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Robert D Feinman

Selective Sharpening

 

Almost all scanned in images require some sharpening.

Here is the raw scan with a small amount of color correction.

Raw Scan
Raw Scan

Here is a magnified part of the upper portion of the image.

The top image shows the orignal scan. Notice the poor contrast around the window frames.

The second image shows sharpening in Photoshop with the Unsharp Mask Filter. The threshold for sharpening was set to 0. This means that all pixel color transitions are sharpened. Notice that the sky has become mottled and that there is a fringe around the building edge.

For the third image, only the face of the building was selected using the color range tool. The sharpening was then applied only to the selected image with the threshold of 0. Notice that we now have improved contrast for the windows without the fringing and without the noise in the sky.

sharpen_building
Sharpen Windows

In this example the top image shows a magnified portion of the name on beside the steps.

The center image shows sharpening with the threshold set to 0. In this case this causes too much noise in the wall behind the letters.

To improve the appearance we select the inverse of the previous sharpening. Thus we get everything execept the bulilding facade. We apply the Unsharp Mask and set the threshold to 6. Now the edges of the letters are improved and the noise is avoided.

By sharpening different parts of the image with different settings we can optimize the appearance while minimizing unwanted artifacts.

sharpen_base
Sharpen Base

The final image shows the results of the sharpening. In addition there has been some adjustment to the color balance and contrast. At the small size displayed here the effects may be hard to see, but when printed out at high enough resolution the result is a subtle improvement in detail. Too many images are over sharpened in an attempt to restore detail that is not available. The goal should be to make the detail stand out better without creating artifacts or an unnatural edgyness.

Click here to see this image full size.

Click here for more on sharpening.

After sharpening
Final Image
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© 2001 Robert D Feinman