# Frequency-Based Adaptive Interpolation Filter in Intra Prediction
## 4 Experimental Results  
The proposed method was implemented in VTM-14.2 [37], the VVC reference software, and conducted in All Intra (AI) configurations under the JVET common test conditions (CTC) [38]. The sequences of classes A1, A2, B, C, and D were tested with Quantization Parameter (QP) values of 22, 27, 32, and 37, respectively. Table 7 shows the sequence name, picture size, picture rate, and bit depth of the CTC video sequences for each class. Figure 6: BD rate reductions in the proposed reference sample interpolation for each threshold, THR1, THR2,..., THR7: (a) cUs with \(nTbS\) = 2; (b) cUs with \(nTbS\) = 5. Table 8 shows the interpolation filter selection method and the interpolation filters applied according to the selected method to test the efficiency of 8-tap/4-tap interpolation filter. Method A uses 8-tap DCT-IF for \(nTbS\) = 2 and 4-tap SIF for \(nTbS\) > 4 and Method B uses 8-tap SIF for \(nTbS\) > 4 and 4-tap DCT-IF for \(nTbS\) = 2, while selecting DCT-IF or SIF in the same way as a VVC anchor. The difference between Method A and the VVC methods is that Method A uses 8-tap DCT-IF instead of 4-tap DCT-IF for \(nTbS\) = 2 only. The difference between Method B and the VVC method is that Method B uses 8-tap SIF instead of 4-tap SIF only for \(nTbS\) > 4. In the case of Method A, the overall increase in the BD rate by \(-0.13\%\), \(-0.12\%\) and \(-0.08\%\) is observed for the Y, Cb, and Cr components, respectively, where the sign (\(-\)) means bit-savings. In the case of Method C, the overall increase in the BD rate by \(-0.14\%\), \(-0.09\%\), and \(-0.11\%\) is observed for the Y, Cb, and Cr components, respectively. Particularly, increments of the Y component amounting to (\(-0.33\%\), \(-0.28\%\)) in classes C with a resolution of \(832\times 480\) and D with a resolution of \(416\times 240\), respectively, at low picture resolutions are achieved in the Method A, the component gain (\(-0.40\%\), \(-0.30\%\)) in classes C and D is achieved in Method C. Methods A and C have in common that an 8-tap DCT-IF for \(nTbS=2\) and a 4-tap SIF for \(nTbS>4\) are applied to each CU regardless of the filter selection method. For Method B, the overall BD rate gains are \(-0.02\%\), \(-0.03\%\), and \(-0.02\%\) for the Y, Cb, and Cr components, respectively. For Method D, the overall BD rate gains are \(-0.01\%\), \(-0.01\%\), and \(0.03\%\) for the Y, Cb, and Cr components, respectively. Method B uses an 8-tap SIF for \(nTbS>4\), and a 4-tap DCT-IF for \(nTbS=2\) and Method D uses an 8-tap SIF or 4-tap DCT-IF in line with the proposed _high_freq_ratio_ for \(nTbS>4\), and 4-tap DCT-IF for \(nTbS=2\). Even though there is almost no overall increase in BD rate with Methods B and D, the increase in BD rate by \((-0.08\%\), \(-0.09\%)\) in Y components in class A1 with resolution \(3840\times 2160\) is obtained in Methods B and D, respectively. The proposed frequency-based adaptive interpolation filtering using _high_freq_ratio_ and \(nTbS\) and the existing VVC method in Table 6 were developed to take advantage of Methods C and D.  
Table 11 shows the percentages of the CUs applying the 4-tap DCT-IF in the VVC anchor and the 8-tap DCT-IF based on the _high_freq_ratio_ in the proposed method for all test sequences. For \(nTbS=2\), the 4-tap DCT-IF is selected \(100\%\) on \(4\times 4\) CU, \(4\times 8\) CU and \(8\times 4\) CU in the VVC anchor, but the 8-tap DCT-IF is selected \(97.16\%\) on \(4\times 4\) CU, \(95.80\%\) on \(4\times 8\) CU, and \(96.77\%\) on \(8\times 4\) CU in the proposed Adaptive Filter Method based on _high_freq_ratio_. The percentage of 4-tap SIF selection with \(nTbS=2\) can be inferred from the DCT-IF selection percentages in Table 11.