LAB Sharpening method

[philcrean]

Hi all

I'm new here and have been searching for a method to sharpen using LAB lightness channel. I can't find any info on this by searching forums or tutorials.
Can someone point me towards something if I've missed it, or, can you offer an insight into this method?

thanks
Phil

[mistermonday]

Phil, welcome to Retouch Pro.
Sharpening a photo in LAB simply involves selecting the L Channel and applying any of you favorite sharpening filters (like UnsharpMask or Smart Sharpen, etc) to it. The Lightness channel is separate from the color information in the A and B channels. By sharpening the L channel you eliminate the halos often produced when you sharpen an image in RGB color space. You can also accomplish this type of sharpening in RGB by applying a sharpening filter and then immediately going to the Edit menu and selecting Edit>Fade Sharpen and selecting the Luminosity Blend Mode. If you have no other reason to go into LAB color space than to sharpen, then the fade to luminosity technique would probably more efficient to your workflow.
By the way, if you are interested in LAB color space and what it has to offer (which is a lot), the recognized best book on the subject is by Dan Margulis and it is called: Photoshop LAB Color; The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace,
Regards, Murray

[philcrean]

Many thanks mistermonday

Phil

[fcc]

I googled sharpen with LAB in photoshop and found lots. When I first learned about it, a couple of weeks ago, I thought I found a tutorial that said to use Gaussian blur on the A and or B channel also.

[Janet Petty]

The LAB sharpening method doesn't use the whole lightness channel. It uses the "shadow" part only. Do a control>alt>tilde (PC), then invert selection. Hide the selection so you can see what you are doing. Go to unsharp mask and use a high number on the first, a number of 1 or 2 on the second and a tolerance of 2. Repeat unsharp mask and lower the top number to around 55-60 and raise the second (radius) to around 6. Leave tolerance set at 2. Do this unsharp mask only on the lightness channel. Don't forget to deselect when you are done. If you do this sharpening on a separate layer, then you can lower the fill or opacity if it looks like too much in the final version.

Good luck,
Janet