High Definition Infrared: The Truth About What You Thought You Knew
This article is based on an original publication by FLIR.
The term "high definition" has become ubiquitous in applications ranging from television to radio and beyond. In fields such as infrared imaging, true HD definition involves a range of HD-capable components engineered to work together seamlessly.
A longtime pioneer of infrared technology development, FLIR is now at the forefront of HD thermal imaging technology.
What Most People Understand
Defined simply, HD refers to any resolution that exceeds the standard. In terms of video, more high-quality pixels equate to better resolution and increased definition. An example of this concept is easily demonstrated with HD TV.
In terms of HD thermal imaging, resolution plays a similar role to that of video or television, meaning that more pixels provide increased clarity, as well as increased detail on heat gradients of an object in view. The latter part is of particular importance for small or distant objects.
Most people understand that when it comes to HD, a bigger number equals a better result. Yet there is more to quality HD than the pixel count. For instance if a TV itself is HD capable, yet the video source is not, the viewer will simply see standard definition. Similarly, if the video feed is HD but the TV is not, the result will again be standard resolution. Although a high pixel count equates to a higher definition video, there is a difference between TV and thermal imaging. While HD TV displays HD content, in thermal imaging there are many additional elements which affect display resolution and quality.
More Than One Step Beyond Standard
The quality of HD thermal imaging is only as good as its source. A true HD camera incorporates HD-capable optics, detector, processing electronics, interface and digital file formats, all of which must be supported by an exceptionally stable gimbal to ensure the highest quality image.
Because HD imaging requires native HD capability in both the optics and the detector, a HD detector behind standard optics will result in a standard resolution image. A full HD thermal imaging system requires high bandwidth digital information to be processed in its native format, but at increased speed to maintain image integrity.
Data output is equally important, and compromising its fidelity during this step can undermine quality. This begins with thermal imagery optics, in which the lens recreates the image for input to the sensor. The lens is therefore a primary component of overall HD quality.
Because the lens impacts image sharpness, sensitivity and contrast, those not designed for an HD system are limited in their capability. The level of definition required by an HD system is far more demanding, requiring a lens of at least 80 LP/mm. When the image is translated through the lens, it must then be captured by a sensor, or detector, which uses focal plan arrays (FPAs) to complete this task.
Often used to increase range performance as well as the brightness and contrast of small or distant objects, optical microscanning technology enhances native resolution. Some IR imaging systems may not have this capacity, and the result is simply filled empty space on a display.
The next step in true HD imaging is image processing, during which individual bits of data from the sensor or detector must be assembled to create a final image for optimal viewing, which is then transmitted to the output interface. True HD imaging incorporates substantially more - and more densely placed - data, which requires more powerful processing electronics.
Actual image quality is dependent on bandwidth available from the interface, with increased bandwidth lending itself to a potentially higher resolution. Maintenance of native data format and file size will provide increased resolution, whereas compressed data streamed via low bandwidth will result in data lost. All compression techniques necessarily result in an image that is no longer HD quality.
What Does High Definition Mean for You?
With a general sense of true HD thermal imaging, users are prompted to ask several pointed questions. An enhanced understanding of HD system and components will result in better application of technology to specific tasks.
- What is the detector resolution of the focal plane array?
Anything less than a 640 x 512 focal plane array (with optical microscanning) and 1280 x 720 resolution is not real HD quality.
- Does the system use HD-capable lenses? What is the line-pairs per millimeter (LP/mm) for the lens?
All lenses should resolve at a minimum of 80 LP/mm to achieve 720p resolution.
- What quality interface does the system use?
Nothing less than an HD-SDI, SMPTE-292M interface should be used for a 720p HD system.