OpenH264帧内预测

//16*16亮度的DC，为上面跟左面32个值的平均值。

void WelsI16x16LumaPredDc_c (uint8_t* pPred, const int32_t kiStride) {
  int32_t iTmp = (kiStride << 4) - kiStride;
  int32_t iSum = 0;
  uint8_t i = 15;
  uint8_t uiMean = 0;

  /*caculate the kMean value*/
  do {
    iSum += pPred[-1 + iTmp] + pPred[-kiStride + i];   //前面是竖着的，后面是横着的
    iTmp -= kiStride;
  } while (i-- > 0);
  uiMean = (16 + iSum) >> 5;

  iTmp = (kiStride << 4) - kiStride;
  i = 15;
  do {
    memset (&pPred[iTmp], uiMean, I16x16_COUNT);
    iTmp -= kiStride;
  } while (i-- > 0);
}

WelsI16x16LumaPredDc_c 的测试函数：

TEST (GetIntraPredictorTest, TestGetI16x16LumaPredDc) {
  const int32_t kiStride = rand() % 16 + 16;  //stride指在内存中每行像素所占的空间

  int i;

  uint8_t* pPred = new uint8_t[256];
  uint8_t* pRef  = new uint8_t[16 * kiStride];
  for (i = 0; i < 16 * kiStride; i++)  //16行，每行stride
    pRef[i] = rand() % 256 + 1;

  pRef += kiStride;   //指向了第二行开始

  int32_t iTmp = (kiStride << 4) - kiStride;  //最后一行开始
  int32_t iSum = 0;
  i = 15;
  uint8_t uiMean = 0;

  do {
    iSum += pRef[-1 + iTmp] + pRef[-kiStride + i];    //前面是竖着的，后面是横着的
    iTmp -= kiStride;
  } while (i-- > 0);
  uiMean = (16 + iSum) >> 5;

  WelsI16x16LumaPredDc_c (pPred, pRef, kiStride);
  for (i = 0; i < 256; i++)
    EXPECT_EQ (pPred[i], uiMean);

  pRef -= kiStride;

  delete []pRef;
  delete []pPred;
}