself. I've scanned tons of colour negs (in fact written two articles about it on this website) and there is no question in my mind that if you don't get the colour balance nearly right at the scan stage, it is difficult to rescue it in Photoshop, regardless of the colour space used.

Anyhow, returning to the blue in the rocks - you want to neutralize that without also neutralizing the blue in the flowers, but then toward the end of the story you report getting inconsistency in hue and saturation through different areas of the image. That comment raises a question about whether you achieved your objective of using Lab curves to eliminate blue from the rock while preserving blue in the flowers. If you succeeded in doing so without using a layer mask, I'd be curious to know how you shaped the *b* curve to achieve it. One possible approach I could see to this challenge is that if the shades of blue between the flowers and the limestone are different enough, you could, in Layer Styles",  isolate the impact of the curve movement to the blue tone on the rock by adjusting the "Blend If" sliders for the *b* curve. Anyhow, however you did it - do tell.

I agree with you that playing with *a* and *b* curves in Lab puts colours on steroids and control is *not easy*, especially when it comes to using them for rebalancing colour. They are much easier to use for saturating colour while retaining the same colour balance, but rebalancing in a way that gives you the "correct" result accross the tonal range for both the *a* and *b* axes is very challenging.

Now, reverting to Jonathan's suggestion made assuming you were adjusting a digital capture, his idea can also be applied to a scanned negative, either by producing two scans with different colour balance settings and layering them, assuming the scanner is dead-on consistent pixelm by pixel from one scan to the next, or by creating a duplicated image layer which you would mask in one way or another, and clip Curves in RGB space to each of the background and the duplicate for the colour balancing, isolated to the effect intended for each layer. I suggest this, because Selective Color, which you mention, is not the first place I would go for altering the colour balance of an image. I would start with the individual R, G, and B 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
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« Reply #81 on: December 04, 2007, 05:31:57 PM »
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Here's the image. The more I go back to it the more I have say to myself what the hell was I thinking?

You'll see from the top Epson Auto Exposure version what I had to deal with compared to the results of Lab at the bottom which looks more to what I imagined it from memory. The flowers were that exact color and limestone was warmish because of how low the sun was set. It still looks off. It doesn't look how I remember the scene.

The flowers were intense and eyepopping and I couldn't get that look editing in RGB, though I tried, from what the Epson and the Kodak negative delivered
[a href=\"index.php?act=findpost&pid=158247\"][{POST_SNAPBACK}][/a]

Sorry - while you were posting I was writing and I saw this after I posted! I see we agree the Limestone should have been warmish - only makes sense, doesn't it   ; then you say the flowers are now "exact", but the scene doesn't look like how you remembered it. It's hard to discuss without knowing more information. It looks to me as if your Lab edit was quite successful, and I see that there is a substantial tonal difference in the blues between the flowers and the rock which would facilitate the use of Lab. In this case, Lab has allowed you to isolate the blues. It looks to me as if you didn't touch the *a* curve, because the reds and greens look relatively unchanged except for a slight increase in yellow, which comes from adjusting the *b* curve. It also looks as if you desaturated the blue somewhat, because the detail in the flowers has improved. It would be good to hear more about how you implemented the Lab edits, and could you explain in what ways the scene still does not look right to you?
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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
Jonathan Wienke
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« Reply #82 on: December 04, 2007, 06:10:32 PM »
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Now, reverting to Jonathan's suggestion made assuming you were adjusting a digital capture, his idea can also be applied to a scanned negative, either by producing two scans with different colour balance settings and layering them, assuming the scanner is dead-on consistent pixelm by pixel from one scan to the next, or by creating a duplicated image layer which you would mask in one way or another,

Can't you open non-RAW files in ACR in CS3, and do WB adjustments that way? If so, you could layer the same scan twice with different WB adjustments, and avoid the registration issues you get from layering multiple scans..
« Last Edit: December 04, 2007, 06:12:42 PM by Jonathan Wienke » Logged

Tim Lookingbill
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« Reply #83 on: December 04, 2007, 06:32:42 PM »
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MarkDS,

Just got your last post. I believe we crossed post.

I've posted a rough version of my Lab curve edits because I did this about a year ago and cleaned house and tossed them. I spent a great deal of time teaching myself how to fix an image like this in Lab-a tweakers paradise. It was my first and a real eye opener and a lot of fun as well.

What looks off about the image to me is a sense of lack of realism mainly due to inconsistant hues. I was shooting for the "you are their" feel which digicams seem do with little effort. I was trying to make a bad scan look as real as what I saw as much as possible.

To be a little more picky I don't like the cyanish green hot spots in the shadows of the flower's leaves compared to the orangish green in the brightly lit portion which I do like.

Getting the limestone to look the right warmish hue as if lit by the sun while at the same time making the shadows texture look right didn't come off like I wanted. The shadows still look too blue. Also adaptation started kicking my butt WB-ing this limestone so the scene looked as if it was lit by an evenly colored lightsource. And I constantly had to zoom in on the area I was tweaking to tame these off hue hotspots that crop up and can't detect in a busy scene like this.

I like how it came out it just I didn't reach the level of realism I was shooting for.

In fact after the Lab edits I went back into Epson scan and tried to emulate the same Lab results shown here and got a lot closer than Epson Auto Exposure. However, it was like whittling Mount Rushmore at actual size, but I saved the edits and applied them to the rest of frames on the strip of negative and all the rest of the images just popped. It was as if the blue flower image acted as a calibration target. I barely had to do any edits on the rest of the images except for an occasional WB tweak. [attachment=4136:attachment]
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Mark D Segal
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« Reply #84 on: December 04, 2007, 06:41:48 PM »
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Can't you open non-RAW files in ACR in CS3, and do WB adjustments that way? If so, you could layer the same scan twice with different WB adjustments, and avoid the registration issues you get from layering multiple scans..
[a href=\"index.php?act=findpost&pid=158261\"][{POST_SNAPBACK}][/a]

Jonathan - yes indeed! EXCELLENT!
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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 #85 on: December 04, 2007, 06:56:23 PM »
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MarkDS,

 [attachment=4136:attachment]
[a href=\"index.php?act=findpost&pid=158268\"][{POST_SNAPBACK}][/a]

Thanks for creating that attachment. I see what you were doing. That kind of curving is really hard to control - I think you pulled it off well considering the challenge. Where it runs into trouble is what happens to various colours along the curve at the points you did NOT select. You're right - as you move off center, you migrate from grey to increasing saturation of some hue, that hue being represented by whatever balance of values between green/magenta or blue/yellow the curve happens to be at from point to point and along the continuum between the points. And because each pixel is usually a combination of values from each curve, as you tweak one you may find it necessary to go back and re-tweak the other. Except for very simple things, it can really be tedious and finicky. I like Jonathan's idea. Added to which, in Camera Raw you have the HSL tab with 24 additional levers - influencing the H, L, and S of 8 colour groups. Much more intuitive than Lab. It may not be as precisely targetable, but it also won't drive you crazy stretching it to the limits of what it can do properly before you need additional work in Photoshop, which by then should not be heavy-lifting.
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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
Tim Lookingbill
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« Reply #86 on: December 04, 2007, 08:33:32 PM »
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Agree MarkDS,

That was a rough curve. I actually did have to lock down the entire curve of both a/b channels with a series of closely spaced tweak points. And you're right it was a daunting procedure with rewards that paid off.

I tried using selective hue/saturation in RGB but it required a lot of -/+ clicking with the eyedropper for each color which ended up amplifying film grain and scanner noise with an increase in saturation for each color selected so much so that I had to keep going back and forth with the eyedropper tool selecting and deselecting. It was just too crude and inprecise way of editing.

Lab was smooth much like sculpting each color as long as you kept certain portions of the a/b curve adjusted in flattened sections where the next selection point for each new section would isolate a certain color like a surgeon's knife. This required zoomed view of course.

It wasn't a quick edit, but a long session of tweaks that allowed me to learn quite a bit about the advantages and limits of working in Lab. Most of the limitations were with my own eyes getting used to look of the tweaks.
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Lightbox
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« Reply #87 on: December 06, 2007, 02:38:28 AM »
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Not too sure if this has been posted previously, but it seems to be a similar technique to what you are trying to achieve with the above flower image.


http://www.largeformatphotography.info/for...ead.php?t=19014


I have set these up and saved them as presets, which can then be used in actions. The de saturation from this curve is still a bit strong, but then you can easily lower the opacity of the effect to suit.


.
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« Reply #88 on: December 06, 2007, 07:26:05 PM »
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again
what you  have to understand is that when you  view an image its in sRGB ( or if you have a CRT or an LCD or PLASMA) maybe in ABOBE1972

your picture is en coded in a space you cant see!

not the editing space!

don't do visual editing on as RGB monitor

the monitor is and is struggling to be to "negative'

its no where near.
[a href=\"index.php?act=findpost&pid=158055\"][{POST_SNAPBACK}][/a]
Ah , so that's where I've been going wrong alll this time. I've been using a monitor to edit my images!  
Damn, I must stop doing that and go back to a more Zen like way of editing. One where's there are no numbers or colour spaces.
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« Reply #89 on: December 07, 2007, 12:30:37 AM »
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Lightbox,

Thanks for posting the link to that thread. I remember reading it when it was originally posted. Chris Jordan's tips were pretty close to what I ended up doing but at a much slower pace.

Did you happen to check his site out. Surprised to find out that's the very same Chris Jordan from the PBS and Colbert Report interviews I recently saw on TV.

My brush with fame.
« Last Edit: December 07, 2007, 12:40:51 AM by tlooknbill » Logged
sniper
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« Reply #90 on: December 07, 2007, 03:48:34 AM »
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Did anybody check out this weeks photoshop tv? Scott kelby does a lab mode conversion and back but says it's not distructive? This thread suggests otherwise.  Wayne
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Mark D Segal
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« Reply #91 on: December 07, 2007, 06:43:44 AM »
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Did anybody check out this weeks photoshop tv? Scott kelby does a lab mode conversion and back but says it's not distructive? This thread suggests otherwise.  Wayne
[a href=\"index.php?act=findpost&pid=158885\"][{POST_SNAPBACK}][/a]

It is by no means agreed in the industry that Lab conversions are not *destructive*. With a web search and you will find the evidence. Most of the destruction is said to happen with the first conversion forth and back. Thereafter, it is suggested, successive conversions of the same image are much less incrementally destructive. The real question is to what extent does the destruction matter - how much difference can you see in a print between an image that has been in and out of Lab versus the same one that has not? I've tried it with some images a couple of years ago and frankly I couldn't detect which was which, BUT at the same time the impact of Lab conversion has been demonstrated. Again, a search through this discussion forum and elsewhere on the internet will reveal that this is hazardous territory for *blanket statements* - it's *shades of grey* - or shall we say - the *L* Channel  
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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
bjanes
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« Reply #92 on: December 07, 2007, 07:44:00 AM »
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Lightbox,

Thanks for posting the link to that thread. I remember reading it when it was originally posted. Chris Jordan's tips were pretty close to what I ended up doing but at a much slower pace.

Did you happen to check his site out. Surprised to find out that's the very same Chris Jordan from the PBS and Colbert Report interviews I recently saw on TV.

My brush with fame.
[{POST_SNAPBACK}][/a]

[a href=\"http://www.brucelindbloom.com/index.html?ColorCheckerRGB.html]Bruce Lindbloom[/url] has a demo with an 8 bit sRGB TIFF containing all possible colors. He converted it to Lab and found that only 13% of the colors were preserved, a substantial loss. In converting it back to sRGB, there was little further loss. With 16 bits there would be less of a loss, and 16 bits/channel is usually recommended for Lab.

Bruce's site does not allow direct links, so click on the Info tab and then go down the page to An RGB Image Containing All Possible Colors

I know Scott Kelby is a popular author. I bought his Photoshop CS2 Book for Digital Photographers and was not impressed. Rather than substance, he spends a lot of time covering flashy tricks for special effects that I would never use, and I seldom refer to his book. Martin Evening's book on the same subject is more to my liking, even though I do not do fashion photography.
« Last Edit: December 07, 2007, 09:21:40 AM by bjanes » Logged
digitaldog
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« Reply #93 on: December 07, 2007, 08:17:55 AM »
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It is by no means agreed in the industry that Lab conversions are not *destructive*
[a href=\"index.php?act=findpost&pid=158901\"][{POST_SNAPBACK}][/a]

I don't know what Scott means by not destructive. If he means there's no data loss in the conversion, well that's clearly way off base. And the reference to Lindbloom's site is worth a visit for anyone wondering about this (someone send a link to Scott). Depending on the original color space, a nice number of levels get tossed away. I wouldn’t call that non destructive but I haven't seen the video in question nor know the context of the comment (visually destructive on screen? On some output device? After X number of further edits to the data? From 8-bit or 16-bit).
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Andrew Rodney
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« Reply #94 on: December 07, 2007, 08:50:26 AM »
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Heres a link to the video (it only there till Monday) I just wondered if anybody had seen it and what they though.  Wayne

link

By the way my comment wasn't ment to be critical of this thread, theres a wealth of expertise on this forum.
« Last Edit: December 07, 2007, 08:52:35 AM by sniper » Logged
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« Reply #95 on: December 07, 2007, 09:53:45 AM »
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Heres a link to the video (it only there till Monday) I just wondered if anybody had seen it and what they though.  Wayne

link
[a href=\"index.php?act=findpost&pid=158932\"][{POST_SNAPBACK}][/a]

He's working in an 8-bit file (you can see this from the menu when he moves to Lab).

He says "It doesn't harm the image, Its a non destructive move..."

(Its at 5:40 within the video time line).
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Andrew Rodney
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bjanes
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« Reply #96 on: December 07, 2007, 10:10:50 AM »
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He's working in an 8-bit file (you can see this from the menu when he moves to Lab).

He says "It doesn't harm the image, Its a non destructive move..."

(Its at 5:40 within the video time line).
[a href=\"index.php?act=findpost&pid=158945\"][{POST_SNAPBACK}][/a]

Sounds like Dan Margulis . Readers who looked at Bruce Lindbloom's analysis might also want to read his Margulis 16 bit challenge.

Bill
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Mark D Segal
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« Reply #97 on: December 07, 2007, 12:55:19 PM »
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He's working in an 8-bit file (you can see this from the menu when he moves to Lab).

He says "It doesn't harm the image, Its a non destructive move..."

(Its at 5:40 within the video time line).
[a href=\"index.php?act=findpost&pid=158945\"][{POST_SNAPBACK}][/a]

Andrew, is this for info purposes only or was there a point you intended to make abouti t?
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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 #98 on: December 07, 2007, 01:03:28 PM »
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Sounds like Dan Margulis . Readers who looked at Bruce Lindbloom's analysis might also want to read his Margulis 16 bit challenge.

Bill
[a href=\"index.php?act=findpost&pid=158952\"][{POST_SNAPBACK}][/a]

Bill, I suspect that Scott is relying on Dan's position here, and perhaps his own observations of not seeing actual destruction moving files back and forth. I have not see from Dan Margulis any technical underpinning for his position on this matter. Perhaps it is also observation-based and if he didn't see destruction ipso facto there is no destruction - but we know from Bruce Lindbloom that is technically not correct.

I think Bruce Lindbloom demonstrates quite conclusively that the procedure is destructive, but as I said above, the real issue is how much destruction does one see on paper. This probably depends on how the image is purposed (small print, big print, paper type, sum total of edits etc.). As soon as I hear an edit is as potentially destructive as Bruce says it is, and if there are alternative less destructive ways of achieving the same results or close enough to, it's a no-brainer what one should (not) do.
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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
digitaldog
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« Reply #99 on: December 07, 2007, 01:20:46 PM »
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Andrew, is this for info purposes only or was there a point you intended to make abouti t?
[a href=\"index.php?act=findpost&pid=159013\"][{POST_SNAPBACK}][/a]

Just stating what I heard him say (and that I don't agree with).
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Andrew Rodney
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