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join:2001-05-08
| reply to prwood
Re: [FYI] Sharpening Tutorial
I use this method all the time. Gives me great control over every aspect of sharpening. I always sharpen the Lightness channel in LAB mode first then after that convert back to RGB to finish the technique below. Thank you for posting this link.
From the article.
Avoiding Halos
As the unsharp mask tool increases the brightness on the bright side and the darkness on the darker side of contrast boundaries, it is very easy to get the settings too high and create so called halos. There are dark and bright halos, but usually the bright ones are the ones that are most irritating and give an image an oversharpened look.
Halos usually happen if you get the radius and/or the amount setting too high. But even if you get the settings spot on, you might still find some halos in your picture, and this is where we get into the topic of halo control.
Halo Control - Advanced Unsharp Mask using Layers
Let me present you with a technique that I learned from Russell Brown. It might seem quite blunt, but it works remarkably well and gives you full control over halos, and it's my most frequently used sharpening method.
Once you're finished editing and resizing your image, create a new flattened layer by pressing Ctrl-Alt-Shift-E (PC) or Command-Option-Shift-E (Mac).
Flattening layers with Ctrl-Alt-Shift-E (PC) or Command-Option-Shift-E (Mac) will preserve your existing layers and create a new layer on top with all your edits in it!
Zoom in to 100% and apply an unsharp mask to that new layer with a setting of 500%, 0.4 pixels and a threshold of 0. And yes, this will give you a very oversharpened look, but we're not done yet. Change the name for this layer to "darken" by double-clicking its name, and then set its blending mode to "Darken" too. You can find the blending modes pulldown at the top of the layers palette. With the "Darken" blending mode selected, the new layer will only help pronounce the dark sharpening halos without touching on the bright ones.
The next step is to duplicate the sharpened "darken" layer by dragging it to the "new layer" icon on the bottom of the layers palette, rename it to "lighten" and set its blending mode to "Lighten".
Reduce the opacity of the "darken" and "lighten" layers to 0 and you're done with the preparations.
Now start to gradually increase the opacity of the darken layer until you find that you have enough sharpness. Do the same with the lighten layer, slowly increase its opacity until you see the first halos appear, then reduce the setting a bit.
You will have to play with those settings, but in general the darker halos are much less detectable for the human eye than the bright ones, so in many cases you'll find that you can dial in much more of the darken portion than you can of the lighter one.
But the really cool thing about this method is that you can now create layer masks on those two new layers in order to fully control halos throughout the picture. Imagine you have the sharpening just perfect for the whole image, but there is one tiny area where a bright visible halo appears. Just mask that portion of the lighten layer away and you're all set.
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