THX spends numerous hours testing and analyzing displays in both laboratory and home theater environments to ensure the highest levels of quality and usability. Months of research went into developing a specification, covering a wide range of tests and hitting more than 400 data points. THX divided the testing into two primary categories: 1) Device Performance Testing; and 2) Video Signal Processing Testing.
Device performance tests are measured according to industry standard guidelines, as specified by VESA, ANSI, and SMPTE. This includes in-depth analysis of display uniformity, luminance and color levels, and resolution. By contrast, the video signal processing tests are defined by THX and include a complete review of each display’s scaling, deinterlacing and overscan capabilities.
And THX certification is not just focused on presenting stellar HD content. While most HDTVs perform well when presenting HD programming, there is a large variation in the performance of standard definition content. Since most home theater enthusiasts have extensive standard definition DVD libraries, it is critical for THX Certified Displays to present legacy content in the best possible resolution. Because scaling content from one resolution to another often degrades the quality of the presentation, THX works closely with its manufacturing partners to ensure that every THX Certified Display seamlessly scales content for the best possible viewing experience.
Unlike other testing and certification programs, which factor in product class, pricing and use cases, THX strictly focuses on display quality and performance. Regardless of the brand name, product price point or technology used, display products must meet the THX performance standards for product certification. There is no grading curve or rating system. With THX certification, it’s either pass or fail.
Below are some highlights of THX testing:
Video Signal Processing Tests
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Deinterlacing: Bob, Weave - since many broadcast signals are interlaces (e.g. 480i, 1080i), it is critical that the image is deinterlaced properly for clean, defect-free images
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Motion Compensation - motion adds complexity to the deinterlacing process, and causes additional artifacts if not treated correctly
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Cadence Detection and Correction - motion pictures and video are produced at different frame rates, and it is critical to convert them properly to the frame rate of the display to minimize visual artifacts
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Jaggies - checks lines or borders at low horizontal or vertical angles as these can appear disjointed, reducing image smoothness and clarity
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Contouring - in scenes with gently changing areas of contrast, such as a cloudy sky, checks for items that look like blocks where there shouldn’t be any
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Twittering - occurs in slow panning scenes of high image detail, where fine details appear to “twinkle” or oscillate, but shouldn’t
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Sharpness-Filter Ringing - the processor’s sharpness filter is adding noise around sharp image transitions, usually around text, reducing readability
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Noise Reduction - tests how well the processor removes noise from the picture, also while distinguishing the noise from real picture data
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Overscan - when images are scales, there can be artifacts at the edges of the display, and these can be hidden by over-scanning the image; ideally a display will not overscan more than a few percent, as it can add other scaling artifacts
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Image Break-up - sometimes occurs in scenes of very fast-moving, highly detailed images, and appears as a garbled image
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Device Performance Tests
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White Luminance of Full Screen - ensure sufficient brightness
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Sequential Contrast Ratio of Full Screen - image clarity in dark scenes
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Checkerboard Luminance and Contrast - clarity and detail in varying luminances
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Gamut and Colors of Full Screen - proper color rendering capability
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Gray Scale of Full Screen and Determination of Gamma - proper display of midtones
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Full Screen Gray-Scale Color Changes and Gray Scale Artifacts - maintain the right color at all luminances
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Maximum Display Resolution as Determined from Contrast Modulation - can the display really make a good image at the rated resolution?
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Luminance and Contrast of Centered Box - substitutes for full screen measurements on PD panel and CRT
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Uniformity and Color of White, Black, Dark Gray - picture level is the same everywhere on the screen
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Four Point Viewing Angle (LCD and RPTV only) - ensures you can see a good image from off to the side
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Convergence (for multi-panel projectors only) - makes sure the colors are aligned properly for good detail reproduction
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Miscellaneous Tests
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Audible Noise (Displays with Cooling Fans Only and plasma) - fan noise and other audible noise can be annoying in scenes of low dialogue, etc.
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Rainbowing (Field Sequential Displays Only) - white objects can appear multi-colored at times
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Image Smearing (LCD Only) - occurs when an image smears due to the slow response time of liquid crystal , appears as trailing streaks
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Digital Photograph Viewing (sRGB mode) - enables correct viewing of photographs with gamma, luminance, etc.
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Screen Door - occurs in displays that have a relatively low pixel “fill factor”, so that viewing it is similar to looking through a screen door
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Dropped Frames - where processors periodically drop a frame, causing a glitch in the picture
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Zoom Lens Efficiency (projectors only) - important when using an extreme zoom setting for an installation, so that luminance does not suffer
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Moire - an interference pattern is present on the screen, which is very distracting and detrimental to the image
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