This article originally appeared in the September 2012 issue of SD&I magazine
For many, the evolution of security cameras is obvious. Housings have gone from the behemoths of the 70s 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.
Second generation: Orca/Beluga
The second generation of Pixim chips was the first mainstream implementation of Digital Pixel System technology. Orca (and a later modification known as Beluga) performed better at high temperatures plus captured higher quality video in low light. These chips enabled Pixim to surpass its first one million units sold and have been used in many famous sites including the Olympic Stadium in Athens, Legoland in the U.K., Yankee Stadium in New York and the Vatican in Rome. The Orca image processor increased the speed of the embedded microprocessor to a 225 MHz ARM 9 and increased the embedded memory on the chip to allow more advanced functions, such as privacy masking, focus detection, and activity zones.
The new Beluga sensor took advantage of CMOS fabrication improvements which included enhanced photodiode formation, thinner metal routing and more optically efficient micro lenses and color filters. This new sensor, together with the Orca image processor, targeted 30p progressive scan capture mode using new camera firmware. Beluga improved dim light color performance by two f/stops over the Orca generation and served as the basis for the first IP cameras powered by DPS technology.
Third generation: Seawolf
Seawolf is a giant step forward in the evolution of Pixim-powered camera technology. For the first time in the history of the security industry, the image sensor and image processor are integrated into a single chip. Single board camera modules based on the Seawolf chip make it easier for manufacturers to develop compact camera formats, a rapidly growing market segment.
The integrated chip reduces manufacturing cost of the camera electronics by as much as 50 percent at the wholesale level. Radically simplified camera design has allowed dozens of additional camera brands to add new Pixim-powered products at distribution price points.
Low-light performance has improved by 10 times versus previous Pixim chips and resolution has increased to 690 HTVL effective. The new low light performance allows the cameras to excel in very dim light environments where color accuracy is critical, such as casinos and restaurants. Seawolf’s focus detection feature lets an integrator know when the camera is properly focused, making life easier for technicians. Seawolf’s unique combination of excellent low-light and high-light (wide dynamic range) performance allow it to be used as a universal camera solution for nearly all security and surveillance applications -from banking, to retail, convenience stores, casinos and transit systems.
Fourth generation: Nightwolf
Nightwolf eliminates hot spots common to infrared (IR) cameras with near-field reflective objects in the scene (such as faces, license plates, road signs, windows) and correctly exposes highlights as well as darker background details simultaneously—an unprecedented capability in the large market for IR-assisted security cameras.
A typical IR-assisted CCD camera attempts to solve the hot spot problem by either closing down a mechanical iris or dimming the infrared LED lights. While either of these compromises can help avoid hot-spot saturation, the resulting side effect is that the camera loses critical shadow detail. This compromise to prevent one problem drastically reduces the image quality of the IR camera by causing another, equally troublesome problem—loss of information. With new imaging algorithms applied to near infrared light spectrum, Pixim Nightwolf is able to capture both foreground and background details even in cases where very strong IR lighting is used. .
Like similar advancements from older, analog systems (TV tubes) to new, fully digital systems (LCD flat panels), Pixim has proven that its DPS technology is here to stay. The technology remains unique in the video security industry and Pixim is developing new products for high-definition cameras. Improvements to the core technology will continue to evolve and improve over the next decade.