static BufferedImage byteArrayToGrayBufferedImage(byte[] pixels, int w, int h) {
  PixelInterleavedSampleModel sm = new(
    DataBuffer.TYPE_BYTE,
    w,
    h,
    1, // pixelStride
    w, // scanlineStride,
    new int[] {0} // bandOffsets
  );
  DataBufferByte db = new(pixels, pixels.length);
  WritableRaster wr = Raster.createWritableRaster(sm, db, new Point);
  ret new BufferedImage(grayColorModel(), wr, false, null);
}