To create the 512x512 texture, did the following:

% unu resample -k box --size 512 512 -i ddro-80.nrrd -o ddr-512.nrrd
% unu minmax ddr-512.nrrd
min: -7.470736
max: 64.226639
% unu affine -7.470736 ddr-512.nrrd 64.226639 0 1 \
  | unu quantize -i - -b 8 \
  | unu save -i - -f png -o ddro-tx.png

<script type="text/javascript">//<![CDATA[
		function toggle_ffErrors() {
			var errorsblock = document.getElementById("ffErrorsBlock");
			var errorsgroup = document.getElementById("ffErrors");
			if (errorsblock.style.display == "none") {
				errorsblock.style.display = "block";
				errorsgroup.style.right = "10px";
			} else {
				errorsblock.style.display = "none";
				errorsgroup.style.right = "300px";
			}
		}
//]]></script>
<div id="ffErrors">
<a href="javascript:toggle_ffErrors();">Click to toggle</a>
<div id="ffErrorsBlock">
	<div class="error">does not end with &lt;/html&gt; tag</div>
	<div class="error">does not end with &lt;/body&gt; tag</div>
	<div class="info">The output has ended thus: 36 ddr-512.nrrd 64.226639 0 1 \
  | unu quantize -i - -b 8 \
  | unu save -i - -f png -o ddro-tx.png</div>
</div></div>
</body></html>