zonfilters

Zonfilters are a class of filters used in optical and digital imaging that apply different processing or attenuation across distinct spatial zones of a scene. In physical form, a zonfilter is an optical element whose transmission varies across the aperture, producing a zoned exposure or color response. In digital form, zonfilters are implemented as spatially varying processing where an image is divided into zones and each zone receives separate adjustments to brightness, contrast, color, or sharpness.

Zones can be arranged as grids, radial sectors, or custom patterns. Boundaries may be abrupt or feathered to minimize visible seams. Per-zone parameters are defined by zone maps or algorithms that assign exposure, gamma, color balance, or noise reduction to each zone. Digital implementations typically rely on masks, shaders, or tiling strategies; physical variants depend on manufacturing methods such as patterned coatings or segmented ND filters.

Applications include photography and cinematography for balancing uneven lighting, preserving detail in shadows and highlights, or achieving stylistic tonal separation. They can also be used in surveillance, medical imaging, or remote sensing where region-specific processing improves feature visibility. The technique shares principles with spatial filtering and local histogram adjustments, but emphasizes controlled, zone-specific variation rather than uniform processing.

History is tied to advances in spatially varying processing and dynamic range technologies, becoming more practical with calibrated color science and GPU-based rendering.