In case you took some photos showing a scene in motion, you probably want to create an animated gif out of them. If you did not use a tripod for fixing your camera, the images will not be aligned perfectly, so that the scene is slightly shifted within the images – which is clearly visible in the animated gif, and doesn’t look too good. I’ve stumbled across this problem recently: there exist several GUI based tools for Linux to do the image alignment and gif creation (such as with using this Gimp plugin), but at least the tools I’ve tried require the user to start much of the processing by hand – which simply eats up too much of my time. Inspired from here I used a combination of align_image_stack and PTblender (part of the Hugin panorama tool suite set I’ve used in automatic panorama creation) and ImageMagick’s convert to automatically align images, equalize brightness and color and create an animated gif from them to save me some time.
Aligning images and equalizing brightness and color
At first we need to align all images with the scene, so that they overlap “perfectly”. In this context, perfectly means adequate for my personal usage in animated gifs, as there are still minor shifts left after aligning. align_image_stack from the Hugin panorama tool suite is designed to do exactly that for aligning HDR images. Therefore, you can use
convert *JPG -resize 1000 +repage resized_%02d.jpg align_image_stack -i -m -s 1 -C -a aligned_ -C resized* PTblender -k 0 -t 0 -p blended_ aligned* convert blended_* -format jpg blendedjpg_%02d.jpg
- copy and resize all *JPG images in the current directory (accelerates consecutive aligning and gif creation, using only the “-s” parameter in the subsequent command would output bigger aligned images),
- align all these downscaled files using align_image_stack. There “-i” corrects image center shifts, “-m” optimized field of view, “-s 1” scales images internally before aligning by a factor of 2¹ (does not scale down aligned output files), “-C” automatically crops images to the area covered by all images, “-a aligned” stands for the command producing .tif files which have this additional prefix, and “-C” stands for the command automatically cropping all images to those areas contained in all images,
- equalize color and brightness across images using PTblender. “-k 0” takes the first of the images as reference image, “-t 0” corrects both brightness and color, “-p blended_” again specifies the output file prefix.
Creating the animated gif
Now we can create an animated gif from the aligned images. ImageMagick’s convert provides all features you need in order to create the gif exactly as you’d like to have it. I personally use the following command to additionally rotate and resize the images, reduce the amount of used colors and create a file name representing the originally used images. You might want to adapt these to fit your needs.
convert -format jpg -rotate "-90" -resize 600 +repage -delay 20 -loop 0 -colors 100 blendedjpg* "`ls *JPG | head -1 | sed s/\.JPG//`-`ls *JPG | tail -1 | sed s/\.JPG//`.gif"
If the gif contains erroneous areas (wrong color or completely black etc.) try a slightly changed color palette and image size or leave out the color palette completely. That’s it, you’ve just created your aligned and animated gif.
If everything worked fine and you are happy with your animated gif: to quickly remove files created as side effect as well as log/debug files of the used tool suites:
rm aligned* blended* resized* Debug.txt zcom_log.txt
Installation on Ubuntu 12.04, 14.04 etc.
As align_image_stack and PTblender come with Hugin, and convert with ImageMagick, you just need to install those two tool suits from the Ubuntu repositories:
sudo apt-get install hugin imagemagick