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Background Statement for SEMI Draft Document 5634D
NEW STANDARD: TEST METHOD FOR COLOR REPRODUCTION AND PERCEPTUAL CONTRAST OF DISPLAYS
NOTICE: This Background Statement is not part of the balloted item. It is provided solely to assist the recipient in reaching an informed decision based on the rationale of the activity that preceded the creation of this ballot.
NOTICE: For each Reject Vote, the Voter shall provide text or other supportive material indicating the reason(s) for disapproval (i.e., Negative[s]), referenced to the applicable section(s) and/or paragraph(s), to accompany the vote.
NOTICE: Recipients of this ballot are invited to submit, with their Comments, notification of any relevant patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this context, ‘patented technology’ is defined as technology for which a patent has been issued or has been applied for. In the latter case, only publicly available information on the contents of the patent application is to be provided.
Background
As high quality properties of digital TV like HDTV, 4K UHDTV and 8K UHDTV have been demanded, it is necessary to present the highest image quality with rich and authentic color, subtle gray and color tone and dynamic contrast, and set the suitable and advanced evaluation methods of display quality. The aim of various methods for measuring color gamut, brightness, and contrast based on human perception have been studied is to match the image quality with human eyes. Even though there are conventional measuring methods like luminance, tristimulus values for the objective evaluation method, there are imperfect methods considering a viewing condition, perceptual parameters.
The basic rationale of this document is the color appearance model which is proposed at CIE in 2002. A new method is to calculate a color volume and contrast with color appearance model which is uniform color space with human visual perception.
The ballot results will be reviewed and adjudicated at the meetings indicated in the table below. Check www.semi.org/Standards under Standards Calendar for the latest update.
Review and Adjudication Information
Task Force Review / Committee AdjudicationGroup: / To be reviewed at the Korea Perceptual Image Quality TF Meeting / Korea FPD Metrology Technical Committee
Date: / May 12, 2017 / May 12, 2017
Time & Time Zone: / 10:00pm – 12:00pm (KST) / 13:00pm – 14:00pm (KST)
Location: / SEMI Korea office / SEMI Korea office
City, State/Country: / Seoul, Korea / Seoul, Korea
Leader(s): / Jong Ho Chong (Samsung Display)
/ JongSeo Lee (Samsung Display)
Il-Ho Kim (LMS)
Standards Staff: / Natalie Shim (SEMI Korea)
82.2.531.7808
/ Natalie Shim (SEMI Korea)
82.2.531.7808
This meeting’s details are subject to change, and additional review sessions may be scheduled if necessary. Contact the task force leaders or Standards staff for confirmation.
Telephone and web information will be distributed to interested parties as the meeting date approaches. If you will not be able to attend these meetings in person, but would like to participate by telephone/web, please contact Standards staff.
SEMI Draft Document 5634D
New Standard: TEST METHOD FOR COLOR REPRODUCTION AND PERCEPTUAL CONTRAST OF DISPLAY
1 Purpose
1.1 This Standard specifies measurement conditions and methods for describing the visual color quality in 3-dimensional color space, and the perceived contrast with perceptual parameters in color electronic display devices.
1.2 The CIE[1] XYZ color space is derived from the experimental results and it has been used to set color performance of displays in CIE xy or u’v’ chromaticity diagram without brightness.
1.3 For measurement, setting test patterns based on Average Picture Level (APL) of IEC[2] 62087:2011 are required, instead of full screen patterns, which are composed with small size of window box. The full screen patterns are not suitable for emissive displays which of luminance are adjusted with contents.
1.4 The contrast ratio has been widely used although the calculated value is dramatically changed by dark state luminance. This metric does not consider human visual characteristics. Therefore, it is more reliable to consider the perceptual indices.
2 Scope
2.1 This Standard is applicable to the color electronic display devices, except on the transparent display.
2.2 This Standard includes the measurement for physical data, analysis, and calculation methods which have perceptual factors.
2.3 The term “perceptual” is subject to CIECAM02 (CIE Color Appearance Model 2002) in this Standard.
NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their use. It is the responsibility of the users of the Documents to establish appropriate safety and health practices, and determine the applicability of regulatory or other limitations prior to use.
3 Limitation
3.1 Measurements are subject to errors or imprecision due to the user, environmental factors, and mis-calibration of measurement system or measurement system limitations.
3.2 Results may vary with ambient illumination conditions or in the presence of uncontrolled stray light reflections.
4 Referenced Standards and Documents
4.1 IDMS
4.1.1 Information Display Measurement Standard (IDMS) 1.0
4.2 CIE Standards
4.2.1 CIE 15.3 — Colorimetry
4.2.2 CIE 159 — CIECAM02
4.3 IEC Standards
4.3.1 IEC 62341-6-2 — OLED Displays — Measuring methods of visual quality and ambient performance
4.3.2 IEC 62087 — Methods of measurement for the power consumption of audio, video and related equipment.
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Abbreviations and Acronyms
5.1.1 APL — average picture level.
5.1.2 FOV — field of view
5.1.3 PCL — perceptual contrast length
5.1.4 VCRC — volume color reproduction capability
5.1.5 LMD — light measurement device
5.1.6 DUT — device under test
5.2 Definitions
5.2.1 brightness — the attribute of a human visual sensation according to which an area appears to emit more or less light
5.2.2 color gamut boundary — the outer surface determined by a color gamut form
5.2.3 perceptual contrast length — the difference of black and white brightness of the screen
5.2.4 volume color reproduction capability — the volume of the perceived color gamut obtained in 3–dimensional color space which is composed of colorfulness, hue and brightness
6 Standard Measurement Condition
6.1 Measuring Conditions
6.1.1 Environmental conditions
6.1.1.1 In order to obtain accurate measured data, the following environmental conditions are required.
· Temperature: 25±2 °C
· Humidity: 25–85 % relative humidity
· Pressure: 86–106 kPa
· Air flow: no wind
· Vibration / Shock: no influence
6.1.2 Ambient conditions
6.1.2.1 Dark room condition
6.1.2.1.1 The luminance contribution from the background illumination shall be less than 0.01 cd/m2.
6.1.2.2 Ambient illuminations
· Uniform hemispherical diffuse light source
6.1.3 Measuring equipment conditions
6.1.3.1 In this Standard, a LMD such as spectral radiometer, at least from 380 nm to 780 nm wavelength ranges or a filter photometer shall be used.
6.1.3.2 The luminance accuracy of the instrument shall be within ±2 %. And the chromaticity accuracy of the instrument shall be below:
Table 1 Chromaticity Accuracy of the Instrument
x,y / ±0.002 (0.001 to 0.05 cd/m2)x / ±0.0015 (0.05 cd/m2 or more)
y / ±0.001 (0.05 cd/m2 or more)
6.1.3.3 The measuring distance could be set 400 mm or 500 mm. For the small size display, the distance can be calculated and set that an LMD should include over 500 pixels of display at 2 degree FOV. The calculated distance should be noted in a report.
6.1.4 Viewing Direction
6.1.4.1 In the case of the uniform hemispherical diffuse illumination conditions, an integrating sphere, sampling sphere, or hemisphere shall be used. The configuration shall follow the Standard di/8° to di/10° illumination/detection geometry, where di is the Standard notation for diffuse. The basic viewing direction of this test is shown in Figure 1. However, for a specific case, other viewing directions, like perpendicular to the display can be used. The placement of the LMD should be located in front of the measurement port in the Fig1. The lamp should have the light intensity at least from 380 nm to 780nm range, continuously.
Figure 1
An Example of Measuring Configuration with Sampling Sphere
7 Summary of Test Method
7.1 Test Patterns
7.1.1 A centered window box occupying 4 ~ 40% of the screen area is used. The 100% intensity (e.g., 255 gray levels in 8 bits) for window box and the 40% intensity (e.g., 102 gray levels in 8 bits) for background are applied. One of the test patterns is shown in Figure 2. Because depending on the window size, the peak luminance would be changed, the window size should be reported.
Figure 2
Test Pattern of 4% Window Box with Black Background
7.1.2 Each of the following eight colors in the 4 ~ 40% window box (The size should be reported.) at the center of the screen is applied. The color order could be changed, depending on the measurement system.
· Red: (255, 0, 0)
· Green: (0, 255, 0)
· Blue: (0, 0, 255)
· Cyan: (0, 255, 255)
· Magenta: (255, 0, 255)
· Yellow: (255, 255, 0)
· Black: (0, 0, 0)
· White: (255, 255, 255)
NOTE 1: It may be necessary to use some kind of a mask or stray–light–elimination tube to avoid veiling glare in the detector when measuring window box colors.
NOTE 2: The intensity of colors is based on 8 bits. However, for the other color bits, like 10 bits or 12 bits, the intensity of color should be changed.
7.2 Measuring Set-up
7.2.1 Electrical conditions, warm-up time and adequate integration time follow section 3.2 of IDMS 1.0 methods.
8 Procedure
8.1 The following measuring procedure is recommended for the measuring of tristimulus values of each of colors.
· Check and measure the conditions described in 6.1.1 and 6.1.2.
· Set the display device and signal generator which can be operated for the test patterns described in 7.1.2.
· Set the distance between display and LMD, which is described in 6.1.3.3.
· Set the LMD which is perpendicular to the display in dark condition with directional light source or set the LMD which is di/8° to di/10° illumination/detection geometry with the sampling sphere.
· Apply the eight test patterns at the display, which is described 7.1.2.
· Measure the spectral radiance or tristimulus values at the center of the window box with eight test patterns, respectively.
· Record the measurement data.
· Record the measurement conditions which are room conditions, aging conditions, and ambient conditions.
9 Calculations
9.1 Analysis Method for Color Reproduction
9.1.1 The 17 gradation points between black and other primary and secondary (RGBYMC) colors using gamma 2.2 should be calculated. The calculation method is described in Appendix 1-2.
9.1.2 The measured and interpolated data for all defined colors shall be transformed into the CIECAM02 3 dimensional color space, which is described in Appendix 1-1. The number of scattered points is 98 without overlapping points.
NOTE 3: For example, the number of points between black and red is 17. Because black is common point, 16 points are considered, respectively, and the number of scattered points is 96(=16 x 6). Finally, black and white points are added. The total number of scattered points is 98.
9.1.3 Color reproduction which is color gamut volume with brightness, colorfulness, and hue of the transformed data is calculated.
· Search the color boundary surface in 3-dimensional color space, which is determined by a color gamut’s extremes.
Figure 3
An Example of Color Reproduction
· Set the smallest triangulation of surface points which are the nearest each other. One of the points ‘inner’ in Figure 4 is located at a middle of black and white points. Brightness (Q) which is related on m is z-coordinate. m value is Q. Colorfulness (M) which is the length from z–coordinate on xy plane and hue (h) which is the angle of colorfulness are related on k and l. k is M x cos(h), which is x–coordinate, and l is M x sin(h) which is y-coordinate.
Figure 4
The Geometry of Trigonal Pyramid of Connecting Points with an Inside Point
· Calculate the color volume of trigonal pyramid and add up all volume of trigonal pyramids. The total number of trigonal pyramids is 192. The calculation procedure to get the total number is described in Appendix 1–3.
where N = {1,2,3, …, 192} (1)
Color Volume
9.2 Analysis Method for Perceptual Contrast
9.2.1 PCL is the length between black and white brightness. The calculation method for brightness is described in Appendix 1–1.
· Calculate the contrast length between black and white brightness.
PCL = white brightness – black brightness (2)
10 Report
10.1 The color reproduction named VCRC (Volume Color Reproduction Capability) in 3D color space is represented with percent relative to sRGB color volume in CIECAM02. An example of report table is shown in Table 2. The color volume of display calculated in clause 9.1.3 should be applied. In this report, sRGB is used as a reference volume. In addition, DCI-P3, AdobeRGB and BT.2020 could be applied as a reference color gamut.
VCRC (%) = (Color Volume of Display/ (Color Volume of sRGB)) x 100 (3)
Table 2 An Example of a Result Report for the VCRCVolume of sRGB / 836,906.93
Color volume of display / 836,906.93
Window size / 4%
VCRC (%) / 100
The illumination of environment / 0 lux
Color temperature of environment / - K
10.2 For the PCL, there is a table of the result report which is shown in Table 3.
Table 3 A Worked Example of a Result Report for the Perceptual Contrast LengthLuminance(cd/m2) / Brightness / PCL
Black / 0.8575 / 61.5 / 228
White / 607 / 289.5
Window size / 4%
The illumination of environment / 0 lux
Color temperature of environment / - K
APPENDIX 1 Color Space Conversion Method
NOTICE: The material in this Appendix is an official part of SEMI [designation number] and was approved by full letter ballot procedures on [A&R approval date].
A1-1 CIECAM02 Color Model
A1-1.1 A color appearance model provides a viewing condition specific method for transforming tristimulus values to and from perceptual attribute correlations. The CIECAM02 is useful for color management applications. This model consists of a chromatic adaptation transform and equations for computing a set of perceptual attribute correlations. A set of perceptual attributes is only focused on dim condition for the display application. Also, brightness color space for color reproduction is used, instead of lightness color space of CIELAB or CIELUV. Brightness is defined by the CIE as the attribute of a visual sensation according to which an area appears to emit more or less light.