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Photoshop Tutorial - Sharpening using "Unsharp mask"


All images from a digital source, whether it be from a digital camera or scanned slide will benefit from sharpening with Photoshop's"unsharp mask" filter (USM) . Just how much will depend on a number of factors, such as whether your camera applies sharpening automatically as part of the in-camera processing and how sharp (in-focus) the original image is to start with.

Sharpening is best achieved as the last process in the digital workflow, so if you can change your camera parameters (via the on screen menus) to little or no sharpening that is preferable. Similarly if you are working with raw files, it is usually better to switch sharpening off in the raw converter.

There are several sharpening tools that Photoshop offers, but the only one I would recommend is the unsharp mask filter. Forget the others they are pretty poor and offer no control.

* Update - In Photoshop CS2 and CS3 there is a new filter called Smart sharpen - which is Adobe's most recent attempt at producing a good quality sharpener with minimal artifacts and holos.It is worth trying this too as it can give excellent results, but runs very slowly on anything but the most powerful of computers.

Back to Unsharp mask.......

Open your image in Photoshop and select filter >sharpen>unsharp mask.


  • Next - and this is very important, view the image at 100% on the screen as I have done above by
    selecting View > actual pixels.This way you can really see what is happening as you make adjustments.
  • You will see three sliders - amount, radius and threshold. These must be juggled to get the best out of the image and I will now show you a simple way of optimising them. I will not resorting to technical
    descriptions
    of what the sliders actually do, as it is not essential for carrying out these adjustments.
    Before making the necessary adjustments, set the sliders as follows:
  • Adjust the amount slider to 200%
  • Set the radius slider to 0.1 which is it's minimum value.
  • Set the threshold slider to 0
  • If you hold the cursor over the image box (in the window over the sliders) you will see that the symbol
    changes from a cursor to a hand. Using the hand you can drag the image around until it contains something critical - like the eye of the subject. You may need to move the image around repeatedly during the adjustments to check that high contrast boundaries are not producing ugly halos, also that you have not sharpened grain in unwanted parts of the image unnecessarily.
  • Increase the radius slider until the desired amount of sharpening is achieved. In the image of the partridge,
    I was watching the eye and subtle feather detail beneath it to gauge sharpness. Then I checked the area of
    high contrast between the breast and the grassy background to ensure I wasn't creating halos.
  • Looking at the degree of grain in the background, adjust the threshold slider until the image remains
    sharp, but the background grain is not excessive. These two sliders are a compromise.
  • Now revisit the amount slider and fine-tune the sharpness up or down until the image looks good. It is
    ok to oversharpen a little at this stage as in the next step we are going to tone it down a little again. Click
    ok to apply the USM filter.
  • Click on Edit>Fade unsharp mask. Change the mode from Normal to Luminosity and adjust the opacity
    slider until the image looks really good and click OK.

    You will usually find that settings for the various sliders end up within the following ranges:
  • Amount - 100-300 depending on how sharp the original image was to begin with. 120%-200% being
    typical
  • Radius - recommended setting is usually between 1 and 2
  • Threshold - recommended setting is usually between 0 and 4. If you have used a low iso setting on the
    camera you can get usually get away with using a setting of 0 - which gives maximum perceived detail
    as grain should be minimal.

    CANON EOS 1D MK II settings.

    This is the camera that I use, and as it has a strong anti-alias filter the images that it produces straight from
    the camera tend to look very soft. Some reviews of this camera complain that the images are not sharp
    with this camera - but that is not true, they sharpen up beautifully with USM.

    An initial setting to try which applies a moderate amount of sharpening is :

    Amount - 300%
    Radius 0.3
    Threshold 0

    You can then tweak from here if necessary.

    ADVANCED USM TECHNIQUES

    There are refinements of the unsharp mask technique, such as selective sharpening using selections,
    sharpening selected channels, progressive sharpening, sharpening with layer masks etc. For more tutorials
    on these subjects please click here:

    Advanced unsharp mask techniques