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Old Jan 11, 2006, 2:11 PM   #1
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Ineed a little help in understanding when to use Un sharp mask or High pass.

I think both of them have their individual purposes but I can't figure it out.

When is High pass better to use than USM or USM better to use than High Pass? Is this just a preference or is there really a time when I should use one or the other or both?
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Old Jan 13, 2006, 5:26 PM   #2
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Okay, Iv'e seen this post up for 3 days now and was hoping someone with real knowledge of the issue would reply. As it hasn't happened, I'll give you something from a book I have. The following quotes are the copywrite of Tom Ang:

"A simple USM....corrects the softness but introduces harsh contrasts. Using the High Pass filter controls contrast and can hide JPEG defects."

"....When working with JPEG compressed images, this filter enables you to judge just how much you can improve sharpness without making the artifacts too evident."

"One technique...combines two steps -- the seeking out of image gradients and exploiting the resulting masking of unwanted areas through the use of layer modes."

"If you are familiar with the Emboss filter you will recognize similarities in the appearance of the result to that from the High Pass filter. Naturally, you can also use the Emboss filter on a Background Copy layer to sharpen an image, exploring layer modes such as Pin Light and Overlay. It can be effective with very soft images."

Obviously, this is inadequate to your question, but if you want the full text from where these quotes were taken, see the book, Photoshop for Photography, by Tom Ang. Even that won't answer all your questions, but it's the only reference I have that mentions this subject.

Grant


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Old Jan 14, 2006, 9:49 PM   #3
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So to you High Pass is more usable than USM, if I read this correct?
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Old Jan 17, 2006, 5:06 PM   #4
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I don't think you can say that HP sharpening is generally more usable than USM; otherwise it would be used a lot more than it is. Out of three books that I have on Photoshop, only one mentions using the High Pass filter in this way.

Here is yet another quote from a short tutorial on HP sharpening that I just found on the Luminous Landscapes website:

"But, as useful as it is, the USM tool has problems, and one of these is that it also increases any noise present in the file. Particularly noisy photographs therefore can suffer when USM is applied."

Click this link for the tutorial: http://www.luminous-landscape.com/tu...arpening.shtml

Actually, I found quite a lot of information on the web just by doing a search on the words, image sharpening high pass filter. Check it out!

Grant
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Old Feb 3, 2006, 9:06 AM   #5
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I don't know what is the common wisdom on that, I can just tell you what I do. Since HP sharpeningdoes not enhance the visibility of the noise I use it on images taken at high ISO. Other than that I've found thatHP changes the perceived contrast somewhat and works better on low contrast images.

The best is to try both on a particular image and see what looks better, neighter is a universal solution.

On a side note if you have a noisy image and you need to apply UM you can create an edge mask and import it as a selection, thus sharpening only the edges.
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