NETD (Noise Equivalent Temperature Difference) is a critical parameter for assessing the performance of IR imaging systems. It reflects the system's temperature resolution for low-frequency scenes (uniform large objects) but does not represent the system's temperature resolution capability for scenes with higher spatial frequencies. Thus, it is incomplete to judge the temperature resolution capability of two IR imaging systems based only on the value of NETD. Even if infrared imaging system A has a smaller NETD than system B, it only indicates that system A performs better with low-frequency scenes, not that system A has a superior temperature resolution capability for all types of scenes compared to system B.

To evaluate the temperature resolution capability of two IR imaging systems, key indicators include both NETD (Noise Equivalent Temperature Difference) and MRTD (Minimum Resolvable Temperature Difference). These two indicators directly reflect the sensitivity and resolution of the IR imaging system to temperature difference.

In the image examples provided:

Figure (a) represents the original image;

Figure (b) is the image with high spatial frequency filtered out, preserving low spatial frequency. This image lacks outlines and appears very blurred, reflecting global information.

Figure (c) is the image with low spatial frequency filtered out, preserving high spatial frequencies, resulting in distinct outlines and detailed information.