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Old Dec 5, 2009, 1:40 PM   #11
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When I use unsharp mask the amount done depends on the resolution of the file. The high res file gets 125% 1.5 pixels at 0. While the low res file gets 75% 1 pixel at 0.
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Old Dec 5, 2009, 4:24 PM   #12
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i always do #3.

and to avoid the artifacting that TCav mentioned, i just modify the sharpening parameters. my starting parameters are pretty close to Bynx's, and I modify it to fit the specific image. for an 800x600 web image, my starting point is usually 80/1/1 and full size is like 140/1.7/1
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Old Dec 6, 2009, 4:32 AM   #13
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The folks at PixelGenius are the real experts on this.

Bruce Fraser and Jeff Schewe have written a few books on sharpening; they divide sharpening into 3 stages:

1. Capture sharpening - correcting sensor and lens issues.
2. Creative sharpening - usually local/masked - e.g. extra sharpening on a model's eyes.
3. Output sharpening - different sharpening is required for different output types, 200dpi inkjet should be sharpened differently to 300dpi inkjet. 800x640 jpgs need different sharpening for 1024x768 jpgs, etc.

http://pixelgenius.com/tipsandtechniques.html

Scroll down to the bottom of the page for a 12-page pdf intro to sharpening by Jeff Schewe.

Lightroom 2.5 and later include a lot of the PixelGenius technology.
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Old Dec 6, 2009, 9:23 AM   #14
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Quote:
Originally Posted by TCav View Post
It seems to me that sharpening lower resolution images would produce more noticeable oversharpening artifacts, while if an image is sharpened at its original size the oversharpening artifacts would be blurred in the process of downsampling. On the other hand, the downsampling is more likely to produce an image that one might think needs to be sharpened.
I hit this problem in 'Landscape photographs' in October. Whatever I did, one particular image of mine (some fussy foliage) looked unsharp when posted here. Jim C rapidly worked out what had happened and sorted me out.

You can see the discussion at...

http://forums.steves-digicams.com/contact-steves/161535-accidental-posting-discovery.html

...and the worked examples at...

http://forums.steves-digicams.com/landscape-photos/161532-autumn-bathroom-window.html

I discovered that the forum's resizing and recompression actually took my image to 799 x 599 pixels, when it had started at 800 x 600. Sharpening is an optical illusion based on emphasising edges, so this tiny error, of a fraction of a pixel for each edge, had inevitably messed up the apparent sharpness. Compressing my original a little more before the sharpening step fixed the problem, because the forum didn't need to do its resize.

Sharpening needs to be done last so the viewing conditions match the intended purpose. The assumption I find satisfactory here in these forums is that most viewers are likely to view in their browsers at image size "100%" or 1:1, pixel for pixel. If most of us view at a comfortable reading distance from our screens this should work.

However, the sharpening won't look so good if people sitting close to huge screens use less than 1 pixel per image pixel, or those on tiny screens use more than 1 pixel per image pixel, unless they happen to give themselves the same apparent magnification as the 'person who did the sharpening' did.

The moral to the tale is to keep an eye on file size, even if you think you have a well-established routine 'workflow'.

Have fun
Alan T

Last edited by Alan T; Dec 6, 2009 at 9:26 AM.
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Old Dec 6, 2009, 12:29 PM   #15
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i also use an external site, to host the pictures and link to them, to prevent the resizing and recompression of the forum.
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Old Dec 6, 2009, 1:54 PM   #16
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I'm coming back with a question: will I have different sharpening results if I sharpen, for instance, using Photoshop, or Irfanview or Noiseware or Picasa3? Are there different sharpening algorithms?

Last edited by Ordo; Dec 6, 2009 at 2:23 PM. Reason: spelling
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Old Dec 6, 2009, 2:19 PM   #17
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Hard to say.

UnSharp Mask (USM) probably has a fairly standard implementation. But certainly different programs will have different sharpening algorithms.
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Old Dec 6, 2009, 3:44 PM   #18
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I just got a new plug in for Photoshop from Nik called Sharpener Pro. So I would imagine there are different methods to sharpen. Some more effective than others. Or at least easier to use. Ive only used Photoshop up til this point. But I will be using Nik as soon as I have something to work on.
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Old Dec 6, 2009, 5:52 PM   #19
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Quote:
Originally Posted by Ordo View Post
...will I have different sharpening results if I sharpen, for instance, using Photoshop, or Irfanview or Noiseware or Picasa3? Are there different sharpening algorithms?
There are different algorithms, but the idea is generally automatically to adjust the contrast locally between adjacent very different pixels, which indicate some kind of edge, and emphasise that edge, heightening the perception of crispness. Unsharp masking (USM) does this by superimposing a fuzzy version of the image, slightly out of register.

I find it very difficult to reproduce the degree of sharpness I can obtain when using different image editors. For example, when batch resizing many images at once, I use Irfanview for convenience & flexibility, but it has only one parameter I can modify to adjust the final sharpening. Almost always there are a few images where my standard setting proves unsatisfactory. For these, and as routine for single images, I prefer Paint Shop Pro's USM facility which has three separate adjustments of 'radius', 'strength', and 'clipping', allowing lots more experimentation chasing a better result, albeit much more time-consuming. PSP also offers a simple 2-level 'Sharpen' and 'Sharpen more', also usually worth a try.

Obviously if you use an external hosting site, you're reliant on their methods of resizing and sharpening according to the size the end-viewer requests, and you have to hope they get it right!

Again it's important to emphasise that the visual effect can be judged accurately only at the final image dimensions and viewing distance, i.e., its ultimate apparent magnification.

Last edited by Alan T; Dec 6, 2009 at 6:02 PM.
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Old Dec 12, 2009, 11:37 AM   #20
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I've tried all 3 different ways and decided that I really need to resize first, sharpen later. If I sharpen before I resize, the image always seems to lose any of the sharpness gained and I have to re-sharpen it again anyhow.
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