[Leica] Sharpening - was: A very fleeting blossom

[abridge at gmail.com (Adam Bridge)]

Hi Ted. Thanks for your comments on the image.

You ask about sharpening of digital images. The answer is that yes,
you should sharpen digital images - at least those that come from the
Canon cameras (Canon recommends this and gives a good starting point.)

In almost all digital cameras there's an "anti-aliasing" filter in the
light path between the back of the lens and the image sensor. It's
there to eliminate artifacts in fine detail caused by the way the
digital cells, which are in a linear array, "sample" the incoming
light.

The people who are concerned with the transformation between analog
and digital worlds are aware that the transformation can cause a
perception of things which are not there. It's just a fact of life -
consider that lots of handwaving, a bunch of math, and a whole lot of
chalkboard illustrations have happened and now you believe that
aliasing actually DOES happen.

So you really do need to do a bit of sharpening to your digital images
after you've imported them into your computer.

To do this open an image in Photoshop and then go up to
Filters>Sharpen>Unsharp Mask which will give you a dialog box with
three controls and a window that shows a small part of your entire
image. There's also a button to make the changes, a button so you can
cancel out, and a check box so you can preview the result on your
screen (which is normally checked).

For my camera (a 1Ds MkII) I set amount to 300, Radius to 0.3 and
Threshold to 0 levels. Then you take your mouse and click in the image
window. What you see with the mouse button held down is the image with
no sharpening applied. Release the button and you'll see what happens
when the sharpening is applied. In portraits you'll be wanting to
focus in on the areas around the eyes. You can click and drag in the
little image preview to look at different parts of the image OR you
can move your mouse pointer over the big image and see that it becomes
a little box that shows you the part of the image that will be
previewed.

You can adjust the "Amount" and "Radius" controls to your heart's
content but in general I do very little sharpening beyond that at
first.

At this point you have accounted for the anti-alias filter that the
manufacturer placed between the lens and image sensor. The digital
image processing that you called up in the form of the Unsharp Mask
has done it's magic.

Is this effect subtle? You bet.

Now when you reduce an image from full-size down to say 800 x 566 or
whatever to put on the web, then you'll want to do a bit of sharpening
again. But the settings you'd use will be vastly different than the
ones you chose at first.

But that's a different story.

I'm sure others on this list can do a better explaination than I have
done. And I'll look online and see if I can find a good, accessible,
tutorial.

I should note that the Leica DMR back does NOT have an anti-aliasing
filter between the lens and the sensor so it should not, in theory,
require this preliminary sharpening. However, I don't believe in free
lunches and all that math I took and all those digital signal
processing courses I took in college just SCREAM at me that the
activity going on within the camera is mucking about with the image as
much as the unsharp function is in Photoshop. But that's just me and
the state of the art in digital signal processing is decades further
along than when I studied it. (Z-transform...shuddering).

I hope this answered your question without raising too many others.

The effects I've discussed are small but real. You can see them in 8 x
10 prints although you need to look. If you print larger then you'll
need to pay a bit more attention to sharpening. I've just done a bit
of a Google search and I can't find a suitable tutorial for you. Like
anything else you can take these tools to the lunatic fringe area and
people do.

So good luck. And feel free to ask more questions!

Adam Bridge

On 2/16/06, Ted Grant <tedgrant@shaw.ca> wrote:
> Adam Bridge showed:
> >We've had extraordinarily warm weather, a few records set, so the
> >trees are blooming. This almond tree in the back yard has had a
> >fabulous blossom set.
> >But tonight we're going to get a freeze, down into the 20s, so these
> >> blossoms are fleeting:
> ><http://www.adambridge.com/Photos/2006/02/15/AlmondBlossom.jpg
> >> Canon 1Ds MkII with Leica 100 APO, hand held, ASA 640. I've done
> >> sharpening but no noise reduction.<<<<
>
> G'day Adam,
> Very nice indeed and a shame to have a freeze move in and put them down.:-(
>
> One can't beat the Leica 100 APO for shooting almost any subject, but
> photographing flowers and similar subjects it's the best. Add the 2X
> extender and it becomes an incredible 200mm lens with a nice reach for many
> subjects beyond garden items.
>
> Question?
> I have just begun using "sharpen & sharpen edges" on a few digital frames,
> not because they were out of focus..... because someone told me it should 
> be
> done as part of the digital "workflow" due to digital frames not being 
> sharp
> no matter what glass. Surely this isn't correct given what I've shot and
> printed.
>
> Do I see any difference after using it? Not really, because to my naked eye
> the photograph appeared right on the mark in focus where it was supposed to
> be.
>
> I believed "sharpen" was merely a tool to "fix the image" due to not 
> focused
> correctly when the picture was taken. As in, it's meant to sharpen out of
> focus photos?
>
> I realize it wont fix a badly focused photo, but is it really something
> necessary on every frame?
>
> Thanks for an answer to this.
>
> ted
>
>
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