Sharpness

Sharpness refers to the clarity and perceived detail of an image, particularly the crispness of edges and fine textures. It is a perceptual attribute that depends on the transfer of high spatial frequency information from the scene to the viewer, and is influenced by optical, sensor, and processing factors. Sharpness is not identical to resolution or sharpness of focus alone; it results from a combination of resolving power and contrast at edges.

In optics, sharpness is often described by the point spread function and its frequency-domain counterpart, the modulation transfer function (MTF). An image with a broad, high-contrast edge will appear sharp, while diffraction, lens aberrations, sensor pixel size, and anti-aliasing filters can attenuate high frequencies and reduce apparent sharpness. Shot texture and noise can also affect perceived sharpness.

In practice, factors that reduce sharpness include misfocus, motion blur, camera shake, and diffraction at small apertures; and lens limitations or poor stabilization. Conversely, appropriate focusing, sufficient shutter speed, and controlled depth of field can enhance apparent sharpness. Lens quality, focal length, and distance to subject influence the optical contribution, while sensor characteristics and image processing affect the digital representation.

Sharpening techniques in post-processing—such as unsharp mask or deconvolution—can enhance perceived sharpness, but excessive sharpening introduces halos and artifacts. Objective assessment uses metrics like MTF50 and edge contrast, alongside subjective evaluation, especially in print or display.