AV News 177 - August 2009
Applying sharpening before other editing processes can lead to unexpected
artifacts; therefore sharpening should be your final editing operation before
saving in .psd format prior to .jpg conversion for sequence use. Ensure that
your image preview is displayed at 100% before applying any sharpening to
enable correct visual assessment. Remember that AV's often project small
images onto large screens, this exaggerates any defects so great care must be
taken when applying any effect including sharpening. Photoshop provides
several tools under the Filters and Sharpen menu i.e. Sharpen, Sharpen
Edges, Sharpen More, Smart Sharpen and Unsharp Mask, of these the
Unsharp Mask is the most useful and controllable.
Its sliders named "Amount" and "Radius"
work in much the same way as those
found in Camera Raw but with greater
levels of adjustment. Because selected
areas can be sharpened individually
many levels of sharpening can be applied
to different parts of any image.
In our example picture (Page 12 Issue
176) of Warkworth Castle we could apply
140% sharpening to the castle
stonework, 65% to the foreground
grasses and zero sharpening to the sky,
or any other combination of values that
we find appropriate. Each image will have
its own particular need in respect of areas
to be sharpened and the amount which
only you as the author can determine.
It is rare for very large amounts of
sharpening to radically improve an image but can actually destroy an
otherwise good one. So what do these controls do? Let's start with the top
control named "Amount", this determines how much to increase the contrast
of pixels, for good quality high resolution images this amount may vary
between 75% and 200% although the maximum level can reach 500% but
this is not recommended. "Radius" determines the number of pixels
surrounding the edge pixels that effect sharpening. The greater the radius
value the wider the edge effect and more noticeable is the sharpening and
contrast change. Setting the radius value to between 1 and 2 is usually
recommended although the maximum is a ghastly 250. "Threshold"
determines how different the sharpened pixels must be from their
surrounding area before they are considered edge pixels and become
sharpened by the filter. Threshold values range from zero to 250, a value 6
for instance effect pixels that have tonal value difference of 6 or more, so if
adjacent pixels have tonal values of 100 and 105 i.e. less than a difference
of 6 they will not be affected. Zero sharpens all pixels in the selected area.
Don't allow these peculiar numbers to confuse you, play around with the
controls and observe.
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