Triangle Orientation Discrimination Threshold Research Articles

TOD Performance Model for Staring Thermal Imager with Machine Vision

A triangle orientation discrimination threshold(TOD) performance theoretical model is derived for the staring thermal imager based on machine vision. Specifically, how to obtain the TOD curve based on machine vision is briefly described. The spatial frequency distribution of the triangle test pattern is first determined. The transform and response characteristics of the non-periodic triangle pattern and its background clutter through machine vision-based thermal imager are analyzed. The three-dimensional matched filter is adopted to characterize quantitatively the spatial and temporal integration of image enhancement algorithms to the output triangle pattern signal, various noise components and background clutter, and the signal-to-interference ratio (SIR) of the triangle pattern output image is derived for the staring thermal imager based on machine vision. Then, the TOD performance theoretical model is established by assuming that the output SIR is equal to the threshold SIR75% determined by the discrimination criteria of machine vision. Preliminary simulation and experimental results show that this theoretical model can give reasonable prediction of the TOD performance curve for staring thermal imagers based on machine vision.

Uncertainty Analysis in Triangle Orientation Discrimination Threshold Measurement

The Triangle Orientation Discrimination Threshold (TOD) is a new figure of merit for characterizing the performance of an infrared imager. In this paper, focusing on a reflective infrared target projector, the TOD curve is measured utilizing four alternative forced choice (4AFC) test method. Furthermore, the dominant sources affecting uncertainties in the TOD measure values, are analyzed in detail, the effective temperature difference, sensor, and observer. And, the variation of the TOD measurement is described quantitatively utilizing the uncertainty analysis theory. Simulation results show that the TOD measurement values vary in a small range, which show a higher stability than minimum resolvable temperature difference (MRTD) measure values.

TOD performance theoretical model for scanning infrared imagers

Since the triangle orientation discrimination threshold (TOD) measure was proposed, good progress has been made in some aspects, such as experimental validation, field performance, and TOD sensor performance model. However, what is still missing is a TOD curve prediction model similar to the minimum resolvable temperature difference (MRTD) equation. In this paper, an equation-based TOD performance model was first developed for scanning thermal imagers. Specifically, the spatial distribution of the triangle standard test pattern is described quantitatively. The resolution transfer characteristic of the scanning infrared imagers is modeled with linear system theory, and system noise is characterized by introducing a three-dimensional noise model. The modulation effect of overall subsystems of scanning thermal imager on the non-periodic standard triangle pattern is analyzed. The matched filter idea is adopted to characterize quantitatively the spatial–temporal integration of the human visual system to signal and various noise components over the triangle pattern area, and the perceived signal-to-noise ratio for the scanning infrared imager is derived. From this, a TOD performance theoretical model is established. Comparisons with experimental results show that this theoretical model gives reasonable prediction of the TOD performance curve for scanning thermal imagers. Although more tests and modifications are required, these preliminary results suggest that this model can be developed into a model that predicts the TOD for all kinds of sensors.

TOD Performance Theoretical Model for Staring Thermal Imagers

The TOD (triangle orientation discrimination threshold) metric, as a promising sensor performance measure, is suitable for all types of thermal imaging systems and corresponds to the field performance very well. Since this method was proposed, a great progress has been made in some aspects, such as experimental validation, field performance, and TOD sensor performance model. However, what is still missing is a TOD curve prediction model similar to MRTD (minimum resolvable temperature difference) equation. Here, an equation-based TOD performance model was first developed focusing on staring thermal imagers. Specifically, spatial distribution of the triangle standard test pattern is described quantitatively. Resolution transfer characteristic of the staring infrared imagers is modeled with linear system theory, and system noise is characterized with the introduction of three-dimensional noise model. The modulation effect of overall subsystem of staring thermal imager on the non-periodic triangle standard pattern is analyzed. The matched filter idea is adopted to characterize quantitatively the spatial integration of the eye to signal and various noise components over the triangle pattern area, and the perceived signal-to-noise ratio of the staring thermal imager is derived. Then, the TOD performance theoretical model is established. Comparing with experimental results, this theoretical model gives reasonable prediction of the TOD performance curve of staring thermal imagers. Although more tests and modifications are required, these preliminary results suggest that this model can be developed into a model that predicts the TOD for all kinds of sensors.

Bias-free procedure for the measurement of the minimum resolvable temperature difference and minimum resolvable contrast

MRTD (Minimum Resolvable Temperature Difference) The characterization of electro-optical system performance by means of the standard minimum resolvable temperature difference (MRTD) or the minimum resolvable contrast (MRC) has a number of serious disadvantages. One of the problems is that they depend on the subjective decision criterion of the observer. We present an improved measurement procedure in which the results are free from observer bias. In an adaptive two-alternative forced-choice (2AFC) procedure, both the standard four-bar pattern and a five-bar reference pattern of the same size and contrast are presented consecutively in random order. The observer decides which of the two presentations contains the four-bar pattern. Misjudgments are made if the bars cannot be resolved or are distorted by sampling. The procedure converges to the contrast at which 75% of the observer responses are correct. The reliability of the responses is tested statistically. Curves cut off near the Nyquist frequency, so that it is not necessary to artificially set a frequency limit for sampling array cameras. The procedure enables better and easier measurement, yields more stable results than the standard procedure, and avoids disputes between different measuring teams. The presented procedure is a 'quick fix' solution for some of the problems with the MRTD and MRC, and is recommended as long as bar patterns are used as the stimulus. A new and fundamentally better method to characterize electro-optical system performance, called the triangle orientation discrimination threshold (TOD) was recently proposed by Bijl and Valeton (1998).