HEVC中的Z-Scan

记录一下HEVC中的Z-Scan概念，如下图：

上图两个g开头的全局变量，来时HM软件。

在HEVC的标准文档中，6.5.2部分，有一个初始化Z-Scan数组的算法，数组的名称为 MinTbAddrZs：

953      # 6.5.2
   954      # MinTbAddrZs[x][y]
   955      diff = csps['CtbLog2SizeY'] - csps['MinTbLog2SizeY']
   956      num_x = csps['PicWidthInCtbsY']  << diff
   957      num_y = csps['PicHeightInCtbsY'] << diff
   958      MinTbAddrZs = [[-1 for j in range(num_y)] for i in range(num_x)]
   959      for y in range(num_y):
   960          for x in range(num_x):
   961              tbX = (x<<csps['mintblog2sizey'])>> csps['CtbLog2SizeY']
   962              tbY = (y<<csps['mintblog2sizey'])>> csps['CtbLog2SizeY']
   963              ctbAddrRs = csps['PicWidthInCtbsY'] * tbY + tbX
   964              MinTbAddrZs[x][y] = cpps['CtbAddrRsToTs'][ctbAddrRs] << (diff*2)
   965              p = 0
   966              for i in range(diff):
   967                  m = 1 << i
   968                  p += (m*m if m&x else 0) + (2*m*m if m&y else 0)
   969              MinTbAddrZs[x][y] += p
   970      cpps['MinTbAddrZs'] = MinTbAddrZs

下面这段文字，说明了z-scan的重要作用：

The CUs inside a CTU are coded in a depth-first order. This coding order is also referred to as z-scan and ... It ensures that for each CU, except those located at the top or left boundary of a slice, all samples above the CU and left to the CU have already been coded, so that the corresponding samples can be used for intra prediction and the associated coding parameters can be used for predicting the coding parameters of the current CU.

遍历CTU中的每一个CU的过程，就是z-scan！

-- EOF --

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