Project Finishing: Sharpening

This exercise is in the section on finishing and looks at the how sharpening requirements differ, whether the intended output is screen or print.

My starting image was this picture of a proud Bedouin:

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I used the sharpening tool in Photoshop, set to remove Gaussian blur. I chose this over the unsharp mask as it is a simpler and slightly more intuitive tool. I prepared 4 further version, with the radius set to 2 pixels, at 50%, 100%, 200% and 300% amount. I was particularly interested in the area around the face, including the red and white scarf (which would have some good detail), the chromatic aberration above his head scarf and the open sky. A4 prints at 100% were made of this area and compared with the on-screen image at actual pixels.

Crops of this area at the various degrees of sharpening are here:

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No sharpening

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50%

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100%

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200%

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300%

Looking at these on-screen, the original looks quite soft. 50% is better but at 100% that the image acquires some crispness, especially noticeable around his glasses and the red detailing on the scarf. This is at the expense of the flesh tones, which are starting to look blotchy. At 200%, the red scarf is looking nice and crisp but the flesh tones are poorer and the image noise in the sky is getting magnified.

In contrast the print at 50% still looks unacceptability soft, 100% is much better and the blotchy flesh tones are not so noticeable. The scarf detailing does not get its crispness until 200%. At 100% the red tinge to the turban is clearly delineated. This is not nearly so noticeable on the screen.

Clearly, this shows that an image destined for print needs more sharpening than one for screen, so we need to know the final intended purpose before sharpening is applied.

Cambridge in Colour [i] has this to say on the subject:

“After capture and creative sharpening, an image should look nice and sharp on-screen. However, this usually isn’t enough to produce a sharp print. The image may have also been softened due to digital photo enlargement. Output sharpening therefore often requires a big leap of faith, since it’s nearly impossible to judge whether an image is appropriately sharpened for a given print just by viewing it on your computer screen. In fact, effective output sharpening often makes an on-screen image look harsh or brittle.”

Further advice on judging print sharpening can be found on dpbestflow [ii]

“How to judge sharpening for output (it’s tricky).

When judging sharpening for print, the image should be viewed at 50% or even 25% (if is a very large image), and not at 100%. Viewing at 50% gives a much better approximation of the actual effect of the sharpening whereas the 100% view will be largely misleading. Appropriate sharpness is definitely a subjective decision. Our advice is to try many techniques until you find one that gives good results and is repeatable. Keep a record of what you like best so you do not have to recreate this part of the wheel each time. Remember that different output devices as well as different substrates may each require very different approaches and levels of output sharpening.”


[i] http://www.cambridgeincolour.com/tutorials/image-sharpening.htm

[ii] http://dpbestflow.org/image-editing/sharpening#output