Color enhancement of highly correlated images. I. Decorrelation and HSI contrast stretches

A new six-channel aircraft multispectral scanner has been developed to exploit mineral signature information at wavelengths between 8 and 12 micrometers. Preliminary results show that igneous rock units can be identified from their free silica content, and that carbonate as well as clay-bearing units are readily separable on the digitally processed images.

Multispectral middle IR (8-13-microm) data were acquired with an aircraft scanner over Utah. Because these digital image data were dominated by temperature, all six channels were highly correlated. Extensive processing was required to allow geologic photointerpretation based on subtle variations in spectral emittance between rock types. After preliminary processing, ratio images were produced and color ratio composites created from these. Sensor calibration and an atmospheric model allowed determination of surface brightness, temperature, emittance, and color composite emittance images. The best separation of major rock types was achieved with a principal component transformation, followed by a Gaussian stretch, followed by an inverse transformation to the original axes.