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L*a*b* question: why can't it be simulated in RGB?

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  #61  
Old 09-15-2010, 11:23 AM
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Re: L*a*b* question: why can't it be simulated in

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Originally Posted by Zampano View Post
Although the tone sometimes seems a little bit harsh, this thread is one of the most interesting ones here at RP...
Thanks a lot to all contributers for all the insights and especially for the example files...!
Yep, online discussion can easily spin out of control... But we're still all friends I think
The great thing here was that everyone had lots of useful information to add!
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  #62  
Old 09-15-2010, 12:03 PM
Flashtones Flashtones is offline
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Re: L*a*b* question: why can't it be simulated in

I think I speak for those who already know a lot more than me when I say: we all came out of it knowing more than we did coming in. And that's saying a lot considering the caliber of some of you.
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  #63  
Old 09-21-2010, 06:42 AM
secretagents secretagents is offline
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Re: L*a*b* question: why can't it be simulated in

One good reason to use the Lab L channel over RGB applied in Lum mode, especially if using CPU hungry filters on large images, may be the gain in processing time which should be in Lab only a third of what it would be in RGB since only one channel is processed instead of three.
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  #64  
Old 09-21-2010, 11:40 AM
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Re: L*a*b* question: why can't it be simulated in

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Originally Posted by secretagents View Post
One good reason to use the Lab L channel over RGB applied in Lum mode, especially if using CPU hungry filters on large images, may be the gain in processing time which should be in Lab only a third of what it would be in RGB since only one channel is processed instead of three.
This is true.
However, I rarely run many heavy filters on only the brightness of the image tho. I guess it could make a difference if you're batching lots of stuff?

However the time same might not be 2/3 - it would depend a lot on what filter it is I think. I did a test with the "Reduce Noise"-filter (as an example of something hungry).
On a 5000x5000 16 bpp image running the filter on the RGB image, or a single LAB-channel reduced processing from 12 to 10 seconds (on a fairly slow computer, restarting Photoshop between each test).
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  #65  
Old 07-17-2013, 12:46 AM
JoeFotosiamo JoeFotosiamo is offline
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Re: L*a*b* question: why can't it be simulated in

I find that the most effective way to heal is to Heal/Clone on a normal unseparated layer for areas between subject and background (ie. Flyaway hair against background, loose clothing thread against the background). Then use Asymmetrical Freq Sep to do skin/hair retouching within the subject's skin (pimples, baby hair on face, etc).

Hope that makes sense to you all =)




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Originally Posted by mistermonday View Post
Chain, , yes all of the color is on the LF layer.

Jonas, good job doing the separation in RGB. The results are identical.

Flashtones, there are advantages of the Asymetric separation but there may also be disadvantages. If you followed my post above you will see that in a symetric separation, healing from one area to an area of very dissimilar color introduces and blends in some of the sampled color into the new area. In actual practice, this does visible because you tend to heal texture from an area of similar color.
Healing on an Asymetric layer guarantees you only bring over texture only, however when you heal with texture where the source has strong contrast, you can also accentuate the edges of the destination where strong color exists. Attached are two examples where I sample the Hair from king's forehead and heal on the edge of his right ear. In the conventional symetric separation, it blends in nicely. With the Asymetric separation it blends very well but you also see the blue edge of the ear/sky interface become more visible. You will have different results if you use the clone stamp. BTW, effects are the same for each type of separation whether you do them in RGB or LAB.
I think the bottom line is that each method of separation could be used to advantage and it is good to have the ability to to use both of them.
Regards, Murray
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  #66  
Old 07-30-2013, 04:39 AM
JoeFotosiamo JoeFotosiamo is offline
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Re: L*a*b* question: why can't it be simulated in

One thing I discovered with the Asymmetric Freq Sep is that it's better to apply the same Blur to the Color layer before merging it to the Low Frequency Layer. Otherwise, you may end up with grey spots in the low frequency layer.
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  #67  
Old 07-30-2013, 02:56 PM
Shoku Shoku is offline
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Re: L*a*b* question: why can't it be simulated in

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Originally Posted by andrewrodney View Post
I try to nail it in capture, not like Dan, after the fact to demonstrate how well I can polish a turd.
Sometimes you need to polish a turd. In the real world retouchers don't always work on their own images. When a client comes to me with a bad image and insists on using it (claiming no ability to get a better one), they rely on me to make it appear as good as possible. LAB often helps, as does RGB and CMYK. I am glad to have the knowledge to use any of those 10 channels when necessary. To the client the end result is what matters - how I get there depends on the original image.
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  #68  
Old 07-30-2013, 04:04 PM
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Tony W Tony W is online now
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Re: L*a*b* question: why can't it be simulated in

You both do realise that this thread is nearly three years since the last post by Chain?
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  #69  
Old 07-30-2013, 06:35 PM
Shoku Shoku is offline
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Re: L*a*b* question: why can't it be simulated in

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Originally Posted by Tony W View Post
You both do realise that this thread is nearly three years since the last post by Chain?
Joe's post got my attention and I began reading from the beginning. I never read this topic before. Once you write something online it never goes away, so the original date is not relevant to anyone viewing it later and wanting to comment. This is all about opinions.
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  #70  
Old 07-30-2013, 11:53 PM
RobertAsh RobertAsh is offline
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Re: L*a*b* question: why can't it be simulated in

Agreed. And in some clear cases more than a little envy at Dan Margulis' fame in the industry

Or the "it's not my idea or approach, therefore it's not as good" syndrome. Not true for Chain and some of the other hotshot retouchers here, of course But even in elite retouch circles it seems there can be an emotional attachment to one approach or another that transcends technical issues. But that's ok as long as each side respects the other side's views.

For me personally, Lab allows me to do color manipulations and enhancements quickly and easily that I can't do in RGB. Notice that I said that **I** can't do in RGB.

Chain can do them, not a problem. But me, I'm a part-timer with very little time to work on images, and for me Lab works better for my landscapes (often with some RGB thrown in ) while RGB works better for my portraits. I'm really glad I bought Dan Margulis' book, and although I'm learning more over time about RGB it's still good to have a quick, easy way to get a look I really like with Lab color.

Last edited by RobertAsh; 08-01-2013 at 03:08 AM.
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