Journal of Digital Information Management Satith Sangpradid, Sunya Sarapirome 12 6 2014 http://dline.info/fpaper/jdim/v12i6/1.pdf To efficiently fuse multi-spectral (MS) and panchromatic (PAN) images acquired from THEOS satellite, the authors offer proper parameters to improve IHS fusion technique based on its spectral responsivity. This concept was originally contributed by Tu et al., applied to IKONOS image fusion. Red and NIR bands of THEOS imagery with lower response were adjusted to be higher and close to the response of PAN band using those new proposed parameters. Indexes including the correlation coefficients (CCs), relative dimensionless global error in synthesis (ERGAS), and relative average spectral error (RASE) of the pan-sharpened and MS images were compared to quantitatively evaluate the quality of pansharpened images. The resulting indexes indicate that the quality of pan-sharpened images obtained from the study be obviously high. Indexes from images transformed by the method of Tu et al. were compared to the indexes obtained from the study as well. The comparison expresses that indexes resulted from the study are better than ones using the method of Tu et al. It can confirm that the fusion method based on the concept of adjustment on spectral responsivity of specific sensor is valid. The new approach provides a satisfactory result of image fusion, both visually and quantitatively.