Deringing

Deringing is a class of image-processing techniques aimed at reducing ringing artifacts that surround sharp edges in digital images. Ringing refers to oscillatory halos or ripples that can appear after compression, filtering, or deconvolution when high-frequency components are altered. The goal of deringing is to suppress these artifacts while preserving true image detail, contrasts, and texture.

Ringing artifacts commonly arise from the Gibbs phenomenon when reconstructing a signal with limited or quantized frequency information, as well as from deconvolution or aggressive sharpening that amplifies high-frequency components. They are especially noticeable near strong edges or fine periodic textures and can degrade perceived image quality.

Techniques for deringing fall into several broad categories. Edge-preserving denoising and smoothing methods use local statistics or non-local means to reduce oscillations near edges without blurring large uniform regions. Frequency-domain or wavelet-based approaches selectively attenuate high-frequency components associated with ringing while preserving edge information. Model-based or regularized deconvolution methods incorporate prior knowledge about image structure, using sparsity, total variation, or edge priors to constrain edits near edges. Some approaches employ edge masks so that deringing acts primarily in regions adjacent to strong edges, minimizing blur in flat areas. Hybrid methods combine multiple strategies for better balance between artifact suppression and detail preservation.

Applications appear in digital photography, video restoration, medical imaging, and astronomy. A key challenge is achieving artifact reduction without over-smoothing or introducing new distortions, particularly around high-contrast features.