Thermal cameras have come a long way since 1929 when the first infrared-sensitive camera was invented. This new technology was initially considered exotic and it was expensive. In the last few years, the cost of thermal imaging technology has come down significantly, although thermal imagers with reasonable image resolution can still be pricey. Thermal fusion cameras, that utilize very low-resolution thermal sensors (80×60), which are enhanced by blending in a standard video signal, can be very inexpensive when compared to medium to high resolution thermal imagers. In certain applications the performance and suitability of images that utilizing thermal fusion can be questionable.
Thermal fusion is achieved when an image from a standard video camera is layered on top of an image from a low-resolution thermal sensor. This produces an image that depicts a black & white or colorized visualization of an object in the field of view of the thermal sensor that is outlined with an edge created from the standard video camera. The two cameras work in conjunction to give you a crude thermal image with enhanced edges. When used in this manner, the low resolution thermal fusion can produce a reasonable and usable thermal image. There are many applications where this approach is effective. It is useful in applications such as inspecting breaker panels, steam pipes, machinery, engines and other inspection applications where there is sufficient light for the standard video camera to produce a good image that can be utilized in the blending process. It also helps to know what you are looking at in advance, this is not always the case in many thermal imaging applications.
The shortcomings of this approach occur when the standard video camera that is producing the edge enhancement overlay on the thermal image doesn’t have enough light to create its outline. The image produced by the thermal fusion camera is now significantly compromised and may be of minimal value. Without the outlined overlay from the standard video camera, the thermal image has such low resolution that the image ends up looking like blotches of ill-defined color. The image may not convey enough detail to make an accurate assessment of individuals and environment. When thermal fusion is utilized in tactical or victim location applications, you may not always have enough illumination for the standard video camera to produce a reasonable image. Additional external IR or white light illuminators will help, but they still might not deliver adequate illumination in all cases. This means that you may not be able to differentiate a partial or even full image of a human, from the background environment.
The ZistosHD Dual Mode Thermal Camera (THC-51D-HD) allows the operator to instantly toggle between a true 320×256 resolution thermal video camera and a 640×480 resolution, low-light, standard B&W video camera. The B&W video camera also has built in IR illumination that can further assist in low light conditions. Instead of overlaying an outline on top of a low-resolution thermal image, we use a higher resolution thermal camera in the same housing and an even higher resolution B&W low-light camera to switch between the two different images. We believe this construction is superior to thermal fusion for the following reasons.
- The higher resolution thermal image produces a usable image without the need of any enhancement.
- The secondary low-light B&W standard video camera can produce a video image that can convey additional visual details of the subject and environment.
- In the THC-51D-HD, the Thermal and B&W IR Cameras are in the same housing. Therefore, there is no need to switch camera heads. It’s all done with system controls.
- If the standard video camera in the thermal fusion process does not have enough light to produce a usable image the result is an extremely low-resolution thermal image which can be of limited value.
- The THC-51D-HD camera’s thermal mode can provide thermal detail regardless of ambient light levels.
All in all, despite thermal fusion being available as a new and low-cost thermal technology it may not be suitable as an imaging tool for many tactical and victim location/rescue missions, or any application where you can’t count on adequate illumination for the standard video camera to function. A higher resolution, standalone thermal image, such as the images produced by the ZistosHD THC-51D-HD camera, will in many instances be of more value than an image produced using a thermal fusion camera.