I get this from trying to run makemask:
makemask(mode='copy',
inpimage=lineimagename+".image",
inpmask=lineimagename+".image:mask0",
output=lineimagename+".mask")
2021-11-09 02:27:10 INFO makemask::::casa ##########################################
2021-11-09 02:27:10 INFO makemask::::casa ##### Begin Task: makemask #####
2021-11-09 02:27:10 INFO makemask::::casa makemask( mode='copy', inpimage='/blue/adamginsburg/adamginsburg/almaimf/workdir/G353.41_B6_spw5_12M_spw5.image', inpmask='/blue/adamginsburg/adamginsburg/almaimf/workdir/G353.41_B6_spw5_12M_spw5.image:mask0', output='/blue/adamginsburg/adamginsburg/almaimf/workdir/G353.41_B6_spw5_12M_spw5.mask', overwrite=False, inpfreqs=[], outfreqs=[] )
2021-11-09 02:27:11 INFO makemask::ImageFactory::createImage Created Paged image '__tmp_outputmask_22199' of shape [1080, 900, 1, 480] with float valued pixels.
2021-11-09 02:27:11 INFO makemask::::casa Summing all T/F mask in inpmask and normalized to 1 for mask
2021-11-09 02:27:51 SEVERE image::regrid Exception Reported: Exception: An image with multiple beams cannot be regridded along the spectral axis. You may wish to convolve all channels to a common resolution and retry.
2021-11-09 02:27:51 SEVERE image::regrid+ ... thrown by std::shared_ptr<casa6core::ImageInterface<T> > casa::ImageRegridder<T>::regrid() const [with T = float] at File: src/code/imageanalysis/ImageAnalysis/ImageRegridder.tcc, line: 102
2021-11-09 02:27:52 INFO deleted table /blue/adamginsburg/adamginsburg/almaimf/workdir/G353.41_spw5_12M_B6/_tmp_copy___tmp_frominmask_22199
2021-11-09 02:27:56 SEVERE image::calc (file src/tools/image/image_cmpt.cc, line 553) Exception Reported: ImageExprParse: '__tmp_fromTFmask_22199' is an unknown lattice or image or it is an unqualified region
2021-11-09 02:27:56 SEVERE image::calc (file src/tools/image/image_cmpt.cc, line 553)+ Scanned so far: iif ("__tmp_fromTFmask_22199"
2021-11-09 02:27:56 SEVERE makemask::::casa Task makemask raised an exception of class RuntimeError with the following message: *** Error (2), in mode copy: *** ImageExprParse: '__tmp_fromTFmask_22199' is an unknown lattice or image or it is an unqualified region
2021-11-09 02:27:56 SEVERE makemask::::casa+ Scanned so far: iif ("__tmp_fromTFmask_22199"
2021-11-09 02:27:56 INFO makemask::::casa Task makemask complete. Start time: 2021-11-08 21:27:09.614534 End time: 2021-11-08 21:27:56.399654
2021-11-09 02:27:56 INFO makemask::::casa ##### End Task: makemask #####
2021-11-09 02:27:56 INFO makemask::::casa ##########################################
2021-11-09 02:27:51 SEVERE image::regrid Exception Reported: Exception: An image with multiple beams cannot be regridded along the spectral axis. You may wish to convolve all channels to a common
resolution and retry.
2021-11-09 02:27:51 SEVERE image::regrid+ ... thrown by std::shared_ptr<casa6core::ImageInterface<T> > casa::ImageRegridder<T>::regrid() const [with T = float] at File: src/code/imageanalysis/Imag
eAnalysis/ImageRegridder.tcc, line: 102
2021-11-09 02:27:56 SEVERE image::calc (file src/tools/image/image_cmpt.cc, line 553) Exception Reported: ImageExprParse: '__tmp_fromTFmask_22199' is an unknown lattice or image or it is an un
qualified region
2021-11-09 02:27:56 SEVERE image::calc (file src/tools/image/image_cmpt.cc, line 553)+ Scanned so far: iif ("__tmp_fromTFmask_22199"
2021-11-09 02:27:56 SEVERE makemask::::casa Task makemask raised an exception of class RuntimeError with the following message: *** Error (2), in mode copy: *** ImageExprParse: '__tmp_fromTF
mask_22199' is an unknown lattice or image or it is an unqualified region
2021-11-09 02:27:56 SEVERE makemask::::casa+ Scanned so far: iif ("__tmp_fromTFmask_22199"
I'm pretty sure the complaint is caused by the top line: there are multiple beams in the image. This is _absurd_, though, because the makemask command should not care at all about beams, there is no spectral regridding happening.
This might be new to CASA 6.4, not sure.
EDIT 2021-11-11 15:51: The workaround is easy and maybe better:
ia.open(lineimagename+".image")
shape = ia.shape()
csys = ia.coordsys().torecord()
ia.close()
ia.fromshape(outfile=lineimagename+".mask", shape=shape, csys=csys, type='f')