Westboro Photonics

1505 Carling Ave, Suite 301 Ottawa, ON K1V 3L7

Wphotonics.com

WP640 Imaging Colorimeter

Backlit Graphics Panel Analysis

Issued: May 5, 2014

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Table of Contents

1.0 WP600 SERIES IMAGING COLORIMETER .................................................................................................................. 3

2.0 MEASUREMENT METHOD ............................................................................................................................................. 4

3.0 RESULTS ........................................................................................................................................................................... 5

3.1 RGB IMAGE ................................................................................................................................................................... 5 3.2 LUMINANCE PSEUDO COLOR IMAGE ............................................................................................................................. 5 3.3 TABULAR DATA .............................................................................................................................................................. 5 3.4 DISTRIBUTION OF AOI’S IN CIE 1931 SPACE .............................................................................................................. 7

3.4.1 All AOI’s ................................................................................................................................................................... 7 3.4.2 Symbols ................................................................................................................................................................... 7 3.4.3 Temerature Dial (Blue) .......................................................................................................................................... 8 3.4.4 Temerature Dial (Red) ........................................................................................................................................... 8

4.0 ANALYSIS ......................................................................................................................................................................... 9

4.1 THRESHOLDING AND EROSION ..................................................................................................................................... 9 4.2 SAMPLE EVALUATIONS ................................................................................................................................................ 10

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1.0 WP600 Series Imaging Colorimeter

The WP600 series colorimeters are Peltier-cooled and stabilized, providing optimal performance and resolution to characterize backlit graphics panels for color and luminance.

The precise matching of the CIE tristimulus filters ensures accurate luminance and chromaticity measurements. Electronic bracketing in Photometrica® ensures that an optimal set of exposures are used to measure each point in a scene, even one requiring a high dynamic range exceeding 100,000:1.

Photometrica® software is included with the WP600 series imaging colorimeter providing users the most productive software environment for simple or in depth analysis. All acquisition and analysis functions of the software can be efficiently automated using the built-in scripting methods, or with the optional Software Development Kit (SDK).

Key Features and Benefits:

Up to 9MP resolution available

Powerful and highly customizable user interface (custom development available)

Thermoelectrically cooled CCD Sensor

High sensitivity and stability

Wide range of lens options available

Smallest footprint available for an imaging colorimeter

Automation friendly Software Development Kit available

Vλ

Xblue

Xred

Z

Lens

Rotating

Filterwheel

Filtered

Light Beam

CCD

Unfiltered

Light Beam

Filtered

Image

Unfiltered

Scene

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2.0 Measurement Method

Sample Details:

Sample No. Description Date Analyzed

1 Automotive

Panel October 24, 2013

Hardware configuration and setup:

A WP640 (S/N 6400113001, demonstrator) with 50mm lens was mounted to a stage on a manual rail system.

The sample was placed on a level stage and the measurement area was aligned using the image preview feature of the Photometrica software. The precise position of the AOI’s on the surface of the sample was not tracked or tightly controlled.

All measurements were performed in a dark room.

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3.0 Results The results below are generated using the character refinement tool in Photometrica. After capture, the software can be configured to automatically locate all graphics within the field of view and report their optical quantities in the AOI summary table. More traditional spot meter measurement can also be performed.

3.1 RGB Image

3.2 Luminance Pseudo Color Image

3.3 Tabular Data

All data of interest is summarized in the AOI table. The table layout and content are fully configurable with standard spreadsheet functions built in (sorting, etc.). Any column can include a Pass/Fail scheme where the values are displayed in red if they are out of spec. Custom columns with more complex pass/fail scenarios can also be created (such as color and luminance PF below).

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Name Luminance cd/m² x y Dominant

Wavelength nm Color

PF Luminance PF

1 2.533 0.1962 0.2247 480.6 Fail Fail

2 5.031 0.2063 0.2489 482.6 Pass Pass

3 5.906 0.2063 0.2478 482.5 Pass Pass

4 5.312 0.2065 0.249 482.6 Pass Pass

5 5.084 0.2056 0.2474 482.5 Pass Pass

6 5.485 0.2063 0.2487 482.6 Pass Pass

7 5.352 0.2051 0.2479 482.6 Pass Pass

8 6.131 0.2043 0.2461 482.4 Pass Pass

9 2.548 0.1968 0.2275 480.9 Fail Fail

10 4.658 0.2117 0.2557 483 Pass Fail

11 4.004 0.2128 0.26 483.4 Pass Fail

12 6.332 0.2059 0.2476 482.5 Pass Pass

13 6.462 0.2068 0.2488 482.5 Pass Pass

14 5.746 0.2059 0.2476 482.5 Pass Pass

15 5.19 0.2044 0.2488 482.7 Pass Pass

16 6.673 0.2065 0.2478 482.4 Pass Pass

17 5.273 0.2052 0.2471 482.5 Pass Pass

18 6.604 0.2041 0.2471 482.6 Pass Pass

19 6.61 0.2043 0.2447 482.3 Pass Pass

20 5.879 0.2073 0.2502 482.7 Pass Pass

21 5.032 0.1503 0.05034 462.5 Fail Pass

22 8.167 0.7176 0.2815 639.6 Fail Pass

23 5.059 0.2076 0.253 483 Pass Pass

24 4.785 0.2076 0.2535 483.1 Pass Fail

25 4.893 0.2083 0.2524 482.9 Pass Fail

26 4.674 0.2061 0.2456 482.2 Pass Fail

27 5.461 0.2049 0.2459 482.3 Pass Pass

28 5.445 0.2048 0.2459 482.4 Pass Pass

29 5.416 0.2038 0.2433 482.1 Pass Pass

31 4.62 0.2059 0.2438 482 Pass Fail

32 4.664 0.2044 0.2453 482.3 Pass Fail

33 5.059 0.2041 0.2436 482.2 Pass Pass

34 6.123 0.2064 0.252 483 Pass Pass

35 4.973 0.2078 0.2566 483.4 Pass Fail

36 5.643 0.2071 0.2481 482.4 Pass Pass

37 5.358 0.2065 0.2487 482.6 Pass Pass

38 5.978 0.2072 0.2479 482.4 Pass Pass

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3.4 Distribution of AOI’s in CIE 1931 Space

3.4.1 All AOI’s

3.4.2 ‘Symbols’ Color Region

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3.4.3 ‘Temerature_Blue’ Color Region

3.4.4 ‘Temerature_Red’ Color Region

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4.0 Analysis

4.1 Thresholding and Erosion

When measuring graphics, it is important to maintain a minimum number of pixels across a stroke to accurately and repeatedly measure a character. Typically, industry standards will recommend between 6-8 pixel stroke width, though 4 is considered the very minimum.

Since edge pixels are not always reliable, thresholding and eroding each character is available for best accuracy and repeatability. The method within Photometrica is quite straightforward and can be fully automated on capture using the available scripting tools:

1. Separate the very edge of the graphic from the background by setting a threshold limit for the glyph edge.

2. Exclude the pixels closest to the edges by eroding the glyph area by one or more pixels

An example of the difference in the measured region with and without erosion is offered below.

NO EROSION

1 PIXEL EROSION

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4.2 Highlight Schemes

In addition to offering visual pass/fail cues in the AOI and Evaluation tables, Photometrica can overlay a pass/fail highlight scheme directly over the characters for faster assessment.

4.3 Sample Evaluations

The Photometrica® software interface has extensive computation ability built into the user interface allowing complex evaluations and analysis to be performed without the need to export the data to external software (excel, etc.) for analysis.

Custom columns in the AOI table can be generated based on calculations (uniformity, etc.) of variables. Geometric information (area, centroid, etc.) can also be displayed as required. The visibility of standard or customized columns is easily configured in the AOI column editor.

An example of some standard AOI columns exported directly from the software has been provided in the preceding sections. These columns allow complex analysis of each individual AOI within the environment.

Further evaluation of the entire measurement environment (not just individual AOI’s) can be performed using the evaluations window contained within the software. Using this tool, the column data for AOI’s can be summarized or evaluated (i.e. mean luminance of all AOI’s, etc.). This utility is particularly useful for production applications where a complex pass/fail algorithm for the entire part can be defined and displayed.

Mean Luminance 5.36

Luminance STD 1.02

Percent Pass 94.59

Mean Luminance PF 72.97

Overall Pass_Fail Fail

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5.0 Automation

Using the native scripting tools in the Photometrica® Software, a custom capture sequence can be generated. For example, with a single click of a button the system will measure the DUT, automatically identify all distinct characters, evaluate their luminance and chromaticity according to user-defined methods and report a summary of any regions which are outside of the tolerances.

Sample automotive panel screenshot after capture without auto-refinement

Panel after applying auto refinement to entire field of view. Each character has been identified (dotted lines around perimeter) and Pass/Fail analysis performed. All in less than 1s.

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Various pseudo-color overlays allow users to quickly reveal the average luminance and chromaticity of each character. Optional highlight schemes can also be applied to visually display the pass/fail condition of each character. The pass/fail definition is highly configurable and can include any number of parameters (luminance, chromaticity, uniformity, etc.).

Panel with optional highlight scheme applied, performed automatically with refinement.

When used in this way, the solution does not require time consuming or expensive setup procedures such as programming or precision positioning of the display. The characters are identified and evaluated regardless of orientation and location without a need for fine alignment of spot meters. Standard spot meter evaluations are also available in the software, where required (see below).