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09/21/2004 02:18:13 AM · #1 |
| What does the unsharp mask in Photoshop do? It seems like it just blurs the image. Hows it different from just blurring the image? |
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09/21/2004 02:19:18 AM · #2 |
blurs??
well its used to sharpen the edges and not blur it in any manner unless I am terribly wrong. |
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09/21/2004 02:29:31 AM · #3 |
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09/21/2004 02:54:41 AM · #4 |
if it sharpens, then why call it unsharp mask? also, there is a sharpen tool... what is the difference between the two?
Message edited by author 2004-09-21 02:54:56.
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09/21/2004 02:57:06 AM · #5 |
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09/21/2004 03:20:31 AM · #6 |
I've not read the article so I can't say how the two differ but I can tell you that unsharp mask is more controllable and seems to do a nicer job than the basic sharpening filter.
Here's what I think it probably does based only on having used it:
USM has three sliders - Amount, Radius and Threshold. What it does is look accross the image for places where adjascent pixels differ from each other. What qualifies as sufficiently "different" is set by the Threshold slider.
When it finds pixels that differ it adds darkens the pixels on the darker side and lightens the pixels on the lighter side - giving the impression of sharpness. The amount of lightening or darkening is controlled by the Amount slider and the number of affected pixels in each direction that are affected is controlled by the radius.
John |
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09/21/2004 09:35:11 AM · #7 |
Originally posted by Anachronite:
if it sharpens, then why call it unsharp mask? also, there is a sharpen tool... what is the difference between the two? |
In the good old days of optical photography, a mask was made by "sandwiching" two negatives (one lightly out of focus) to create a mask (I think of the edges only) through which the "edges" would get the differential exposure. The mask itself was made by "unsharpening" the image.
Sharpen does somewhat the same thing, but with fix/arbitrary settings; USM has controls.
floyd's description is pretty accurate. If you do a Forum search, you'll find some other, slightly more detailed responses.
I have some examples in this gallery at pBase.
Message edited by author 2004-09-21 09:59:49. |
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09/21/2004 09:42:50 AM · #8 |
| There is also a good tudoral dealing with digital sharpening on this site. Click here to look at it |
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