Fix setting output size image

[ericpre]

Progress of the PR

• [x] Fix setting output size image,
• [n/a] update docstring (if appropriate),
• [n/a] update user guide (if appropriate),
• [x] add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• [x] Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:rosettasciio build of this PR (link in github checks)
• [x] add tests,
• [x] ready for review.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 86.36%. Comparing base (0646b2c) to head (0f8daf0).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #244 +/- ## ======================================= Coverage 86.36% 86.36% ======================================= Files 83 83 Lines 10604 10606 +2 Branches 2307 2307 ======================================= + Hits 9158 9160 +2 Misses 930 930 Partials 516 516 ```

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