Archive

Tag Archives: time lapse

3d stereo experiments.009

Yogi from Mars 3D

Going off-piste again this week, kinda. Randomly, I wondered just how easy it would be to capture and process stereo 3D timelapse with open-source tools. Having mostly ignored 3D, and being largely unimpressed by its cinema application, I was still wondering what the killer application for stereoscopic photography.

These days, a number of single lens cameras have a “3D” function which stitches together a number of exposures into a navigable image that allows the point-of-view (POV) to be changed, interactively. To my mind this is not really 3D, it’s like the moving lenticular images we used to collect in the 1970s. What I am interested in is true stereoscopic imaging, which requires genuine binocular vision to give a convincing effect of depth.

Tim Dashwood has written an excellent introduction to stereo/3D photography that I do not intend to duplicate, but what I am going to cover is the specifics of doing it with CHDK, FFMpeg and ImageMagick.
http://www.dashwood3d.com/blog/beginners-guide-to-shooting-stereoscopic-3d/

This is just an introductory blog post and I’m not going to get to any workflows just yet.

Stereo imaging has been around since 1840, almost as long as photography itself, and here are some amazing stereographs captured during American Civil War.
http://www.theatlantic.com/infocus/2012/02/the-civil-war-part-3-the-stereographs/100243/

Some of these give away the fact that they were show with one camera in two positions.

Landscape

I was introduced to stereoscopic 3D it in the 1970s via my sister’s View-Master, but this was not much more sophisticated than the widely available stereo viewers from the nineteenth and early twentieth centuries.

Stereoscoop_VM

The documented optimum lens separation for human vision is 65mm, give or take, and my eyes are pretty much exactly that distance apart. However, according to various sources larger separations work fine for some subjects and for landscapes and distant objects, a larger separations will work fine. I will be doing some tests with different sized subjects.

For reference, I am not interested in red/cyan anaglyph type image, because of the weird colour effects, but I am going to use this technique for the sake of being able to display them on vanilla monitors. Not everyone can do it, but I can also do the cross-eyed right-left trick too, although it’ not practical for any length of time.

Recently, I bought a 3D LED TV that supports passive polarised glasses and I saw an excellent demo of a Fujifilm W3 3D camera displaying media on LG monitors at a photography trade show in 2010.

There are some excellent existing resources for shooting stereographs with CHDK, including the StereoDataMaker site, and Gentles Ltd, and I’ll add more info about other resources soon.

I have mixed feelings about 3D and am not sure just what I really want to do with it, but how hard can it be? I was not sure how to prepare the media and assumed it would be more difficult than it is. Turns out processing pairs of images is very easy in ImageMagick, and as far as the polarised light monitors go, all the cleverness is done in the screen so you just have to give it 2 images side-by-side.

It never occurred to me that it would be so easy.

So, side-by-side is my eventual destination format, but using red/cyan anaglyph for convenience and online dissemination.

Anyway, I’m running out of time, but I might update this post later. In the meantime here are a few links and I’ll post more soon with come code and practical tests.

Stereoscopy.com
http://www.stereoscopy.com/gallery/

History of Sterography
http://www.arts.rpi.edu/~ruiz/stereo_history/text/historystereog.html

Advertisements

A640 rotated_84_2

Having been flying around the country over the past couple of weeks, I’ve shot a lot of timelapse out of the front windscreen. Just because I can.

It’s largely thanks to CHDK and I have managed to record myself getting lost on routes between Sheffield, Lancaster, Leeds, Newcastle, Nottingham and York. I have a few plans for this media, but one journey is already online here:

This was quite a successful Flying Monkey TV experiment and I had it edited and online within three hours of getting home.

These journeys were mostly shot on a Canon PowerShot A560, timelapse-enable with CHDK, and mounted on the inside of the front windscreen with a suction mount (see below). I mounted the camera hanging from the top of the screen, upside down. This meant that it was in line with the passenger side roof pillar and hence did not obscure my view.

I don’t use the auto-rotate feature in most cameras because it sometimes gets confused and can give you a few incorrectly rotated frames here and there. Consequently, shooting this way, I end up with an upside-down video that then needs rotating.

559CANON_full_2048_03pct

I used to drop them into Final Cut Pro, render them and export them to a new movie file, which works fine, but I think it’s time to write a Bash script to do it.

No sooner said than done! Well, not quite, but it was much easier than I imagined. As usual Google managed to find some very helpful resources for me to cannibalise. Writing the code is much faster than documenting it into a usable blog post.

I started by reminding myself how to create a basic for-next procedure (detail included here for other noobs). Here is a bit of basic code with lists the files in the present working directory ending in “.JPG” (don’t forget this is case-sensitive) and echos them to the screen. The semicolons separate the statements and the “done” terminates it.

for i in $(ls *.JPG); do echo $i; done

For the next step, instead of just listing the file names to the screen, I added the ImageMagick step to rotate the image and write it over the original.

for i in $(ls *.JPG); do convert $i -rotate 180 $i; done

As you might have already gathered, I like some progress feedback so added an echo with the file count and file name.

for i in $(ls *.JPG); do convert $i -rotate 180 $i; x=$(($x+1)) ;echo “$i $x”; done

However, a current file number is only of use if you know how many more to go. A bit of googling revealed this forum thread and the code:

ls -l | wc -l

This lists all the files in the current directory and then pipelines that list to give an integer count of the items in that list. It’s not necessary if this is just a temporary folder and it’s cleared between uses, but if you want to filter the file types you can add a wild card search like this:

ls -l *.JPG | wc -l

I found information about the two commands on linux.about.com and a forum thread which combines the two on unix.com.
http://linux.about.com/od/commands/l/blcmdl1_ls.htm
http://linux.about.com/library/cmd/blcmdl1_wc.htm
http://www.unix.com/unix-dummies-questions-answers/36490-ls-command-listing-number-files.html

So my final piece of code (for this iteration at least) is here:

x=0; c=$(ls -l *.JPG | wc -l); for i in $(ls *.JPG); do convert $i -rotate 180 $i; x=$(($x+1)) ;echo “$x /$c $i”; done

This sets x to be 0, c to be the number of files with filenames ending in “.JPG” in the current directory, rotates each one of them by 180 degrees, overwrites the original file and echos the file number, the file count and the filename. It’s pretty basic and I’ll roll it into a script soon.

There may well be better ways of doing this, but it worked well as an exercise to reinforce my learning.

The script here is only a slightly cleaned up version of the previous one, but also with a major addition. A timer.

It may be just that I’m new to Linux, but getting the syntax correct was very unintuitive. It took a lot of trial-and-error to get the spaces in the right place, and it reminds me a lot of programming in the 1980’s where you just get a “syntax error” message and nothing else.

This timer function uses the classic technique of storing the system time at the start of the script and then again once the script has finished, subtracting the former from the latter and the difference is the time taken.

This function only returns an the number of seconds as an integer, and a result of “1350575350” might as well be in grains of sand. So, I have then reformatted the output to a more human-readable minutes and seconds by dividing the number of seconds elapsed by 60 to get the minutes and deriving the modulus (what’s left over) for the number of seconds. I could also do a similar thing with the value 3600 if I wanted to format it in hours, minutes and seconds.

Strangely, when I tried date +%2s (which returns the current system time in seconds) at the command line in OS X it failed, but not on the same machine whilst booted into the Linux partition. Turns out, it was a typo but Linux is happy to ignore this glaring mistake (should be date +%s) whilst OS X is not. Strange when it’s so particular about other syntax.

However, all complaining aside, I have got some actual useful working code up and running much more easily than I had expected.

# !/bin/bash

clear
echo “Hello Monkey Planet”
starttime=$(date +%s)

cd /home/richard/Desktop/RBTest/newtest
rm *.JPG
rm *.jpg

cd /home/richard/Desktop/RBTest/testtemp
rm *.JPG
rm *.jpg

cd /home/richard/Desktop/RBTest/newtest
#gphoto2 –get-all-files

x=1; for i in $(find $(pwd) -name \*.JPG | xargs ls -t -r); do counter=$(printf %04d $x); ln “$i” /home/richard/Desktop/RBTest/testtemp/img_”$counter”.jpg; x=$(($x+1)); done

cd /home/richard/Desktop/RBTest/testtemp
ffmpeg -r 25 -i img_%04d.jpg -s 640×480 -qscale 1 -vcodec mjpeg movie.mov
rm *.jpg

stoptime=$(date +%s)
fulltime=$(expr $stoptime – $starttime)
fulltimesecs=$(expr $fulltime % 60)
fulltimemins=$(expr $fulltime / 60)

echo “$fulltimemins minutes $fulltimesecs seconds”

I suppose it would be good to structure this programming at some point, such as the timer function, so that I could call it from any script. There probably is a function in Linux already.

More soon…

Well, FFMpeg is a monster. Getting it to work with some default settings was easy, but the number of parameters is breathtaking. I work in professional video on a daily basis but can hardly understand any of the plethora of options. There is extensive documentation on ffmpeg.org but most of it is meaningless unless you already know what it means.

Below is the basic structure of a Bash script. It requires the #!/bin/bash at the beginning

#!/bin/bash
clear
echo “Hello world.”

This script clears the screen and prints the words “Hello world”.

An excellent beginners’ tutorial is here and I’m not going to to duplicate it.
http://linuxcommand.org/wss0010.php

This process reminds me of teaching myself to program back in the 1980s. In a good way and a bad way. One frustratingly fatal error after another is a real test of application, and that’s the discipline, but teaching yourself may be very time-consuming but it is also very educational.
After some head scratching I got this to work. It’s a bit of a Frankenstein lash-up with bits of code I got from various places, but also with a little bit of my own intuition. I discovered by trial and error how to change the target directory on-the-fly within the script and this made it much simpler.

It’s still a bit clunky and needs the download-from-camera stage adding but it works. I decided to include absolute paths to the work directories and point the script at them in turn, and so far I am running the script using the command ./myscript from the current directory.

# !/bin/bash
cd /home/richard/Desktop/RBTest/newtest
x=1; for i in $(ls -t -r *JPG); do counter=$(printf %04d $x); ln “$i” /home/richard/Desktop/RBTest/testtemp/img_”$counter”.jpg; x=$(($x+1)); done
cd /home/richard/Desktop/RBTest/testtemp
ffmpeg -r 25 -i img_%04d.jpg -s 640×480 -qscale 1 -vcodec mjpeg movie.avi

The next bit I need to add is the download stage using gPhoto2 to get the images from the camera so that I can have a single workflow to download and assemble the thousands of images files in separate directories into a single usable video file.

Some of this coding documentation needs expanding and tidying up, but stay tuned for more soon.

There are some technologies that none of us will miss, such as CRTs, the SCSI interface, VHS and (for me) optical storage media (CDs and DVDs). But one technological era I am particularly glad to leave behind is the 1980s, characterised by cassette-loading or actual typing in of huge BASIC programs, distributed in magazines.

These days we have an embarrassment of riches in the form of the internet. For a programmer, it's a goldmine of free resources. However, something that is often missing is an exhaustive deconstruction of the code, particularly useful to noobs. I'm a lapsed programmer, so I don't find it too hard, but Linux is new to me and has some strange “conventions”.

Anyway, as promised here is some actual code that I found (well, Google found it and I copied it) with some explanation about what the bits and pieces do. I will probably update this a bit and please let me know if you spot any errors.

FFMpeg requires an unbroken sequence of image files starting at 1 and will fail if the numbers are not continuous. This is not optional and so it is best to rename them as a matter of course.

The following two code snippets are from stackoverflow.com and I've adapted them slightly.

http://stackoverflow.com/questions/2829113/ffmpeg-create-a-video-from-images

This is the script for renaming the files.

x=1; for i in *jpg; do counter=$(printf %03d $x); ln "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done

And here is the original FFMpeg command from the same source.

ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg

Note:

24 seconds to ininitalise the Powershot A640 and another 9 minutes to download 2,595 images totalling 2.7 Gb (over USB 2 on 1st generation MacBook (1.83 GHz Intel dual core) running Ubuntu Linux 11.04.

Sort by creation date/time

x=1; for i in $(ls -t -r *JPG); do counter=$(printf %04d $x); ln “$i” /tmp/img_”$counter”.jpg; x=$(($x+1)); done

The $( some stuff ) contruct eveluates everything within the brackets before using the result. In this case, $(ls -t -r *JPG) returns a list of files ending in “JPG”, sorted by ascending creation time. The for i in $(ls -t -r *JPG) is a for..next loop where i is each file ending in “JPG”, sorted into creation time order.

The snippet counter=$(printf %04d $x) resolves the integer variable x into a 4-digit decimal number with leading zeros and puts it into the variable counter. The leading zeros are necessary in order to maintain the 8-character file names so that they sort alpha-numerically. The snippet x=$(($x+1)) increments the variable x by integer 1 after each renaming operation.

It’s important to get the capitalisation correct and the destination pathname, or it will just fail.

The -t modifier sorts by creation time in reverse order, most recent first. The -r modifier reverses that order to, in this case, change the order back to the correct chronological order.

Canon Powershot cameras automatically number the images files in the format “IMG_0001.JPG” and restarts the numbering after 9,999 images. It will automatically create a new folder every 2,000 images and will create a new folder and restart from 0001 once it gets to IMG_9999.JPG.

Consequently, it is possible that for a timelapse shoot, the file names will not be in continous alpha-numeric order. Sometimes they will be, but it’s as well to assume that they won’t. Also, gPhoto2 does not preserve the folder structure if you download using the gphoto2 –get-all-files command, and will dump the whole lot into a single folder.

In this case, it is very likely that the alpha-numeric order will not be strictly chronological. As a result, it was necessary to include an amendment to the code that will order them into chronological order before renaming them.

More soon.