I don't mean to pick on you or argue with you. I prefer to keep conversation on a friendly level...especially here on the Panny forum. But I'm interested to know how you define the difference between "resolution" and "sharpness".
I think you'll find they're indistinguishable from each other...
Were not talking about in-camera processing sharpness, we're talking about lens sharpness itself. If a lens is "sharper", it will always add "resolution" to any camera.
To the best of my knowledge, 'resolution' is a quantitative quality, i.e. one which can be measured, whereas sharpness is a qualitative property and as such is not so easily measured.
Examples of the definition of the "Resolution" of the eye are the ability to distinguish between two closely separated objects such as a pair of dots or between alternate black and white lines of equal thickness.
The generally accepted resolution for the human eye is 1 arc minute which is equivalent to about 0.3 milliradian, mR. That figure corresponds to 1/a = 1.7 for visual acuity specified in the following link:
http://webvision.med.utah.edu/KallSpatial.html .
You may also find the following links of interest.
http://en.wikipedia.org/wiki/Visual_acuity
http://www.madsci.org/posts/archives/1997-05/864446241.Ph.r.html
Now let us consider the case of a camera making an image of a grating, i.e. a pattern of alternate black and white lines.
For a grating in which each line has a width of 0.5 mm, the pitch between a pair of black or white lines is 1.0 mm and the grating is described as having a spacing of 1 line pair per mm, LPM.
Now consider what happens when a lens is focussed on such a grating as it is moved away gradually. As the image of the grating becomes smaller, a point will eventually be reached where the lines in the image blend together and can no longer be distinguished as pairs of alternate dark and light lines. If at the last point at which the lines in the image can be distinguished as pairs, the pitch between a pair of dark or light lines is 0.01 mm then the “Resolution” of the lens is defined as 100 LPM.
In the above example the lines in the grating are alternately black and white like a checkerboard. It is also possible to have a grating in which the change from black to white and back again occurs gradually from the centre of the black lines to the centre of the white lines. That change could take a variety of forms from a simple straight line variation to a sine wave or any other shape you care to think of.
In each case the “Resolution” would be the same, since it is “mathematically defined” from the pitch between consecutive dark or light bands. However the appearance of these gratings or of images of similar form would be quite different. It is the difference between the sharply defined edges of the first example, which is like a square wave and the smoother changes of the triangular, sinusoidal or some other wave form which are qualitative rather than quantitative that I have described as “Sharpness”.
For a fuller description here is the Wikipedia definition of Sharpness.
Perceived sharpness is a combination of both resolution and acutance: it is thus a combination of the captured resolution, which cannot be changed in processing, and of acutance, which can be so changed.
Properly, perceived sharpness is the steepness of transitions (slope), which is change in output value divided by change in position – hence it is maximized for large changes in output value (as in sharpening filters) and small changes in position (high resolution).
Coarse grain or noise can, like sharpening filters, increase acutance, hence increasing the perception of sharpness, even though they degrade the signal-to-noise ratio.
The term "critical sharpness" is sometimes heard (by analogy with critical focus) for "obtaining maximal optical resolution", as limited by the sensor/film and lens, and in practice means minimizing camera shake – using a tripod or alternative support, mirror lock-up, a cable release or timer, image stabilizing lenses – and optimal aperture, usually 2–3 stops down from wide-open.
I trust that is sufficient to explain how I define the difference between "resolution" and "sharpness".
Jimmy
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J C Brown
