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From: "Larry N. Bolch" 
To: 
References: 
Subject: Sharpening and grain control with Lab mode.
Date: Fri, 21 Mar 2003 19:56:38 -0700
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chris.kenward{at}fanciful.org at chris.kenward{at}fanciful.org wrote:

> Just a quick note to let you know I have posted a number of new photos
> on PhotoSIG since I last posted here. You can browse them at:
>
> http://www.photosig.com/userphotos.php?id=1610
>
> I would sincerely appreciate any comments of constructive nature you
> might have for me.

I really like your double portait of the two women "friends" - very
spontaneous. There was some nit-picky about grain and sharpening, and I have
a tip that may help. It is mostly for colour shots, but also works with
desaturated images as well.

In Photoshop, switch to Lab mode with the image view at 100%. Select only
the Lightness channel from the Channel window. Apply Unsharp Mask on a
***sub-pixel*** level!!!!

As a starting point, I set my radius to 0.3 and an the amount to 350. If you
are getting a lot of sparklies, back off a bit on amount. If it will take
it, go all the way to an amount of 500. Do not touch the a and b channels.
Then return to RGB. Most natural looking sharpening you could possibly
imagine. This should always be the very last step of the process, after the
image is sized, balanced and adjusted to match what you saw in your mind
when you took it.

One can use a similar technique to reduce the impact of grain, with minimal
impact on detail. This should be the very first step of the process right
after the scan or right after the unprocessed image is opened.

Once again, with the image view set at 100% go to Lab mode, and select the
Lightness channel. Using Gaussian blur, try a radius of 0.5 to start with
and fiddle with it until the grain just blends enough to be no longer
obtrusive. Now switch to the a and b channels and blur them considerably
more. If the Lightness channel only requires 0.4 or 0.5, blur the a and b
channels with a radius of 1.0. If the lightness channel requires 0.8 to 0.9
go all the way up to 3.0 to 4.0. Beyond a radius of 4.0, the blurring begins
to intrude. If you overdo it, back out with the undo history and try again
with slightly lower values. Undo is your best friend.

When finished with all other interpetative steps are done, use the
Lab/Unsharp Mask to return the accutance.

larry!
ICQ 76620504
http://www.larry-bolch.com/

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