Eberhard Effect

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Deduction of a positive, Eberhard effect through development without movement

The Eberhard effect (after Gustav Eberhard (1867–1940)) or edge effect (also: fringing effect ) is a development effect in analog photography that describes the increase in edge blackening at the border between strongly and weakly exposed - i.e. dark and light - areas.

If there is no or insufficient movement of the developer , used substances of the developer concentrate over the dark areas of the image. In the case of abrupt light-dark transitions, the developer that has already been used diffuses over the light image areas and prevents complete development there. Conversely, unused developer passes from bright parts of the image to neighboring dark areas; there the blackening therefore takes place more rapidly. In this way, light borders are created around dark and at the same time dark borders around light objects.

The increase in the contrast at the edges is often perceived visually as an improved sharpness ( subjective impression of sharpness ). Due to the lack of movement in the developer bath, however, there is often the acute risk that large areas of the motif will "cloud over" due to uneven blackening.

With color film there is the interimage effect ; this is related to the Eberhard or edge effect. Without impairing the overall contrast and exposure latitude, it increases the color saturation . This is achieved in the corresponding processes (e.g. C-41 ) using DIR couplers , which prevent the formation of further silver in the vicinity of highly exposed areas during development.

The edge sharpening in computer graphics (which is almost always a pseudo sharpening, because information that is no longer available cannot simply be "conjured up" again) produces a comparable sensory impression . The pixels of high-contrast transitions of the motif are pulled together (or better: added together). In contrast to the general sharpening, this largely avoids the excessive emergence of the image noise and gfs. of compression - artifacts in large area of the image.

The fact that the Eberhard effect is closely related to the Sabattier effect (also: pseudo-solarization ) is clearly rejected in the literature.

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Individual evidence

  1. ↑ H. Frieser, G. Haase and E. Klein: Basics of the photographic processes with silver halides .