Using a sharpening filter is really contingent upon the content of an image. Increasing the size of a filter may have some impact, but it may also have no perceptible impact – what-so-ever. Consider the following photograph of the front of a homewares store taken in Oslo.
The image (which is 1500×2000 pixels – down sampled from a 12MP image) contains a lot of fine details, from the stores signage, to small objects in the window, text throughout the image, and even the lines on the pavement. So sharpening would have an impact on the visual acuity of this image. Here is the image sharpened using the “Unsharp Mask” filter in ImageJ (radius=10, mask-weight=0.3). You can see the image has been sharpened, as much by the increase in contrast than anything else.
Here is a close-up of two regions, showing how increasing the sharpness has effectively increased the contrast.
Now consider an image of a landscape (also from a trip to Norway). Landscape photographs tend to lack the same type of detail found in urban photographs, so sharpening will have a different effect on these types of image. The impact of sharpening will be reduced in most of the image, and will really only manifest itself in the very thin linear structures, such as the trees.
Sharpening tends to work best on features of interest with existing contrast between the feature and its surrounding area. Features that are too thin can sometimes become distorted. Indeed sometimes large photographs do not need any sharpening, because the human eye has the ability to interpret the details in the photograph, and increasing sharpness may just distort that. Again this is one of the reasons image processing relies heavily on aesthetic appeal. Here is the image sharpened using the same parameters as the previous example:
There is a small change in contrast, most noticeable in the linear structures, such as the birch trees. Again the filter uses contrast to improve acuity (Note that if the filter were small, say with a radius of 3 pixels, the result would be minimal). Here is a close-up of two regions.
Note that the type of filter also impacts the quality of the sharpening. Compare the above results with those of the ImageJ “Sharpen” filter, which uses a kernel of the form:
Notice that the “Sharpen” filter produces more detail, but at the expense of possibly overshooting some regions in the image, and making the image appear grainy. There is such as thing as too much sharpening.
So in conclusion, the aesthetic appeal of an image which has been sharpened is a combination of the type of filter used, the strength/size of the filter, and the content of the image.