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Recent Standardization Efforts and Measurement Procedures of German Automotive OEM

and German Flat Panel Forum (DFF)

Recent Standardization Efforts and Measurement Procedures of German Automotive OEM and German Flat Panel Forum (DFF)

Karlheinz Blankenbach*, Udo Krüger**, Hans-Ulrich Lauer***, Martin Zobl**** * Pforzheim University, Display Lab, Pforzheim, Germany

** TechnoTeam Bildverarbeitung, Ilmenau, Germany *** Visteon Electronics, Karlsruhe, Germany

**** BMW Group, Munich, Germany

Abstract The requirements of automotive displays differ to a large extent from consumer and industrial displays. In order to reduce the effort in specifying and evaluating high quality displays, German automotive OEMs, Tier 1/2 and the German Flat Panel Forum have launched a cooperation.

Author Keywords automotive displays; measurements; MURA; gamma curve; sticking image

1. IntroductionDisplays are integrated today in every car. From early Seg 8 clocks they have reached “glass cockpit” status in some luxury cars. Many functions like navigation, radio and climate control of intermediate cars are controlled via displays. Therefore it is essential to achieve a high quality. However the annual mass production of automotive displays is small compared to consumer volumes. Therefore some German car manufacturers and their suppliers started some years ago towards standardization. The benefits of a common specification along the value chain from e.g. display manufacturers (Tier 2) over display integrators (Tier 1), electronics (incl. interface) and measurement companies to car manufacturers (OEM) are:

- Common understanding on minimum requirements and relevant optical parameters.

- Unification of measurement and evaluation methods, as many standards exist which cover only partially the automotive needs like ambient light, eye-box or large temperature range; see e.g. [1].

- Adaptation of current standards to automotive needs.

- Rise of efficiency in terms of time (see Fig. 1) and cost (high volume of standardized displays).

- Support of automotive specific technology development

Fig. 1 top shows how an “OEM A” has to deal with the supply chain – with many suppliers in parallel (black lines). And the suppliers have to discuss the same topics with several OEMs (magenta and brown lines, black curves). It is obvious that this method is not efficient. Therefore two groups were established (Fig. 1 bottom):

- An OEM group where car manufacturers’ specialists discuss future trends and common interests towards standard automotive displays called “OEM display specification”.

- The “automotive platform” of the German Flat Panel Forum (“Deutsches Flachdisplay Forum” e.V., DFF) where DFF members bring in their expertise along the automotive displays value chain. Feedback to the OEM spec is provided and the “DFF display measurement specification” is developed for evaluation of the OEM spec.

In the past years German automotive OEMs and the German Flat Panel Forum (DFF) have started to issue the “OEM Display Specification” and the “DFF Display Measurement Specification”. Selected topics are presented here. Both documents are updated when new topics come up.

Figure 1. Cooperation models: Top: Typical situation where the companies have to deal with many others which is not an efficient way. Bottom: Organization scheme for automotive display cooperation involving all players effectively.

2. German Automotive OEM Specification Fig. 2 shows the beginning of the table of displays requirements. This document describes the requirements of the OEMs mainly in terms of optical topics like luminance, grey scale and color under various conditions. Examples are:

- Fig. 3: The polar chart for viewing angle shows the eye box for driver and co-driver. As these incident angles differ at minor extent from car to car, standardization is very reasonable as measurement effort is reduced.

- Fig. 4: Instead of defining the usual K W response time @ +25°C, the “Grey-to-Grey” response time (TG2G) for different temperatures is requested. Beside this, the “Motion Picture Response Time” (MPRT) is as well defined. However, as MPRT determination requires huge effort on measurement equipment (see e.g. [2], [3]), TG2G is as well accepted. This is also an example of the efficiency of discussion in networks / platforms.

Figure 2. Excerpt of the table of contents of the “OEM Display Specification for Automotive Application”.

Figure 3. Viewing angle for automotive displays: The blue line embraces the eye box for driver and co-driver.

Figure 4. Example of advanced switching time requirements beyond K W response time

3. German Flat Panel (DFF) Automotive Display Measurement Specification

As the OEM display specification describes mostly requirements, the way how to measure them must be described more in detail. This is done in the “DFF Display Measurement Specification”; its current table of content is provided in Fig. 5. Many measurement procedures refer to basic methods of [1] and other standards. However it is obvious that for high quality automotive displays, many topics must be added. Fig. 6 and Fig. 7 show the gamma measurement for approval and series production as an example.

In the following sections three examples, which demonstrate new approaches to qualify automotive displays, are presented.

Figure 5. Table of contents of the “DFF Display Measure-ment Specification” issued by the DFF automotive platform.

Figure 6. Gamma for Production Part Approval Process (PPAP, top) and for displays during series production (bottom).

Figure 7. Best practice examples for reporting of basic measurement values for evaluating grey scale performance.

Measurement of Uniformity (Black Mura)

Uniformity is usually determined by measuring the luminance of 9 defined locations on a display (see e.g. [2], [3]). This definition does not adequately address uniformity issues of high quality displays. Uniformity is named as MURA when the whole area is taken into account. There are some MURA measurement devices commercially available like “MURATest 16M” by ELDIM or “TrueMURA” by Radiant Vision Systems. The algorithms are vendor specific and not suitable for standardization as the algorithms are not published. Therefore a team of automotive specialists [4] started work on uniformity testing towards measurement standardization. Reproducible measurements and algorithms have to be correlated to vision (perception models). Fig. 8 shows the raw data of a luminance measurement for black (left) and a calculated result for comparison with evaluation by subjects.

Figure 8. Black Mura luminance measurement (left, false colour display) and gradient image (right) [4].

Measurement of Gamma

Fig. 9 shows examples of luminance measurements before and after gamma correction. Opposite to other standards which determine gamma piecewise from luminance measurements, limit curves (tolerance band) for the luminance at different gamma values over all grey levels are defined [5]. It is obvious that values outside the tolerance curves will result in noticeable distortions of high quality automotive HMIs with contain smooth grey level transitions.

Figure 9. Luminance curves before (top, linear plot) and after gamma correction (bottom, log plot) [5].

Measurement of Sticking Image

“Sticking Image”, also named as image sticking, residual image etc. is often tested using a checkerboard (see e.g. [2]). It has been found that this test pattern has some limitations; therefore a “3 Level Burn-In Pattern” is proposed in the “DFF Display Measurement Specification” (Fig. 10): This pattern consists of white and black areas which are additionally surrounded by areas with the inspection level grey (usually GLmax/2 like 128 for 8-bit) [6]. The presence of grey reference areas enables direct separation of black and white image sticking with one measurement and elimination of grey non-uniformity of the display.

Fig. 11 shows a typical result: The false color luminance image (left) with “blacked” transition zones shows the issue of uniformity for sticking image measurements. Vertical luminance profiles are shown in the center of Fig. 11 directly after switching to inspection grey (red curve, 0 s) and after 1,200 s (green curve).

Figure 10. Sticking Image test pattern “3 Level” recommended by the “DFF Automotive Display Measurement Specification”.

Figure 11. Top: Luminance (false color) of a sticking image measurement using “3 Level Burn-In Pattern” (see Fig. 10). Center: Vertical luminance curve (top: dashed box) after switching to inspection grey level (red, 0 s) and after long time (green, 1,200 s) showing vanishing sticking image. Bottom: Relaxation curves of sticking image (Lsi, difference black-white) and black (Lsi,b) and white (Lsi,w) test boxes [6].

It is clearly measured that vanishing image sticking happens; the chart (Fig. 11 bottom) shows that for 0 s to 300 s: strong sticking image is observed for black and white. The red curve is the effective image sticking of black and white which falls exponentially (line in log-plot) within 150 s below the typical Weber-Fechner threshold of 0.01.

4. Impact & Summary Automotive displays have significantly higher requirements than consumer products. However the mass production of cars is significantly lower than for many consumer products. Therefore these automotive displays should be standardized as far as possible. German OEMs and the German Flat Panel Forum (DFF) made successful effort on those topics:

- Joint OEM display parameters like viewing angles, luminance, contrast ratio, gamma, color coordinates, response time, ...

- Joint DFF measurement specification for automotive displays

- OEMs and suppliers along the value chain discuss reasonable test methods for PPAP and series production

The process of our automotive standardization is not finished, it is an on-going task as new challenges like free-form, curved, and flexible displays enter pre-production status and higher ppi require new effort on the characterization of surfaces. An example is provided in Fig. 12.

Figure 12. Advanced automotive displays, source: BMW.

5. Acknowledgements We acknowledge XTRONIC GmbH (http://www.xtronic.de/), Germany for their continuous work for the “German Flat Panel (DFF) Automotive Display Measurement Specification”.

6. References [1] SAE J1757, ISO 15008, IEC 61747, IEC 62341, IEC TC 110,

ITU-R BT.709-5, ISO 9241, ISO 13406, …

[2] SID International Committee for Display Metrology, “Information Display Measurements Standard”, SID (2012).

[3] K. Blankenbach: “Display Metrology” (Chap.) 11 in J. Chen, W. Cranton, M. Fihn (eds) “Handbook of Visual Display Technology,” Springer (Heidelberg), 2275 – 2471 (2012).

[4] U. Krueger, M. Kreuzer, T. Fink: “Black MURA Measurements – Experience with a current standard and ideas for further development”, Proceedings electronic displays Conference (2012).

[5] H.-U. Lauer: “Gamma Correction for TFT-LCDs”, SID Mid Europe Meeting (2000).

[6] H.-U. Lauer, C. Beutel, J. Faber: „Extended analysis of sticking image by using a 3-level burn-in pattern“, Proceedings electronic displays Conference (2013).

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Visteon is a global company that designs, engineers and manufactures innovative cockpit electronics products and connected car solutions for most of the world’s major vehicle manufacturers. Visteon is a leading provider of driver information and controls, audio and infotainment, and domain controllers; its brands include Lightscape®, OpenAir® and SmartCore™. With corporate offices in Van Buren Township, Michigan, (U.S.); Shanghai, China; and Chelmsford, UK; Visteon has more than 40 facilities in 18 countries. Learn more at www.visteon.com.

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