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.

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.

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.

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.

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.

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.

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)

Equipment: Deadly Silence

Advantages and disadvantages of noise canceling headsets on the battlefield.

(Source: StrategyPage.com)

Human Visual System: Fun optical illusions for a Friday

Fun video of optical illusions for a Friday.

Admin: MacBook replaces lemon Windows notebook

I won't bore everyone with details about the last rites on my old notebook, but suffice it to say that the manufacturer agreed to fully refund the purchase price of the notebook and I am back to blogging again.

What may not be so boring is that I replaced that Windows notebook with a MacBook.  The MacBook has a dual core Intel processor and is running both Apple's OS-X and Microsoft's Windows XP Pro.  The Windows operating system is running in virtualization mode using a program called Parallels (note: I had to purchase a copy of Windows and Parallels separately, but they were fairly inexpensive).

As far as audio and video processing goes, I have been able to load and run Acoustica, Audacity, Audition, Clarifying Technologies, and Signalscape on the MacBook and all have worked in real-time for the types of files I tested with.  Due to work commitments, I have not been able to take enough time to "make friends" with the native Mac sound and video applications, but hope to do that slowly over the next few months. I'll report back my on observations.  If anyone has a preference as to a specific application for audio or video forensics they would like me to give priority to, just let me know in the comments or off-line.

In the meantime, Brian Dipert (Senior Technical Editor over at EDN) has also been transitioning over to a MacBook and has blogged about his experiences in several posts, this one being the latest as of this writing.

Image Recognition: License plate scanners

The technology manufacturing cycle is at work with license plate (tag) scanners - decreasing prices lead to more sales and deployments, which lead to further cost decreases and so on.  We've all seen it with personal computers, cell/mobile phones, DVD players, flat screen displays, and a multitude of other devices.  Now this market force is at work with license plate scanners , which are now being deployed on police cars.  The scanners are automating what was before a completely manual process - namely running stolen tag numbers and such - and doing it much faster.

Human Auditory System: Mobile/Cell Phones Can Harm Hearing

I have not tracked down the conference paper on this yet, but the results do go hand in hand wiht what I have noticed with my own hearing - talking on a cell/mobile phone for over an hour a day can harm your hearing.  The research was conducted by Dr. Naresh Panda (an ear, nose, and throat specialist in India).

Some time ago, I began noticing the feeling of my ear warming up - as was described in the article - and I associated it with a decrease in my sensitivity of hearing.  At first, I just made a point of switching the phone to the other ear every few minutes.  Over time, I switched to speaker phone mode when possible and ear buds when not.  That is how I still behave today. Of course, I try to be overly protective of my hearing anyway - for example, when using ear plugs on airplanes and when operating lawn mowers and blowers.  Better safe than sorry, as the saying goes....and in this study, it seems that I may have erred on the correct side.

Human Auditory System: Ability to listen to two things at once is inherited

Researchers at the National Institute on Deafness and Other Communication Disorders (NIDCD) have found evidence that the ability to listen to listen to and comprehend two things at once was mostly an inherited skill.  

On a personal level, I have known for a long time that my wife can do this while I can not, and assumed that there might be a gender-based component to the cause.  Hmm... Might be time for a re-think of that hypothesis.

Aero-Acoustics: Making airplanes quieter

Here is an article in the Deccan Herald on redesigning aircraft engines, engine placement, and landing approach procedures to reduce noise levels on the ground by up to 25 dB (a very significant decrease if achieved).  The article is very readable.  Enjoy!