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DPChallenge Forums >> Tips, Tricks, and Q&A >> AOTD: Sharpening painlessly
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Showing posts 1 - 9 of 9, (reverse)
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 10/23/2002 11:46:29 AM · #1
How to sharpen an image - how to use unsharp mask and
some other techniques (Not all DPC legal)

Article is here
 10/23/2002 12:55:01 PM · #2
Thank you Gordon, this is very interesting.
 10/23/2002 12:55:05 PM · #3
Gordon,

this is particularly interesting... I stumbled across one concept offered in this article yesterday afternoon when i was working on some print files for DAPrints... I had been doing my sharpening before I resampled up. I did get a lot better results by doing my resampling and then applying the unsharp mask as needed.

The other tip I learned in this article that will be quite useful is to view my image at 100% while applying the unsharp mask. This will give a much cleaner impression of what the filter is actually doing...

:)

 10/23/2002 01:04:17 PM · #4
I was actually a little curious about the suggestion to sharpen at 100% -- I thoroughly agree in terms of sharpening for the web, but I'm not so certain when it comes to sharpening for prints. Perhaps I'm slightly misinterpreting what he means.

Doesn't it make more sense to view your image at print size when sharpening for prints? (EG at 24% for a 300 dpi image.) In a manner of speaking, that is 100%, so maybe that's where I'm getting confused.
 10/23/2002 04:09:29 PM · #5
Gordon,

Thanks for posting that... it's a bookmark now! I had always simply used "Sharpen" or "Sharpen More," which seems to be a very frowned-upon method around these parts, so I've been forcing myself to use the "Unsharp Mask" more often. Problem is that I've just been sliding the little controls back & forth without knowing what the heck they do -- this was a very helpful article!
 10/23/2002 04:27:55 PM · #6
I just downloaded a program called Pixelnhance
There sharpen program look like
10/23/2002 04:57:06 PM · #7
Originally posted by m_square:
I just downloaded a program called Pixelnhance

can I use all the features?
Will I be breaking the rules because of the noise adjustment.

It's probably legal; different terminology for the same technology.

I'd suggest you take a small sample image and run a bunch of variations; use extremes of the settings so you can easily see what's going on. If you can post or email the samples it will be easier to tell if there's a problem...or maybe someone else is already familiar with this...
 10/23/2002 05:02:23 PM · #8
Originally posted by Patella:
I was actually a little curious about the suggestion to sharpen at 100%.


If you view at any other magnification you screen is re-sampling and anti-aliasing the image for display, so you can't really tell how much effect the filter is having. It's easy to over-sharpen if your display shows the final "print" size. At 100% you see the actual color changes pixel-by-pixel. Of course, when I'm all done, I zoom out to the final size as well...

I just remembered...I have a gallery of examples of Unsharp Mask effects at pBase.

* This message has been edited by the author on 10/23/2002 5:04:54 PM.
 10/23/2002 05:30:19 PM · #9
Originally posted by Patella:
I was actually a little curious about the suggestion to sharpen at 100% -- I thoroughly agree in terms of sharpening for the web, but I'm not so certain when it comes to sharpening for prints. Perhaps I'm slightly misinterpreting what he means.

Doesn't it make more sense to view your image at print size when sharpening for prints? (EG at 24% for a 300 dpi image.) In a manner of speaking, that is 100%, so maybe that's where I'm getting confused.


Well, the thing is, if you don't sharpen at 100% you don't actually
see the effect of sharpening.

See, resampling is the biggest cause of 'softer' images, and when you are
looking at a zoomed version of your image, you are looking at a very
quick and nastily resampled version of the underlying image.

so if you sharpen the zoomed version (either in or out from 100%) you'll
see aliasing over the top of the sharpening you've done - so it could
well look softer than it 'actually' is.

The resampling thing is also the reason why you should sharpen _after_
you've sized your image. Resizing tends to smooth/ blur edges and
this is what you want to fix by sharpening. Sharpening then resizing will
either reduce the sharpness you've achieved and/or spread the noise and
haloing caused by sharpening further.

I can spend a whole lot more time talking about aliasing and sampling
effects and the problems of interpolation on edges if you like, but I
don't feel like writing a maths paper today.
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