A theoretical evaluation of aliasing and misregistration effects on pansharpening methods

Abstract

The characteristics of multispectral (MS) and panchromatic (P) image fusion, or pansharpening, methods are investigated. Depending on the way spatial details are extracted from P, such methods can be broadly labeled into two main classes, roughly corresponding to component substitution (CS), also known as projection substitution, and methods based on multiresolution analysis (MRA), i.e. on digital filtering. Theoretical and experimental results carried out on QuickBird and Ikonos data sets evidence that CS-based fusion is far less sensitive than MRA-based fusion to registration errors, i.e. spatial misalignments between MS and P images, possibly originated by cartographic projection and resampling of individual data sets, and aliasing occurring in MS bands and deriving from a modulation transfer function (MTF) of each MS channel that is excessively broad relatively to the spatial sampling interval. Simulated misalignments carried out at full scale by means of a suitable quality evaluation protocol have evidenced the quality-shift tradeoff of the two classes: MRA methods yield a slightly superior quality in the absence of misalignments, but are more penalized, whenever shifts between MS and P are present, than CS methods producing a slightly lower quality in the ideal case, but that are intrinsically more shift tolerant.