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(un)Sharpen in LAB mode...
Old 04-22-2006, 01:57 AM   #1 (permalink)
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I came across this technique somewhere and I've been using it a lot. I think I can actually see a difference than to (un)Sharpen in RGB mode.

Once you get to the final (or next to final) stage in editing your image try changing your mode to LAB, only have the LIGHTNESS channel open (everything should turn to grey) and apply the USM to this channel. Once you have the image to the sharpness you want click on the top channel (LAB) and make all the channels active again. This technique only sharpens the Alpha channel and does not affect the color pixels. You can then change the mode back to RGB if you are going to save to a JPG.

Note: there is one miserable thing about this. In order to change modes you have to flatten the image. This may not be good for further tweaking but it's another way of sharpening.
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Re: (un)Sharpen in LAB mode...
Old 04-22-2006, 10:11 AM   #2 (permalink)
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This sharpening technique actually gave me another option to take an rgb image and see it in a form of grayscale. It was this technique that began my appreciation for looking at things in black and white as well.

There are a lot of sharpening techniques and this is one of them I use on occassion. Mainly for web presentation from an already sized/compressed jpeg to resave it again and I have found the technique comfortable.

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Re: (un)Sharpen in LAB mode...
Old 04-22-2006, 11:18 PM   #3 (permalink)
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I use that method all the time. Although I use PSE, so I really don't have LAB mode, but, I do know how to split the tone and color and work with each separately
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Re: (un)Sharpen in LAB mode...
Old 04-23-2006, 01:01 AM   #4 (permalink)
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Quote:
Originally Posted by RHWeiner
I came across this technique somewhere and I've been using it a lot. I think I can actually see a difference than to (un)Sharpen in RGB mode.

Once you get to the final (or next to final) stage in editing your image try changing your mode to LAB, only have the LIGHTNESS channel open (everything should turn to grey) and apply the USM to this channel. Once you have the image to the sharpness you want click on the top channel (LAB) and make all the channels active again. This technique only sharpens the Alpha channel and does not affect the color pixels. You can then change the mode back to RGB if you are going to save to a JPG.

Note: there is one miserable thing about this. In order to change modes you have to flatten the image. This may not be good for further tweaking but it's another way of sharpening.
There are a number of variations and extensions to this technique. You can check out Kelby's book "The Photoshop CS2 Book of Digital Photographers" and the section that starts on page 374 for more details.

Also, you might try the poor man's method of doing something similar. Just do this. Press Ctrl Alt ~ (that's the tilde key - next to the one on your keyboard) at the same time. This will make a selection that you'll find quite interesting. Now do an unsharp mask and then Deselect.

Cheers,
rfs
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Re: (un)Sharpen in LAB mode...
Old 04-29-2006, 10:31 AM   #5 (permalink)
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I usually do almost all touch-up on the luminocity channel only. esp. if the makeup is being emphasized.
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Re: (un)Sharpen in LAB mode...
Old 04-29-2006, 01:13 PM   #6 (permalink)
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Quote:
Originally Posted by RHWeiner
I came across this technique somewhere and I've been using it a lot. I think I can actually see a difference than to (un)Sharpen in RGB mode..
Well...like anything this is not a perfect thing. We already know that the image has to be flattened before the switch from RGB to LAB will work. But I also came across some more information that makes me question whether this is the way to go or not.

I just picked up the May/June2006 issue of "PHOTO Techniques" and in there is an article by "Ctein" (pg.41) dealing with LAB. An interesting segment of this article related to manipulating in LAB and then resetting mode to RGB talks about this process as being 'lossy'. I'll quote the paragraph that deals with that...

"Another reason for not switching a lot is that the conversion process from RGB to Lab and back again is a lossy one; colors can't be converted perfectly. Figure 3 shows the histograms for the photograph in figure 1 in both the original RGB photograph, after converting to Lab and back to RGB once and after converting it to Lab and back to RGB twice. Notice how the histogram is getting spikier with each pass. That's an indication that losses and distortion are taking place. You can minimize that loss by working on images in 16-bit mode. The fourth histogram on the right shows two conversion passes in 16-bit mode; it's very close to the original histogram." [The reference to Figure 3 and histograms are for illustrations in the article itself.]

Due to the nature of Digital sensors we all have to apply a bit of sharpening in our images. I had thought I found a good way to not affect color information, but I guess not. The loss may not be discernable if the switch over is left till the very end of your work, but still there is some loss and in my mind any loss is not good.
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Re: (un)Sharpen in LAB mode...
Old 04-29-2006, 02:30 PM   #7 (permalink)
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[quote=I just picked up the May/June2006 issue of "PHOTO Techniques" and in there is an article by "Ctein" (pg.41) dealing with LAB. An interesting segment of this article related to manipulating in LAB and then resetting mode to RGB talks about this process as being 'lossy'. I'll quote the paragraph that deals with that...[/QUOTE]
While there may be a small amount of loss in going back and forth I have never found it to make any difference. But in Photoshop CS2 you would experience no loss if you use Smart Objects. By doing that and by imbedding the orignal image (even the RAW image) as a smart object, all of the processing would always go back to the original image.
But sharpening as developed into almost a religious issue. There are hundreds of techniques and there are whole groups that grow up defending one against another and so forth.
As for me, I use whatever works best for the situation. Not every technique is usuable for every situation. For my general work, I do a two pass sharpening. When I have done my post processing and any selective sharpening as I've already shown in two tutorials, I then often use a second overall sharpening pass using CSPro.

Cheers,
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