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Posted on 06/05/08 11:05:42 PM |
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chris berry
Overhead Overlord Posts: 724 Reply  |
Unsharp mask
Okay - here's another one. What does unsharp mask do? Chris |
Posted on 07/05/08 03:14:09 AM |
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cy98
** Posts: 115 Reply  |
Re: Unsharp mask
Did you ever hear the Abbott and Costtello routine "whos on first?" Well the unsharp mask is kind of like that, it is used to sharpen the image. edit: There is a good explanation of unsharp mask in PhotoShop Help file. |
Posted on 07/05/08 08:01:16 AM |
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Steve Caplin
Administrator Posts: 7068 Reply  |
Re: Unsharp mask
Unsharp mask sharpens an image by enhancing transitional areas between regions of different tone. It's a tricky one to get your head around, which is why I gave it two pages in the book - pp 86-87 in the current edition. |
Posted on 07/05/08 08:27:52 AM |
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chris berry
Overhead Overlord Posts: 724 Reply |
Re: Unsharp mask
Thanks Steve and Cy98. Steve, is Unsharp Mask covered in the third edition? (I'm going to have to get updated). C |
Posted on 07/05/08 1:46:27 PM |
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Nick Curtain
Model Master Posts: 1768 Reply  |
Re: Unsharp mask
Chris As Steve has suggested, Unsharp Mask can be complicated and you often see images in web galleries where it has been overdone. The results can be overwhelming and full of artifacts. The amount used depends on the resolution of the image and whether it will be presented on screen or in print. With the latter you need a higher degree to compensate for the 'loss' during printing, particularly with inkjets. For a 2 to 3 mb image I would typically use a raduis of 0.5 to 1.5 px, an amount of 150 and threshold of 2/3. However, much will depend on the subject. With portraits, the eyes are key and people will not thank you for sharpening their skin. Always sharpen on a new layer, so you can mask where appropriate. Also, try Filter / Other/ High Pass as an alternative. Copy the layer and change the blend mode to Soft Light. If you apply the filter first, the layer will turn grey and the effect is hidden, but the other way round allow you to adjust while the dialogue box is open. Overlay will offer a stronger effect Nick |
Posted on 07/05/08 4:53:41 PM |
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GKB
Magical Montagist Posts: 4057 Reply  |
Re: Unsharp mask
Another technique is to convert to Lab mode and sharpen just the Lightness Channel. That way you don't sharpen the colours and get coloured artefacts. When you have finished convert back to RGB/CMYK. You might want to tweak the colours in Lab while you're at it but that's a different (and interesting) game compared to RGB. See Scott Kelby's Photoshop Channels book for more info. Gordon |
Posted on 07/05/08 9:04:48 PM |
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dave.cox
Marquee Master Posts: 518 Reply  |
Re: Unsharp mask
This is a tough one to get a grasp on, and the strange name doesn't help. But what is does, is it increases the contrast between light and dark pixels around pixels that have a large change in luminance. Of course the amount determines how much of the affect that you are going to apply. The Radius determines the number of pixels surrounding the pixel being adjusted to is being affected. The has the affect of adjusting how big the halos are that is created by the unsharp filter, or the thickness of the lightening and darkening around the edges. The Threshold adjustment, limits the adjustment to the number of luminance levels that must exist between neighboring pixels before the filter is applied. The name unsharp mask comes from the way that photoshop applies the affect. The appearance of sharpening is applied by applying a gaussian blur around the edges, and then masking the blur. I had trouble with this one to0, until I went through some training put together by Deke McClelland. The above if paraphrased from his training modules. |
Posted on 08/05/08 05:19:47 AM |
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Nick Curtain
Model Master Posts: 1768 Reply |
Re: Unsharp mask
Picking up on Gordon's comment above, this method can be shortcut by changing the blend mode of the sharpen layer to luminocity. I sometimes use the fade command and change the blend mode there. Nick |
Posted on 08/05/08 08:50:45 AM |
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chris berry
Overhead Overlord Posts: 724 Reply |
Re: Unsharp mask
Thanks everyone. Much appreciated Chris |