Here are the differences between the last metadata file and the one
we suggest to standardize on. They are just a handful of minor changes,
that we comment inline below

--- metadata_test2.xml	2020-05-04 16:48:33.320669802 +0200
+++ metadata_test3.xml	2020-05-04 17:49:15.002814601 +0200

1) use as external identifiers the part of the DOI that comes after https://doi.org/10.5201/ 

-        <external_identifier>2018-236</external_identifier>
+        <external_identifier>ipol.2018.236</external_identifier>

2) use <codemeta:author> instead of <author> for authors, and if possible add affiliations,
as shown below

-        <author>Jose-Luis Lisani</author>
+        <codemeta:author>
+	  <codemeta:name>Jose-Luis Lisani</codemeta:name>
+	  <codemeta:affiliation>Universitat Illes Balears, Spain</codemeta:affiliation>
+	</codemeta:author>

3) Use more explicit material for the release notes. The descriptive text from the Demo might be a good option.

-        <codemeta:releaseNotes>On-line demo available at IPOL webpage</codemeta:releaseNotes>
+        <codemeta:releaseNotes>
+	Given an input image this demo computes the result of the three versions of the MLHE algorithm described in the associated article: MLHE HE, MLHE PAE and MLHE CLAHE. The users can select the parameters of each method. The default parameters are the same described in the article. For comparison, the results of classical histogram equalization (HE) and CLAHE are also displayed. We use obtained the Matlab implementation of the CLAHE algorithm. Both HE and CLAHE are applied on the intensity component of the input image and the output color image is obtained as in the MLHE methods.
+	</codemeta:releaseNotes>

4) add the downloadUrl pointing to the tar/zip/tgz archive

+	<codemeta:downloadUrl>https://www.ipol.im/pub/art/2018/236/mlheIPOL.tgz</codemeta:downloadUrl>