What is Signal and Image Processing?
Signal Processing and Image Processing sound like arcane mathematics, but they only appear that way because they operate under the hood as “stealth” technologies. Both are used for many down-to-earth and practical jobs.
While not as visible as self-driving cars or cell phones, they are critical for just about every high-tech product that exists. Much of the benefit of a Tesla AutoPilot, or the usefulness of a smart-phone, resides in these products’ signal processing capabilities.
The Signal in Signal Processing is a list of numbers which represents a measurement. Processing means transforming those numbers into something valuable, such as the sound of a symphony orchestra, or the rate at which blood flows in a vein. Image in Image Processing refers to doing the same thing with images or video. Image Processing is a branch of signal processing, but since humans are so visual, it’s a large branch. Every time you use your phone to snap a picture, a great deal of image processing takes place. It’s math inside the phone which makes the picture you see far better than the pattern of light falling on the sensor.
Signal processing has its origins in classified research performed during World War II on aiming anti-aircraft guns. When this work became publicly accessible in the late 1940s, people at MIT realized it could be applied to oil exploration. The technology quickly became of enormous importance to oil companies, and later expanded into almost every electronic product.
What does signal processing look like? When making integrated circuit chips, silicon wafers are heated rapidly to over 1000oC, and it is important to know their temperature. You can’t touch the wafer with a thermometer, because that would contaminate it. But the wafer glows in the heat, so the light coming from it can be sensed.
However, the color of light from the wafer it not what is needed. The temperature is. These quantities are related, and signal processing is the tool which lets us extract the temperature we desire from the light we can measure.
An Example, as explained by an image processing expert witness
Automatic payment of bridge tolls is popular with both governments and drivers. But the cameras which figure out the account to deduct the toll from (or where to send the citation!) have to deal with moving vehicles, rain, and changes in lighting. Here is an example of a poor-quality image which is of no use to the bridge authority:
Image processing can come to the rescue here. Because we know a lot about what motion and out-of-focus lenses do to images, processing can improve these data a lot. Critically for the government agency, the license plate can now be recognized.
Litigation Requiring Image and Signal Processing Expert Witness
Signal and image processing technologies are ubiquitous, and due to their economic importance, they are the subject of much litigation. Here are two recent examples.
Frequent travelers enjoy having the low-pitched drone of an engine blocked out by headphones with active noise cancellation. These products include a microphone to detect ambient sounds. Signal processing then uses what the microphone hears to decide how to produce the best sound isolation. The trick is to do this without compromising the music being enjoyed by the user. In a case involving two titans of consumer electronics, Bose and Beats (later acquired by Apple) the litigants argued about five patents covering Bose’s signal processing, which Beats was alleged to be infringing.
Pulse oximetry is a way of measuring the amount of hemoglobin carrying oxygen in the blood. The body controls this Oxygen Saturation precisely – it is critical to health. In the patent case of Masimo v. Mindray, no fewer than nine signal processing patents were at issue. The reason the signal processing in Masimo’s SET (Signal Extraction Technology) is so critical is that the measurements of light passing through the patient’s finger are far from what the physician needs to know: how well the blood is carrying oxygen. It’s the job of the signal processing to translate the signals from the optical transducers into something medically comprehensible.
These illustrations show how signal and image processing has become part of life. While often operating in the background, these technologies have assumed a giant role in creating successful products.
References
Bose Corp. v. Beats Electronics LLC, 1:14-cv-00980 (United States District Court for the District of Delaware, July 25, 2014). This case was also reviewed at the US International Trade Commission: investigation 337-TA-927.
Masimo Corp. v. Shenzhen Mindray DS USA Inc., 8:12-cv-02206 (United States District Court for the Central District of California, Dec. 21, 2012).
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