Abstract: Any type of sensor,including aerial camera,is an information transmission channel.A formula based on the digital image processing was theoretically analysed for quantitatively estimating the information content on the aerial negative.Major emphasis focuses on the idea of "bitslicing" for determining the effective bit number. As the information content for a given aerial negative deals with resolution,granularity and image contrast,a criterion for evaluating the imge quality both in the macro and micro structure was established.The idea described here can readily be adapted to any other type of sensor to estimate the information content in remote sensing.