"You never had to sharpen your photos when you were using film, so why do digital photos need it? Because film and digital cameras record images differently, young padawan. Read on... Digital cameras have a fixed grid of pixels, each of which can only capture one color or shade at a time. Say you take a picture that has a sharp edge between black and white. The razor-thin boundary of that edge would look half black and half white to the human eye. But the single pixel that records that hairline edge can only record one color, so it renders it as gray. What we think of as sharpness is actually the contrast we see between different colors. A quick transition from black to white looks sharp. A gradual transition from black to gray to white looks blurry. So when we look at the picture you just took of that sharp black & white edge, the gray pixels along the edge will make the photo look blurry."
I must agree with this article in that the idea of sharpening a blurry image just seemed more frustrating to me than useful. I don't think I have ever gotten a blurry image sharp enough where I was satisfied with the reduction in blur without increasing the noise in the image to a point of intolerance. So my alternatives have either involved being more aggressive about deleting blurry images as I see them or since my DSLR (as do most other cameras) takes fairly high resolution images, just reducing the size of the image. I find that the sampling algorithms when reducing the size of the images work far better at hiding the blur in images than just plain sharpening. Having said that, it is not like I have given up or anything like that, so I am going to try what this article recommends.
Sharpen Your Images - Unsharp Mask Explained
Linear Mode
