About This Digital iDarkroom Primer

This Primer on the new digital darkroom is provided on this blog to arm new DSLR photographers with the fundamental knowledge needed to become familiar with the evolving digital technologies and be able to apply them to their emerging interest in the photographic art. To read this Primer in logical order, please begin with the oldest post and read to the most current. Click HERE for Table of Contents.

Along the way, you'll find, photography tips, photography techniques and an ample dose of solid photo basics to help you feel comfortable in your digital darkroom.

A sister site, Hub's Camera, covers the fundamental mechanics of using your new DSLR camera. Then visit Hub's Photography Tips for basic but essential tips on all things photographic. Links to both of these sites can be found in the right-hand column of this page. Happy shooting!

"Hub's iDarkroom" is a non-commercial, educational service of Hubbard Camera LLC.

Thursday, September 25, 2008

Part 13 - Sharpening, Less is Better

For those just getting started with digital imaging software, the "sharpening" tool is often misunderstood and misused. This post will provide a basic understanding of what sharpening is, and what sharpening isn't. Two of the most important points to remember are:
  • sharpening isn't a quick fix for out-of-focus images (out of focus images will always be out of focus)
  • all digital images require some degree of sharpening.
So what is sharpening?

Software capable of performing sharpening uses sophisticated algorithms and programming that has matured over the past two decades to selectively increase the contrast along borders of different densities appearing in an image (for example, the edge lines between the veins in the flower petals below). The result is the "illusion" of increased image sharpness -- when in reality it's selective contrast that has been achieved.

Sharpening is one subject that is best explained using lots and lots of picture examples. Most technical articles about sharpening generally use professionally made, resolution test charts to show the effects of focus and sharpening. I'm using a real world picture to help beginners recognize sharpening effects as they would appear in their own prints or monitor. The picture below will be used to demonstrate the operation and effects of sharpening.

This flower picture may well be one of the most carefully set up and taken images I've ever shot. I wanted a picture that was as absolutely "in focus" and sharp as my camera could capture for this sharpening discussion. Here's how the picture was taken:
  • outdoor lighting with a slightly overcast sky
  • no wind to cause subject movement
  • shutter speed, 1/250th of a second
  • aperture, f/11
  • ISO setting, 125
  • camera mounted on a very stable tripod
  • focus point, center of flower
  • image saved in RAW format.
Once this picture was taken, I took a second picture of the same flower but just slightly out of focus:

The second image is just BARELY out of focus

To see the effects of sharpening, we need to examine these images more closely in detail. The red box on the picture below will be enlarged for both flower images to reveal the impact sharpening has on our photography:

Both images were stored as RAW files. Below is this portion of each image (in focus and out of focus picture) as it was brought into Photoshop without any sharpening applied in the RAW converter:

The "in focus" image with NO sharpening applied

The "out of focus" image with no sharpening applied

With the images enlarged, it's easier to see that the bottom picture is not quite in focus compared to the top photo. Remember these are the images brought directly from the camera's RAW files and opened in Photoshop.

Because of the limitations of our photo sensors and the way light is collected/recorded at each pixel site, it is necessary to apply a small amount of sharpening to EVERY image. For this example, all sharpening will be done inside Photoshop using the software's "Unsharp Mask" feature -- located inside the "filter/sharpen" menu. (You're right. "Unsharp" seems counter-intuitive. But it's a term inherited from the world of the printing press.)

Unsharp Mask control window next to our flower image

It is very easy to over sharpen an image (more on over sharpening later).
As a starting point, try these settings then click OK. Notice, if you check the preview box the sharpening effect can be seen on your image before you click OK. In most cases, this is just enough to overcome the shortcomings of the camera's sensor without leaving any unwanted traces (called artifacts) in the images. The result of applying this degree of sharpening to our two flower images is shown below:

"In focus" flower with normal sharpening applied

"Out of Focus" flower with normal sharpening applied

Both flowers look better. The in-focus flower is very sharp and shows all the detail in the center of the flower and nearby petals. The out-of-focus flower appears to be more in focus, but still is not as sharp as the flower that was shot in focus. This relationship of apparent focus between the two flower images will ALWAYS exist.

So what happened to the image when sharpening was applied?

Unsharpened image enlarged to show individual pixels

If we enlarge the picture further, the individual pixels that make up the flower image can be seen. This first picture shows the "in focus" image BEFORE sharpening was applied.

Same image after sharpening and enlarged to show individual pixels

Photoshop searched the first image to detect the lines that identify the border between areas of different densities. Once these borders were located, the software increased the contrast level between the two adjacent areas to create the sharpening illusion. If you look closely at each picture you will see areas where one pixel has been lightened while the adjacent pixel has been darkened -- as compared to the unsharpened picture.

It would seem that if more sharpening was applied then the out of focus picture could be salvaged and made to appear in focus. There is a point of diminishing returns with sharpening. Apply too much sharpening and image quality suffers as well as becoming visibly noticeable and distracting in the final print.

Visible artifacts become distractions when too much sharpening is applied

Above is the out of focus picture for the last time. It has been sharpened to the point where it approximates the sharpness of the original "in focus" picture. This much sharpening is too much. Artifacts or imperfections are noticeable along the sharp edges of the elements that make up the picture. (This is a very small picture and at monitor resolution, but as an actual print you would be disappointed.)

In the end, the sharpest prints start with original camera files that are "in focus". As far as sharpening is concerned, like so many other things, "less is better".

If you save your files in JPEG format in your camera, I recommend setting the camera's internal sharpening feature to minimal or off. It's my experience that the sharpening functions in today's imaging software do a better job.

If you have questions or comments, please let me know.

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