KontrastStrecken

KontrastStrecken, or contrast stretches, is a class of image processing operations that increase the contrast of digital images by redistributing pixel intensity values. The goal is to make features more distinguishable by spreading the histogram over a broader dynamic range, often with saturation at the extremes to reduce the influence of outliers.

Global KontrastStrecken apply the same transfer function to all pixels. A typical linear stretch maps input intensities I within a chosen range [I_min, I_max] to an output range, often [0, 1] or [0, 255], saturating values below I_min and above I_max. Piecewise-linear versions introduce additional breakpoints and slopes to emphasize midtones, highlights, or shadows according to the desired effect.

Local or adaptive KontrastStrecken adjust the transfer function according to local image statistics. These methods aim to enhance details while avoiding global over-saturation. Examples include histogram equalization, histogram specification, and adaptive approaches such as Contrast-Limited Adaptive Histogram Equalization (CLAHE). Local methods can reveal textures and edges that are not visible under global stretching but may introduce artifacts if overused.

Applications include digital photography, medical imaging, remote sensing, and pre-processing for computer vision. They are widely used to improve visibility, segmentation, and feature extraction, particularly when the original image has a narrow dynamic range or uneven illumination.

Limitations and considerations include potential amplification of noise, halo artifacts around edges, and non-linear distortions of brightness relationships. Careful parameter selection (range boundaries, clipping, and algorithm choice) is essential to balance detail enhancement with artifact control.

Terminology and history: The term KontrastStrecken is common in German-language literature; in English, the concepts are generally referred to as contrast stretching or histogram stretching, with global and local variants documented since the early era of digital imaging.