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Image sharpening in Photoshop 6


manhattan88 19 14
1 Sep 2002 6:28PM
Hi
After investing the proceeds of the sale of my granny in a Nikon D100, I have a query about image sharpening on photoshop 6.0

On the camera I have it set to Normal sharpening. Which means it definitely could benefit from photoshop sharpening.

I tend to use UNSHARP MASKING a lot but am unsure as to what extent/degree it should be used. I find that if you over unsharp the image, it prints noisy! Is there an optimum level of unsharp masking?

I currently have the unsharp masking set to 100% at 1.5pixels with a threshold of 5

How does that sound?

THANKS!!!
mad-dogs 19 2.2k England
1 Sep 2002 11:10PM
Set the mode to LAB ( IMAGE > MODE > LAB ) and open the channel palette.

Click on the 'L' ( Lightness ) channel and apply unsharp mask to the channel.

Click on the LAB channel to view the effect in colour and then revert the mode to RGB via Image > Mode > RGB.

You will have to experiment with the amount of unsharp masking . If you are sharpening withing the camera software, I would not recommend applying too much unsharp masking - start at approx 40%. If the results are not sharp enough press ctrl+F to apply the filter again.

cheers

Dave
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shooter 19 105 Canada
10 Sep 2002 5:15AM
I agree that USM should be applied to the L channel; that results in less edge artifacs and doesn't colour haloes.

There's an easy way to do this WITHOUT changing modes that isn't well known. If you combine it with a methodical USM technique, you'll be able to control the results very well.

First, Use the USM filter, and set the amount slider at 500% (yes, maximum, ALL the way!). Threshold and Radius are left at minimum for now.

Slide the radius out until you see substantial sharpening (viewing at 100% and ONLY 100%) while watching for haloes. If there's too much haloing, back off.

At this point, the edges are the correct sharpness (RADIUS) but sharpness overall will look excessive, and there'll be ugly noise. We'll take care of that now.

Advance the NOISE slider until the excess noise disappears. Watch especially in the blacks and in even flat areas like blue sky.

Now the edges are sharp, noise isn't a problem any more, but the overall amount of sharpening is still excessive. Just back off the AMOUNT until it looks just a LITTLE too sharp. Because a printer blurs the image through diffussion of the ink drops, a *tiny* bit of OVERsharpening is your friend. AND...we'll back off some sharpness later.

We are finished with USM and have a very sharp yet not noisy image. It may have a few edge artifacts, which we'll now get rid of. Go to FADE (like UNDO, but controlable) and set the mode to LUMINOSITY. The effect will be done in the L component of the RGB image without switching modes overall. Back off that excess oversharpness by dragging the slider down to 95% or whatever amount you like. DONE!

You have ideal sharpness, with controlled noise and no edge artifacts. Cool, eh?

Al Schietzsch
ARS Technical Images, Edmonton, Canada
That sounds good advice Al, but I have an Epson printer which I'm sure increases sharpness to avoid the inkjet blurring you mention. That would end up producing unnaturally sharp pictures wouldn't it?
shooter 19 105 Canada
10 Sep 2002 4:35PM
If your Epson behaves that way, it would look odd, GT.

In that case it'd just require a slight modification. When you do the Fade Sharpen, back it off a little more.

Al Schietzsch
ARS Technical Images, Edmonton, Canada

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