duplicate standard output

To duplicate std output of a program (here my_prog) in bash

./my_prog | tee logfile.txt

Script to test if ethernet interface eth3 is up

#!/bin/bash
var="down"
while [[ $var != "up" ]]
do
    var=$(</sys/class/net/eth3/operstate )
    echo $var
done

Downloading big files from camera

On Mint downloading files from a camera using the gphoto2 automount and caja can be very slow on big files. An efficient alternative is to use gphotofs.

First create a directory for further mounting of the camera


sudo mkdir /media/mtp 
sudo chmod 777 -R /media/mtp

Then  unmount the device automatically mounted by gphoto2 and then you can mount your camera as follows

sudo gphotofs /media/mtp -o allow_other

To unmount

sudo fusermount -u /media/mtp

Then you can use a terminal and copy files, e.g.

cd /media/mtp/*
cp */*.MOV~/Images

This process is much faster than with caja

swap blue and red

to exchange red and blue channel in an image file with imagemagick, I found this command

convert salle_test3.png -separate -swap 0,2 -set colorspace RGB -combine -set colorspace sRGB salle_test.png



The reason for specifying the colors pace is not clear to me. Not doing so however clearly changes the lightness of the image.

webcam libav

I tried to read from a webcam using the libav library or the ffmpeg equivalent, which are obviously not well documented w.r.t. this specific matter. I realized that the following call is required at the beginning of the program :

avdevice_register_all();

not to mention
av_register_all();

To install  ffmpeg and the corresponding original libraries  on Mint, the following tutorial works well:
http://trac.ffmpeg.org/wiki/UbuntuCompilationGuide

A working code example
https://github.com/j0sh/thesis/blob/master/capture.c