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color corection by the numbers

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  #11  
Old 07-19-2005, 11:44 AM
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Cameraken Cameraken is offline
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Victoria.
Thank you for your reply.

One reason for my questions is that I downloaded Curvemeister demo from
http://www.curvemeister.com/
It watermarks the results but it is fully functional and I liked the idea of being able to pin skin tones, hair etc all in one tool.

But I suppose a tool like this would be more useful to a learner, and someone more advanced would not really need these extra curves features. Like you have just explained it still cannot do everything.


Ken
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  #12  
Old 07-19-2005, 02:38 PM
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Hi Ken,

sorry for being so unprecise. What I meant by saying "find a neutral spot", I'd post an example:

Imagine you have a photo with a sever blue cast, anything on the picture is blue. Then just locate a spot on your picture that you know right from your mind that it's supposed to be gray, white or something in between, without any color. This is a neutral!

Does that lighten things up?
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  #13  
Old 07-20-2005, 04:11 PM
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Patrick.
Thank you for your reply. I think I’m beginning to understand.

I am at the moment trying to work through this workflow
http://www.luminous-landscape.com/tu...orkflow1.shtml

It seems pretty good and I think Dawghair may be interested in reading it.

I just wondered what you all think of a workflow like this. Is there anything missing?

Sorry if this is off topic a bit

Ken
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  #14  
Old 07-20-2005, 04:37 PM
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I had a quick view of this workflow, but I guess it's worth looking a little bit closer

Two things popped into my eye:

- The author says it's needed (somewhere in the middle) to convert to LAB. I see no use in converting an image and losing valuable information occuring when converting 8-bit RGB to LAB (oh my god what a sentence)

- I also discourage using the Levels to "stretch" a histogram. If an image really has no white or black spots anywhere, why should I create them and ruin the midtones?

*goingonreading*
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  #15  
Old 07-21-2005, 01:32 AM
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Quote:
Originally Posted by PatrickB
- The author says it's needed (somewhere in the middle) to convert to LAB. I see no use in converting an image and losing valuable information occuring when converting 8-bit RGB to LAB (oh my god what a sentence)
I'd always understood, Patrick, that converting to and from LAB was lossless. Not quite sure where I read that, and I haven't got time to look right now as I'm meant to be getting ready for work! Any thoughts though?

Victoria
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  #16  
Old 07-21-2005, 04:21 AM
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Quote:
Originally Posted by v.bampton
I'd always understood, Patrick, that converting to and from LAB was lossless. Not quite sure where I read that, and I haven't got time to look right now as I'm meant to be getting ready for work! Any thoughts though?

Victoria
Well, following up from my own thought, I went hunting for where I'd read it. Seems there's quite a debate going on! Anyone who's crazy enough to want to get bogged down in the debate, you'll find it here http://www.ledet.com/margulis/ACT_po...LAB-damage.htm Dan Margulis, Chris Murphy, Andrew Rodney, and some of the other colour correction bigwigs have been debating the point.

End result seemed to be that any conversion, whether it be to LAB or anything else, does result in some data loss, but the conversion to and from LAB is pretty close to lossless, and therefore not a problem in a real world environment unless you plan on converting the file back and forth a few hundred times.
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  #17  
Old 07-21-2005, 07:25 AM
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ok, i got lost a long time ago on this thread.... what is LAB? i know rgb, cmyk and hsl, but what is LAB?

Craig
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  #18  
Old 07-21-2005, 08:54 AM
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Quote:
Originally Posted by Kraellin
ok, i got lost a long time ago on this thread.... what is LAB? i know rgb, cmyk and hsl, but what is LAB?

Craig
Sorry Craig! LAB is another colour mode, like RGB, CMYK etc, but it's device-independant. You'll find it in the Image > Mode menu along with the others. In short, the L channel is lightness or luminosity, with A & B holding the colour information. It's great for being able to make changes without affecting the colour at all - it's often used for sharpening, where you don't want to introduce any coloured halos, so you just sharpen the L channel. You can get a nice black and white by changing to LAB and throwing away the A & B channels too. There's a quick intro here http://www.creativepro.com/story/feature/12869.html
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  #19  
Old 07-21-2005, 09:00 AM
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v.bampton,

thank you. i use paint shop pro 7.xx and i simply dont have this mode. i figured it was another mode like you said, but just wanted to clear this up a bit to be sure. and yes, i could see where just sharpening the 'L' would have advantages. one of these days i'll upgrade

Craig
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  #20  
Old 07-21-2005, 01:31 PM
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Hm, may I add my two cents about sharpening in LAB?

I used to do that as well, but there's a way to avoid the problems when sharpening in LAB:

- Stay in RGB or CMYK, as you prefer and sharpen as usually.
- Immediately after applying the sharpening filter, go to Edit/Fade. Leave the slider as is but change the blending mode to Luminosity.

Same effect, but without the conversion to LAB

Patrick
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