[CinePaint] how can we change aspect ratio without resizing?

after seeing these screenshots:
http://www.cinepaint.org/pix/last.samurai/index.html i start thinking
about one question: how can we change the aspect ratio of a picture
without resizing? (just like found on relatively recent versions of
Photoshop)

the fact is:
35mm is something around 4x3 and 3x2 formats
(http://en.wikipedia.org/wiki/35_mm_film)
2k and 4k are 16x9 format (2048x1080 and 4096x2160 -
http://en.wikipedia.org/wiki/2K_resolution )
Early DLP projectors are 5x4 format (1280x1024 -
http://en.wikipedia.org/wiki/2K_resolution )

the final format displayed usually from movies like that Last Samurai
link above seems to be 7x3 (or 21x9), which would be much more
comfortable editing it with aspect ratio adjusted to our eyes (and
perceptions) than struggle on editing on them squeezed

thanks,
p

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