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Old Apr 3, 2004, 12:14 PM   #1
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Default Sharpening Pictures

Hi All,

Up till recently I hadn't really mucked around with Editors as there is so much to learn, but I'm really seeing a benefit so I'm trying dig deeper and learn.


I was going through some of my pictures with a very simple editor just doing sharpening. None, Low, Med, and High, are my only choices. Some of my pictures look fine with none, but I noticed many of them just seemed to pop out better when I changed the sharpening to med or high ... as if they are suddenly in focus and they weren't before. Can someone explain to me what Sharpening does and would you use the same amount on all shots or does it depend. From one of my manuals, I read this: "Sharpness can be increased to make outlines more distinct, or lowered to soften outlines". I understand that... it's pretty straight forward, but I guess what I'm not understanding is if I pull a picture straight from my camera and the focus is on the money, why does sharpening make it appear even more in focus. Why do I need to do it? Does sharpening help a picture look in focus if it is not?

Thanks
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Old Apr 3, 2004, 5:57 PM   #2
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All that sharpening does is localized contrast increasement. Now say that 10 times fast.

It increases contrast in specific places... where it thinks there are edges or details. So if you have a pine table on top of a black rug, you have a light edge (the side of the table) next to a dark patch (the rug.) The software will find this large difference in contrast and say "this is an edge, I need to increase the contrast!" and it will do that.

The more common situation is when you have a person standing in front of the sky. The sky is very light, the person is dark. So an edge is found and the contrast is increased. This causes the sky right around the edge of the person to be lightened, and the edge darkened.

The problem with this situation is that the person will develop a "halo" or lighter glow around their edges. This is an obvious sign that the picture has been over sharpened. It is not uncommon, unfortunately. Sharpening isn't hard, but doing it well is not.

This article might help:
http://www.luminous-landscape.com/tu...harpness.shtml

This is actually a really good website in general, with a fair number of digital editing articles. The writing is top knotch, as is the info. Well worth looking around at other things.

Eric

ps. Oh ya, and it has some really good pictures too!
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Old Apr 3, 2004, 8:03 PM   #3
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Thanks Eric. You're explanation is great and so is the website. I have probably just been digging around and printing from this web site for the past hour; I have a lot of good reading material,

and the pictrures are very nice. I wish I could do half as good .... One day maybe.
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Old Apr 3, 2004, 8:30 PM   #4
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Glad I could help.

I wish I could take many of the pictures there too. I do almost exclusively wildlife, not landscapes... I just don't have the eye for it. I look at some of the shots there and go "what?" 'cause I don't get it. But for most of them I go "wow! I wish I had taken that!"

I should spend more time there too. There really is a wealth of info there.

Eric
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Old Apr 4, 2004, 1:12 AM   #5
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Default Re: Sharpening Pictures

Quote:
Originally Posted by mdparker
why does sharpening make it appear even more in focus
It provides an optical illusion by exaggerating edges. Lots of digicams do this by default, which is why their results often look stunning when displayed at the right size. You can see what's going on if you inspect sharpened images on your computer screen at high magnification.
Quote:
Originally Posted by mdparker
Why do I need to do it? Does sharpening help a picture look in focus if it is not?
Yes, you do, because we lose sharpness when we resize & compress for places like this bulletin board, and we need the optical illusion to make things look better.

What no-one has mentioned yet is that if you use sharpening to make a picture look better for display (on a wall or on a computer screen), you should do it *last* thing *after* everything else is complete. It needs to be done by experiment and inspection. There are no hard & fast rules.

Good luck!
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Old Apr 4, 2004, 1:19 PM   #6
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Thanks Chester. Between you and Eric, and a few articles, I think I'm covered except for 1 think. I use Elements and in Elements there is the unsharp mask just as in CS. It has 3 fields, amount, radius, and Threshold. I read around and found what they mean and what they do, but I've not been able to find a good article on how to come up with the values. I know it is trial and error, but I can't figure how when i should tweak the amount vs the radius for instance.

Also is there a better way to do shapening. I read one article that suggested using the high pass filter. Any benefits to one over the other?

Thanks
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Old Apr 4, 2004, 5:24 PM   #7
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I almost always do what is called "lab sharpening".

Unfortunately, I don't believe Elements can chance mode. Lab mode just represents the picture in a different way. Instead of in RGB it uses brightness, two color channels and a "lab" channel that I don't know what it is.) I imagine it like RGB (Red-Green-Blue) vs. CMYK (Cyan-Magenta-Yellow-blacK). Both are different ways to represent the same picture. Well, Lab mode is just anothe way.

When you do lab sharpening you switch into Lab mode and select the luminous channel (or brightness). And you sharpen that one with USM.

I've been using 85, 1, 4 for most of my USM needs... but it is situational. The other problem is that sharpening can bring out the noise in the picture. So watch the darker spots (often in the background) to see if they look grainy or noisey after you sharpen (I almost always sharpen and then toggle back-and-forth with undo-redo (control-z) to look at the before & after. And I try to see what changed... that often shows me if halos are too strong or if too much noise is now visible.)

I am no expert in USM, though. I can recommend "The Photoshop CS book for digital photographers" (there is a non-CS version as well.) I've leard a lot about USM from there, but I have more to learn.

Eric
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