Every electronic display device will degrade. When has it degraded to the point of not being acceptable? The traditional approach to display performance evaluation is to view a test pattern, in which results depend upon the knowledge and skill of the viewer. The alternative is to undergo rigorous laboratory analysis with very expensive measuring equipment. There is a need for a quick and easy means to confirm that display performance is suitable for the task at hand without the unknowns and variations in visual interpretation. Video Instruments has developed this capability. Now that displays are computer compatible, it is simple to insert test stimuli in software form, providing a reference image without having to disconnect equipment and place it on a laboratory bench. A variety of test patterns can be presented, but there remains the question of interpretation. Video Instruments has solved this problem by providing carefully crafted symbology to be interpreted. The viewer then enters into the computer what that symbology is, confirming that the computer based system is operating properly, that through transmission and display a suitable image is being presented, that viewing conditions are acceptable, and that the viewer has the abiity to discern critical information.
Video systems in military platforms are typically used to display sensor video and imagery for sensors such as forward looking infrared (FLIR), low light level television (LLLTV), synthetic aperture radar (SAR), and laser radar (LADAR), in addition to graphics and alphanumerics. The performance of these systems may need to be characterized during initial testing or in support a potential upgrade to the sensor. To be able to sense and deliver the best quality of video to the warfighter, it is critical that the system designer have a well-characterized video system, so he or she can make the appropriate performance, cost and schedule tradeoffs. Modulation Transfer Function (MTF) is one of several metrics that can be measured when characterizing a monochrome video system and can be very useful in optimizing the system for either initial design or for an upgrade. The use of MTF in determining resolution throughout a video system, including the application of useful metrics such as MTF area (MTFA) and square root integral (SQRI), is presented in this paper. Issues regarding hybrid video systems, which incorporate both analog and digital components in the video chain, are addressed. Practical methods for MTF testing of both displays and electrical components in the video chain are also presented. The paper discusses the practical application of video test patterns to perform an efficient component evaluation. The use of photometric testing of displays is touched on briefly. And lastly, the final topic to be addressed in this paper is the use of the time domain reflectometer in testing cables in the video chain for impedance mismatches.
Meaningful performance evaluation of video equipment can be complex, requiring specialized equipment in which results must be interpreted by technically trained operators. The alternative to this has been to attempt evaluation by visual inspection of patterns such as the SMPTE RP-133 Medical Imaging Standard. However this involves subjective interpretation and does not indicate the point in a system at which degradation has occurred. The video waveform of such a pattern is complex and not suitable for quantitative analysis. The principal factors which influence quality of a video image on a day-to-day basis are resolution, gray scale and color, if employed. If these qualities are transmitted and displayed without degradation beyond acceptable limits, suitable performance is assured. Performance evaluation by inspection of the image produced on a video display monitor is subject to interpretation; this is resolved by inserting, at the display, the original 'perfect' electronically generated waveform to serve as a reference. Thus the viewer has a specific visual comparison as the basis for performance evaluation. Another valuable feature of the test pattern insert is that a test segment can be placed on recorded images. Thus each image recalled by tape playback or from digital storage will carry an integral means for quality assurance.
A technique and instrumentation were developed which permits a relatively non-skilled operator to make a complete performance check of an electronic display in a very few minutes, providing a go/no-go indication can be configured to indicate the area of failure. The instrument is designed so that a performance profile of each display device or type can be kept on file if desired. This paper reviews test criteria selected for the performance `check' and the novel interrelationship between test stimulus and measuring instrument created for this testing.
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