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Background Statement for SEMI Draft Document 5633E
NEW STANDARD: TEST METHOD FOR VIEWING ANGLE CHARACTERISTIC USING MIXED COLOR ON VISUAL 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.
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Background
The viewing angle characteristic of display panel is one of the most important components of image quality. Even though there are several viewing angle measuring methods for luminance and color, they do not sufficiently deal with natural or mixed real world color for viewing angle. This proposal suggests new viewing angle measuring method which evaluate the variation of mixed color (not only for luminance, R, G, B primary colors), such as cyan, magenta, yellow colors and natural colors based on perceptual difference measure CIELAB.
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 Viewing Angle 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): / Myongyoung Lee (LG Electronics)
/ 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 5633E
New Standard: TEST METHOD FOR VIEWING ANGLE CHARACTERISTIC USING REFERENCE COLOR ON VISUAL DISPLAYS
1 Purpose
1.1 The viewing angle characteristic of display panel is one of the most important components of image quality.
1.2 Even though there are several viewing angle measuring methods for luminance and color, they do not sufficiently deal with natural or real world mixed color for viewing angle.
1.3 A new viewing angle measuring method is suggested which evaluates the variation of mixed color using reference color patches based on CIELAB color difference metric.
2 Scope
2.1 This Standard is applicable to large screen flat panel display such as TV and monitor in a dark room.
2.2 The scope of the term “viewing angle characteristic” is related to both luminance and color variation in this Standard.
2.3 This Standard defines only horizontal and vertical viewing angles for measurement.
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 Referenced Standards and Documents
3.1 CIE1 Standards
3.1.1 CIE[1] 1931 — Color space
3.1.2 CIE — Standard colorimetric system
3.1.3 CIE 15:2004 (3rd Edition), Colorimetry
3.1.4 CIE S 014-4/E:2006: Colorimetry - Part 4: CIE 1976 L*a*b* Colour Spaces.
3.2 ICMD2
3.2.1 Information Display Measurement Standard (IDMS) 1.03, 2012
3.3 SMPTE3
3.3.1 Color Reference Pattern, SMPTE 303M-2002, 2002
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
4 Terminology
4.1 Abbreviations and Acronyms
4.1.1 DUT — display under test
4.1.2 LMD — light measuring device
4.1.3 FOV — field of view
4.1.4 APL – average picture level
4.2 Definitions
4.2.1 CIELAB — a uniform color space defined by the CIE in 1976, officially known as CIE L*a*b*. L* stands for luminance, a* is the red-green axis, and b* is the blue-yellow axis
4.2.2 Color difference — the Euclidean distance between two colors in a specific color space.
4.2.3 Viewing angle — the horizontally and vertically inclination angle (degree) to the normal direction to the plane of the display surface. This Standard adopts right-handed x-y-z Cartesian coordinates with origin at the center of the screen.
4.2.4 Viewing distance — the distance between screen centre and watching or measuring location. In case of TV, it is generally recommended as 3 times of the screen height.
5 Summary of Test Method
5.1 Measuring Conditions
5.1.1 Environmental conditions
5.1.1.1 The following environmental conditions are required to make accurate measurement.
· Temperature: 25±2°C
· Humidity: 25 – 85% relative humidity
· Air flow: no wind
· Dark room: All measurements shall be carried out in a dark room normally under 1 lux.
5.1.1.2 When any of these conditions is not met, they shall be noted on the report.
5.2 Measurement Setup
5.2.1 The measuring equipment shall consist of DUT, light measuring device (LMD), signal generator, and control PC (if used) as shown in Figure 1. For color viewing angle measurement, the measuring location is the center of effective screen area of the display.
5.2.2 Measuring Distance
5.2.2.1 It is recommended that the measuring distance of LMD is set to include over 500 pixels of display at 2 degree FOV.
5.2.2.2 Generally, it is recommended to be same as the viewing distance of the display. The calculated distance should be noted on the report.
5.2.3 Viewing Direction
5.2.3.1 The viewing direction is specified by the horizontal θH and vertical φV as shown in Figure 2.
Figure 1
The Measurement Setup
5.2.3.2 The horizontal and vertical viewing directions (θH, φV) are defined as θH (-60°, -45°, -30°, -15°, 0°, 15°, 30°, 45°, 60°) and φV (-10°, 0°, 10°), respectively, where (-) symbol means downward and sideways to the left.
5.2.4 Optical Measuring Devices
5.2.4.1 In this Standard, a LMD such as spectroradiometer or a filter photometer shall be used for photometric measurement.
5.2.4.2 It requires the photometric accuracy of the LMD within ±2% and colorimetric accuracy within ±0.001 in Δu’v’.
5.2.5 Warm-up time
5.2.5.1 Warm-up shall be achieved before measurement and it must ensure that the luminance approaches a stable value.
5.2.5.2 This warm-up time shall be longer than 30 minutes or follow the instructions determined by manufacturer.
Figure 2
Horizontal and Vertical Viewing Angles Used in this Document
5.2.6 Ambient Illumination Condition
5.2.6.1 All measurements shall be carried out in a dark room less than 1 lux. However, various ambient illumination conditions can be used for different applications.
5.2.6.2 When a different illuminance or ambient illumination condition is used, it shall be noted on the report.
5.3 Measuring Method
5.3.1 Measurement Color Patterns
5.3.1.1 For measurement of the viewing angle characteristic of mixed color, the 18 reference color samples shall be used as shown in Figure 3.
5.3.1.2 The colors were chosen to represent various natural objects and colors that are problematic for color reproduction.
5.3.1.3 In this standard, 18 color samples shall be used for the evaluation of mixed color viewing angle.
5.3.1.4 The colors are uniformly spread in CIELAB color space.
5.3.1.5 Two test patterns can be used for measurement. First, a color array pattern consists of 18 reference color patches and white in a screen with a rectangular box which is measured in the center of the screen. The reason for using color array pattern is to maintain a specific APL of the screen area while measuring the all 18 reference colors and white input. In the figure 4, the area of the fixed APL pattern input is 23.5%. The color patches are positioning at left and right side to reduce error by stray light of different colors. In this layout, each patch of the color array is swapped with the center white patch in order to be measured.
5.3.1.6 Second, a box pattern can be also available which has 4% size of the whole screen in the central test region as shown in Figure 4. The pattern used in the measurement shall be noted on the report.
5.3.1.7 The background signal level is generally black, that is, 0% signal level. However, specific background signal level can be used for some applications. In that case, it shall be noted on the report.
5.3.1.8 8 bit R, G, and B input data for the 18 reference color patches and white are shown in Table 1.
Figure 3
CIE a*b* Coordinates Plot of the 18 Reference Color Inputs
Table 1 8bit RGB Input Values of Reference Color Patches
No. / Color sample / Input data (8 bit, 0~255) /R / G / B /
1 / Dark skin / 116 / 80 / 66
2 / Light skin / 196 / 149 / 129
3 / Blue sky / 95 / 122 / 155
4 / Foliage / 87 / 107 / 65
5 / Blue flower / 132 / 130 / 176
6 / Bluish green / 102 / 189 / 169
7 / Orange / 217 / 122 / 46
8 / Purple blue / 75 / 92 / 164
9 / Moderate red / 196 / 86 / 98
10 / Purple / 93 / 62 / 107
11 / Yellow green / 158 / 186 / 64
12 / Orange yellow / 229 / 161 / 49
13 / Blue / 49 / 64 / 150
14 / Green / 71 / 149 / 71
15 / Red / 177 / 51 / 60
16 / Yellow / 237 / 199 / 32
17 / Magenta / 187 / 85 / 147
18 / Cyan / 0 / 136 / 165
19 / White / 255 / 255 / 255
(a) Fixed APL pattern for the 18 reference color and white input
(b) 4% box pattern for the 18 reference colors and white input
Figure 4
Test pattern for Reference Color inputs: Fixed APL (upper) and 4% Box Pattern (lower)
6 Procedure
6.1 The following measuring procedure is used for the measuring of mixed color viewing angle characteristic.
6.1.1 Check and measure the room temperature, humidity, air condition, and the illumination of the measuring room.
6.1.2 Set up the DUT, signal generator, and computer system for signal control (if it is required for test pattern).
6.1.3 Determine the distance from LMD (Light Measuring Device) to center of DUT.
6.1.4 Set up the LMD to measure the center of the DUT, perpendicular to it (for 0° viewing angle).
6.1.5 Display the color-bar or 4% box pattern for the reference color inputs on the screen.
6.1.6 Measure the luminance and chromaticity coordinates or tristimulus values at the center of the pattern to be measured and record the data.
6.1.7 For the color-bar pattern, another color pattern shall be centered for next measurement by replacing the already measured pattern with a pattern to be measured next.
6.1.8 Repeat the measurement for all defined mixed color patterns by circulating or changing the patterns.
6.1.9 Repeat above procedure for the different viewing angle.
6.1.10 To reduce the number of measurement for all possible cases, viewing angles to be measured can be reduced. In this standard, however, it is recommended to include seven kinds of viewing angle of θH (0°, ±30°, ±60°) at φV (0°) and φV (±10°) at θH (0°) at least.
7 Calculation
7.1 Calculation of CIELAB color coordinates
7.1.1 The 18 reference colors and white patch of normal direction are calculated and compared with the other 19 data from a viewing angle.
7.1.2 The measurement data for all mixed color for each viewing angle shall be transformed into the CIELAB color coordinate as follows:
L*=116×fY/Yn-16
a*=500×fX/Xn-fY/Yn (1)
b*=200×fY/Yn-fZ/Zn
where
f(t)=t1/3 t>6293132962t+16116 otherwise
7.1.3 Where X, Y, Z are the measured CIE tristimulus values of the mixed color and Xn, Yn, Zn are CIE tristimulus value when the white pattern of the display inputs in each direction.
7.1.4 The reference white data, Xn, Yn, Zn and ambient illumination for a measurement condition shall be noted on the report because there can be various cases of white point according to TV picture mode.
7.2 Calculation of CIELAB color difference
7.2.1 In this documents, CIELAB color difference metric ΔE00 is used which is considering the luminance variation according as the viewing angle as well as conventional color variation metric such as Δu’v’.
7.2.2 To calculate the color variation by viewing angles, CIELAB color difference metric shall be used as follows:
(2)