Question about high pass sharpening

Zeus1

I am using Photoshop CS4 Extended.

I have read about high pass sharpening, but there seem to exist two variants of this technique:
a] Duplicate layer > Filter > Other > High Pass; choose a radius, hit enter and done.
b] As under a, but after choosing the radius, choose Levels (Command -L) and approach the white and black markers as close as possible to the beginning of the curve (symmetrically).

Method b seems to result in a more pronounced, harsher form of sharpening. Under method a, I usually choose a radius of 3-5 with Overlay blending, while using method b I use a radius setting of 1-2 and Soft Lighting

Can somebody please explain exactly what this levels option for High pass sharpening does, and when to use it?

Zeus1

Time for a discreet BUMP, me thinks

TonyCooper

I use Option A quite a bit. Option B is new to me, but I just tried it on a shot. Quite a dramatic difference. As far as when to use it, I can only say "when it improves the image". That's kind of a lame answer, but that's the rule for most alterations.

Drazick

Is It For Pure Sharpening?
If you're after the best way to sharpen your image there many better ways.

Try Topaz Denoise for instance.
The Linear filters in Photoshop easily creates Halos.

arodney

Zeus1 wrote:

Can somebody please explain exactly what this levels option for High pass sharpening does, and when to use it?

The question should also be, what values and for what type of sharpening?

[url]Http://www.creativepro.com/story/feature/20357.html[/url]

gmitchel850

I explain how High Pass sharpening works in my eBook and video on sharpening.

http://www.thelightsright.com/SharpeningYourPhotographsED

It wasn't designed for sharpening. It was designed for converting continuous tone photos into line art or bitmap images.

The High Pass filter works only on high frequency details. That's where most of the edges in a photograph are found. It boosts their contrast and their saturation. (It's especially the later that can give you some unwanted color shifts with High Pass sharpening).

When you apply High Pass sharpening with an Overlay, Soft Light, or Hard Light blend, you are relying on the fact that middle tone gray prevents any sharpening effect. If you've ever looked at the result from High Pass, you;ll notice that low frequency details are rendered as midtone gray. That's where the "magic" of High Pass sharpening lies.

Now, why does manipulating the Levels command give a "harsher" looking result? Well, that depends on what you do with it. You could also adjust the settings for a "softer" result, too. But, back to the example on this thread, what you're doing is boosting contrast. As a result, more features are interpreted as edges and are receiving a sharpening effect from the High Pass filter.

Cheers,

Mitch