Smoothing Filter-based Intensity Modulation: A spectral preserve image fusion technique for improving spatial details

TLDR

Image fusion integrates lower‑resolution multispectral images with higher‑resolution panchromatic images, yet existing methods often distort spectral properties or require complex, time‑consuming processing. The authors developed the Smoothing Filter‑based Intensity Modulation (SFIM) technique to enhance spatial resolution of multispectral images while preserving spectral fidelity. SFIM modulates spatial details by applying a smoothing filter to the high‑resolution image, computing the ratio with the original, and transferring this ratio to the co‑registered lower‑resolution multispectral image, thereby preserving spectral properties. Experiments on TM and SPOT images from south‑east Spain show that SFIM preserves spectral characteristics and improves spatial detail, outperforming HSI and Brovey transforms in visual and statistical assessments.

Abstract

Image fusion techniques are widely used to integrate a lower spatial resolution multispectral image with a higher spatial resolution panchromatic image, such as Thematic Mapper (TM) multispectral band and SPOT Panchromatic images. However, the existing techniques either cannot avoid distorting the image spectral properties or involve complicated and time-consuming frequency decomposition and re-construction processing. A simple spectral preserve fusion technique: the Smoothing Filter-based Intensity Modulation (SFIM) has thus been developed based on a simplified solar radiation and land surface reflection model. By using a ratio between a higher resolution image and its low pass filtered (with a smoothing filter) image, spatial details can be modulated to a co-registered lower resolution multispectral image without altering its spectral properties and contrast. The technique can be applied to improve spatial resolution for either colour composites or individual bands. The fidelity to spectral property and the spatial textural quality of SFIM are convincingly demonstrated by an image fusion experiment using TM and SPOT Panchromatic images of south-east Spain. The visual evaluation and statistical analysis compared with HSI and Brovey transform techniques confirmed that SFIM is a superior fusion technique for improving spatial detail of multispectral images with their spectral properties reliably preserved.