Imaging and a little bit of OSS

In order to convert files in .img and .hdr format to a single .nii file, we first need to install the nifti tools toolbox for matlab.

nifti tools

Once the path for nifti tools has been set in matlab, the files in .hdr and .img format can be combined to create a .nii file by running the following two commands:

nii=load_nii(‘filename_with_hdr_extension’);
save_nii(nii, ‘desired_filename_for_niftifile.nii’);

To gzip the nifti file for use in freesurfer:

gzip filename.nii filename1.nii.gz

This will create a gzipped nifti file.

To automatically segment the structural volume:

recon_all -i filename1.nii.gz -subjid SUBJID -all

This will segment the structures containing in the structural file filename.nii.gz. Complete information on using recon-all for freesurfer can be found at FreeSurfer Wiki.

For some reason, Freesurfer seems to work well in tcsh. I’ve often encountered problems of weird nature when running it under bash. In order to run your autosegmentation with freesurfer type in tcsh at the terminal, since by default it is set to bash in most linux distros.

slash_boot Imaging image processing, Imaging, mri, segmentation

I had to create a movie/animation out of a series of images that I had in my folder. There were several methods described on several forums which suggested using GIMP for creating GIF files from JPG or PNG files when one is using Linux. Now the problem was that I had 70 files in total and it would have taken me a long to time to add all those images to GIMP in order to create my animation file.

Then I read somewhere that we can actually create GIF images in command line mode using Imagemagick. But to do so you need to have Imagemagick installed on your system. To install it in Ubuntu, run:

sudo apt-get install imagemagick

This program has several features that would let you do all sorts of things with images. I was interested in converting a bunch of PNG files into an animated GIF file. To do so, we need to  rename the files in a way that they would lie in a sequence when arranged alphabetically (if you plan on doing it the easy way). Suppose you have files named slide_01.png, slide_02.png, slide_02.png….slide_xx.png, and you want to convert them to movie.gif, we run:

convert -delay 10 -loop 0 slide*.png movie.gif

The parameter delay inserts a desired delay between two consecutive slides. The number x used for delay inserts 10x milliseconds of delay between two frames. Loop parameter 0 makes it repeat infinitely.

If you had files with non-uniform names, then you need to input each of them in a sequence after the delay and loop parameters. Suppose you have file summer.jpg, fall, winter.jpg, fall.jpg and spring.jpg and you want to order them as fall, winter, spring and summer in the gif image seasons.gif with a 1 second delay between each of them, use:

convert -delay 100 -loop 0 fall.jpg winter.jpg spring.jpg summer.jpg seasons.gif

Here are some animations of numbers from 0 to 9 with varying delays.

The delay values specified the above cases were: 1, 5, 15, 25, 50 and 100.

GIF animation with 10 millisecond frame delay

GIF animation with 50 millisecond frame delay

GIF animation with 150 millisecond frame delay

GIF animation with 250 millisecond frame delay

GIF animation with 500 millisecond frame delay

GIF animation 1 second frame delay

=================

slash_boot Imaging, Linux and OSS conversion, imagemagick, Imaging, jaunty, Linux and OSS

This evening I took a snapshot of my desk (which holds my desktop) with my cellphone camera. After transferring it via bluetooth, I opened the image and it was rather amusing to see the exact image of desk inside of an identical image. So just out of curiousity I snapped another photo with roughly the same FOV as before and loaded it on the computer, and again took a picture of that.

Photo iterations: or photo within photo

The picture looks quite interesting, as it depicts the same object at different time points within the same spatial space. I don’t see any artistic value in this picture, but what I do see is a lot of potential for philosophical discussion about time and space and how we can represent variations in time within a 2D space.

slash_boot Imaging Imaging, philosophy