A new technique for temporally decimating an image soquence is presented where the amount of decimation in the time direction varies with the local temporal activity. The technique is used to reduce the average frame rate of an image sequence before compression to achieve high-compression ratios. One trivial form of achieving temporal decimation is by periodically dropping whole frames from the image sequence. However, dropping whole frames from the image sequence may cause objectionable temporal aliasing artifacts, especially in regions where temporal activity is high. Hence, to avoid the temporal allasing artifacts, we propose to adaptively adjust the amount of decimation in the time direction depending on the local activity. The temporal decimation procedure can be combined with several strategies for reduction of spatial redundancy. We have utilized subband coding and block-based transform coding for still image compression in our experiments. The proposed International Standards Organization (ISO) standards, the Consultative Committee on International Telephony and Telegraphy (CCITT) H.261, and the Motion Picture Expert Group (MPEG) proposed standard are described, and we illustrate how our contribution fits into these frameworks. The algorithm is demonstrated for a wide range of compression ratios. The examples include CCITT video sequences and medical ultrasound.