29/12/2009
Let’s say we want to mix three channels onto two because the communication device has only two available channels but we still want to emulate a three channel link. If we can afford coding, then it’s not a problem because we can build our own protocol so add any number of channels using a structured data stream. But what if we cannot control the channel coding at all? In CDs, for example, there’s no coding: there are two channels encoded in PCM and a standard CD player wouldn’t understand the sound if it was encoded otherwise.
The solution is to mix the three channels in a quasi-reversible way, and in a way that the two channels can be listened to without much interference. One possible way is to mix the third channel is to use a phase-dependant encoding. Early “quadraphonic” audio systems did something quite similar. You can also use a plain time-domain “mixing matrix” to mix the three channels onto two. Quite expygeously, let us choose the matrix:
![M=\left[~\begin{array}{ccc} \frac{2}{3} &0&\frac{1}{3}\\ 0 &\frac{2}{3}&\frac{1}{3}\end{array}~\right]](https://s0.wp.com/latex.php?latex=M%3D%5Cleft%5B%7E%5Cbegin%7Barray%7D%7Bccc%7D+%5Cfrac%7B2%7D%7B3%7D+%260%26%5Cfrac%7B1%7D%7B3%7D%5C%5C+0+%26%5Cfrac%7B2%7D%7B3%7D%26%5Cfrac%7B1%7D%7B3%7D%5Cend%7Barray%7D%7E%5Cright%5D&bg=ffffff&fg=333333&s=0&c=20201002)
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algorithms, data compression, Mathematics, Science, signal processing | Tagged: CD, channel mixing, least mean squares, least squares, linear algebra, linear regression, matrices, Matrix, mixing matrix, Moore-Penrose, PCM, pseudo-inverse, quadraphonic, rgb, surjection, surjective function |
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Posted by Steven Pigeon
22/12/2009
The other day—well, a year ago or so—I was invited to visit CBC’s digital TV studios in Montréal by the SMPTE Montréal. We were shown around, even in the somewhat small control rooms. Amongst all the displays, dials, monitors, and misc. blinkenlights, I noticed a small LCD display showing an hexagonal projection of the current show’s color gamut in
(or maybe
?), probably for quality assessment purposes. I thought it was pretty cool, actually.

Let’s see how we can realize this projection with as little CPU time as possible.
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algorithms, bit twiddling, C, embedded programming, hacks, Mathematics, programming | Tagged: animated gif, blinkenlights, camel, CBC, colorspace, digital tv, DTV, folding, folding function, gamut, gif, pairing, pairing function, real time, realtime, realtime rendering, rgb, studio, tuple, tv studio, ycrcb |
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Posted by Steven Pigeon
18/12/2009
A few days ago, I changed my machine and upgraded to Ubuntu 9.10 (Karmic Koala) and everything went fine, except for the screen-saver that would activate properly but not switch the screen into sleep mode after a while. I found a couple of fixes because despite being a documented bug, there’s not definitive fixes yet.

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Bash (Shell), hacks, Life in the workplace | Tagged: Annoyances, DPMS, Eclipse, Icons, Karmic Kaola, Koala, Moon, screen-saver, screensaver, X, X11 |
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Posted by Steven Pigeon
15/12/2009
Building a decent personal library is not very difficult but it can be really expensive. It doesn’t have to, you just have to know where to look for.

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algorithms, Books, Life, Mathematics, Science | Tagged: book shops, Dover, Used Books |
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Posted by Steven Pigeon
08/12/2009
Certain numbers keep showing up in nature. The Golden Ratio,

is one of them. It shows up in cats, sunflowers, and Egyptian pyramids.

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hacks, Inoffensive Rant, Life, Mathematics | Tagged: Ancient Egypt, apophenia, archeology, Cat, Cats, Egypt, Giza, Gizeh, golden ratio, Golden Section, Great Pyramid, Kheops, numerology, Pet theory, Phi, Pyramids |
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Posted by Steven Pigeon
03/12/2009
Christoph Niemann — The Pet Dragon: A story about Adventure, Friendship, and Chinese Characters — Greenwillow Books, 2008, 40 pp. ISBN 978-006-157776-5

(Buy at Amazon.com)
I greatly appreciate Niemann’s graphic style. He’s original and kept his playful side. This short book—a kids’ book—is full of his odd poetry and graphic genius. The Pet Dragon is built around the analogies between what we can imagine chinese character represents and pictograms. A short à la Petit Prince story, just a lot less pretentious.
The book’s website
The author’s website.
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Suggested Reading |
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Posted by Steven Pigeon