 |
 |
Dear Dr. Brett: Just revisiting the issue one more time: > Analyze images consist of a (rather complex) .hdr file, with lots of > information in it, and a very simple .img file, which simply contains > all the voxel values for the image, in x, y, and then z order (at least > for SPM). This means that, for an 8 bit image, all the voxel values have > to be between 0 and 255. SPM extends this a bit, by using one of the > spare fields in the .hdr file to 'scale' the image (the scale factor). What is the purpose of doing that? Is it just to increase the dynamic range of the image? > Thus, to get actual voxel values, you read in the numbers from the .img > file (0-255 in an 8 bit image), then multiply these values by the value from > the scale factor, from the header. That is, SPM itself does not scale the images? Then, the scale factor is taken into account when SPM does global normalization? Now, to our specific problem. Our images are all 16-bit, and we use the full dynamic range, so the maximum value is 32767. The field Funused of the Analyze header is always 1. This field is not changed during any of SPM preprocessing steps, so I assume that in my case, no scaling is involved, right? Many thanks, Vitaly Furman %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%