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Joined: Mon Feb 20, 2006 9:19 pm

Sharpening RGB Or LAB Mode

Fri Aug 31, 2007 12:18 am

I've been reading some interesting articles that advocate the use of LAB mode and with it the Lightness channel for use when applying sharpening - USM. I know from other threads it's a topic of frequent debate so i thought I'd share my findings.

The benefit seems to be that rather than sharpening the colour channels (RGB) and risk introducing colour artifacts, you apply the sharpening to the Lightness channel, which is black & white, and then convert back to rgb.

It would be interesting to hear from anyone who has experience of this method of sharpening and their findings as its benefits seem to be excellent over and above the 'normal' rgb method.

For those who want to try it you change the image mode to LAB, apply a duplicate layer, select channels palette and then lightness, then apply your usm at whatever levels normally used. Once complete convert back to rgb mode. If your familar with layers and can get around photoshop it's easy enough to do.

Views/comments welcome.
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Joined: Sat Mar 19, 2005 9:41 pm

RE: Sharpening RGB Or LAB Mode

Fri Aug 31, 2007 12:25 am

I saw a dramatic increase in noise when I sharpened the lightness layer in LAB mode.

But I do use lab mode to aid in my selective sharpening. I duplicate the lightness channel, find the edges, blur it with gaussian blur at about 2, and then I use the magic wand to select areas I don't wont to sharpen, sky etc. Once I have my selection I just click over to the layers tab and sharpen away.

I would love to fly a cargo plane full of rubber dog shit out of Hong Kong!
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RE: Sharpening RGB Or LAB Mode

Fri Aug 31, 2007 3:50 am

Scott Kelby, at his International Society for Aviation Photography talk last March, recommended sharpening the lightness channel in Lab mode. I have been doing that in my workflow ever since. Though I still get a lot of soft rejections here, I like it on my overall photography.
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