Performance of liquid-crystal displays for fire-service thermal-imaging cameras

As use of handheld thermal-imaging cameras (TICs) becomes more prevalent in the first-responder community, it is important that standard test metrics be available to characterize imaging performance. A key performance consideration is the quality of the image presented on the TIC display. This paper focuses on TICs that use liquid-crystal displays to render an image for the user. Current research on TIC performance for first-responder applications makes use of trained observers and/or composite-video-output-signal measurements. Trained observer tests are subjective and composite video output tests do not evaluate the performance of the complete imaging system. A non-destructive objective method was developed that tests the performance of the entire thermal-imaging system, from the infrared sensor to the display. A thermal target was used to correlate the measured thermal imager composite video output signal with the luminance of the display. A well-characterized charge-coupled-device (CCD) camera and digital recording device were used to measure the display luminance. An electro-optical transfer function was determined that directly relates the composite video output signal to the luminance of the display, providing a realistic characterization of system performance.