This is a note to self about how to programmatically resize and crop many images using ImageMagick.
It all started with a folder full of photos with different pixel sizes and ratios. That is because they had been captured with various cameras and had also been manually cropped. This could be verified by running this command to print their pixel sizes:
identify -format "%wx%h\n" *.JPG
Fortunately, all the images had a reasonably large pixel count, so I decided to go for a 5MP pixel count (2560×1920 in 4:3 ratio). That was achieved with this one-liner:
for i in *.JPG; do convert "$i" -resize 3000x1920 -crop 2560x1920+0+0 "$i"; done
The little script looks for all the image files in the folder and starts by resizing them to the preferred height (1920 pixels) and then cropping them to the correct width (2560 pixels). The result is a folder full of equally sized images.
Ps: the script above overwrites the original files in the folder.
My new book will be published Open Access, and I also aim only to use open-source tools as part of the writing process. The most challenging has been to figure out how to make nice-looking illustrations.
Parts of the book are based on the Ph.D. dissertation that I wrote a long time ago. I wrote that on a MacBook and made all the illustrations in OmniGraffle. While it was quite easy to make the switch to Ubuntu in general, OmniGraffle has been one of the few programs I have really missed in the Linux world. True, many graphics tools are available, but none with the same type of finesse as OmniGraffle.
After trying and failing with many of the most popular vector graphics tools, I have ended up using LibreOffice Draw to make all the illustrations. It is more limited than, say, Inkscape but provides the tools I need. It was also easy to get used to the workflow. The only thing I have struggled with figuring out is how to create nice-looking soft drop shadows. In OmniGraffle, the shadow function immediately looks nice, such as in this illustration of how one can think of an instrument as the mediator between action and sound:
My first attempts at adding a shadow in LibreOffice Draw ended up with a gruesome non-soft shadow:
I searched around, but could only find all sorts of complicated solutions. This was last year, and I decided to move on with the project without shadows. I could have moved to another graphics tool but had already spent quite some time making Draw figures. So I decided that shadows were not that important after all.
As part of the final manuscript completion, I am currently making minor changes to all the figures. Out of the blue, I found out that the latest version of Draw now has a more developed shadow section.
Hooray! By changing the “distance,” “glow,” and “transparency” settings, I now finally have soft drop shadows in place:
Draw does still not provide the same smooth user experience as OmniGraffle. But getting the soft drop shadow function in place helps a lot!
I have recently played with AudioStellar, a great tool for “sound object”-based exploration and musicking. It reminds me of CataRT, a great tool for concatenative synthesis. I used CataRT quite a lot previously, for example, in the piece Transformation. However, after I switched to Ubuntu and PD instead of OSX and Max, CataRT was no longer an option. So I got very excited when I discovered AudioStellar some weeks ago. It is lightweight and cross-platform and has some novel features that I would like to explore more in the coming weeks.
Samples and sound objects
In today’s post, I will describe how to prepare short audio files to load into AudioStellar. The software is based on loading a collection of “samples”. I always find the term “sample” to be confusing. In digital signal processing terms, a sample is literally one sample, a number describing the signal’s amplitude in that specific moment in time. However, in music production, a “sample” is used to describe a fairly short sound file, often in the range of 0.5 to 5 seconds. This is what in the tradition of the composer-researcher Pierre Schaeffer would be called a sound object. So I prefer to use that term to refer to coherent, short snippets of sound.
AudioStellar relies on loading short sound files. They suggest that for the best experience, one should load files that are shorter than 3 seconds. I have some folders with such short sound files, but I have many more folders with longer recordings that contain multiple sound objects in one file. The beauty of CataRT was that it would analyse such long files and identify all the sound objects within the files. That is not possible in AudioStellar (yet, I hope). So I have to chop up the files myself. This can be done manually, of course, and I am sure some expensive software also does the job. But this was a good excuse to dive into SoX (Sound eXchange).
SoX for sound file processing
SoX is branded as “the Swiss Army knife of audio manipulation”. I have tried it a couple of times, but I usually rely on FFmpeg for basic conversion tasks. FFmpeg is mainly targeted at video applications, but it handles many audio-related tasks well. Converting from .AIFF to .WAV or compressing to .MP3 or .AAC can easily be handled in FFmpeg. There are even some basic audio visualization tools available in FFmpeg.
However, for some more specialized audio jobs, SoX come in handy. I find that the man pages are not very intuitive. There are also relatively few examples of its usage online, at least compared to the numerous FFmpeg examples. Then I was happy to find the nice blog of Mads Kjelgaard, who has written a short set of SoX tutorials. And it was the tutorial on how to remove silence from sound files that caught my attention.
Splitting sound files based on silence
The task is to chop up long sound files containing multiple sound objects. The description of SoX’s silence function is somewhat cryptic. In addition to the above mentioned blog post, I also came across another blog post with some more examples of how the SoX silence function works. And lo and behold, one of the example scripts managed to very nicely chop up one of my long sound files of bird sounds:
The result is a folder of short sound files, each containing a sound object. Note that I started with an .AIFF file but converted it to .WAV along the way since that is the preferred format of AudioStellar.
SoX managed to quickly split up a long sound file of bird chirps into individual files, each containing one sound object.
To scale this up a bit, I made a small script that will do the same thing on a folder of files:
#!/bin/bash
for i in *.aif;
do
name=`echo $i | cut -d'.' -f1`;
sox "$i" "${name}.wav" silence 1 0.1 1% 1 0.1 1% : newfile : restart
done
And this managed to chop up 20 long sound files into approximately 2000 individual sound files.
The batch script split up 20 long sound files into approximately 2000 short sound files in just a few seconds.
There were some very short sound files and some very long. I could have tweaked the script a little to remove these. However, it was quicker to sort the files by file size and delete the smallest and largest files. That left me with around 1500 sound files to load into AudioStellar. More on that exploration later.
Loading 1500 animal sound objects into AudioStellar.
All in all, I was happy to (re)discover SoX and will explore it more in the future. I was happy to see that the above settings worked well for sound recordings with clear silence parts. Some initial testing of more complex sound recordings were not equally successful. So understanding more about how to tweak the settings will be important for future usage.
I am often dealing with folders with lots of files with weird file names. Spaces, capital letters, and so on, often cause problems. Instead of manually fixing such file names, here is a quick one-liner (found here) that can be run in the terminal (at least on Ubuntu) to solve the problem:
rename 'tr/ A-Z/-a-z/' -- *
It is based on a simple regular expression, replacing any spaces with hyphens, and changing any capital letters to lower case.
I take a lot of timelapse shots with a GoPro camera. Usually, I do this with the camera’s photo setting instead of the video setting. That is because I find it easier to delete unwanted pictures from the series that way. It also simplifies selecting individual photos when I want that. But then I need a way to create a timelapse video from the photos easily.
