Wednesday, October 31, 2007

Military: Concealment and Deception or a "Magic Trick"?

The British Ministry of Defence is making news with its "invisible tank" demonstration.  Not to trivialize what their engineers have accomplished, but there are obvious parallels between what they've done and magic tricks - controlled conditions, including the viewing angle of the observers, and unseen technology, including cameras and projectors.  

That is exactly what "concealment and deception", as it is called, is all about, isn't it?  Exploit your control of the local environment and the limitations of your "opponent" to deceive them.  In this case, it involved a tank and not David Copperfield and the Statue of Liberty  (YouTube).

Monday, October 29, 2007

Human Auditory System: Blind detectives

The International Herald Tribune (US center-left newspaper published in Europe) has a very interesting article on a group of blind detectives working for the Belgian Federal Police.  This group puts their more sensitive and highly trained hearing to good use by picking up on clues that normally-seeing detectives would often miss, such as accents, background noises, and softer or obscured sounds.  If there hasn't been one already, we should expect an episode of CSI to feature blind detectives just as soon as they can get one shot!

Acoustics: Noise levels at college football game

I have mixed feelings about my alma mater, Clemson University, holding the record for 126 dB (decibels) of sound pressure at a football game, but it does get the nod in this article about noise levels and hearing safety.  Go Tigers (but heaven help our ears)!

Wednesday, October 24, 2007

Human Auditory System: Researchers identify how blind people hear better

If you have ever wondered if there was any truth to the idea that blind people can hear better than sighted people, now you have a scientific answer - apparently it is so.   Alexander Stevens at Oregon Health & Science University has just published the results of an imaging study to identify which areas of the brain are activated when blind (at birth) people hear sounds.  It turns out that part of the area normally used for vision processing is co-opted into performing aural processing. New Scientist has a short write-up and a link to the journal article abstract.

Tuesday, October 23, 2007

Computer: MacBook update

In case you are interested in the experiences of a recent convert to the "Cult of Apple", my impressions of the Apple MacBook are still very positive. At this point, I have had far fewer issues with this laptop than with any previous laptop that was 'designed and built for Windows'.  I phrased it that way because, as you might recall, I am running Mac OS-X and Windows XP Pro on this machine.  I've had no significant problems with either one.

As far as tested software packages, I've extended the list of applications I've installed and tested on the Mac OS to include Matlab (a signal processing software environment useful for filtering and plotting data, including audio and video), Octave (a freeware alternative to Matlab), Remote Desktop (for connecting to a networked Windows desktop in the office), QuickSilver (a desktop search application to beat all desktop search applications), and Gimpshop (a freeware alternative to Adobe Photoshop).  I haven't fully tested all of them, but I can say that they all install and run correctly.  Octave did give a bit of trouble during installation, but once I got it to launch the first time, it seems to be behaving properly now.

Photography: Google Earth

Technology Review (a technical magazine published by MIT) has an excellent article on the technology behind Google Earth - the satellites, the airplanes, the corrections (filtering), elevation mapping, data streaming, et al.

Thursday, October 18, 2007

Photography: Cleaning digital camera sensors

For the amateur and professional photographers out there interested in cleaning their digital camera sensors, I highly recommend checking out episode 90 of the Shutters Inc podcast by Shelton Muller and Bruce Williams (who also does the excellent Sine Language and Building the Pod podcasts).  Mr. Williams reports on his own DIY (Do It Yourself) experience cleaning his camera.  During all this, he mentions a very informative website, which I will give the link to - Cleaning Digital Cameras.  There is some follow up information on cleaning in episode 91 also.

Tuesday, October 16, 2007

Fun: How To video on making your own infrared goggles

Geeks are Sexy Technology News links to a Metacafe video clip on how to make your own low-cost infrared goggles out of a pair of welding safety goggles and some red and blue light filter material.  The basic idea is that the human visual system can see into the near infrared spectrum and by blocking out visible red and blue light, one can see the left-over infrared.  Watch the video to get an idea of the effect.

Forensics: Power Line Signatures and other Audio Forensics in the news

A frequent contributor to this blog (a.a.) found this Wired article about audio forensics that came out of the annual AES  (Audio Engineering Society) convention in New York City (USA) last week.  Aural steganography (hiding data in audio files, such as MP3s), power line signature recognition, and digital editing/tampering all get mentioned.

Aside: a.a. and I have discussed the technique of power line signature recognition on several occasions.  The basic idea of this technique is that the the fundamental frequency of each local power grid varies over time. In other words, if you measured the frequency at your wall outlet, it would not read 50 Hz or 60 Hz, depending on what country you are in, exactly and constantly.  Instead, the frequency would constantly move around a little bit, perhaps as much as a few Hz up and down, all day and night, in a somewhat random fashion.  This power line "hum" leaks out too - into devices that are plugged into the power grid and even out through the air into nearby devices such as handheld audio recorders.  If one can then extract this frequency or its harmonics (i.e. multiples) from a recording and compare this "signature" to a database of the frequency variations of the same power grid, one could theoretically determine what time the recording was made.

Returning to the article, one has to wonder exactly how power line signature recognition could be used to determine the date of a recording made in a cave - do they typically wire up caves to the power grid?  I could believe that a cave would have a portable power generator, but how would the examiner get a record of its frequency variations?  Perhaps I am missing something here or the author misunderstood something from the presentation and/or interview.

Thursday, October 11, 2007

Photography: What can you do with a 1.4 BILLION pixel camera?

Hunt for killer asteroids, that is what!  It is going to be part of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Maui, Hawaii, USA.  By the way, it took sixty digital image sensor chips to construct the imager.  A news article can be found at New Scientist.

Wednesday, October 10, 2007

Forensics: Reversing digital image masking

Interpol has released pictures of a suspected pedophile who had posted incriminating pictures of himself on the Internet.  His face was masked in the images using a standard Photoshop filter but Interpol's forensic unit was able to reverse the effect to restore those portions of the images.  A news report about the case can be found here.  

In filtering terminology, this can be thought of as "image restoration", i.e. the restoration of an image to its condition before the addition of "noise". In this case, the noise was an intentional blurring or smearing of the image pixels by twirling.  It appears that the particular Photoshop filter in question did not alter the pixel values (at least significantly but possibly not at all).  Instead, it simply moved the pixels' locations.  

To reverse the effect required figuring out where the correct pixel locations should be.  In general, this process is known as image deconvolution.   Deconvolution can be done completely blind (where the filtering algorithm is operating "in the dark" and has to estimate the pixel relocation parameters automatically) but works best when there is a priori information (i.e. where helpful information is known "prior" to the filtering).  

Image deconvolution has been used in astronomy for some years now to reverse the effects of smearing by Earth's atmosphere and motion of the telescope optics, which make the images of the deep space and other objects appear less sharp.  In the last eight years or so, deconvolution to deblur images suffering from focus and motion blur has been taken up by the image forensics community, thanks in part to my own efforts (Aside: I hope I don't break my arm off patting myself on the back).

In this case, the Photoshop filter is well known and available, and therefore, once the particular filter was identified, it made it possible to identify how it behaved in order to help in the deconvolution (as a priori information).  Very elegant image forensic work indeed.

Monday, October 08, 2007

Document Forensics: Recovering Archimedes' prayer book

Multi-spectral and x-ray fluorescence imaging were needed to recover the text and diagrams from a long-lost copy of Archimedes' own prayer book.  The book was in very bad condition (written on parchment that had since been re-used to make another book) and it has taken nearly a decade to recover the content. Details can be found in this Science News Online article. Fascinating stuff, not just because of the insights gained into Archimedes, but also from the laborious forensic work required to recover the content.

Sunday, October 07, 2007

Human Auditory System: Protecting your hearing

MacWorld has a comprehensive article on protecting your hearing using different aids - ear plugs, muffs, noise-canceling headphones, etc.

Thursday, October 04, 2007

Noise: Learning problems associated with noise

The issue of noise in everyday life seems to be getting more and more attention from health advocates and researchers.  The latest thing I've come across is this medical news report on schools and noise.  It struck home with me because my wife and I just recently toured an elementary school where the cafeteria was so reverberant that it was uncomfortable and even painful to be anywhere in it.  I didn't have a sound pressure meter with me, but it was easily in the 90+ dB SPL-A range.  My ears are not as young as they used to be, as they say, so I could not tolerate it for long.  I think that we will be hearing more and more about this type of thing (pun intended) and, as far as I am concerned, that is a good thing.

(Source: Medical News Today)