Hi Guillaume - sorry for the delay.

CMTK actually has an image conversion tool, convertx, which supports pixel type conversions.

As for the question why your average images exceeded the value range of the input images - when you reslice images using higher-order interpolation (cubic or sinc), then such overruns can occur simply because of the coefficients of the interpolation kernels. Not sure this is what happened here, but if you did use higher-order interpolation, it would be absolutely expected.

Best,
  Torsten