Dear Yune:
> -----Original Message-----
> From: SPM (Statistical Parametric Mapping)
> [mailto:[log in to unmask]] On Behalf Of Yune Lee
> Sent: Tuesday, October 09, 2007 7:35 AM
> To: [log in to unmask]
> Subject: [SPM] Q) spm_vol
>
> Hello,
>
> So, after typing V= spm_vol ('bold_001.img'), I've got
> answers as following.
>
> ans =
>
> filename: 'bold001.img'
> dim : [80 80 36 4]
> mat : [4X4 double]
> pinfo : [3X1 double]
>
> .
> .
> .
>
> I looked up the help spm_vol and they explain that each
> number in dim is about x, y, and z dimensions of the volume,
> and the data type of the image.
> I wonder what the scale is (i.e., mm, cm)
THE SCALE IS IN VOXELS.
> and what 4 means in the 4th column?
THIS IS A DATA TYPE IDENTIFIER. SEE SPM_TYPE FOR MORE INFORMATION. TYPE
SPM_TYPE(4) AT THE MATLAB PROMPT TO RETURN THE DATA TYPE.
> in the 4th column?
> Also, if I type V.pinfo, I get answer 1
> 0
> 0 Can
> any one tell me what each number means?
SEE SPM_VOL WHICH EXPLAINS EACH NUMBER. IN BRIEF, THE SCALING FACTOR ALLOWS
REPRESENTING DATA IN A MORE COMPACT FORMAT, ALBEIT WITH SOME ROUNDING ERROR.
FOR EXAMPLE LET'S SAY YOU HAVE AN IMAGE WITH ONE PLANE IN WHICH ALL THE
VOXELS HAVE A VALUE OF 0.5 AND IN WHICH THE SIZE OF THE IMAGE IS 10 X 10
VOXELS. REPRESENTING THE IMAGE DATA AS DOUBLES IN MATLAB WOULD REQUIRE 10 X
10 X 8 (bytes) = 800 BYTES. HOWEVER, IF I SET THE SCALING FACTOR TO 0.5 I
CAN THEN REPRESENT ALL THE VOXEL VALUES IN THE IMAGE BY ONES AND THE IMAGE
COULD BE SAVED AS TYPE CHAR (1 BYTE PER VOXEL), SO NOW THE IMAGE DATA ONLY
TAKES UP 10 X 10 X 1 (byte) = 100 BYTES.
REGARDS
darren
>
> Thanks!!
>
>
>
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