To convert an interlaced video into a progressive one effectively, de-interlacing techniques have been developed. However, existing de-interlacing techniques can not perfectly remove high frequency alias components inherently existing in the interlaced video. In this paper, based on the theory of POCS, we propose a video enhancement technique to improve the visual quality of de-interlaced video. We introduce novel constraint sets that are suitable for the characteristics of de-interlaced video and derive the projection operators for those sets. These projection operators using multiframes can reduce high frequency alias components of the de-interlaced video effectively. Extensive computer simulations show that the proposed method significantly improve the quality of the de-interlaced video by restoring the meaningful frequency information of the original progressive video.