Are resolution and sharpness the same? By looking at the images shown above, one can quickly determine which image is sharper. Although the image on the left comprises twice as many pixels, the image on the right, whose contrast at coarse details is increased with a filter, looks at first glance to be distinctly sharper.
The resolution limit describes how much information makes up each image, but not how a person evaluates this information. Fine details are irrelevant to a person’s perception of sharpness—a statement that can be easily be misunderstood. The human eye, in fact, is able to resolve extremely fine details. This ability is also valid for objects at a greater distance. The decisive physiological point, however, is that fine details do not contribute to the subjective perception of sharpness. Therefore, it’s important to clearly separate the two terms, resolution and sharpness.
The coarse, contour-defining details of an image are most important in determining the perception of sharpness. The sharpness of an image is evaluated when the coarse details are shown in high contrast. A plausible reason for this can be found in evolution theory: “A monkey who jumped around in the tops of trees, but who had no conception of distance and strength of a branch, was a dead monkey, and for this reason couldn’t have been one of our ancestors,” said the palaeontologist and zoologist George Gaylord Simpson. It wasn’t the small, fine branches that were important to survival, but rather the branch that was strong enough to support our ancestors.
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