Quantification of sharpness?

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river251
river251 Regular Member • Posts: 464
Quantification of sharpness?

Having acquired some new lenses, and taking an interest in testing their sharpness and focus, I have an idea--or perhaps flight of fancy, or perhaps psychotic delusion --about quantifying sharpness. I deal with signals in my day job, as do people in a vast variety of professions. I've had this idea keep coming to mind. One thing you can measure about a signal is its smoothness. It's kind of the opposite of variance but not exactly. Suppose you take an image's first row of pixels and then append the second row and so on, to make one long vector of all the rows of pixels in the image. What value for each pixel is used? Could be a few, including brightness, but I might think of using the color value (in some colorspace). Then, the smoothness of this vector would seem to be negatively correlated with the image's (or lenses') sharpness. This treats the whole lens as one entity, not separating center and edges. Still, if it works maybe it would be a useful measure. If there are faster transitions because the lens is resolving details, then this vector should be less smooth. Conversely, a softer lens would have smoother transitions across pixels, and more smoothness overall.

If that day job did not have me slammed all the time, it would be fun to write a little matlab or python script to try this. Both would have algos for smoothness.

Crazy?

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