ContrastLimited

ContrastLimited is a concept used in image processing to bound the amount of contrast enhancement applied to image data, particularly in histogram-based methods such as contrast-limited adaptive histogram equalization (CLAHE). The core idea is to prevent excessive amplification of noise and homogeneous regions by clipping the local histogram, rather than applying a global transformation.

In practice, image enhancement is performed by dividing the image into a grid of tiles. For each tile, the histogram of pixel intensities is computed and clipped to a specified clip limit. The excess mass beyond the clip limit is redistributed among the histogram bins, and a tailored contrast stretch is applied within the tile. The tile results are then blended across boundaries to avoid seams, producing a smoother overall image.

The clip limit is a user-controlled parameter. A low limit preserves a natural appearance and suppresses noise but may yield modest enhancement; a high limit yields stronger contrast but can amplify noise, create artifacts, or overshoot in flat regions. The choice depends on image content, noise level, and the desired result.

Contrast limiting is also used to stabilize adaptive algorithms and separate signal from noise in applications such as medical imaging, remote sensing, and photography. Related concepts include histogram equalization, adaptive histogram equalization, and CLAHE, which incorporates the contrast-limiting step to improve robustness across diverse images.