Sharpening In
Photoshop CS2
by Steve Randles
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No
matter how good your camera or photographic skills
you will on some photos need to sharpen them. Digital
photographers have never had it so good as some
of the newer models have built in sharpening. There
also exists many software products that will sharpen
your photograph for you, This writing is using Photoshop
CS2, and contains as much info that I know about
various methods of sharpening a photograph.
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First
of all, what is sharpening? Well its really about
contrasts where two edges, colours or even different
hues meet. The software finds these areas of differing
pixels and changes the colours of these meeting points,
to ensure there is a definable difference between
the two areas. Look at these simple grey blocks below
they are all zoomed in to 1200% but show the affect
sharpening has. The first is just shades of grey,
the second has had a sharpen filter run on it (Filter/Sharpen/Sharpen)
and the third image has had the sharpen filter run
on it twice.
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You
can see how in the second image, after the sharpen
filter has been used there are clearly two extra lines
of pixels and that the colour has changed in those,
on the dark grey side the line is darker and on the
lighter grey side the line is lighter, the contrast
between the two is easier to see, therefore it is
sharper. In the third image, where the sharpen filter
was used twice, these darker and lighter lines are
now more so, the contrast is greater, so the effect
is a little bit more sharp. You could at this point
say that the third image has gone too far, and it
probably has, but remember that these images are zoomed
to 1200%. One more thing we can learn from these images
is that the extra lines in the 2nd and 3rd images
are referred to as a "Halo" or "Haloing" which I'm
sure you will have heard before, or if you have not
you will at some point.
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Sharpening
Filters in Photoshop CS2
If
you click on Filter/Sharpen you will see a sub-menu
containing the following Photoshop Filters:
Sharpen
Sharpen Edges
Sharpen More
Smart Sharpen
Unsharp Mask
With
one of these filters, you can sharpen the contrast
on your photograph so that details appear to become
clearer, you can even clean up slight camera shake
too. But lets first look at each of the filters
and what they where designed to do.
Sharpen
(Filter/Sharpen/Sharpen)
The
Sharpen filter does just that, it will sharpen the
whole photograph without allowing you to change
any of the settings.
Sharpen
Edges (Filter/Sharpen/Sharpen Edges)
The
Sharpen Edges filter looks for areas of significant
colour change, ie edges ... and sharpens those.
Smart
Sharpen (Filter/Sharpen/Smart Sharpen)
Smart
sharpen goes a little bit further and allows you
to choose how much sharpening you want in both the
shadows and highlights, it also allows you to choose
the type of blur you want to remove, ie, Gaussian,
lens or motion blur. The latter being that of camera
shake, and you can also set the angle or direction
of the shake to be removed.
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Unsharp
mask (Filter/Sharpen/Unsharp Mask)
Probably
the most used of all the sharpening methods, and
the least understood in its use is the "Unsharp
Mask". Google unsharp mask and every piece of writing
you see on the subject will give you a start point
for the three settings contained there, the settings
are "Amount, Radius and Threshold" Well its hokum
pokum that the settings have a start point, if you
understand what each of the three settings do, you'll
no longer need to use the same settings as a start
every time you sharpen with the unsharp mask. Its
using start point settings that contributes to so
many over processed images online.
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Threshold
Lets
start with the setting at the bottom "Threshold",
this controls how much definition there needs to
be for the software to find edges or how much difference
there is between one pixel and it neighbour. The
software will analyse the threshold, then assess
the radius you want and apply the amount. If its
set at zero, the threshold will find many differences
in the photograph to sharpen, however if its raised
to 2 or 4 it will find less and less details to
sharpen. Do be cautious of taking this number too
high as you will end up sharpening in some areas
whilst ignoring others.
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Radius
This
controls how far "spread out" you want your sharpening
to be, for example if you had a photograph of a
match and you sharpen it with a radius of 1 or 2,
the width of the sharpened area would be about the
size of a thread of cotton or thinner. If you increased
the radius to around 30 the sharpening would blur
slightly but also increase to around a couple of
matches width, thus "spreading out". The bigger
the number here the larger the sharpening area becomes,
and blurred too. We can see how radius affects the
actual sharpening by zooming into pixels and changing
the setting below. This will help you see that at
web size or full resolution these sizes will be
different, hence why I have said there is no magic
starting point for USM settings.
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Amount
This
controls how strong the sharpening is that your
applying, the higher the number, the stronger it
will be. This should be your final adjustment before
hitting the OK button to finally apply your unsharp
mask settings to your photograph This can go all
the way up to 500%, but if you use all the settings
correctly you wont need to go that high. You can
see an example of amount in use below, to my mind
the image on the left is about right whilst the
image on the right is overdone. You'll see many
photographs online like the one on the right, with
that harsh almost prickly feeling to it, it just
looks too sharp to be realistic. Notice how the
stone bottom right has had its colour changed by
oversharpening in the second picture.
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How
I sharpen using the unsharp mask
First
of all, I make ALL of the other adjustments that
I want to make first, sharpening is the last thing
I want to do before I click save as. If I want different
sizes of image, ie for printing, web viewing and/or
thumbnails I will, before sharpening, copy the whole
document (Image/Duplicate) and resize each one for
each of the uses I need them for. Then I save the
document as a ".psd" (Photoshop) file....only now
am I ready to sharpen!
I
click Filter/Sharpen/Unsharp Mask and first of all
I make sure there is a tick in the preview box,
(a small window is in the unsharp mask that you
can zoom in and out of to view as you make changes
to the settings and by left clicking and dragging
you can move the previewed photo around I always
use this!) Now to adjust the first setting, threshold,
by default its set to zero so I use this to start
with and move on to "Radius", now using the knowledge
written above I know that there will be differences
in the radius between photos that are resized differently
that's why we are sharpening last and for each different
sized one. Between photos that are sized 3072 x
2048 and 800 x 533 a radius of lets say 2 will make
a huge difference on one and none at all on the
other.
So
with the threshold set at zero I set the radius
at one and then move to amount and start pushing
the slider up in chunks to see how its looking,
I'll probably jump about a bit say 100%, 200% then
move the preview photo around to see how the changes
take effect, (incidentally clicking on the preview
image will temporarily remove the previewed sharpen
effect) If the effect is too harsh I will move the
radius to two and then continue to amount again
and go through it as described above, 100%, 200%
previewing again. If its still too harsh a look
I'll continue raising the radius until either the
effect is spreading too much or I have a good sharp
image. There does come a point though, especially
in web size photos (800 x 533px for example) that
the radius will start to merge with the effect with
the next part of the image, so we return to the
start and raise the threshold to 1, then go to radius,
start at one again and raise your amount by 100%,
200% etc etc...previewing all the time, moving the
preview around. If necessary, if its too harsh still
raise the radius again and continue onto amount
etc etc.
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Here
is a numerical explanation of the last paragraph;
Threshold = T, Radius = R Amount = A:
T=
0
R= 1
A= 100%, 200%, 300% (If the effect is too harsh,
move to the next set)
T=
0
R= 2
A= 100%, 200%, 300% (If the effect is too harsh,
continue to increase the radius, testing the different
amounts. If that does not yield results then move
to the next example below)
T=
1
R= 1
A= 100%, 200%, 300% (If the effect is too harsh,
move to the next set)
T=
1
R= 2
A= 100%, 200%, 300%
This
is the best way to determine the settings for unsharp
mask, there are no start points, aside from starting
at zero and working up.
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Oh, Ow or Wow?
By
now you should have an understanding of what each
of the settings in the unsharp mask do, and how
to apply them for the best results for the different
sizes of photographs your likely to want to edit.
I can sharpen an photo in less than 30 seconds,
if its your first time using unsharp mask it may
take you five minutes, so what who cares how long
it takes to sharpen when you consider that sharpening
will make the difference between "Oh" (its just
a photograph) "Ow" (that hurts my eyes - oversharpened)
and "Wow" (Would you look at that, what a fantastic
photo, its the best one I have seen all year!!!)
So what do you want it to be, Oh, Ow or Wow?
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Sharpening
using the "High Pass Filter"
Nice
and simple this one and worth a try, again have
every thing done to the photo that your likely to
want doing and save a copy of the file before continuing.
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1. In the layers palette, duplicate your layer.
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2. Click Filter/Other/High Pass and your photo will
now turn grey as the high pass filter box opens
Ensure the preview box is ticked.
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3. Move the slider up or down until all of the
picture is grey but not flat grey, you want it
just grey so that no colour from your photo is
showing. Click OK when done.
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4. Go to your layers palette and select either Soft
Light/Hard Light/Overlay from the blending modes dropdown
box.
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5. When your happy, flatten your image (Layer/Flatten
Image) and save using "Save as". |
All
done, quite a striking difference!!
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when you sharpen a photograph you can suffer from
"colour noise" this will show as multicoloured speckles
on you photograph and it can become a trade off to
add sharpness at the cost of adding noise, or removing
noise and also removing sharpness. However there is
a little known way of sharpening that addresses this
issue, read on. |
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Sharpening in Lab Mode
This
is sharpening of the details held within the lightness
channel of your image, this avoids sharpening the
colours which are held in the a & b channels.
Normally we work in RGB mode in Photoshop as photographers,
now we are going to break that and swap to "Lab
Color" (this article is long enough so I'll spare
you a Lab color description - Google it!) This method
is best suited to full resolution photos. Lets get
started: For this part I'll be working on a photograph
3072 x 2048 but zoomed out to keep the screenshots
small for here.
Make
all your adjustments to your photograph, save a
copy.
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1. Click on Image/Mode then click on "Lab Color" |
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2. Hold down the "Ctrl" and "Alt" keys and press
the "1" key, this loads the lightness channel
as a selection.
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3. Now click Select/Inverse to inverse your selection
then hold "Ctrl" and press "h" to hide the selection
border.
4. Now go to your channels palette and select the
lightness channel, (this is the one we will sharpen
and because this channel does not hold the colour
we are avoiding colour noise artefacts) Your photo
will turn Black and white.
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5. Now click Filter/Unsharp Mask and try amount 400%,
radius 1 and threshold 2 and click okay
6. Click again on Filter/Unsharp Mask and leave amount
set at 400% and threshold at 2, but now bring the
Radius all the way to the left (zero) and start moving
it to the right until shape appears to come back to
the photo, that should be somewhere between 10-30,
(don't worry about the overall look here) once shape
has returned to the photo lower the amount to around
50 or what looks good to you and click okay.
7. Now hold the "Ctrl" key again and press the "d"
key to cancel the selection.
8. And back in the channels palette click the "Lab"
channel to reveal your nicely sharpened photo.
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9. To finish off click on Image/Mode/RGB Colour
and you can then save your finished sharpened image.
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Remember
in all Photograph editing that "Less is more"
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