Defining the Differences Between IP and Analog
The CCTV industry is abuzz with talk of an IP (internet protocol) camera takeover. Yet reports of the death of analog cameras are premature. While some IP (or network cameras as they are sometimes called) versions can potentially deliver higher resolution images, analog CCTV cameras continue to offer greater efficiency, lower cost and reliability overall. Before deciding on IP cameras versus analog, it is advisable to first understand exactly what an IP camera is, and is not.
IP and analog cameras are more alike than they are different. The first step in creating an image occurs when the shutter to the camera lens opens and light is projected onto an electronic sensor, which is either a CCD (charged couple device) or a CMOS (complementary metal oxide semiconductor). Next, the image is processed after having the analog CCD or CMOS converted to digital with an analog-to-digital converter. At this juncture, it either remains digital if it’s IP, or it is converted back to analog by use of a digital-to-analog converter. If the image remains analog, it is transmitted to the DVR or NVR to be encoded. If it is IP, it is encoded in the camera.
The CCD and the CMOS have some fundamental differences on how they handle the resulting image but both require an image processor. The quality difference between CMOS and CCD can be narrowed down to a few areas: dynamic range, uniformity, shuttering, responsiveness, speed, windowing, anti-blooming, biasing and clocking.
Both CCD and CMOS image sensors are made of pixilated metal oxide semiconductors. These image sensors are primarily analog. Accordingly, most CCTV camera images begin as an analog picture at the edge (with one exception, which we will address shortly). These image sensors contain millions of capacitors. When you hear the word megapixel, it refers to how many millions of capacitors there are in the image sensor. These capacitors measure the intensity of the light. There is more detail and potential for quality the greater the number of megapixels.
Probably the most important concern for surveillance is picture quality across a broad spectrum of lighting conditions. In this aspect, CMOS has some significant weaknesses compared to CCD. CMOS technology tends to have inferior low light ability and is more prone to producing motion artifacts due to the use of a rolling shutter.
Shuttering is the starting and stopping of exposure, arbitrarily. It is inherent to CCDs and interline transfer devices. CCDs provide excellent electronic shuttering via the use of analog summing. Summing combines the signal from adjacent rows (interlaced video) and provides a good signal-to-noise ratio in low light conditions with minimal fill-factor compromise.
CMOS has issues with this type shuttering and attempts to correct it by using a non-uniform shutter called a rolling shutter, which exposes different lines of an array at different times. This methodology works well for consumer applications such as still images on cell phones. However, when moving images are introduced motion artifacts arise.
Due to high demand from consumer appliances, CMOS sensors are not widely used or designed for the security market. Last year, nearly 800 million cell phones with cameras were sold worldwide. The entire market for CMOS CCTV cameras was less than 3 million. The technology for CMOS applications is in its infancy and the leap from low quality still images to reliable, high quality surveillance video is a long way off.
Meanwhile, a newer technology developed by Pixim, Inc. has evolved and shows great promise. Pixim uses digital image sensing pixel by pixel. CCD and CMOS imagers measure the image as one entire scene at the sensor and attempt to balance all the characteristics with a broad stroke. In challenging lighting conditions the result is noisy pictures and dark shadows. Many people know the Pixim technology as “wide dynamic range” which produces some amazing results in picture clarity. What Pixim does differently is it processes each pixel independently by means of an analog-to-digital converter on each pixel. Each individual pixel in essence is its own camera and adjusts for conditions accordingly.
You may ask what all this has to do with IP cameras vs. analog cameras. IP is merely a “transmission method.” Analog also is a transmission method.
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