WP640 Imaging Colorimeter. Backlit Graphics Panel Analysis

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1 Westboro Photonics 1505 Carling Ave, Suite 301 Ottawa, ON K1V 3L7 Wphotonics.com WP640 Imaging Colorimeter Backlit Graphics Panel Analysis Issued: May 5, 2014

2 Table of Contents 1.0 WP600 SERIES IMAGING COLORIMETER MEASUREMENT METHOD RESULTS RGB IMAGE LUMINANCE PSEUDO COLOR IMAGE TABULAR DATA DISTRIBUTION OF AOI S IN CIE 1931 SPACE All AOI s Symbols Temerature Dial (Blue) Temerature Dial (Red) ANALYSIS THRESHOLDING AND EROSION SAMPLE EVALUATIONS Westboro Photonics Page 2

3 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. Unfiltered Light Beam V λ Filtered Light Beam Filtered Image Lens CCD Unfiltered Scene Z X red X blue Rotating Filterwheel 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 Westboro Photonics Page 3

4 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 , 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. Westboro Photonics Page 4

5 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). Westboro Photonics Page 5

6 Name Luminance cd/m² x y Dominant Wavelength nm Color PF Luminance PF Fail Fail Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Fail Fail Pass Fail Pass Fail Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Fail Pass Fail Pass Pass Pass Pass Fail Pass Fail Pass Fail Pass Pass Pass Pass Pass Pass Pass Fail Pass Fail Pass Pass Pass Pass Pass Fail Pass Pass Pass Pass Pass Pass Westboro Photonics Page 6

7 3.4 Distribution of AOI s in CIE 1931 Space All AOI s Symbols Color Region Westboro Photonics Page 7

8 3.4.3 Temerature_Blue Color Region Temerature_Red Color Region Westboro Photonics Page 8

9 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 Westboro Photonics Page 9

10 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 Mean Luminance PF Overall Pass_Fail Fail Westboro Photonics Page 10

11 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. Westboro Photonics Page 11

12 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). Westboro Photonics Page 12