Early extracellular recordings from turtle visual cortex have shown the existence of a wave of depolarizing activity as a response to a localized light flashes presented in the turtle visual field. Experiments using voltage sensitive dye techniques have supported this observation. The dynamics of the cortical wave might be responsible for encoding the parameters of an unknown input stimulus. We develop a data compression algorithm for representing the cortical response elicited by a family of stimuli. To process image data we use the principal components analysis method and we provide a consistent way of choosing the number of principal modes necessary for effective data representation.