Directionally-encoded colour (DEC) data are stored as 4D images with three volumes; the non-negative values in each of these volumes correspond to the red, green and blue components of the colour / intensity of each voxel. This should be evident in the output of
Assuming the data have been generated correctly, which should be the case if
mrview shows it correctly, I can think of two things that may conceivably lead to issues:
Other softwares may require that the values stored within a DEC image lie within the range [0, 1], and fail to display as such / produce an error if this is not the case. FA values may exceed 1 in the presence of negative eigenvalues. You could try running
mrstats on the image, and check the minimum / maximum values.
I was going to suggest that other softwares may have been expecting a NIfTI Intent Code to display a DEC image; but there doesn’t actually appear to be an intent code for such…
In MRIcro, is it a greyscale FA image that is shown, or the first volume of the image (i.e. the left-right component of the first eigenvector, scaled by FA)? You can visualise the latter in
mrview by changing the colour map from RGB to greyscale.