The heightmap importer for .r16 files has a "size" input field. This appears to be width * height, but because they cannot be specified separately the code effectively only supports square heightmaps.
I tried replacing the heightmap importer with a generic raw data importer two years ago. Conceptually it worked, but because Krita requires importer/exporter code to associate with a given file extension I ended up shelving it. I'll see if I can adapt the code to work with the current r16 import/export code.
Git commit b4b9021616edcfb1e6bfd084c5567f69da7668fa by Victor Wåhlström. Committed on 14/07/2017 at 19:27. Pushed by victorw into branch 'master'. Add support for non-square heightmap import/export and various related improvements/bugfixes * Support for non-square heightmap files (.r8, .r16) * New heightmap import/export dialog * Fixed issue where imported heightmap is "transposed" * Fixed issue where saving an r16 heightmap file as r8 or vice versa only changes the extension Related: bug 381830, bug 381866 Differential Revision: https://phabricator.kde.org/D6460 M +10 -0 libs/ui/kis_config.cc M +3 -0 libs/ui/kis_config.h M +4 -0 plugins/impex/heightmap/CMakeLists.txt M +39 -44 plugins/impex/heightmap/kis_heightmap_export.cpp M +1 -17 plugins/impex/heightmap/kis_heightmap_export.h M +50 -35 plugins/impex/heightmap/kis_heightmap_import.cpp M +1 -1 plugins/impex/heightmap/kis_heightmap_import.h A +230 -0 plugins/impex/heightmap/kis_wdg_options_heightmap.cpp [License: LGPL (v2.1+)] A +52 -0 plugins/impex/heightmap/kis_wdg_options_heightmap.h [License: LGPL (v2.1+)] M +170 -59 plugins/impex/heightmap/kis_wdg_options_heightmap.ui A +10 -0 plugins/impex/heightmap/tests/CMakeLists.txt A +- -- plugins/impex/heightmap/tests/data/results/test_512x256.r16.png A +- -- plugins/impex/heightmap/tests/data/results/test_512x256.r8.png A +- -- plugins/impex/heightmap/tests/data/results/test_512x512.r16.png A +- -- plugins/impex/heightmap/tests/data/results/test_512x512.r8.png A +- -- plugins/impex/heightmap/tests/data/sources/test_512x256.r16 A +1 -0 plugins/impex/heightmap/tests/data/sources/test_512x256.r8 A +- -- plugins/impex/heightmap/tests/data/sources/test_512x512.r16 A +1 -0 plugins/impex/heightmap/tests/data/sources/test_512x512.r8 A +36 -0 plugins/impex/heightmap/tests/kis_heightmap_test.cpp [License: GPL (v2+)] A +31 -0 plugins/impex/heightmap/tests/kis_heightmap_test.h [License: GPL (v2+)] https://commits.kde.org/krita/b4b9021616edcfb1e6bfd084c5567f69da7668fa