Photoshop 101 – Lesson 2 – Sharpening

Take a look at this original unsharpened photo:

Something not quite right, eh?
The lighting is dramatic, with the sun providing a strong backlight, and fill-flash on the camera filling in the shadows and providing a highlight in the eyes. Exposure is correct.
But there’s still something not right…

Ah… The wrong part of the picture is sharp.
If you look carefully, the tree bark above her head is sharp, but her eyes are not sharp and the hair is quite blurred.

Can we improve this shot? Yes.
Can we make it perfect? No, not without some very advanced Photoshop work

Let’s get one thing straight -
Sharpening DOESN’T make unsharp photos sharper.
Sharpening DOES make slightly unsharp elements sharper

Huh… ?

• If it’s grossly out of focus, sharpening usually makes it worse.
• If it is slightly out of focus or afflicted with a tiny bit of motion-blurring, you might get lucky and get an apparent improvement if you don’t look too closely.
• If it’s just very slightly unsharp, the sharpening tool can make improvements if used judiciously.
• If it is sharp already, the sharpening greatly improves the texture.

Sharpening is used to increase the contrast of a change in colour at the junction between those colours.

To quote Dan Margulis (Photoshop grandmaster):
Sharpening, or, to use the technical term, unsharp masking, is an artificial method of creating apparent focus. It’s needed in most images, not because photographers are congenitally incapable of providing a properly focused product, but because the
output process messes things up.

What Dan means by this is that since a picture is made up of a number of pixels and a transition of one colour to another is never one dark pixel and the very next pixel is much lighter, but rather a gradual transition of pixels from one colour to the other. The following series of magnifications should make this clear.

Let’s look at a piece of the bark above her head that is in focus:

Looking closely at the bark, we see it looks reasonably sharp. Not very contrasty but sharp. Now look closely at the black crack in the middle of the picture (in the shape of a crescent). There is a sharp fall off from dark to light between the black crescent and the surrounding bark.

Oh Yeah?

Let’s look at it even closer at pixel level:

We see that it’s actually not such a sharp a fall-off at all. In fact, to go from a dark tone (the crescent shape) to a light tone (the surrounding bark) takes between 3 and 5 pixels in this particular image.

Now, what sharpening does is to increase the CONTRAST of that fall off, so that it appears to be sharper – i.e., it takes a transition of less pixels to go from one tone to another.

So we use the UNSHARP MASK tool (the most commonly used sharpening tool in Photoshop’s arsenal) to reduce the number of pixels used for the transition. We find this on the “Filter” pull-down menu (all versions of Photoshop):

Filter> Sharpen>UnsharpMask…

• Make sure the “preview checkbox is ticked so you can see the effect of the sliders.
• Drag the “amount” slider up and down and observe the results. We’ll take it to 300%.
• Set the radius at 1 pixel and the threshold at “0″ levels.
• Unless you are trying for a special effect, always leave the “Radius” and “Threshold” at these values, and play with the “amount” slider.

Look at the result and compare it to the previous image at pixel level.

It looks harsher and more contrasty because it uses less pixels to go from a dark to a light tone. Zooming out a bit and just looking at the bark, we see that it is a great improvement over the previous bark image:

Now if we finally zoom out to the whole image (shortcut: [Ctrl] [0] ) we see something very interesting:

The bark (which was already sharp) looks so sharp it looks quite rough! A large improvement.
The eyes look a little clearer.
The hair seems to be unchanged.

Let’s look at a close-up of the eyes and then see what happens when we over-sharpen…

The original eyes (no sharpening) looked like this:

The sharpened eyes (using an amount of 300%) look like this:

Looking back to the picture (full size), it’s a significant improvement over the original picture (at the beginning of this lesson).

If we sharpen another 300 % you begin to see some strange artifacts. The eyes begin to look a bit weird. A big enlargement will look like this:

However, looking at the full picture at full size, we can still get way with it around the eyes, except that now the bark is over-sharpened, starts glistening, and loses it’s richness:

Again look at the hair. After a total of 600% sharpening, there is no change to the hair at all!
Why? – Because the blur doesn’t have any sharp edges (by definition of a blur) that could have their contrast increased.

So – believe me now?

• Sharpening DOESN’T make blurred photos sharper.
• Sharpening DOES indeed make slightly out of focus elements sharper.