24.4: Display Sparkle Measurement and Human Response

Abstract

A new method for quantifying "sparkle" uses a simple measurement which includes a pixelated source, a test sample, and an eye simulator. The degree of sparkle is calculated from the standard deviation of the pixel powers across a portion of the display. Measurements show excellent correlation to human response studies. Author KeywordsSparkle; Display Metrology; Human Response; Perception. Objective and BackgroundDisplay "sparkle" or "dazzle" is a generally undesirable side effect that can occur when introducing antiglare or light scattering surfaces into a flat panel display (FPD) system such as, for example, a liquid crystal display (LCD), an organic light emitting diode (OLED), touch screens, or the like. Sparkle is associated with a very fine grainy appearance of the display. To an observer, this grainy pattern appears to shift with changing viewing angle. This sparkle effect is observed when combining pixelated displays such as that of a LCD with antiglare (AG) or other textured surfaces and differs distinctly in type and origin from the more commonly known "speckle" effect that is observed and characterized in projection or laser systems. The physical origins of sparkle have not been previously well understood, and there has been substantial confusion in the related art between the different types of sparkle or speckle that can be visually observed in projection, laser, or pixelated flat-panel displays. In part due to the lack of basic understanding of the root cause of pixelated FPD sparkle, there have not previously existed any quantitative methods for measuring FPD sparkle that have been shown to correlate well to visual human observations. We demonstrate a system for measuring sparkle which is sensitive to very low levels of sparkle and is linear in response to increasing levels of sparkle. The measurement apparatus consists of an image capture system designed to simulate the response of the human eye. It obtains a high-resolution image of a standardized LCD in which only one color of sub-pixel is illuminated and over which a textured test sample is placed. Within each captured image, a computer algorithm is used to integrate the power within each display pixel and to remove any background light level. The value of sparkle severity is calculated by taking the normalized standard deviation of the pixel powers, which we have termed pixel power deviation (PPD). In this paper, we will discuss the measurement apparatus and image processing algorithm and show the correlation between measured PPD and perceived level of sparkle. ResultsNumerous pixel geometries and pitches are available in today's emissive display technology. The level of sparkle a given textured sample will exhibit is dependent on the pixel geometry and texture to pixel distance of the specific display on which it is used.To provide a quantitative measure of the sparkle inherent to a given textured sample, we choose a single display with square pixels on a 180 μm pitch to use as our emissive source (Lenovo U110 notebook computer display...

Perception of sparkle in anti‐glare display screens

“…To test the usefulness of the PPDr measure, in an unpublished experiment, Gollier et al . asked observers to rate the perceived sparkle of 10 textured glass AG samples using a categorical rating procedure.…”

“…To test the usefulness of the PPDr measure, in an unpublished experiment, Gollier et al 4 asked observers to rate the perceived sparkle of 10 textured glass AG samples using a categorical rating procedure. They found excellent linear correlation between PPDr and perceived sparkle and in addition were able to estimate the absolute threshold for perceived sparkle at 1-3% PPDr.…”

Microcapsules diffuser screen for speckle noise reduction

“…Speckle measuring methods have been proposed such as measurement system using frusta, 5 calculating image processing, and comparing speckle contrast at some capturing condition. [6][7][8] We used simple measuring method as relative evaluation for speckle contrast difference at some driving condition of the microcapsule diffuser screen. Table 3 presents the measurement conditions.…”

65-5L:Late-News Paper: Sparkle Evaluation with Visual Weighting

“…Measurement and evaluation of sparkle, a disturbing and thus unwanted random pattern of dots that change luminance and chromaticity with direction of observation, is usually carried out by filtering of recorded images in the spatial domain in order to separate the periodic modulations of the pixel matrix from the random modulations that are visually perceived as sparkle [1,2,3]. An analysis of the periodicities and spatial frequencies involved in this process is given in [4].…”