Evolution in Action

The evolution of camera image sensors has been profound, and enlightening


For many, the evolution of security cameras is obvious. Housings have gone from the behemoths of the 1970s and ’80s to the compact versions we see today. Images have gotten clearer and have changed from black and white to color. But what has driven these remarkable changes? The cameras can’t get smaller unless the components inside the camera get smaller and use less power. Video can’t improve unless the image sensors and processors work better. Let’s focus on the evolution of one of the components inside a typical security camera and learn more about the inner workings of this quintessential security tool by looking at the products of Pixim Inc., Mountain View, Calif., a provider of imaging chips for security cameras.

Image sensors are typically categorized into three types: charge-coupled devices (CCD), complementary metal oxide semiconductor (CMOS) Active Pixel Sensor (APS), and Pixim’s Digital Pixel System technology. Even though analog CCD sensors are an old technology, requiring complicated implementation systems and costly manufacturing processes, they are still the most common image sensor used in the security industry. CMOS APS products were developed in the early 1990s as a result of emerging CMOS manufacturing technology and have been the principal alternative to CCD sensors at the low end of the market.

Digital Pixel System (DPS) technology was invented at Stanford in the late 1990s. The biggest difference between Digital Pixel System technology and CCDs is that DPS sensors are never analog, but always digital. With CCD sensors, signal readout is an analog voltage, which is then converted to digital signals using additional, high-speed electronic components. Image quality is affected because signals are converted from analog to digital far away from the original point of capture.

Pixim was founded in 1999 to productize DPS technology and became the exclusive licensor and developer of the technology. At that time, the six big market segments for image sensors were (and still are): digital-still cameras, camcorders, broadcast cameras, machine-vision cameras, surveillance cameras and a new emerging idea of embedding camera modules directly into mobile phones. Pixim studied these opportunities and decided to focus on the video security market since it was poised for steady growth, which accelerated after 9/11.

 

Camera building blocks

Image sensors capture and measure light photons hitting each pixel (imagine thousands of little buckets of light). The imaging system determines optimal time to sample and store pixel information before pixels are saturated (the buckets are completely filled) and can no longer hold additional charge. DPS technology measures the light digitally and stored values of information (intensity, time, noise offset) captured at each pixel are then processed in parallel and converted into high-quality, complete images. In contrast, other technologies typically set one exposure time for frames and sample each pixel at that time, resulting in images with some pixels that are underexposed (too dark) and others that are overexposed (too bright).

The image processor takes raw sensor data and converts it into video—the better the raw data which is initially captured, the better the resulting video after processing. DPS technology uniquely provides highly accurate data even in extreme lighting conditions. The image processor calculates exposure, white balance, gamma curve, gain, sharpness, color reproduction and dozens of other parameters critical to overall image quality.

 

First generation: Dyna

This initial product family proved the commercial viability of Digital Pixel System technology. It was well suited for the security market due to the wide variety of lighting issues. As a first generation product, cameras powered by Pixim’s Dyna chip set based on an 81MHz ARM 7 embedded RISC CPU tended to be costly and power hungry, but a small group of enthusiastic OEMs and integrators came to respect the technology for its ability to capture video with natural color in extreme lighting where no CCD ever could. Similar dynamic range was previously only available in Hollywood movie cameras costing $100,000 and more. Dyna camera pioneers included JVC, Honeywell, Pelco and GE.

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