Announcement

Collapse
No announcement yet.

[Definition] Unsharp Masking

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • [Definition] Unsharp Masking

    "Unsharp Masking" sounds like a bit of an oxymoron. The term goes back to pre-digital prepress days when they'd make an image appear sharper by sandwiching it with a slightly blurred (unsharp) copy of the same image.

    The effect then was the same as the digital effect now: the intersecting areas of light and dark in the image have an increased local contrast, which gives the appearance of increasing sharpness.

    You can see the process more clearly if you grossly overapply USM to an image. The intersection contrast will be exagerated to a degree where they'll actually bloom over into each other, causing the "halo" effect so typical of oversharpened images.

    Calculated the actual degree of USM to apply is actually rather complicated, since you need to take into consideration the qualities of the output device, the size of the image, and even the typical viewing distance.

    It's important to remember that you're only giving an impression of increased sharpness, not actually increasing the sharpness, and that you're technically degrading the image. Also, since there are so many variables, you'll probably want to make separate printing copies of your image clearly labeled as to destination and apply USM specifically for that destination. This allows your original to remain unsharpened so you can make another copy should you need to prepare it for a different destination.
    Learn by teaching
    Take responsibility for learning

  • #2
    When sharpening. I do a channel,by channel sharpening.
    When in CMYK, I sharpen the black and cyan channels only. When in RGB, I sharpen the red channel only. When in LAB, the L channel only. And always fading the effect of the sharpening to Luminosity mode. No color shifts this way.

    Just so happens, here's an article on this method.

    Sharpening

    Comment


    • #3
      Thanks for that VERY useful tip, John. I'm off to try it out right now!!

      Comment


      • #4
        Chuck, it depends on whether the R or G is best in RGB (and perhaps even the B in some cases) - if the image is of one major hue only. In general for an image with a good range of luminosity and colour, then the G is often the best choice for a luminosity blend sharpen.

        I personally prefer a luminosity blend or fade rather than converting to LAB or HSB or anything. Where possible I avoid mode changes or do these in a dupe for targeted reblending back into the original in luminosity or colour blend modes.

        As John mentioned, when doing separate channel sharpening - the luminosity blend is important to stop colour halo shifts (just as luminance sharpening is important when sharpening the colour composite channel).

        More links on sharpening can be found at my links to more links:

        http://members.ozemail.com.au/~binar...V_links.html#S

        Regards,

        Stephen Marsh.

        Comment


        • #5
          <<Therefore, I would have thought that the green, rather than red channel would be the one to filter.>>

          As Steven just stated...... That depends on the channel. Let me explain why I sharpen as I stated. I deal with a lot of faces. So the red channel is best for me. But one thing.... You have to look in your channels to see what going on in them, like noise,artifacts,ect...ect.. which you don't want to sharpen.
          Btw. Steven has a great web page with links as well that go into this. Check it out. Btw. I don't have a web page for P.S. .Just don't seem to have the time. Anyway it would take me forever to make(type) one.
          John

          Comment


          • #6
            And the reason why the red(when in rgb) channel. Since its lighter in faces, so the sharpening that takes place. It will not sharpen the detail in the faces. While sharpening other parts of the picture(hair,clothing, eyes,ect...ect...)

            You can also sharpen with layer masks,actions,custom filter, but when using these things. You have to know whats going on and how these things affect the image when sharpening.
            Like some plug-ins for sharpening. Their not bad. If one does not understand the sharpening process. But you can do the same in P.S. and better when you know the sharpening process in p.s., and the techniques that go beyond the typical all channel sharpen.

            I feel its very important to look in your channels, when sharpening. Sometimes one doesn't have that kind of time though when working on a lot of images a day. So that's where actions, plug-ins and an all channel sharpen comes in handy for sharpening.
            It's like in martial arts. You have to know when to use your feet instead of your hands. Execpt in kempo. That form is more, using your hands than your feet.

            Comment

            Related Topics

            Collapse

            • Ed_L
              Sharpening without an Aura
              by Ed_L
              Patrick,

              I have two questions (and that's before I tried the technique) .
              You suggest changing from 8 bit to 16 bit mode so as not to lose histogram quality. I've always been under the impression that changing from 8 bit to 16 bit mode does nothing for the quality of the image....
              11-24-2001, 03:54 PM
            • philcrean
              LAB Sharpening method
              by philcrean
              Hi all

              I'm new here and have been searching for a method to sharpen using LAB lightness channel. I can't find any info on this by searching forums or tutorials.
              Can someone point me towards something if I've missed it, or, can you offer an insight into this method?

              ...
              05-27-2009, 07:00 AM
            • snead
              Fine Adjusting your Sharpening
              by snead
              I have found in my RGB work flow there is a fine line between sharpening images properly and over sharpening. I have been playing with a simple method of “peaking” the image sharpness without going over the edge (pardon the bun!). Here's how;

              After a preliminary modest sharpening,...
              01-12-2004, 09:27 AM
            • skydog
              There must be a better way...
              by skydog
              Any suggestions on avoiding or retouching halos? I have a decent camera and good glass, but when I sharpen...even a little I see those dreadful halos. I typically used layer>desaturate>a little highpass filer and overlay to sharpen which does a good job, but I hate the halos. Typically I shot...
              10-18-2009, 07:50 PM
            • VCOOPER
              Sharpening photos
              by VCOOPER
              Working with restorations and even with current photos I have found that the photos tend to be blurry if they are aged or if there was underexposure or camera movement. For CS3 it appears there are many plugins for purchase and also recommendation of using USM on the LAB mode. I have not really been...
              08-25-2008, 07:24 PM
            Working...
            X