Sharpness Children pictures can be sharp or soft, to varying degrees. In the sharpest photographs we see fine detail clearly, especially the edges between different parts of the subject. If a photograph is soft we donít see fine details, and instead edges are blurred. Sometimes we want children pictures to be soft, e.g. to hide skin blemishes in a close-up portrait or to convey a dreamy atmosphere. Sharpness depends on several factors (discussed below).
Contrast is the difference between dark and light tones in subjects or photographs, and may be defined in different ways.
Global contrast is the distance from the darkest tone to the lightest tone in a subject or image, and is sometimes called (long or short) tonal scale. In subjects or photographs with high global contrast we see an extensive range of tones from very dark to very light (e.g. a child partly in sunlight and partly in deep shadow). In a histogram there is a lot of information from one side of the histogram to the other. In subjects or photographs with low global contrast we see fewer tones, e.g. we may see only dark tones, only light tones, or only mid-tones. There is a lot of information in only one or a few parts of the histogram.
Local contrast is the abruptness of the passage from dark to light. In children pictures with high local contrast we see strong tonal differences in parts of the image (e.g. mid-tones). In children pictures with low local contrast we see little difference in tones in parts of the image (e.g. shadows). Normal contrast can be expressed as a diagonal line on a graph. The steeper the line (toward vertical) the higher the contrast; the flatter the line (toward horizontal) the lower the contrast.
Resolution is the ability of an imaging system (lens, film, sensor, the human eye) to distinguish details and tones. Resolution is usually measured by photographing a flat test chart, and expresses the visibility of fine details in the center, edges and corners of the image field. The visibility of details and tones from the near to far elements of an image, or what might be described as three-dimensionality, can only be perceived by photographing a three-dimensional subject, not a flat test chart. The maximum resolution of the normal human eye is when the subjects (e.g. photographs) are about 10 inches away.
Sufficient contrast is essential to resolve subtle tones and fine detail; but excessive contrast or insufficient contrast may obscure subtle tones and fine detail. Digital cameras and film cameras are both capable of photographs with high sharpness, good contrast and remarkable resolution. Since children usually have few or no blemishes, we can sometimes get away with high resolution in close-up portraits. The importance of film/sensor and lens quality are often overestimated, since the fundamental elements of photographic quality are usually other factors: accurate focus, lack of subject or camera movement, and flare control.