The image tool “Unsharp Mask” was used to sharpen the close-up of a butterfly. This tool is a powerful instrument
to create images that are laser sharp - or to use excessive sharpening as a creative effect. Comparing the original
with the result demonstrates the need to operate with a gentle touch.
As the name “Unsharp Mask” implies, this
tool functions by first creating an
intentionally softened version of the
image. Combining that version with the
original will yield a mostly gray mask, but
with edges well defined.
The mask is then applied against the
original with an algorithm that amplifies the
edges, giving the image extra sharpness.
The “Radius” controls the number of pixels
involved in creating the softened version
of the original. This value depends on the
overall image size. An image with a large
number of pixels might require a larger
radius. Too large a radius can result in a
halo along the edges.
“Calculate on Luminance only” is set by
default and prevents undesirable color
hues along the edges.
The “Threshold” defines the difference in brightness between neighboring pixels before an edge is assumed and
sharpening is applied. When adding sharpness, one has to be careful about unwanted graininess or “noise”. A
higher threshold value will limit this side-effect. The default threshold is set to 0, which means that all pixels of
the mask are included in the sharpening.
Portraits often require a
higher threshold to
maintain the soft skin
With digital photography,
some sharpening is almost
always warranted. There is
no perfect recipe for the
“Unsharp Mask” tool; each
image will require careful
adjustments of the tool’s
settings. However, the
potential for greatly
improving an image more
than makes up for the time
invested in experimenting
with this tool.