4BlkIdx]is equal to 7. This mode shall be used only when the samples p[ x, -1] with X = 0..7 are marked as "available for Intra_4x4 prediction". The values of the prediction samples pred4x4L[ with X, y=0..3, = are derived as follows: If y is equal to 0 or 2, pred4x4L[x,y]=(p[x+(y>>1),-1]+p[x+(y>>1)+1,-1]+1)>>1 (8-65) Otherwise (y is equal to 1 or 3), (8-66) 8.3.1.2.9 Specification of Intra_4x4_Horizontal_Upprediction mode This Intra_4x4 prediction mode is invoked when Intra4x4PredMode[luma4x4BlkIdx]is equal to 8. This mode shall be used only when the samples p[-1,y] with y = 0..3 are marked as "available for Intra_4x4 prediction". Let the variable zHU be set equal to X + 2 * y. The values of the prediction samples pred4x4L[ X, y ], with X, y = 0..3, are derived as follows: If zHU is equal to 0, 2, or 4 pred4x4L[x,y]=(p[-1,y+(x>>1)]+p[-1,y+(x>>1)+1]+1)>>1 = (8-67) Otherwise, if zHU is equal to 1 or 3 (8-68) Otherwise, if zHU is equal to 5, x4[x,y]=(p[-1,2]+3*p[-1,3]+2)> (8-69) Otherwise (zHU is greater than 5), pred4x4L[x,y]=p[-1,3] (8-70) 8.3.2 Intra_8x8 prediction process for luma samples This process is invoked when the macroblock prediction mode is equal to Intra_8x8. Inputs to this process are the values of Intra4x4PredMode (if available) or Intra8x8PredMode (if available) from the neighbouring macroblocks or macroblock pairs. Rec. ITU-T H.264 (01/2012) Outputs of this process are 8x8 luma sample arrays as part of the 16x16 luma array of prediction samples of the macroblock predL. The luma component of a macroblock consists of 4 blocks of 8x8 luma samples. These blocks are inverse scanned using the inverse 8x8 luma block scanning process as specified in clause 6.4.5. For all 8x8 luma blocks of the luma component of a macroblock with luma8x8BlkIdx : 0..3, the derivation process for Intra8x8PredMode as specified in clause 8.3.2.1 is invoked with luma8x8BlkIdx as well as Intra4x4PredMode and Intra8x8PredMode that are previously (in decoding order) derived for adjacent macroblocks as the input and the variable In