Digital Scan Converter Forward Looking Infrared (FLIR) Characterization

Abstract

A parallel scan forward looking infrared (FLIR) with a digital scan converter (DSC) electronically reformats parallel input analog data into serial digital output data. This digital data can be supplied directly to a subsystem for further processing. Prior to returning to the analog domain to create the video image, the digital data passes through a line-to-line interpolation operator, gamma correction look up table and a histogram processor. Because of the video processing, the characteristics of the analog signal different than the digital signal. Line-to-line interpolation can provide √2 signal-to-noise (SNR) improvement. Frame integration, depending upon the scheme used provides additional improvement to the SNR. Clearly, the video image may not be representative of what actual signals are being supplied to the subsystem. Since the characteristics are different, it is essential to measure the system intensity transfer function (SITF), and noise equivalent temperature difference (NEDT) in both the analog and digital domains. Appropriate digital data display (histogram of values) permits easy assessment of data quality. Examples of missing data bits (dead lines) are shown. Lower order missing bits can affect a subsystem but the effect is minimized on the display due to the line-to-line interpolation scheme. The NEDT, SITF and noise spectral density in the digital and analog domains are compared. The implications of the difference in both domains are discussed.