Quality In Image Fusion

The assessment of the quality of the multispectral images enhanced by the means of a panchromatic image of higher spatial resolution is a critical issue.

Several methods are proposed to produce multispectral images with enhanced spatial resolution using one or more images of the same scene of better spatial resolution. If the main concern of the user of such sharpened images is the quality of the transformation of the multispectral content when increasing the spatial resolution, the assessment of the quality of the fused product is a critical issue.

The major difficulty encountered in quality assessment is the lack of reference against which one may compare properties of the fused image as demonstrated by Thomas (2006).

The protocol proposed by Wald et al. (1997) remains presently the most solid approach to the assessment of quality. It defines the properties of such enhanced multispectral images. It then proposes both a formal approach and some criteria to provide a quantitative assessment of the spectral quality of these products. Five sets of criteria are defined. They measure the performance of a method to synthesize the radiometry in a single spectral band as well as the multispectral information when increasing the spatial resolution.

Thomas proposes a revision of this work and refines the protocol for quality assessment. An empirical survey about the changes in quality budget within scales completes the description of the protocol. She proposes a categorization of distances found in literature, and adds a new distance for geometrical quality assessment, based on the Modulation Transfer Function. She proposes a selection of a group of distances to form quality budgets in order to obtain a complete overview of the quality reached by fused products.

Wald L., Ranchin T., Mangolini M., 1997. Fusion of satellite images of different spatial resolutions : assessing the quality of resulting images. Photogrammetric Engineering & Remote Sensing, 63, 6, 691-699, 1997.

Thomas, Claire. Fusion d'images de résolutions spatiales différentes (Fusion of images of different spatial resolutions). Thèse de Doctorat en Informatique temps réel, Robotique, Automatique, Ecole des Mines de Paris, 11 décembre 2006 (165 p. + annexes).