Embed Size (px)
Citation preview
Strictly Private and Confidential
Brian Hayden, Robert Belke, Paul Weindorf, Dr. Carl Evans andK. Matsuo – Visteon Corporation
S. Miyahara
5.6 – Anti-Glare Film Sparkle Optical Modeling & Prediction Method
Outline
Introduction
Background & Objective
Description
Conclusions
Page 2
Introduction
Due to the increase in the complexity and expected functionality of electronics in vehicles there has been a trend to add touch panels to display systems.
Page 3
With the addition of a touch panel in front of a display, there is a greater interest in treating these materials to reduce the total reflection of the system and allow full functionality in strong sunlight conditions.
Typically this can be done by adding either an anti-reflective (AR) film or an anti-glare (AG) film onto the top surface.
Introduction
Shown here are photographs and imaging photometer measurements of high sparkle and low sparkle screens
Page 4
High Sparkle (left) and Low Sparkle (right)
Background / Objective
There have been several methods proposed to measure and predict the perceived sparkle as observed by the human eye.
Page 5
The method shown here proposed by Dr. Carl Evans, measures the standard deviation of peak TFT pixel luminance and relates this to the luminance sensitivity of the eye.
Background / Objective
This method shows excellent correlation between perceived sparkle and the measured standard deviation of the pixelated luminance levels.
Page 6
However, the underlying cause of sparkle is only discussed in generalities when the “display pixel size becomes small enough to be comparable to the feature size in the AG film”Perceived Sparkle versus Measured Data
Background / Objective
In order to understand how to model an AG surface structure, we must first look at the surface topologies of AG films whose sparkle performance was evaluated.
Page 7
Determination of the AG surface structure turns out to be non-trivial due to the limited depth of field associated with high magnification optical microscopes as shown in this example.AG Film Surface
1000X Optical Microscope
1000X Enhanced Optical Image of J36 Lens AG (#2)
Background / Objective
To help understand the AG surface feature structure is through the use of the Wyko NT Series Optical Profiler which performs non-contact, 3D surface detail measurements using vertical scanning interferometry
Page 8
Wyko 3D Surface Analyses
High Sparkle (Left)Low Sparkle (Right)
Description
To model AG sparkle, Synopsys LightTools 3D optical engineering and design software was utilized.
Refractive optical surface structures were created using standard object dimensions based on measured surface topologies of two different AG films.
Page 9
Standard AG Refractive Cone Element High Sparkle Model
ParametersLow Sparkle Model
Parameters
Description
Page 10
Example of AG Surface Model
In addition to the AG model, the TFT pitch structure was also modeled as shown below
The structure element pitch was randomized (±25%) and over 100,000 cone elements were created to model the AG surface.
Description
Page 11
The luminance at the AG lens surface can now be determined and is consistent with the method used to perform sparkle measurements.
LightTools Simulation
Description
Page 12
Simulation Luminance Profiles; High Sparkle (Left); Low Sparkle (Right)
Luminance profiles for the different surface structure sizes and conic angles.
Results show the semblance of sparkle for the larger structure size irrespective of conic angle whereas the smaller structure size shows very little sparkle.
Description
Page 13
Luminance and Spectral ComparisonsHigh Sparkle (Left); Low Sparkle (Right)
Shown are luminance values across one TFT pixel row for each configuration along with it’s FFT spatial frequency domain components. A reference contrast sensitivity function (CSF) of the human eye is also shown.
An inverse FFT is applied to each CSF filtered spatial frequency component, the results (red) are plotted in the spatial domain.
Description
Page 14
For reference, if the AG texture is removed from the lens surface, the results exhibit no sparkle. The results obtained by optical simulations are similar to and mimic measured results.
Smooth Lens Surface Simulation
Description
Page 15
Additional insight may be gained as to the mechanism causing sparkle by overlaying the simulation profile with the surface structure model.
When the large diameter structure elements align within a TFT pixel, light is scattered in the local structure element area and therefore does not appear as bright. When there is no structure within a TFT pixel, no scattering occurs an the pixel appears brighter.
The small diameter structure elements provide an averaging effect of the scattered light and therefore the TFT pixel luminance is much more uniform.
50μm, 10° Cone Structures with Luminance Map Overlay 10μm, 10° Cone Structures with Luminance Map Overlay
Conclusion
Refractive modeling techniques may be useful to predict display sparkle caused by AG surface structures. More modeling based on actual sample feature sizes and subsequent correlation to sparkle testing is required to fully validate the modeling technique. In the future, these techniques may be utilized to determine the AG structure sizes required to minimize perceived sparkle.
Page 16
Page 17
www.visteon.com
