Sharpness of an image describes its edge contrast, in other words how well defined edges are in the scene. Sharp images are clear and defined, easy for the eyes to follow and decode. Non-sharp, or soft, images have blurred edge lines that makes them more elusive to the eyes.
Sharpness processing involves the areas along edges, where there is already a demarcation between two areas. Increasing sharpness amplifies the edge effect, thus making it more evident and generally more appealing; this action is described as sharpening. Decreasing the edge effect, softens the demarcation between two areas, making it less evident; this action is described as softening and in some cases blurring.
Sharpness in camera
Sharpness can be controlled in camera at capture time. Lenses are praised for their sharpness, and their price reflect this. On the other hand, special softening filters can be added to the front lens to create a mild softened effect. Aperture, affecting depth of field, will generally blur and reduce sharpness of those parts of the scene that are not in focus. Out-of-focus pictures tend to not be sharp, but you generally would discard those, unless it was the desired controlled effect.
Sharpness manipulation
Manipulating sharpness is a bit tricky, as it can amplify noise, overly emphasize texture (over-sharpening) and in general produce unnatural results.
So, while most of digital images need some sharpening, you should take some care in doing so. Keep also in mind that JPEG images are already sharpened, and generally need less than RAW. A great tutorial on this topic written by Nasim Mansurov explains very clearly what to look out for, and how to perform good sharpening in Adobe Lightroom.
Sharpness and skin
While large smooth areas are not interested by sharpness, speckles present on it are. This is particularly important when sharpening skin, as its pores, hair and imperfections get greatly amplified by a sharpening action.
As to get an idea, you would want to soften skin in its wider areas, as to blend blemishes, and increase sharpness around the edges. Please do refer to tutorials specialized in portrait and skin processing, as there’s much more to skin smoothing than just softening.
Sharpness in Adobe Lightroom
In Adobe Lightroom, sharpness can be modified in the Develop module.
Sharpness has four settings, amount, radius, detail and mask, which may be named differently in other software products.
Amount controls the intensity of the effect, radius how deeply to process the edge contours, and mask allows to select where you want the sharpening action to be focused on.
Note that increase in sharpness will not recover a blurred image, neither the out-of-focus ones, much less the motion-blurred ones. It may make it better for mild softness, but never perfect.
For more controlled effect, the Adjustment Brush allows you to select the areas where to modify sharpness. Blur – including gaussian blur – is something more advanced and available in editors like Adobe Photoshop and the likes.
Summary
Let’s now summarize the key points around sharpness that we have covered above:
Sharpness measures the edge contrast of an image
Increasing sharpness amplifies the edges and creates more separation of elements in the scene
Decreasing sharpness softens the scene by blending smaller objects first.
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Sharpness is when fine details are clear and distinct (think of a close-up shot of fine watch or crisp landscape). Lens quality, shutter speed, camera stability, and focus are critical to capturing sharp images.
Sharpness describes the clarity of detail in a photo, and can be a valuable creative tool for emphasizing texture. Proper photographic and post-processing technique can go a long way towards improving sharpness, although sharpness is ultimately limited by your camera equipment, image magnification and viewing distance.
Image sharpness can be measured by the “rise distance” of an edge within the image. With this technique, sharpness can be determined by the distance of a pixel level between 10% to 90% of its final value (also called 10-90% rise distance; see Figure 3).
Oversharpening, illustrated on the right, can also degrade image quality (especially at large magnifications) by causing "halos" to appear near contrast boundaries. Images from many compact digital cameras and phones are oversharpened.
Sharpness in any area of an image is determined by two factors: resolution and contrast. Resolution is the ability to resolve detail in an area and contrast is the ability to separate adjacent micro areas between the resolution lines (how clearly two near white tones can be differentiated from each other.
With most TVs, it actually masks fine detail. That means when your sharpness is set too high, you could lose some of the crisp detail possible on that new TV. In some cases, the best sharpness setting is actually zero, while on most TVs the setting is best in the bottom 20% or so.
Software sharpening finds the sharp edges in your photograph and increases the contrast of the edges, This gives the image more defined edges and a look of being sharper.
Generally speaking, for almost every lens, you'll get a sharper image―with all other factors being equal―at the middle apertures and not at its widest or smallest aperture.
Sharpness – : clear in outline or detail : DISTINCT. : set forth with clarity and distinctness. Resolution and visual sharpness are different items because resolution is a one dimensional parameter and sharpness as the eye sees it is two dimensional.
A higher f-number (technically a smaller aperture) contributes to sharpness in two ways. Firstly the depth of field is increased, thus objects which would appear blurry are now rendered sharp. Secondly a smaller aperture reduces aberrations which cause the image to appear soft even at the plane of focus.
People tend to judge images with higher acutance as being sharper, even though this is not necessarily associated with higher resolution. By increasing tonal differences along edges in an image, we can make it appear sharper, even though the actual resolution of the image may be reduced.
Think of resolution as the "density" of the image, referring to the number of pixels and detail displayed for a particular image size. Resolution describes the sharpness and clarity of an image.
Also known as the “Zone of Acceptable Sharpness”, the 'Depth of Field' is the distance across the part of the picture that is acceptably sharp to the eye. When a lens focuses on a subject it creates only one point of clarity in the image. There is a gradual fall-off of sharpness either side of that point.
Sharpness Sentence Examples. The sharpness of his tone made her jump. Dean was startled by her sharpness, chastising himself for underestimating the young girl. Thus the two images under measurement are not defined with equal sharpness and symmetry.
Resolution and sharpness are two different beasts. Sharpness can be subjective and the perception of sharpness is influenced by a handful of factors like aperture, depth of field, shutter speed, lens resolution, and camera sensors. It has a lot to do with contrast too, especially along the edges of objects in a frame.
Contrast and sharpness have great impact on perceived quality of an image . Contrast refers to difference in gray scale or color exists between image features. It is related with discrimination of objects or content within an image. Sharpness of an image refers to clarity of detail and edges.
So what exactly sharpen means and how does it differ from clarity? Roughly: Sharpen will increase contrast along edges which already have higher contrast than surrounding pixels. Clarity generally includes some sharpening but also includes local contrast, as the idea is borrowed from the slider in lightroom.
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