Category Archives: Wheezy

Dynamic webcam control (update)

Raspberry Pi, Wheezy, , , , , ,

Several weeks of testing revealed that my Python script for time-dependent webcam control works quite reliable. However, there were a few over-/or underexposed images close to sunset or sunrise. Turning off auto-exposure during daytime helped to prevent overexposed pictures, especially on bright and sunny days.

These fixed exposure settings resulted in too dark images on rainy and cloudy days. Since most webcams are optimized for indoor use, it is safe to use auto-exposure settings under these weather conditions. But how to let a script decide about that? For this purpose, I adopted the ImageStat function of the Python Imageprocessing Library (PIL), which allows to calculate an average arbitrary value for brightness. If it drops below a certain threshold level, auto-exposure settings are activated. Before calculation of brightness, the image is converted to gray-scale. The whole operation is done in memory, without the need to save a temporary file to disk.

Pages: 1 2

Dynamic webcam control using (py)ephem

Linux, Programming, Raspberry Pi, Wheezy, , ,

Time-dependent webcam control

For taking still images with a webcam looking outside my sleeping room window, I’ve attached a Logitech C510 to my RasPi. At first, I used the fswebcam program to acquire still images, which can be easily configured using a fswebcam.conf file as follows:

quiet device v4l2:/dev/video0
input 0
skip 50
palette MJPEG
background
resolution 1600x1200
set "White Balance Temperature, Auto"=1
set "Exposure, Auto"=3
set "Backlight Compensation"=1
#set "sharpness"=100
#set "gain"=0{c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}
#set "exposure"=1
#set "brightness"=35{c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}
#set "contrast"=10{c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}
#set "saturation"=60
#set hue=10
#top-banner
#font /usr/share/fonts/truetype/msttcorefonts/arial.ttf
title "RasPi-Cam"
timestamp "{c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}d-{c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}m-{c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}Y {c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}H:{c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}M:{c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}S ({c7f7cb1468c0d02af358b3ce02b96b7aadc0ce32ccb53258bc8958c0e25c05c4}Z)"
jpeg 50
save /var/www/data/snaps/snap.jpg

Some settings required careful tweaking, since most webcams are optimized for indoor use. Although the settings above resulted in pictures of reasonable quality, I noticed that they were pretty much overexposed on bright sunny days. And they were far too dark at night. It turned out that the auto exposure function of my webcam is unable to deal with changing light conditions.

Therefore I did some research on how to change the settings dynamically, depending on time of day. It turned out to be a simple task using some python scripting.

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Music Player Daemon (MPD) Workaround for the Firefox Minion Plugin

Linux, Networking, Uncategorized, Wheezy, , ,

There are a lot of tutorials out there on how to install the music player daemon (MPD) on a Raspberry Pi. Therefore, I’ll not describe it here in detail. On a freshly installed Debian Wheezy it should work out-of-the-box. An “apt-get install mpd” and editing /etc/mpd.conf should do the trick.

However, if you wish to control MPD with your browser using the FireFox Minion Plugin, you’ll certainly face the problem that it’s configuration dialog for the server’s IP-address/ port number appears to be broken.

minion

Whatever you enter into the dialog will be ignored, and Minion will stay disconnected. It’s a bug, not a feature!

In order to set the IP-address and port number you have to type about:config into Firefox’ address bar and search for the string extensions.mpm.server.

minion1
Then, double-click on the entry and enter the desired IP:Portnumber.

Furthermore, depending on where you store your audio files (I keep them on a USB stick), file permissions can be an issue, if MPD is unable to see your files. Make sure that the folder containing the audiofiles is readable for the desired users.