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Dear Saad, Hello. Thank you for the feedback. I am actually looking for the arctan to calculate the angles. And what is make_dyadic_vectors used for? And how can I find out more about how this function works? Thank you, Jason. ----- Original Message ---- From: Saad Jbabdi <[log in to unmask]> To: [log in to unmask] Sent: Monday, July 16, 2007 1:38:17 PM Subject: Re: [FSL] Arc Tangent of images Hi Jason - Calculating the tangent of an angle (in radian) using fsl tools is straightforward if you take advantage of make_dyadic_vectors. all you need to do is provide two images: make_dyadic_vectors image1 image2 output where image2 is all zeros and image1 are your angles x. then the ouput is a 4D image where the 4th dimension has the following entrie: [sin(x)cos(0); sin(x)sin(0); cos(x)] then you divide the 1st by the last entry to get the tangent! for the arctangent, it is a little bit trickier... but i'm not sure which one you really want given your email? i hope this is helpful... saad On 16 Jul 2007, at 16:12, Jason Steffener wrote: Hello all, Is there any way of taking the arc tan (or sine/cosine) of two images in FSL? I can easily do it in MatLab but am trying to set up a "pure" FSL analysis. Thank you, Jason. --------------------------------------------------------------------------- Saad Jbabdi, Postdoctoral Research Assistant, Oxford University FMRIB Centre FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222545 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~saad ---------------------------------------------------------------------------