AI算法模型输入的格式转换函数HWC -> CHW或者CHW->HWC

/**
 * convert input from HWC format to CHW format
 * \param input A single image. The byte array has length of 3*h*w
 * \param h image height
 * \param w image width
 * \param output A float array. should be freed by caller after use
 * \param output_count Array length of the `output` param
 */
static void hwc_to_chw(const png_byte* input, size_t h, size_t w, float** output, size_t* output_count) {
  size_t stride = h * w;
  *output_count = stride * 3;
  float* output_data = (float*)malloc(*output_count * sizeof(float));
  for (size_t i = 0; i != stride; ++i) {
    for (size_t c = 0; c != 3; ++c) {
      output_data[c * stride + i] = input[i * 3 + c];
    }
  }
  *output = output_data;
}

/**
 * convert input from CHW format to HWC format
 * \param input A single image. This float array has length of 3*h*w
 * \param h image height
 * \param w image width
 * \param output A byte arra