ESP32-Cam Pixel Downsampling - read out downsampled RGB pixels pretty pretty fast!

ESP32-Cam Pixel Downsampling

// Code based on BITLUNI's ESP32-cam work

// the size you want to downsample to
int newWidth = 40;
int newHeight = 30;
int DSF = 160 / newWidth; // Down Sampling Factor - ideally DSF should be 4, 8 or 16.. so that the bitshifting happening below is accurate

void downSample(unsigned char *frame)
{

  for (int y = 0; y < newHeight; y++)
  {
    for (int x = 0; x < newWidth; x++)
    {
      int r = 0;
      int g = 0;
      int b = 0;
      for (int j = 0; j < DSF; j++)
        for (int i = 0; i < DSF; i++)
        {
          unsigned char p[3];
          getPixel(x * DSF + i, y * DSF + j, frame, p); // this summarizes a "DSF" amount of camera pixels into the new down-sampled pixels, and sends it to getPixel which returns p[3] filled with rgb values.
          r += p[0];
          g += p[1];
          b += p[2];
        }
      // reducing/averaging the summarized pixels
      newImage[y][x][0] = r >> DSF;
      newImage[y][x][1] = g >> DSF; 
      newImage[y][x][2] = b >> DSF;

      // averaging rgb into one greyscale value
      grayscale[y][x] = (newImage[y][x][0] + newImage[y][x][1] + newImage[y][x][2]) / 3;
    }
  }
}

void getPixel(int x, int y, unsigned char *image, unsigned char *pixel)
{
  int p = image[(y * 160 + x) * 2 + 1] | (image[(y * 160 + x) * 2] << 8);
  pixel[0] = (p >> 11) << 3;
  pixel[1] = ((p >> 5) & 0b111111) << 2;
  pixel[2] = (p & 0b11111) << 3;
}