Most images need to be sharpened because of the way they are digitized. Because of aliasing, elements in an image that are of lower frequency than the sampling frequency will be averaged out and look more blurry. Sharpening helps by accentuating edges. The large number in the middle of the convolution matrix makes the pixel in the middle darker while subtracting the colors around it that may blur it out. That is why the brick edges are much more defined after sharpening.
Most images need to be sharpened because of the way they are digitized. Because of aliasing, elements in an image that are of lower frequency than the sampling frequency will be averaged out and look more blurry. Sharpening helps by accentuating edges. The large number in the middle of the convolution matrix makes the pixel in the middle darker while subtracting the colors around it that may blur it out. That is why the brick edges are much more defined after sharpening.