Why all Digital images need SHARPENING

[ricktas]

I thought it would be good to explain why ALL digital images need to undergo some sharpening.

A digital camera sensor is made up of millions of tiny lenses, each one captures one colour and a brightness level. Then through an amazing process, this analogue light capture is turned into the digital colour image we see on our LCD's and Computer screens.

Below is an image of a sensor, sitting on a Bayer pattern filter, one of a few methods used to capture our images, but probably the most common.



Now each pixel site is a small (we are talking microns) width, and they laid out side by side, checker board style on the image sensor. Like this:


(image courtesy IBM, taken with an electron microscope of an actual image sensor)

Notice how each pixel site is separated by that small area (the tan part in the image above), well that is the reason why ALL digital images need sharpening. Your images when captured have a small area between each pixel site on the sensor where no light is captured (we are talking really small), but that 'dead' area, means that all digital images are not as sharp as they could be straight out of the camera. The technology inside your camera fills in this 'dead' area by alligning the data from each pixel up against the data from the neighbouring pixels, it is clever, but the result is your digital images straight from your camera will always be a little soft.

So sharpening your digital images is an important part of your workflow.

There are various methods of sharpening available, most commonly used would be USM (Un-Sharp Mask) a term carried over from film and dark room processing. It is worth investigating other sharpening methods (and there are a few).

I hope this has helped members understand why they need to sharpen their digital images.

I am leaving this thread open as members can discuss the various methods they employ to sharpen their images, and other members can learn of maybe better ways to do it.

[ricktas]

I never use USM.

My personal way of sharpening, i used to do step-by step, (before i knew how to create actions).

But now the wonderful people at Action Central have basically made an action that does what i was doing (actually a bit better than i was achieving).

I use Dave's Sharpening Actions - in particular the High Pass Sharpening, from www.atncentral.com

[hoffy]

What is the difference/benifit of using this action as opposed to USM?

[ricktas]

High Pass sharpening has two big advantages. The first advantage is that the sharpening is done on a separate layer. With High Pass sharpening applied on a separate layer, not only can the sharpening be adjusted at a later date but also can be completely undone simply by deleting the layer that was added during the High Pass Sharpening process.

The second advantage is that the High Pass sharpening technique uses the High Pass filter, which isolates the edges. Thus, High Pass sharpening applies sharpening primarily to the edges where it is needed and protects smoother areas from the sharpening.

[ricktas]

this is how you can do High Pass Sharpening manually.

On the Layer palette select your Background Layer and right click. Select Duplicate Layer.

With this new layer highlighted select Filter / Other / High Pass. Set the Radius to 10 and click OK.
Zoom into your image to Actual Pixels level so you can better see what you're going to do next.
Go back to the Layer Palette and select Hard Light (you can also select soft light for a variation) from the left drop down.
Now go to the Opacity Slider and select a level of sharpening that seems best to you. Usually something between 20% and 70% will be best.

[hoffy]

OK, thanks! Looks like I had part of it right!. My action was to create a separate layer & apply USM to that (really go over the top with it). I would then reduce the opacity of the USM layer to what looks acceptable.

I will try the High pass method. Sounds interesting

[arthurking83]

This small tidbit of info is specific to Nikon(D70s in particular!)
In camera Sharpening is simply USM, but on the camera.

From the info I've read on this phenomenon, the images straight form the camera also have to deal with an 'anti alias filter' which also determines how sharp an image come straight from the camera without any in camera sharpness applied.
Each camera has different strengths of AA filter, and the D70s has quite a strong application.
Problem is that you get moirè in high frequency repetitive patterns!

All my PP is done in CaptureNX, and after reading a few bits of info on how to use it more effectively, I've read that settings between 45-55% intensity, 4 or 5 radiusand 4 or 5 threshold is about the ideal, if you applied no image sharpening at all in camera.
That's what I used to use regularly as a general default for all my images, up till the D300 came along.

From this I assume that each camera is different and requires different settings for optimal IQ.

I know from reading that D50 and D80 has a weaker AA filter and I assume a D200 would too whereas a D100 I think has a stronger AA filter. So if you had a D50 and use NX, you may want to apply slightly stronger USM settings.
The info is out there, and many folks have experimented and posted their findings.. somewhere?

The moral of the story is that various models of camera may require different levels of adjustment .. so what works for 'him', may not necessarily work for 'her'

Hope this helps too!

[hoffy]

I am also under the impression that the best way to apply sharpness is at the PC, not at the camera (from the resources that I have read)

[I @ M]

I know from reading that D50 and D80 has a weaker AA filter and I assume a D200 would too whereas a D100 I think has a stronger AA filter. So if you had a D50 and use NX, you may want to apply slightly stronger USM settings.

I am in the middle of sorting and processing 380 images taken yesterday, they will all be saved in their NEF form on the backup but during processing they are receiving around the 20 % to 30% USM as the last stage before conversion to JPEG.
Once converted to JPEG they are receiving between 10% and 20% USM.
The amount of sharpening needed on this batch is being dictated by the amount of noise reduction applied to some images.

A very timely and well put together article Rick.

[Sammi]

In the january issue of Australian Photography it has a large article on the different types of sharpening, worth the look
Also has a good section on wildflower macro photography and at $6.75 its pretty darn cheap

[cwphoto]

Another reason is that pixels aren't very good at resolving edges when the edge lies partly over a pixel, the resultant 'exposure is say grey instead of black or white. So sharpening can increase the contrast level at this edge to compensate.

[jim]

Hi Rick. Your brief High Pass Sharpening tutorial is about the same as the one I copied off The Luminous Landscape a few months ago. I really must give it a go, using USM I really tend to stuff up my BGs.

[ricktas]

Hi Rick. Your brief High Pass Sharpening tutorial is about the same as the one I copied off The Luminous Landscape a few months ago. I really must give it a go, using USM I really tend to stuff up my BGs.

Yeah, i think thats where i got it from to start with, I have a word doc with all sorts of stuff like that in it, that i can refer to on occasions.

[Helen S]

In the january issue of Australian Photography it has a large article on the different types of sharpening, worth the look
Also has a good section on wildflower macro photography and at $6.75 its pretty darn cheap

As a member of the Australian Photographic Society it's even cheaper.

Evening all. When sharpening an image I change to LAB colour mode and only sharpen the Lightness Channel. This seems to work quite well for the most part.

Canon actually recommend that images are sharpened post process because of the AA filter. They recommend that you start at 300% in Photoshop and then bring the slider back to what is acceptable. I have a complete PDF file on this on one of my hard drives.

[Sammi]

[QUOTE=Osprey;85304]As a member of the Australian Photographic Society it's even cheaper.
QUOTE]

Being a student i get it for $47 a year,12 issues which is a big bonus.

[DanNG]

As a member of the Australian Photographic Society it's even cheaper.

Evening all. When sharpening an image I change to LAB colour mode and only sharpen the Lightness Channel. This seems to work quite well for the most part.

Canon actually recommend that images are sharpened post process because of the AA filter. They recommend that you start at 300% in Photoshop and then bring the slider back to what is acceptable. I have a complete PDF file on this on one of my hard drives.

I also change to LAB and sharpen the lightness channel, I find smart sharpen works quite well. Im quite addicted to adding local contrast enhancement... using USM. (10/15/0)

[Shane.R]

Yesterday I was playing around with an old pic that has being cropped shopped cut n paste. I enlarged pic to 7000pixels then applied some sharpening. Then reduced to original size. (if you don't have a super dooper fast computer - I don't) then your patience may be tested.

[jim]

You can also:

-Sharpen with Unsharp Mask (oversharpen a little)

-Go to EDIT > Fade Filter and change the blend mode to Luminance

-Use Fade Opacity slider to adjust to the required level of sharpening.

[mickeymoo21]

I also change to LAB and sharpen the lightness channel, I found this method in one of Scott Kelby's Adobe Photoshop books I think, seems to work alright for me.

[I @ M]

Ever since Rick posted this thread I have been trying to get my head around the processing of photos and the importance of the sharpening aspect.

This thread has been invaluable for me, getting the correct amount of sharpening in a shot provides much more than just crisp edges, it can create a lot of depth and a certain amount of contrast to a shot that you knew was there but didn't see on the screen when you first looked at it.

I thought I would contribute a rundown of the directions to using the high pass sharpening method in Capture NX. The method below is taken from another site and it explains step by step how to achieve a very good natural looking sharpening result.

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Capture NX
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On the Edit List:
Click New Step (at the bottom).

On the New Step:
Click Select Adjustment > Focus > High Pass to bring up the High Pass popup.

On the High Pass popup set the Radius and exit:
Slide Radius = 2 px (or fill in box).
Click OK to exit.

You will now see your photo turn grey only the edges of your subject highlighted.
Be patient with NX here. Sometimes it takes a few seconds for the highlighting to appear
depending on what else you are running.

On the High Pass Step (back on Edit List):
Click Opacity to bring up the Opacity popup.

On the Opacity popup:
Click All > Luminance & Chrominance
Click Blending Mode > Overlay
Slide Opacity (Luminance Channel) > 100%
Slide Opacity (Chrominance Channel) > 0 %
Click OK to exit.

Now you will see your photo restored with the High Pass Overlay sharpening applied everywhere.

If you want to selectively apply the sharpening to certain areas of your photo,
then on the F6 panel:
Click Brush Tool + to bring up a brush.
Right click the circular brush pattern to set your Brush's Size, Hardness and Opacity as desired.
I usually use about 50-75% brush Hardness to start with and 100% brush Opacity.
Now just brush over the areas you wish to sharpen. Adjust your brush size as needed.

While applying this sharpening, I suggest having the photo at 50% size at least.
If you are sharpening small details, then you might want to go to 75-100% size.
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Selecting Radius:
Usually 1, 2 or 3 pixels of High Pass is sufficient for Overlay sharpening.
You want to choose a radius that provides you with the highlighted edges of your subject
without those edges becoming too wide.
If you begin to see lots of colour, you've set the radius too large.
The idea in keeping the radius small is to avoid "sharpening halos".

Feathering the Sharpened Area:
Feathering provides some gradation between those areas where you have applied a Brush effect
and those areas left un-Brushed.
Feathering when sharpening helps avoid halos
and keeps sharpening from slopping over too much
into areas like sky where you don't want sharpening artifacts.

Re-adjusting the Opacity:
If the High Pass sharpening you have applied looks too strong when you are done,
you can try resetting Luminance Opacity slider to something less than 100%.

"Erasing" Sharpening:
If you accidently sharpened something, you can click the Brush Tool (-) to erase the sharpening.
Be sure that you have the High Pass Step on the Edit List expanded when you do this.

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The method listed above is simple, totally reversible and doesn't need a any applications of layers etc. Depending on the photo being sharpened, the application of varying degrees of the luminance or chrominance channels can alter the sharpening effect to quite a strong degree, but as the instructions listed above say, it generally looks better with the chrominance channel set to zero.