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This paper proposes the directional filtering transform (dFT, in order to distinguish from the common usage on DFT) to better exploit intra-frame correlation in H.264 intra-frame coding. It consists of a directional filtering and an optional DCT transform. In the proposed directional filtering, there are two different approaches. One is the uni-directional filtering (UDF) that is similar to H.264 directional intra prediction. In this approach, only samples from neighboring blocks can be used in prediction. Another is bidirectional filtering (BDF) that exploits the correlations among samples from not only neighboring blocks but also the current block. The prediction structure in this approach is hierarchical multi-layer. In this paper, we present mathematical analyses on UDF and BDF and show the advantage to combine them together. The proposed dFT is integrated into H.264 intra-frame coding too. The preliminary experimental results in H.264 demonstrate its superiority.