ORGANIC LIGHT EMITTING DIODE OLED DISPLAYS – Part 6-2: Measuring methods of visual quality and ambient performance 1 Scope This part of IEC 62341 specifies the standard measurement con
Terms and definitions
3.1.1 visual inspection a means for checking image quality by human visual observation for classification and comparison against limit sample criteria
Subpixel defects in color displays occur when one or more subpixels, the smallest color elements, appear noticeably brighter or darker than adjacent subpixels of the same color These defects are categorized based on the quantity and arrangement of multiple subpixel issues within a specific area of the display.
Dot defects in monochromatic displays refer to a single subpixel or a portion of it that appears noticeably brighter or darker than adjacent dots These defects are categorized based on the quantity and arrangement of multiple subpixel defects within a specific area of the display.
3.1.4 bright subpixel defect subpixels or dots which are visibly brighter than surrounding subpixels of the same colour when addressed with a uniform dark or grey background
3.1.5 dark subpixel defect subpixels or dots are visibly darker than surrounding subpixels of the same colour when addressed with a uniform bright background (e.g > 50 % full screen luminance)
A partial subpixel defect occurs when a subpixel or dot has a portion of its emission area obscured, leading to a noticeable difference in brightness compared to adjacent subpixels of the same color.
3.1.7 clustered subpixel defects subpixel or dot defects gathered in specified area or within a specified distance Also known as “close subpixel defect”
3.1.8 unstable subpixel subpixel or dot that changes luminance in an uncontrollable way
3.1.9 pixel shrinkage reduction in the active emissive area of one or more subpixels (or dots) over time
3.1.10 panel edge shrinkage reduction in the active emissive area from the edges of the display area over time
3.1.11 line defect vertical or horizontal bright or dark line parallel to a row or column observed against a dark or bright background, respectively
3.1.12 bright line defect a line appearing bright on a screen displaying a uniform dark or grey pattern
3.1.13 dark line defect a line appearing dark when displayed with a uniform bright or grey pattern
The mura regions refer to areas of luminance and color non-uniformity that typically exhibit a more gradual variation compared to subpixel level defects For proper classification, the maximum dimension of these mura regions should be less than one-fourth of the display's width or height.
Line mura refers to variations in luminance that manifest as one or more lines extending either horizontally or vertically across a display This phenomenon can occur across the entire screen or just a portion of it, often resulting from threshold voltage variations in TFT technology due to laser-induced crystallization.
3.1.16 colour mura mura that appears primarily in only one colour channel and results in a local variation of the white point (or CCT)
3.1.17 spot mura region of luminance variation larger than a single pixel appearing as a localized slightly darker or brighter region with a smoothly varying edge
3.1.18 stain mura region of luminance variation larger than a single pixel appearing as clearly defined edge bordering a region of brighter or darker luminance than surrounding regions
3.1.19 mechanical defects image artefacts arising from defects in protective and contrast enhancement films, coatings, mechanical fixturing, or other elements within in the active area of the display
3.1.20 scratch defect defect appearing as fine single or multiple lines or scratches, generally light in appearance on a dark background, and independent of display state
3.1.21 dent defect localized spot generally white or grey in appearance on dark background and independent of display state
3.1.22 foreign material defect caused by foreign material like dust or thread in between contrast enhancement films, protective films, or on emitting surface within the active area of the display
3.1.23 bubble defect caused by a cavity in or between sealing materials, adhesives, contrast enhancement films, protective films, or any other films within the visible area of the display
3.1.24 ambient contrast ratio contrast ratio of a display with external natural or artificial illumination incident onto its surface
NOTE Includes indoor illumination from luminaires, or outdoor daylight illumination
3.1.25 colour gamut boundary surface determined by a colour gamut's extremes
3.1.26 colour gamut volume a single number for characterizing the colour response of a display device in a three- dimensional colour space
NOTE Typically the colour gamut volume is calculated in the CIELAB colour space
3.1.27 ambient colour gamut volume number for characterizing the colour response of a display device, under a defined ambient illumination condition, in a three-dimensional colour space
NOTE Typically the colour gamut volume is calculated in the CIELAB colour space.
Abbreviations
CIE International Commission on Illumination (Commission internationale de l’éclairage)
ISO International Organization for Standardization
OLED organic light emitting diode
QVGA quarter video graphics array
SDCM standard deviation of colour matching sRGB a standard RGB colour space as defined in IEC 61966-2-1
The system diagrams and/or operating conditions of the measuring equipment shall comply with the structure specified in each item
Standard measuring environmental conditions
Electro-optical measurements and visual inspections must be conducted under standard environmental conditions, specifically at a temperature of 25 ºC ± 3 ºC, relative humidity between 25% and 85%, and pressure ranging from 86 kPa to 106 kPa Any deviations from these conditions should be documented in the visual inspection or ambient performance report.
Standard lighting conditions
Dark-room conditions
The luminance contribution from the background illumination reflected off the test display shall be ≤ 0,01 cd/m 2 or less than 1/20 the display’s black state luminance, whichever is lower
If the specified conditions are unmet, background subtraction must be performed and documented in the ambient performance report Furthermore, if the LMD's sensitivity is insufficient for measuring at low levels, the lower limit of the LMD should also be recorded in the report.
NOTE Unless stated otherwise, the standard lighting conditions shall be the dark-room conditions.
Ambient illumination conditions
5.2.2.1 Ambient illumination conditions for visual inspection
Ambient lighting significantly affects an inspector's ability to detect defects, as large fluctuations in light intensity can cause fatigue and reduce sensitivity to imperfections For optimal illumination conditions during visual inspections of pixel defects, refer to ISO 9241-310.
To ensure inspector comfort and consistent inspection conditions, it is recommended that the ambient illuminance in the inspector's work area be maintained between 50 lx and 150 lx This illuminance can be measured using an illuminance meter positioned upward at the inspector's eye level It is important to utilize diffuse illumination and textures in the inspection environment to minimize glare in the inspector's visual field.
To ensure accurate testing of the display, it must be positioned to minimize direct exposure to ambient room light Dark, light-absorbing materials should cover any specular surfaces that could reflect the display's light, preventing interference during inspection Furthermore, to maintain optimal display contrast, the ambient illuminance on the display surface, measured with the display turned off, should be less than 20 lx If the ambient light exceeds this threshold, it must be documented in the visual inspection report.
Figure 1 – Example of visual inspection room setup for control of ambient room lighting and reflections
1 Numbers in square brackets refer to the Bibliography
5.2.2.2 Ambient illumination conditions for electro-optical measurements
For accurate electro-optical measurements of displays under various ambient lighting conditions, specific illumination setups are recommended Indoor room lighting and outdoor daylight should be represented by a combination of two geometries Uniform hemispherical diffuse illumination simulates background lighting in a room or skylight conditions with the sun blocked Additionally, a directed light source in a dark environment mimics the impact of directional lighting from fixtures or direct sunlight on the display.
Some displays can emit photoluminescence (PL) when exposed to certain light The relative impact of PL on the reflection measurement can be determined, and is described in Annex A
When measuring reflections, it is crucial to carefully consider illumination conditions that may lead to significant measurement errors due to photoluminescence (PL) If the same spectral distribution and geometry are maintained for both illumination and detection, PL can be integrated into the reflection coefficients However, if there is a notable difference in the illumination spectra used, the reflected component must be measured independently from the PL component, a scenario not covered in this document.
The following illumination conditions shall be used to simulate indoor and outdoor display viewing environments:
For uniform hemispherical diffuse illumination, it is essential to utilize a light source that closely resembles CIE Standard Illuminant A, CIE Standard Illuminant D65, or the fluorescent lamp FL1 as specified in CIE 15 To prevent sample heating from the illuminants, the incorporation of an infrared-blocking filter is advisable Additionally, all light sources must have the UV region (wavelengths less than 380 nm) effectively cut off.
When using FL1 as a light source, the lamp's chromaticity tolerance must remain within 5 standard deviations of color matching (SDCM) as specified in IEC 60081 Additionally, the fluorescent lamp should be stabilized through a 100-hour aging process and should not be used beyond this period.
For spectral measurements, a display must show minimal photoluminescence (PL) of less than 1% when using selected reference source spectra If this condition is met, a spectrally smooth broadband source, like an approximation to CIE Standard Illuminant A, can be utilized to measure the spectral reflectance factor Additional sources may be employed based on the specific application requirements.
PL measures the spectral reflectance factor using a broad source, such as Illuminant A, allowing for the calculation of ambient contrast ratio and color for reference spectra like D65 For typical TV viewing rooms, the indoor room contrast ratio is calculated with 60 lx of hemispherical diffuse illumination, while 300 lx is used for office environments Higher illumination levels may be necessary for accurate hemispherical diffuse reflectance factor measurements, and results are subsequently scaled to the required illumination levels.
Directional illumination requires the same source spectra as hemispherical diffuse illumination Any variation in the spectral source must be documented in the ambient performance report Additionally, the presence of significant photoluminescence (PL) should be assessed for the measured source, with applicable limitations applied when PL is detected For a typical TV viewing room, the indoor room contrast ratio or color should be calculated using directional illumination of 40 lx incident on the display surface.
For optimal measurement accuracy in an office environment with vertically oriented displays, a minimum illumination level of 200 lx is recommended Higher illumination levels may be necessary for precise reflectance factor measurements The light source should be positioned at an angle of 35° above the surface normal, with an angular subtense not exceeding 8° This angular subtense refers to the total angle span of the light source from the center of the display's measurement area.
For calculating the ambient contrast ratio in indoor lighting conditions, it is permissible to use illumination levels beyond those specified It is essential that around 60% of the total illuminance is hemispherical diffuse, while the remaining 40% should be directional illumination.
For uniform hemispherical diffuse illumination, it is essential to utilize a light source that closely resembles skylight, specifically with the spectral distribution of CIE Illuminant D75 Depending on the application, other CIE daylight illuminants may also be applicable To prevent sample heating, an infrared-blocking filter is recommended, and the UV region below 380 nm should be eliminated from the light source Spectral reflectance factor measurements can be conducted using a spectrally smooth broadband source, such as an approximation to CIE Standard Illuminant A, provided that the display does not show significant photoluminescence for a 7,500 K correlated color temperature source The contrast ratio and color should be calculated for the D75 Illuminant spectra, with daylight contrast ratio and color determined using 15,000 lx of hemispherical diffuse illumination on a vertically oriented display surface Actual hemispherical diffuse reflectance factor measurements can be performed at lower illumination levels.
Directional illumination should closely resemble CIE daylight Illuminant D50, with the option to use additional CIE daylight illuminants based on the specific application To reduce sample heating, an infrared-blocking filter is recommended, and the UV region below 380 nm must be eliminated If it can be shown that the display does not exhibit significant photoluminescence under a light source similar to Illuminant D50, a spectrally smooth broadband source, like CIE Standard Illuminant A, may be utilized for measuring the reflectance factor The ambient contrast ratio or color can later be calculated using the D50 illuminant spectra, with the daylight contrast ratio or color determined at 65,000 lx for a directed source at a 45° angle to the display surface Actual reflectance factor measurements can be conducted at lower illumination levels, with the contrast ratio and color adjusted for the appropriate illuminance The directed light source should have an angular subtense of approximately 0.5°.
For calculating daylight contrast ratios and colors based on spectral reflectance factor measurements, it is essential to utilize the relative spectral distributions of CIE Illuminant A, lamp FL1, D65, D50, and D75 as outlined in CIE 15 Furthermore, additional CIE daylight illuminants should be derived using the relevant eigenfunctions specified in the CIE 15 publication.
Standard setup conditions
General
Standard setup conditions are given below Any deviations from these conditions shall be noted in the ambient performance report.
Adjustment of OLED display modules
The display's luminance, contrast ratio, and correlated color temperature must be adjusted to their nominal values and documented in the ambient performance report For full-color displays, the white color chromaticity should also align with the nominal product design values In the absence of specified levels, the maximum contrast or luminance should be utilized, with these settings recorded in the report All adjustments must remain consistent for all measurements unless otherwise indicated.
Starting conditions of measurements
Measurements should commence only after the OLED display modules and measuring instruments have stabilized It is essential to allow adequate warm-up time for the OLED display modules to attain a luminance stability level within ± 5% throughout the entire measurement for a specific display image.
Conditions of measuring equipment
a) The standard measurement setup is shown in Figure 5 The LMD must be a luminance meter, or a spectroradiometer capable of measuring spectral radiance over at least the
The wavelength range of 380 nm to 780 nm is essential for achieving smooth broadband spectra, with a maximum bandwidth of 10 nm For light sources exhibiting sharp spectral features, such as LEDs and fluorescent lamps, the bandwidth must not exceed 5 nm Additionally, the spectral bandwidth of the spectroradiometer should be an integer multiple of the sampling interval, allowing a 5 nm sampling interval to be compatible with both 5 nm and 10 nm bandwidths.
To ensure optimal performance, the light-measuring device must possess sufficient sensitivity and dynamic range, with the measured LMD signal being at least ten times greater than its dark level Additionally, the device should be focused on the image plane of the display and aligned perpendicularly to its surface, unless specified otherwise Maintaining the relative uncertainty and repeatability of all measuring devices is crucial, which can be achieved by adhering to the calibration schedule recommended by the instrument supplier.
Field of View Angular Field of View
Measurement-Field Angle Measurement-Field Angle
The LMD integration time must be an integer multiple of the frame periods, or exceed two hundred frame periods For matrix display measurements, light measuring devices should cover a field that includes over 500 pixels, with smaller areas requiring confirmation of equivalence to 500 pixels The standard measuring distance, denoted as \( l_{xo} \), is set at \( 2.5 \times V \) for \( V \geq 20 \) cm, or 50 cm for \( V < 20 \) cm, where \( V \) represents the height of the display's active area This distance must be documented in the ambient performance report The angular aperture should not exceed 5°, and the measurement field angle should be limited to 2° Adjustments to the measuring distance and aperture angle are permissible to ensure a field greater than 500 pixels if necessary Additionally, display modules must operate at their designated field frequency, and any separate driving signal equipment used must be recorded in the ambient performance report.
6 Visual inspection of static images
General
Recent advancements in automated machine vision inspection aim to identify visual defects; however, a comprehensive system linking human physiological responses to various defect measurements is still lacking Consequently, human visual inspection, alongside comparison with limit samples, continues to be the most widely used method for grading and classifying visual defects To effectively communicate failure modes and establish specification criteria, a standardized classification scheme and measurement method for the visual inspection of OLED display panels and modules is essential.
Classification of visible defects
Classification scheme
A classification scheme for visual defects is essential for effective communication and identification of failure modes As illustrated in Figure 6, defects can be categorized into two main types: electro-optical and mechanical Electro-optical defects are ranked by the clarity of their edges, while mechanical defects typically arise from process damage or contamination.
Figure 6 – Classification of visible defects
Reference examples for subpixel defects
Figure 7a illustrates a subpixel bright defect in red, green, and blue, with the defect designations applicable to various subpixel arrangements, including those with a white subpixel Figure 7b presents examples of two adjacent bright subpixel defects, which can be either connected or disconnected in both horizontal and vertical orientations Additionally, Figure 7c depicts three adjacent bright subpixel defects that are connected in horizontal and vertical orientations.
Figure 7a – Single bright subpixel defect
Figure 7b – Two adjacent bright subpixel defects
Figure 7c – Three adjacent bright subpixel defects
Subpixel defects are categorized based on their proximity to one another If multiple defects are a specified distance apart, they are considered individual subpixel defects Conversely, if they are located within a specified distance, they are classified as close or cluster subpixel defects Figures 8a and 8b illustrate the classification criteria for bright and dark subpixel defects, respectively, which are identified as close subpixel defects when they fall within a minimum specified distance \(d\) It is important to note that this distance \(d\) applies to the separation between subpixels in any direction.
Clustered defect Bright subpixel defects
Figure 8a – Bright subpixel criteria for clustered defect classification d ≥ minimum d < minimum
Clustered defect Dark subpixel defects
Figure 8b – Dark subpixel to dark subpixel
Figure 8 – Criteria for classifying bright and dark subpixel defects
Reference example for line defects
Line defects appear as horizontal or vertical bright or dark lines that can extend partially or fully across an image, often caused by electrical shorts or disconnects An example of this is illustrated in Figure 9, which shows multiple bright and dark line defects.
Figure 9 – Bright and dark line defects
Reference example for mura defects
Mura defects are characterized by areas of uneven luminance and color that change more gradually than subpixel defects Their visibility is influenced by the defect's length scale and the local peak-to-peak luminance variation, which can be noticeable even with variations as small as 1% to 2% Typically, these features have a minimum width or height ranging from approximately 0.5 mm to 2 mm.
An example of a line mura defect in an OLED display driven by an LTPS backplane is shown in Figure 10, where non-uniform lines appear across the screen when displaying a uniform white background.
Figure 10 – Sample image of line mura defect associated with TFT non-uniformity
Spot mura refers to non-uniform luminance variations that are limited in both width and height An example can be seen in Figure 11 Additionally, defects that show non-uniformity in both color and luminance are categorized as color mura.
Figure 11 – Example of spot mura defect in a grey background
Visual inspection method and criteria
Standard inspection conditions
Unless stated otherwise, the standard environmental conditions for visual inspection will be used
6.3.1.2 Ambient lighting conditions for visual inspection
Unless stated otherwise, the standard ambient lighting conditions for visual inspection shall be used Any deviation from these conditions shall be noted in the visual inspection report
Ambient lighting conditions for inspecting OLED display panels should align with the inspection purpose, even if they are not ideal for inspector comfort or defect sensitivity Any deviations from standard room lighting must be documented in the visual inspection report, including measurements of illuminance normal to the display surface, average ambient illuminance in the inspector's work area, and other relevant environmental details, such as the use of a dark room or direct light sources.
Proper lighting conditions must be ensured throughout the inspector's session and consistently maintained between different inspectors Inspectors should acclimate to the lighting conditions for at least 10 minutes before starting an inspection.
Visual inspection shall be conducted nominally viewing the display at normal incidence unless otherwise stated
The visual inspection report must include the distance between the OLED display panel and the inspector's eyes An inspector with a visual acuity of 1.0 can resolve features spaced at 0.3 mrad (1 arcmin) It is recommended to maintain an optimal viewing distance, \(D_{opt}\), which is calculated as \(D_{opt} = \frac{2 \times L}{0.3 \text{ mrad}}\), where \(L\) is the horizontal distance between subpixels For instance, a 2.2” (56 mm) diagonal QVGA display with approximately 50 µm subpixel width should be viewed from 330 mm.
(1 920 ì 1 080) with 140 àm subpixel width, the recommended viewing distance is 950 mm The minimum viewing distance shall be 300 mm
Inspectors must possess normal color vision and a visual acuity of at least 1.0 in decimal notation, as verified by a qualified eye care professional The International Council on Ophthalmology recommends using the Ishihara test for color vision assessment and the Snellen or Landolt C test for measuring visual acuity.
6.3.1.5.1 Driving condition of OLED display panels or modules
Value of driving voltage shall be supplied on specification of OLED display panels or modules
The test patterns to be used for visual inspection shall include full screen patterns with 0 %,
Test patterns for monochrome displays should feature full-screen patterns of all color subpixels, including red, green, blue, or white, at grey levels of 0%, 10% to 30%, and 100%, tailored to application requirements The specific grey level for these patterns must be outlined in the detailed specifications.
Standard inspection method
6.3.2.1 Set up the inspection equipment and OLED display panels or modules
The DUT will be mounted on a fixture that allows for adjustments in both horizontal and vertical viewing angles After activating the direct current power supply and pattern generator, the appropriate driving current and pattern will be supplied to the OLED display panel or module for each specific defect inspection.
To minimize ambient light scattering in the observer's visual field, the area around the display, which subtends an angle of 70°, will be constructed from a light-absorbing diffuse material, as illustrated in Figure 12 This design ensures that the angle θ is greater than or equal to 70°.
Figure 12 – Setup condition for visual inspection of electro-optical visual defects
6.3.2.2 Inspection method for electro-optic defects
A full screen black test pattern (0 % grey level, display in turned-on state) is applied to inspect for bright subpixel defects
To inspect for mura defects, a full-screen test pattern with a grey level between 10% and 30% is utilized, with 10% being the standard unless specified otherwise The luminance level must be documented in the visual inspection report, and any observed defects should be compared to limit samples.
A test pattern of full screen white (100 % grey level) is applied to inspect for dark subpixel defects
For color displays, test patterns for individual color channels can be utilized to identify and clarify subpixel and mura defects, as specified in the detailed specifications.
Observed defects shall be recorded in the visual inspection report
6.3.2.3 Inspection method for mechanical defects
For optimal inspection of mechanical defects, side illumination of the display through edge lighting is recommended, achieving an average illuminance of over 500 lx across the display area Inspections should be performed from various viewing angles, ensuring that the inspector does not have direct line of sight to the light source.
Two test patterns shall be applied for mechanical defect inspection: a full screen black signal
To identify visible defects in films and coatings that scatter incident light, a 0% grey level is utilized, while a full screen white signal at 100% grey level is employed to detect mechanical defects that obstruct part of the display area It is important to ensure that edge lighting is turned off when using the full screen white pattern.
The inspector shall record observations and classification of mechanical defects in the visual inspection report
6.3.2.4 Inspector and limit sample for visual inspection
Inspectors must undergo regular training conducted by a qualified individual, accompanied by documented procedures and limit samples for visual inspections It is essential that these limit samples are preserved by a qualified person to guarantee their effectiveness.
6.3.2.5 Inspection and record of result
Inspector shall record the results of each test in the visual inspection report.
Inspection criteria
The maximum number of each bright defect shall be specified in specification
The article outlines various types of subpixels as specified in the detail specification, including partial subpixels of any color, subpixels of any color, and clustered subpixels Additionally, it mentions the total number of bright subpixels, all of which are detailed in the specification.
The maximum number of each dark defect shall be specified in specification
Partial subpixel (any colour) -Specified in the detail specification
Subpixel (any colour) -Specified in detail specification
Clustered subpixels -Specified in detail specification
Total number of dark subpixels -Specified in detail specification
All kinds of unstable subpixel defects are not allowed
All kinds of bright line defects such as vertical, horizontal or cross are not allowed
All kinds of dark line defects such as vertical, horizontal or cross are not allowed
A limit sample that demonstrates variations in luminance or color representative of different classifications of mura defects serves as a benchmark for acceptable mura defects This sample must maintain an average luminance comparable to the Device Under Test (DUT) within a tolerance of ± 20% Additionally, color mura limit samples should match the chromaticity coordinates averaged over the display area of the DUT, adhering to the criterion of ∆ u’v’ < 0.006 as specified in CIE 15 Any mura defects that exceed the parameters set by the limit sample must be documented in the visual inspection report.
The scratch, dent, foreign material, and bubble defect criteria are defined in Table 1 and Figure 13 The symbol of “a” and “b” indicates the major and minor axis of the defect
Table 1 – Definitions for type of scratch and dent defects
Scratches Linear (a > 2b) minimum ≤ width [mm] ≤ maximum, minimum ≤ length [mm] ≤ maximum,
Dent Elliptical (a ≤ 2b) minimum ≤ average diameter, (a+b)/2 [mm] ≤ maximum,
Foreign materials minimum ≤ a(major axis)[mm] ≤ maximum, N(number of defects) ≤ maximum
Bubble minimum ≤ a(major axis)[mm] ≤ maximum,
NOTE 1 Extraneous substances which can be wiped off, like finger prints, particles, etc are not considered as a defect
NOTE 2 Defects which are on the black matrix (outside of Active Area) are not considered defects a b
Figure 13 – Shape of scratch and dent defect
7 Electro-optical measuring methods under ambient illumination
Reflection measurements
Purpose
This method aims to assess the reflection properties of an OLED display module under specific indoor or daylight illumination conditions If the OLED shows notable photoluminescence (PL), this PL will be included in the reflection coefficient Consequently, the measurement method remains applicable when the same illumination spectral distribution is utilized to determine the ambient contrast ratio and color.
Measuring conditions
For accurate spectral measurements, it is essential to utilize a spectroradiometer capable of measuring luminance and spectral radiance, along with a calibrated white diffuse reflectance standard that has known hemispherical and directed spectral reflectance factors In photometric measurements, a detector that measures luminance is necessary, paired with a white diffuse reflectance standard calibrated for the specific measurement geometry and source spectra, which also has known luminous hemispherical and directed reflectance factors.
For indoor spaces, standard ambient illumination conditions should align with clear sky daylight Depending on the specific application, additional illumination conditions may be applicable It is important to note that all conditions, aside from the standard ambient illumination, are considered standard conditions.
Measuring the hemispherical diffuse reflectance factor
To begin, position the display within the integrating or sampling sphere, as shown in Figure 2 Next, activate the hemispherical diffuse illumination of the sphere to achieve the desired correlated color temperature (CCT) and allow the light source to stabilize before taking measurements.
NOTE 1 Any change in sphere illuminance can be monitored by a photopic detector attached to the sphere b) Set the test input signal to the display to generate a full white screen (100 % grey level) For natural static image and video applications, a 4 % area window at a 100 % grey level may also be used to characterize the contrast ratio, or a variety of display colours can be measured with the 4 % window to determine the colour gamut The 4 % window shall be 1/5 the width and height dimensions of the active area, and located in the centre of the display A contrast ratio measured with a small area window will be referred to as a highlight contrast ratio The ambient performance report shall note when a highlight measurement is used c) Align the LMD through the measurement port, focused at the centre of the display, and at an 8 ° to 10 ° angle to the display surface normal Turn room lights OFF Measure the spectral radiance L W,hemiON (λ) or luminance L W,hemi-ON at the centre of the white pattern with the hemispherical surround ON For spectral measurements, the white display luminance L W,hemi-ON can be calculated using Equation (1):
L 683 ( ) ( ) (1) where V(λ) is the photopic luminous efficiency function as defined is publication CIE 15
NOTE 2 In this document, spectral measurements like spectral radiance will be specifically identified by its wavelength dependence (e.g L W,hemiON ( λ )), whereas its photometric equivalent luminance will have no explicit wavelength dependence (e.g L W,hemiON ) d) Align the LMD to the centre of the calibrated white diffuse reflectance standard and measure its spectral radiance S W,hemi-ON (λ) or luminance S W,hemi-ON with the hemispherical surround ON and the display in its white state For the sampling sphere case, the S W,hemi-ON (λ) or S W,hemi-ON is the spectral radiance and luminance, respectively, measured from the sphere wall adjacent to the sample port e) Align the LMD to the centre of the display Set the display to a 0 % grey level and measure the black screen spectral radiance L K,hemi-ON (λ) or luminance L K,hemi-ON in the centre of the display with the diffuse surround ON f) Align the LMD to the centre of the calibrated white diffuse reflectance standard and measure its spectral radiance S K,hemi-ON (λ) or luminance S K,hemi-ON with the surround ON and the display in its black state g) Turn OFF the integrating sphere or sampling sphere hemispherical diffuse illumination This may be accomplished by turning off the light source If the sphere light is input by a portable source (like an optical fibre bundle), then the light can be turned OFF by disconnecting at the light source end so that the interior conditions and performance of the sphere are not changed h) Align the LMD to the centre of the display Set the display to a 0 % grey level and measure the black screen spectral radiance L K,hemi-OFF (λ) or luminance L K,hemi-OFF in the centre of the display with the diffuse surround OFF i) Align the LMD to the centre of the calibrated white diffuse reflectance standard and measure its spectral radiance S K,hemi-OFF (λ) or luminance S K,hemi-OFF with the surround OFF and the display in its black state j) Align the LMD to the centre of the display Re-establish the prior white pattern at the
To ensure accurate measurements, set the display to 100% grey level and allow the emission to stabilize before measuring the white screen spectral radiance \( L_{W,\text{hemi-OFF}}(\lambda) \) or luminance \( L_{W,\text{hemi-OFF}} \) at the center of the display with the diffuse surround turned off Next, align the LMD to the center of the calibrated white diffuse reflectance standard and measure its spectral radiance \( S_{W,\text{hemi-OFF}}(\lambda) \) or luminance \( S_{W,\text{hemi-OFF}} \) with the surround off and the display in its white state Finally, calculate the hemispherical diffuse spectral reflectance factor \( R_{W}(\lambda) \) or luminous hemispherical diffuse reflectance \( R_{W} \) of the white display pattern at the 100% grey level based on the measured illumination and detection geometry.
For spectral measurements, the following relation is used:
OFF hemi , ON hemi hemi ,
The luminous hemispherical diffuse reflectance factor, denoted as \( R_{W,\text{hemi}} \), of a display at 100% grey level is calculated using the known hemispherical spectral reflectance factor \( R_{\text{std,hemi}}(\lambda) \) for the white diffuse reflectance standard or sampling sphere wall This calculation is performed under the same geometry and utilizes the desired hemispherical diffuse illumination spectra.
The relative spectral distribution of the desired illumination is represented by E(λ) For this purpose, the spectral distributions of CIE Illuminant A, lamp FL1, D65, D50, and D75, as specified in CIE 15, should be utilized If additional daylight illuminants are required, the corresponding relation from CIE 15 must be applied.
E = + + (4) where the E 0 , E 1 , and E 2 eigenfunctions are tabulated in CIE 15, and M 1 and M 2 are eigenvalues defined in the same document For example, M 1 and M 2 are given in Table 2 for the case of D50 and D75
Table 2 – Eigenvalues M 1 and M 2 for CIE Daylight Illuminants D50 and D75
For luminance measurements, the photometric equivalent of Equation (2) is used:
[ , , hemi hemi ON ON , , hemi hemi OFF OFF ] hemi , hemi
The luminous hemispherical diffuse reflectance factor \( R_{W,\text{hemi}} \) of a display with a white screen, along with the white diffuse reflectance standard \( R_{\text{std,hemi}} \), is applicable solely to hemispherical diffuse light sources that share the same geometry and spectral distribution as those used in the measurement Consequently, any calculations of ambient contrast ratio or color that utilize the luminous hemispherical diffuse reflectance factor \( R_{W,\text{hemi}} \), as determined by the photometric method in Equation (5), are only valid for light sources with comparable spectra and geometry.
NOTE 3 To ensure measurement integrity, the reflected component of the sphere illumination shall be much greater than the display emission (i.e L W,hemi-ON ( λ ) >> L W,hemi-OFF ( λ )) The same applies for the photometric equivalents in Equation (5) m) Calculate the hemispherical diffuse spectral reflectance factor R K,hemi (λ), or luminous hemispherical diffuse reflectance factor R K,hemi , of the black screen display at the 0 % grey level for the measured illumination/detection geometry
For spectral measurements, the following relation is used:
OFF hemi , ON hemi hemi ,
The luminous hemispherical diffuse reflectance factor R K,hemi of a display at 0 % grey level at the desired hemispherical diffuse illumination spectra is determined following the same form as Equations (3) and (4)
For luminance measurements, the photometric equivalent of Equation (6) is used:
[ , , hemi hemi ON ON , , hemi hemi OFF OFF ] hemi , hemi
The photometric method for determining R K,hemi through Equation (7) is only applicable for light sources that have similar spectra and geometry to those used in the measurement It is essential to document the CCT of the display test illumination, the test configuration, R K,hemi, R W,hemi, and the illuminance E K,hemi-ON on the white diffuse reflectance standard while the display is in its black state in the ambient performance report For spectral measurements, the corresponding values must be accurately recorded.
E K,hemi-ON is determined by using S K,hemi-ON (λ) in the following general equation:
E = S (8) where R(λ) = R std,hemi (λ) in this case
The illuminance E V can be obtained from the spectral irradiance E(λ) by
For luminance measurements, the illuminance E K,hemi-ON is obtained by the photometric equivalent of Equation (8) using the white standard luminance S K,hemi-ON
The ambient performance report must include the recorded details of the color temperature, illumination levels, detector parameters such as incident angle, measurement field angle, and distance to the sample, as well as the geometry of the illumination source used during the measurements.
Measuring the reflectance factor for a directed light source
To accurately measure display performance, align the LMD perpendicular to the screen and assess the spectral radiance \( L_K(\lambda) \) or luminance \( L_K \) at the center of the display under dark room conditions with a full black screen at 0% grey level The black screen luminance can be calculated using Equation (1) Next, set the input signal to create a full white screen (100% grey level) and, for natural static images and videos, utilize a 4% area window at this grey level to evaluate the highlight contrast ratio, ensuring the window is centrally located and one-fifth the width and height of the active area Document in the ambient performance report when a highlight measurement is taken Measure the spectral radiance \( L_W(\lambda) \) or luminance \( L_W \) at the center of the white pattern under the same dark conditions, with calculations based on Equation (1) Position the directed light source according to the defined geometry for indoor or daylight conditions, typically using isolated directed source geometry unless strong matrix scatter is present Activate the light source at the desired CCT, allowing it to stabilize, and adjust the intensity for optimal signal reflection at the LMD Finally, replace the display with a calibrated white diffuse reflectance standard in the same measurement plane and measure the spectral radiance \( S_{W,dir}(\lambda) \) or luminance \( S_{W,dir} \) from the standard, using Equation to determine the spectral irradiance \( E_{W,dir}(\lambda) \) on both the standard and display.
In the context of photometric measurements, the display illuminance \( E_{W,dir} \) can be determined using Equation (9) The spectral reflectance factor \( R(\lambda) \) corresponds to the known standard for white diffuse reflectance in the same geometry, as defined by \( R_{std,dir}(\lambda) \) Additionally, the relationships \( E(\lambda) = E_{W,dir}(\lambda) \) and \( S(\lambda) = S_{W,dir}(\lambda) \) are established in this framework.
E W,dir e) Replace the display at the LMD measurement plane, and re-establishe the prior white pattern at the 100 % grey level Measure the spectral radiance L W,dir (λ) or the luminance
The luminance \( L_{W,\text{dir}} \) from the center of the emitting display, with directed source illumination activated, can be determined for spectral measurements using Equation (1).
NOTE 1 To ensure measurement integrity, the display ambient spectral radiance with directed source ON will be much greater than the display spectral radiance in a dark room (i.e L W,dir( λ ) >> L W( λ )) The same applies for the photometric equivalents f) Calculate the spectral reflectance factor R W,dir (λ), or luminous reflectance factor R W,dir , of the white display pattern at the 100 % grey level with directed illumination for the measured illumination/detection geometry
For spectral measurements, the spectral reflectance factor R W,dir (λ) is determined using the following equation [2]:
The following equation shall be used to calculate the luminous reflectance factor R W,dir for a white display pattern with directional illumination having the desired spectral distribution:
For indoor contrast ratio measurements, the relative spectral distribution for the desired illumination spectra, denoted as E(λ), must utilize the same source spectra as the hemispherical diffuse reflectance factor In contrast, when calculating the outdoor ambient contrast ratio, CIE Illuminant D50 should be applied for E(λ).
For photometric measurements, an analogous relation to Equation (10) is used: dir , dir dir ,
NOTE 2 The luminous reflectance factor in Equation (12) will only be used to calculate the ambient contrast of the same source spectra and geometry as that used in the measurement g) Set the display to a 0 % grey level and measure the black screen spectral radiance L K,dir (λ) or luminance L K,dir in the centre of the screen with direct illumination ON For spectral measurements, the black screen luminance L K,dir with direct illumination ON can be calculated using Equation (1) h) Remove the display and place the white diffuse reflectance standard in the same measurement plane of the LMD Measure the spectral radiance S K,dir (λ) or luminance
The illuminance \( E_{K,\text{dir}} \) on the black screen is calculated using Equations (8) and (9) based on the calibrated white diffuse reflectance standard For photometric measurements, this illuminance is derived from the \( S_K \) measurement, utilizing the photometric equivalent of Equation (8) Additionally, the spectral reflectance factor \( R_{K,\text{dir}}(\lambda) \), or luminous reflectance factor \( R_{K,\text{dir}} \), of the white display pattern at the 0% grey level is determined under directed illumination for the specified illumination and detection geometry.
For spectral measurements, the spectral reflectance factor R K,dir (λ) of the black screen with direct illumination is determined using the following relation:
The luminous reflectance factor R K,dir for a black field display with directional illumination having the desired spectral distribution E(λ) shall be calculated following the method in Equation (11)
For photometric measurements, the analogous relation to Equation (12) is used to determine the reflectance factor of the black screen R K,dir
NOTE 3 The luminous reflectance factor R K,dir determined through photometric measurements will only be used to calculate the ambient contrast of the same source spectra and geometry as that used in the measurement j) Record the CCT of the display test illumination, the test configuration, R W,dir, ,R K,dir , and the measured illumination level E K,dir in the ambient performance report
The ambient performance report must include the recorded details of colour temperature, illumination levels, detector parameters such as incident angle, measurement field angle, and distance to the sample, as well as illumination source parameters including incident angle, angular subtense, distance to the sample, and beam divergence.
Ambient contrast ratio
Purpose
The purpose of this method is to determine the ambient contrast ratio of an OLED display module under defined indoor or daylight illumination conditions
NOTE If the OLED exhibits significant PL, then the ambient contrast ratio calculation is only valid for the same illumination spectra and geometry used to measure the reflection coefficients.
Measuring conditions
A luminance meter or spectroradiometer that can measure luminance; driving power source; and driving signal equipment b) Illuminance condition:
For indoor spaces or under clear sky daylight, standard ambient illumination conditions should be applied Depending on the specific application, additional illumination conditions may also be utilized It is important to note that all conditions, aside from the standard ambient illumination, are considered standard conditions.
Measuring method
The ambient contrast ratio is calculated using reflection measurements of a display under both hemispherical diffuse and directed illumination conditions The methods for determining the hemispherical diffuse reflectance factor and directed reflectance factor are outlined in earlier sections These reflection parameters enable the calculation of the combined luminance for a display with both black and white screens at specified illuminance levels Ultimately, the ambient contrast ratio represents the ratio of the combined luminance of the white screen to that of the black screen.
To measure black luminance (L K), assess it at the center and perpendicular to the display with a 0% grey level on a full black screen in a dark room Next, set the input signal to create a 100% grey level across the entire screen or within a 4% window at the center, depending on the application Measure the white luminance (L W) at the center and perpendicular to the white display pattern under the same dark room conditions Finally, calculate the indoor or daylight contrast ratio for a full white screen or the highlight ambient contrast ratio for the 4% window using the specified equation.
ACR cos cos dir dir hemi , hemi , dir dir , hemi hemi ,
(14) where the default parameters are E hemi = 60 lx, θ s = 35 °, and E dir cosθ s = 40 lx for a TV viewing room; E hemi = 300 lx, θ s = 35 °, and E dir cosθ s = 200 lx for an office; and
The outdoor daylight contrast ratio is defined with an illuminance of \$E_{hemi} = 15,000 \, \text{lx}\$, an angle of incidence \$\theta_s E^\circ\$, and a direct illuminance of \$E_{dir} \cos \theta_s = 65,000 \, \text{lx}\$ Any additional geometries or illuminance levels utilized must be documented in the ambient performance report, and all values used for calculating the ambient contrast ratio should be recorded in this report as well.
Ambient display colour
Purpose
The purpose of this method is to measure the ambient colour of an OLED display module under defined daylight illumination conditions
NOTE If the OLED exhibits significant PL, then the ambient display colour calculation is only valid for the same illumination spectra and geometry used to measure the reflection coefficients.
Measuring conditions
A spectroradiometer that can measure spectral radiance; driving power source; and driving signal equipment b) Illuminance condition:
The standard ambient illumination for clear sky daylight should be utilized, with the option to incorporate additional lighting conditions based on specific applications All conditions, aside from the standard ambient illumination, are considered standard conditions.
Measuring method
The chromaticity of a display is influenced by both its intrinsic light emission and the reflected ambient light under hemispherical diffuse and directed illumination The ambient chromaticity at a specific color state, such as white, black, red, green, or blue, is determined by the equivalent ambient tristimulus values, which can be measured in a dark room These values are obtained through reflection measurements of the display under various illumination conditions The methods for measuring the hemispherical diffuse and directed spectral reflectance factors of the display have been detailed in earlier sections.
To measure the spectral radiance \( L_Q(\lambda) \) at the center and perpendicular to the display in the desired color state \( Q \) (such as a white screen), conduct the assessment under dark room conditions The total ambient spectral radiance \( L_{Q,\text{amb}}(\lambda) \), captured by a detector positioned perpendicular to the display, incorporates reflections from both hemispherical diffuse and directional sources.
( , hemi hemi , dir dir amb
The irradiance spectra for standard hemispherical diffuse and directed sources are represented by \( E_{\text{hemi}} \) and \( E_{\text{dir}} \), respectively The relative irradiance spectra of CIE Illuminants D75 and D50 for daylight illumination are defined by specific equations and tables The values of \( E_{\text{hemi}}(\lambda) \) and \( E_{\text{dir}}(\lambda) \) are derived by multiplying the relative spectra by a constant, resulting in default illumination levels of \( E_{\text{hemi}} = 15000 \, \text{lx} \) and \( E_{\text{dir}} \cos \theta_s = 65000 \, \text{lx} \) at \( \theta_s E^\circ \) for outdoor daylight under clear sky conditions The effective ambient tristimulus values of the display are calculated under these illumination conditions.
The ambient chromaticity coordinates of the emitting display at the desired color state Q, under specified illumination conditions, are represented by the color matching functions x(λ), y(λ), and z(λ) as defined in CIE 15.
Ambient colour gamut volume
Purpose
This method aims to assess the ambient color gamut volume of an OLED display module under specific daylight illumination conditions The measured color gamut volume will be compared to the IEC sRGB standard (IEC 61966-2-1) color gamut volume, utilizing a D65 white point It is important to note that this method is applicable only to OLED display modules featuring RGB primaries.
If the OLED shows considerable photoluminescence (PL), the calculation of the ambient color gamut volume is only applicable when using the same illumination spectra and geometry that were employed to measure the reflection coefficients.
Measuring conditions
A spectroradiometer is essential for measuring spectral radiance, supported by a driving power source and signal equipment This signal equipment is responsible for providing the necessary analog or digital output to the OLED display module, enabling the generation of the desired color test pattern Additionally, the illuminance conditions must be considered for accurate measurements.
The standard ambient illumination for clear sky daylight should be applied, as outlined in section 5.2.2.2 Depending on the specific application, additional illumination conditions may also be utilized It is important to note that all conditions, aside from the standard ambient illumination, are considered standard conditions.
Measuring method
The ambient colour gamut volume is determined using the reflectance factor and tristimulus values for each displayed colour, adhering to the outlined procedures Consistent measurements and calculations are conducted within a 4% box window colour against a black background.
The ambient colour gamut is defined by the range of display colours under specific ambient lighting conditions within the CIELAB colour space To determine the volume of this colour space, a 4% box window pattern is applied to at least eight defined colours that uniformly sample the display's colour capabilities, including red, green, blue, cyan, yellow, magenta, black, and 100% grey level white Each colour, except black, is displayed at its maximum signal level Additionally, the dark room spectral radiance and spectral reflectance factor for each display colour are measured If the spectral reflectance factor remains consistent across displayed colours at maximum signal level, a common hemispherical diffuse or directional spectral reflectance factor can be utilized Finally, the ambient tristimulus values for each display colour under the specified illumination conditions are calculated using established equations.
Table 3 – Example of minimum colours required for gamut volume calculation of a 3-primary 8-bit display
The RGB color model defines colors through specific values: Red (255, 0, 0), Green (0, 255, 0), Blue (0, 0, 255), Yellow (255, 255, 0), Magenta (255, 0, 255), Cyan (0, 255, 255), White (255, 255, 255), and Black (0, 0, 0) To analyze these colors, the normalized ambient tristimulus values are converted into the CIELAB color space, as outlined in publication CIE 15 This transformation allows for the plotting of each color point on the L*, a*, and b* axes, referencing the peak white ambient tristimulus values (X W,amb, Y W,amb, and Z W,amb) using specific transformation equations.
* f Y Q , amb Y W , amb f Z Q , amb Z W , amb b = × − (23) where
An example of the ambient colour data in the CIELAB uniform colour space is given in Figure 14 a* b*
The CIELAB colour space illustrates the range of colours produced by a display, as shown in Figure 14 To determine the colour gamut volume of the ambient display colours, refer to the detailed analysis in Annex B Alternative methods for calculating the gamut may be employed, provided they produce results consistent with the reference method outlined in Annex B.
Reporting
The CIELAB colour gamut volume must be included in the ambient performance report, along with the characteristics of the ambient illumination used Any additional colour spaces should also be reported, along with the spectral reflectance factors All measured ambient tristimulus values must be documented as shown in Table 4, which should present the original effective tristimulus values without normalization to 100 Separate tables are required for each ambient illumination condition The correlated colour temperature (CCT) and white point, calculated using Equations (19) and (20) under both darkened room and ambient conditions, should be reported in Table 5 Additionally, the percentage of colour gamut volume relative to the IEC sRGB standard colour space (IEC 61966-2-1) with a D65 white point must be presented as outlined in Table 6.
Table 4 – Measured tristimulus values for the minimum set of colours
(see Table 3) required for gamut volume calculation under the specified ambient illumination condition
Red Green Blue Yellow Magenta Cyan White Black
Table 5 – Calculated white point in the darkened room and ambient condition
Table 6 – Colour gamut volume in the CIELAB colour space
Ambient illumination Percent relative to sRGB (8,20 × 10 5 )
Measuring relative photoluminescence contribution from displays
The purpose of this method is to estimate the relative amount of PL emitted by a display under illumination relative to the reflected component
A spectroradiometer that can measure spectral radiance over at least the 380 nm to
The article discusses a spectrally tunable unpolarized light source that operates within the 380 nm to 780 nm wavelength range, specifically at 780 nm It emphasizes the importance of stability, requiring both the light source and detector to maintain stability within < 1% during measurements Additionally, it specifies that the spectral bandwidth of both the detector and light source must not exceed 10 nm, and that the bandwidth of the spectroradiometer should be an integer multiple of the sampling interval.
For accurate measurements under clear sky daylight conditions, standard ambient illumination must be utilized The photoluminescence (PL) is considered linear within the relevant illuminance range, allowing for the use of any illumination levels that yield a strong signal It is important to note that the results are only applicable to the specific spectral distribution employed during the measurement Additionally, all measurements, aside from those involving defined illumination sources, will take place in a dark room with the display turned OFF or in a black state.
A.3 Measuring the bi-spectral photoluminescence of the display a) Place the display to be measured in the hemispherical diffuse or directional illumination geometry of interest (as defined in Clause 5) For simulating the affect of PL under standard daylight illumination, the directional source geometry is recommended as an initial test case b) The spectroradiometer shall be focused on the display surface and centred on the active area c) The tunable light source shall produce uniform illumination (within ± 5 %) over the measurement field area of the display d) The spectroradiometer shall measure the spectral radiance L(λ, λ ex ) for monochromatic source illumination E 0 (λ ex ) at each wavelength λ ex e) Replace the display with a white diffuse reflection standard with known spectral reflectance factor R std (λ ex ) for the illumination/detection geometry used The reflection standard used shall not exhibit any PL over the wavelength range of interest f) The spectroradiometer shall measure the reflected spectral radiance S(λ, λ ex ) for monochromatic source illumination E 0 (λ ex ) at each wavelength λ ex
A.4 Determining relative PL contribution from display a) The spectral radiance L E (λ, λ ex ) of the display spectra under the desired reference spectral irradiance E(λ ex ) at the same illumination/detection geometry can be calculated from the measured spectral radiance L(λ, λ ex ) at each illumination wavelength λ ex using the relation below:
( ex ex ex std ex ex ex
An example of the three dimensional representation of the scaled bi-spectral display response is given in Figure A.1
E m issi on w av el engt h (n m )
Log (s pec tral ra di anc e)
Figure A.1 – Scaled bi-spectral photoluminescence response from a display
The pure reflection signal, indicated by the red diagonal peak in Figure A.1, does not show a wavelength shift Photoluminescence (PL) is always emitted at wavelengths longer than λ ex, resulting in PL contributions being limited to the upper diagonal elements in Figure A.1 To estimate the relative contribution of PL, the data in Figure A.1 can be decomposed into its PL component (upper diagonal) and the reflection component (diagonal peak), as illustrated in Figure A.2 Subtracting background noise is essential for enhancing the accuracy of the analysis.
E m issi on w av el engt h (n m )
E m issi on w av el engt h (n m )
The decomposed bi-spectral photoluminescence response from a display, as shown in Figure A.2, indicates that when the display is illuminated with the full illumination spectra \(E(\lambda_{ex})\) simultaneously, the radiance contributions from both the photoluminescence (PL) and reflected components can be determined by integrating over the row elements depicted in the figure.
For wavelengths ranging from \$\lambda \leq (\lambda_{ex} + \frac{\Delta\lambda}{2})\$ to \$\lambda \geq (\lambda_{ex} - \frac{\Delta\lambda}{2})\$ (A.3), where \$\Delta\lambda\$ represents the bandwidth of the spectral radiance reflection peak at each \$\lambda_{ex}\$, the photopically-weighted contributions of the photoluminescence (PL) component (\$L_{PL}\$) and the reflected component (\$L_{Refl}\$) can be determined using the results from Equations (A.2) and (A.3) in conjunction with Equation (1) Furthermore, the ratio of the photopically-weighted contribution of the PL component to the total can be expressed as \$f_{l_{PL}}\$.
Calculation method of ambient colour gamut volume
The purpose of this method is to describe a procedure to calculate the colour gamut volume of scattered colour points in the three-dimensional CIELAB colour space
B.2 Procedure for calculating the colour gamut volume
Measure the spectral radiance of colour
Calculate/mesure gradation of colour between black and the others
Convert all XYZ to CIELAB
Define tetrah edrons in CIELAB hull
Calculate and sum the volume of tetrah edrons
Figure B.1 – Analysis flow chart for calculating the colour gamut volume
Measure the red, green, blue, cyan, magenta, yellow, black, and white colors of the display under specified ambient conditions as outlined in section 7.4.3 For instance, Table B.1 illustrates the use of sRGB primaries in a dark room setting, with the white luminance (Y) normalized to 100%.
Table B.1 – Tristimulus values of the sRGB primary colours
Convert all colours points into the CIELAB colour space using Equations (21) to (23) See Table B.2 and Figure B.2 for an example of the sRGB colour set in the CIELAB colour space
Table B.2 – Example of sRGB colour set represented in the CIELAB colour space
Figure B.2 – Graphical representation of the colour gamut volume for sRGB in the CIELAB colour space
To compute the color gamut volume, sum the volumes of all tetrahedrons formed by the displayed color points and express this as a percentage of the sRGB color gamut volume An example illustrating this calculation in a dark room, using the CIELAB color space, is presented in Table B.3.
Table B.3 – Example of sRGB colour gamut volume in the CIELAB colour space
B.3 Surface subdivision method for CIELAB gamut volume calculation
This algorithm processes a specified set of gamut corner cases using CIE 1931 XYZ tri-stimulus values, requiring at least eight colors: red, green, blue, cyan, magenta, yellow, black, and white The XYZ values are organized in rows within the input variable P, and the output is the computed color gamut volume.
The colour gamut in the CIE XYZ colour space is defined as the convex hull of specific corner cases In contrast, the colour gamut in the CIELAB colour space is derived from this convex hull, normalized in CIE XYZ space using the corner case with the highest luminance, identified as the white point This transformation into CIELAB colour space results in a shape that is no longer entirely convex.
1) Obtain the convex hull 2 of the colour corner points in P Store the tessellation of the surface of this hull in T Initialise a total volume v to 0
2) Calculate the average of the points P to be used as a gamut mid-point and store in Pm
3) For each triangular surface tile in T a) Let s equal the number of edges that have extents 3 in L*, a*, b* coordinates greater than 10 b) If s = 0 then calculate the volume defined between the vertices of the surface tile and
To calculate the mid-points in CIEXYZ space, if \( s = 3 \), subdivide the triangular tile into four sub-tiles using each corner vertex and the two nearest mid-points, along with the three mid-points This process should be repeated for each triangular sub-tile Conversely, if \( s = 1 \) or \( s = 2 \), determine the mid-point of the edge with the largest extents in CIELAB and divide the triangular tile into two sub-tiles along the line connecting the mid-point to the opposite vertex, repeating this for each triangular sub-tile.
4) Return the total volume now contained in v
2 Where the corner points are the standard RGBCMYKW
3 Extents are used rather than length as they are faster to calculate
CIELabVol_subd.m function [v] = CIELabVol_subd(P)
%Each row of P contains XYZ tri-stimulus values of gamut corner points
%The 3D gamut is defined as the convex hull of these points in XYZ space
%The surface is recursively subdivided down to a threshold scale in CIELAB
%and the volume made by each surface tile to a central point is summed thresh; %CIELab subdivision threshold
%Get the hull defined by the points
%Get the white point (taken as the primary with the maximum Y)
%Normalise the gamut to the white point
%add-on the CIELab points
Pn=[Pn, XYZ2Lab(Pn)];
Pm=[Pm, XYZ2Lab(Pm)];
%calculate and sum the Lab volume of each surface tile to the mid-point v=0; for n=1:size(T,1), v=v+SubDLabVol(Pn(T(n,:),:),Pm,thresh); end
% XYZ2Lab converts XYZ values arranged in columns to L* a* b* function [ t ] = XYZ2Lab( t ) i=(t>0.008856); t(i)=t(i).^(1/3); t(~i)=7.787*t(~i)+16/116; t=[116*t(:,2)-16, 500*(t(:,1)-t(:,2)), 200*(t(:,2)-t(:,3))]; end
%Recursive function to devide up the surface tile then return the volume function [ v ] = SubDLabVol( vp,c,th )
%Get the max extent of each edge (quicker than length calculation) m=max(abs(vp-circshift(vp,1)),[],2);
To determine the number of edges exceeding a specified threshold, calculate \( s = \text{sum}(m > \text{th}) \) If \( s = 0 \), indicating no edges are larger, return the volume using the formula \( \text{vs}(\text{det}(vp(:,4:6) - \text{repmat}(c(1,4:6), 3, 1)) / 6) \) Conversely, if \( s = 3 \), meaning all edges exceed the threshold, divide the tile into four sections.
%get edge mid-points ip=(vp(:,1:3)+circshift(vp(:,1:3),1))/2;
%calculate CIELab points of the mid-points ip=[ip,XYZ2Lab(ip)];