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In theory, bigger pixels on full-HD CCD image sensors are better for global security applications because they are more sensitive for improved low light performance. The drawback is that bigger optics are required so size, weight, power, and cost (SWaP-C) requirements are challenged. As many systems are upgrading from standard definition to full-HD cameras or adding HD daylight cameras for full motion video, the question is how to find the optimal balance.
The pixel size is of course correlated with the image sensor size:
Figure 1: Pixel Dimension vs. image sensor size for full-HD
High-end applications, such as long range targeting or in very low light, which are moving to full-HD resolution will still require 2/3” sensors. Over the last few years, there have been dramatic improvements in Qe and read noise of image sensors to make 1/2” full-HD sensors with the sensitivity required for many applications. In parallel with the sensor improvements, there have been many developments in 1/2” long focal range optics and zoom optics as a necessary complement.
For upgrades, this provides the option to use the same optical format, but have more pixels and more sensitivity. This can be a cost-effective approach although new optics are still required.
Not all of the 1/2” optics available meet the full MTF so the camera provides a better image quality than the lens. The resulting image might not have the sharpness required by high-end applications. The optics are getting better and better though.
To use smaller and even lower cost optics, it is attractive to go below the 1/2” sensor size, for instance 1/3” CCD image sensors. Not only does the image sensor performance go down, but the available optics quality also decreases.
1/3” CMOS image sensors can offer good low light performance, but 1/3” CMOS sensors utilize a rolling shutter as compared to global shutter available in CCD and larger CMOS image sensors. Currently rolling shutter is not well received in the industrial and military applications as a blurring effect occurs with movement. Global shutter CMOS is more complex and will take further development to shrink for smaller pixels.
For now, 1/2” image sensors provide a sweet spot for many global security applications with acceptable sensitivity and the ability to use small, low cost optics. As I mentioned, for more demanding applications, 2/3” image sensors may be required.
Figure 2: Summary of the benefits of different full HD sensor sizes
In the near future 1/3” full-HD image sensors may become more interesting as the optics are improved to allow for additional reductions in SWaP-C. Further testing may show that rolling shutter is acceptable in outdoor, moving applications with higher frame rates, such as 100 fps, so that the blurring effect is not evident.
