Photo Editing - Sharpening
First of all let me say that not all blurred pictures
will be saved by the 'sharpen' filter. Sharpening
a photo in Photoshop will not save any shot that is
very blurred, nor will it save photos where the point
of focus is in the wrong place, but it may help with
a picture that is a little bit 'soft' due to a shortage
of light forcing the use of a slower than ideal shutter
speed.
In Photoshop, under the filters menu, there is a
submenu called 'Sharpen' where you will find several
choices. The bottom two choices, 'Unsharp Mask' and
'Smart Sharpen' open boxes full of faders that you
can twiddle. The other choices are presets that will
give you a quick fix in a hurry but do not have any
adjustments, so we will ignore them. At this point
I have to confess that I am still using Photoshop
CS2 so there might be new filters in CS3 that I am
not aware of, in fact I have only just discovered
the 'Smart Sharpen' option while preparing for this
article. I will leave the 'Smart Sharpen' option until
later and start with my tried and tested favourite
the 'Unsharp Mask'. |
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There are three sliders in the 'Unsharp
Mask' window, the top one 'Amount' does what it says
on the can, it adjusts the amount of sharpening.
The 'Radius' slider adjusts the width of the halos
that are created. Basically the way sharpening works
is that it finds the edges in your picture by looking
for areas of high contrast and increases the apparent
sharpness by adding dark and light halos. If you look
at the edge of the apple in the picture on the left
you can see a dark line, rather like a pencil line
along the edge.
The 'Threshold' slider allows you to specifly how
much contrast difference there has to be before that
area is sharpened. Set this fader too low and the
picture will appear grainy as there will be a sharpening
halo around almost every pixel. Set the value too
high and only clearly defined edges will be sharpened
which can make the blurred bits look even more blurred.
This filter needs to be used very carefully to achieve
the best effect. Too much sharpening can make the
picture look false. On the other hand, if you look
for every single little tell-tale detail and every
little line, you end up not using the filter at all. |
How Much Sharpening?
What Settings to Use?
The final adjustment of the sliders is down to you
and will vary from picture to picture, but here are
some guidelines to get you started. The amount of
sharpening you can get away with, especially the 'Radius'
settings, depend on the resolution of the image. If
it is an image destined for viewing on the screen
the resolution of the image should be 72 pixels per
inch. (some say 96ppi) If the image is destined for
print the resolution should be 300ppi or as near as
you can get it to that.
If you are planning to change the size of an image,
by this I mean the file size, make sure you do the
sharpening after the sizing, especially with JPEGS.
Sharpening should be the last thing you do in Photoshop.
For an image that is 72ppi you should use a radius
setting of about 0.4 or 0.5 pixels. Use less than
this and you won't see much happening, use more and
the halos will start to look too obvious. For a print
image, 300ppi, start with a setting between 1 pixel
and 1.7 pixels.
I prefer to use as small a 'Radius' setting as possible
and push the 'Sharpen' slider quite high.
I read somewhere a while ago that the 'Threshold'
slider should be set at about 3 levels. But I find
that I use it anywhere between 0 and 20 or so. This
is one you have to play with yourself as it really
does depend on the type of picture. |
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Here's a picture ripe for sharpening, although
I used a tripod it was taken at a very slow
shutter speed in available light. The depth
of field is not great so we are never going
to get the whole photo in focus but at least
the middle apple should be sharp. I have made
the pictures nice and large so you can see the
effects better.
As we are using this on the web, the radius
setting should be about 0.4 pixels. So set that
first and then set the 'Threshold' slider to
zero for now. Move the 'Sharpen' slider from
side to side to see what it will do. Normally
you need to move it past 80 to see anything
happening at all. If you get all the way to
500 and the picture is still not sharp enough
then you need to set the 'Radius' higher.
Below you can see the settings I chose and
the result. Overall it is probably the best
compromise. There is a white halo around the
stalk which is a bit more obvious than I would
like and the black line between the apples is
a bit bold but, as I said before, if you look
for every bit of evidence you would end up not
using the filter at all. The low 'Threshold'
setting has sharpened up the skin of the apple
which is where we really wanted to see the improvement.
The stalk of the middle apple is now as sharp
as you could want.
Sharpness always used to be the ultimate goal
in my pictures but nowadays I can see that you
can sometimes have too much sharpness and soft
focus has it's place too. |
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Here's a version that has been
sharpened way too much, just so you can see
all the bad things to watch out for. You can
clearly see the black and white halos around
all the edges. This is what we need to minimise.
So, use the sharpening filter with great care,
better still, get the focus right in the camera.
Finally a quick look below at the 'Smart Sharpen'
filter. This has many more knobs and dials to
play with and so is a bit confusing at first.
The left tab is much the same as we saw before
but we now have a drop down menu with three
different types of blur to choose from. 'Gausian
Blur' is what we have been fixing with the other
filter so 'Lens Blur' in this case or 'Motion
Blur' when appropriate would be a better choice
for photographers. The shadow and highlight
tabs give you a chance to minimize the halos
and, as you can see from the preview, they can
be greatly reduced. The halo around the stalk
is gone and the black line between the two apples
is almost gone.
This filter then, used carefully, can give
you a more subtle effect. Look at all three
pictures carefully, the second picture is obviously
sharper but with a few tell-tale signs of sharpening,
the bottom picture is more subtle but does not
appear quite so sharp.
In the end, the choice is up to you. You will
probably find that you over sharpen everything
at first, so make sure you work on a copy file
and keep the original safely out of harm's way.
I now keep all original files straight from
the camera and only ever work on copies. That
way, as my skills improve, I can go back to
the original and try a new edit. |
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