George, The transformation from the Demons algorithm is a vector field. You can write out the vector field using ImageFileWriter (templated over an image of vectors). You can later read the vector field back in. I usually use the Meta format (mhd) to store the output of the Demons. There was a bug in reading vector images that was fixed a few months ago. So if you are using a cvs version of ITK, you can successfully read the vector fields back in. If you are using an older version of ITK, you'll need to write out each component of the vector into a separate file. Here you use a number of VectorIndexSelectionCastImageFilter to separate the vector field into a set of scalar files and pass each scalar field to an ImageFileWriter. Jim -----Original Message----- From: GEORGE XU [mailto: Subject: [Insight-users] How to write transformation matrices to file? Hello, I am using the demons deformable registration to match two MRI brain scan images. I would like to save the transformation so that it can be used again at a later stage. Is there a way that I can save the transformation and write it to a file? Thanks, George _______________________________________________ Insight-users mailing list Source.