utput of this process is a predicted luma sample value predPartLXL[ XL, YL ]. Rec. ITU-T H.264 (01/2012) Gabch hijkm Figure 8-4 - Integer samples (shaded blocks with upper-case letters) and fractional sample positions (un-shaded blocks with lower-case letters) for quarter sample luma interpolation The variable refPicHeightEffective, which is the height of the effective reference picture luma array, is derived as follows: If MbaffFrameFlag is equal to 0 or mb_field_decoding_flag is equal to 0, refPicHeightEffective1_ is set equal to PicHeightInSamples, Otherwise (MbaffFrameFlag is equal to 1 and mb_field_decoding_flag is equal to 1), refPicHeightEffective is set equal to PicHeightInSamples / 2. In Figure 8-4, the positions labelled with upper-case letters within shaded blocks represent luma samples at full-sample locations inside the given two-dimensional array refPicLX of luma samples. These samples may be used for generating the predicted luma sample value predPartLXL[ XL, ]. The locations (xZL, yZL ) for each of the corresponding luma samples Z, where Z may be A, B, C, D, E, F, G, H, I, J, K, L, M, N, P, Q, R, S, T, or U, inside the given array refPicLX of luma samples are derived as: xZL = Clip3( 0, PicWidthInSamples_ - 1, (8-239) yZL = Clip3( 0, refPicHeightEffective - 1, yIntL yDZL) (8-240) Table 8-11 specifies xxZZL, yDZL) for different replacements of Z. Table 8-11 - Differential full-sample luma locations A BCDEFGHIJKLMNPQRST xDZL 0101-2-10123-2-10123010 yDZ-2-2-1-10000001111112233 Given the luma samples 'A' to 'U' at full-sample locations (xAL, yAL ) to ( xU L, yUL), the luma samples 'a' to 's' at fractional sample positions are derived by the following rules. The luma prediction values at half sample positions are derived by applying a 6-tap filter with tap values (1, -5, 20, 20, -5, 1). The luma prediction values at quarter sample Rec. ITU-T H.264 (01/2012) positions are derived by averaging samples at full and half sample positions. The process for each fractional position is described below. The samp