At this time, the phenomenon called metamerism refers to the situation in which people perceive two stimuli as the same if the eye cone signal is the same even though the spectral distribution of the light source is different. The CIE 1931 Standard Colorimetric Observer was used as a standardized color matching function to indicate color until now. A new problem occurred that even if CIE 1931 coordinates are used to match the same coordinates, the appearance of the two colors differs from each other.
This paper aims to show observer metamerism in displays with different spectral characteristics and propose the need for individual color matching functions that can well represent the human visual system. In this paper, two psychophysical experiments were conducted: the color matching experiment and the color change experiment and the performance test of the color matching function. Through color matching experiments, the color matching data set was obtained for different types of display and the metamerism of the observer was analyzed by showing the colors in the CIE 𝑢′10𝑣′10 plane and calculating the color difference using.
The results showed that people perceive colors with different XYZ tristimulus values as the same colors, and each person's corresponding result is all different; 3.31 △𝐸00. Then, a color difference experiment was conducted to confirm how people perceive others' color matching meaningfully from a color difference perspective.
80 Figure 4-2 Example of Color Difference Experiment Result ________________________ 82
LIST OF TABLES
46 Table 3-4 Summary of Color Matching Experiment based on Different Spectral Characteristics
46 Table 3-5 Information on Metameric pairs for Each participant in Each session of the Color
- Introduction
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Background
The Commission Internationale de l’Eclairage (CIE) proposed the CIE 1931 Standard Colorimetric Observer as a standardized color matching function that represents the visual perception of all humans (Vos, 1978; Broadbent, 2004). Objects look the same to one person but different to another, a phenomenon called observer metamerism. In other words, even if the spectral distribution of light is different, two stimuli are recognized as having the same color if the cone signal is the same.
The reason that metamerism of monitors has become a major issue in recent years is the emergence of wide-gamut displays. According to the CIE 1931 Standard Colorimetric Observer, even after matching colors with the same color coordinates, it is possible to notice the difference in color appearance (Alfvin & Fairchild, 1997; Bodner, Robinson,. In addition, it can be seen that people perceive two colors that have different color coordinates as the same color.
The experimental result showed that the colors that people perceive as the same are completely different from the reference coordinates and that the colors that people match differ from person to person. In other words, it can be seen that the existing color matching function does not accurately express people's color matching (Shaw & Fairchild, 2002; SONY Corporation, 2013; Hu, Wei, & Luo, 2020).
Aim of the Research & Novelty
Research Outline
Literature Review
- Introduction
- Human Eye
- Metamerism
- Definition of Metamerism
- Types of Metamerism
- Metamerism Issues & Solutions
- History of Color Matching Function .1 CIE 1924 Luminous Efficiency Function
- Principle of Color Matching Method
- CIE Standard Observer (CIE 1931 2°, CIE 1964 10°)
- CIE 2015 Cone Fundamental based Color Matching Function
- Previous Research on Individual Colorimetric Observer Model
- Individual Colorimetric Observer Model
- Sarkar’s CMF Derivation from Color Matching Experiment
- Asano’s Individual Colorimetric Observers for Personalized Color Imaging
- Metamerism on Color Matching with Displays
- Evaluating Metameric Failure of CIE 1931 Standard Observer
- Correcting Metameric Failure of CIE 1931 Standard Observer
- Modeling of Observer Metamerism Impact
- Colorimetry
- CIE XYZ Tristimulus Values
- Chromaticity
- Color Space
- Color Difference
Color matching properties are determined by the spectral responsivity of the three types of cones. A new function was proposed taking into account not only the color matching experiment, but also the physiological characteristics of the human eye. Solid lines represent 2° and dashed lines represent 10° of the CIE 2015 cone-based color matching function.
An individual colorimetric observer model was proposed for the prediction of the color adaptation function of the normal color population (CIE). One of the color matching experiments was performed using Sony BVM CRT and HP Dreamcolor Wide-Gamut LCD (LP2480zx) with LED backlight. As a result of During the experiment, the colorimetric observer categories and the color matching function were derived in two stages.
Questions have been raised about whether the CIE 1931 color matching function best represents the human cone response. First, it was checked whether the standard observer can represent the color matching of the real observers. As a result of the experiment, it was concluded that the physiologically based color matching function can reduce the magnitude of potential observer metamerism.
S(λ) stands for the spectral power distribution of the light source, R(λ) stands for the spectral reflectance of the object, and 𝒙̅(λ), 𝒚̅(λ), 𝒛̅(λ) represents the color matching function.
Color Matching Experiment
- Introduction
- Experimental Settings
- Psychophysical Experimental Method
- Test Displays
- Experiment Session
- Participants
- Experimental Results .1 Data Analysis Method
- Observer Performance Test 1 _ Matching Accuracy Performance Test
- Observer Performance Test 2_ Individual Repeatability
- Observer Performance Test 3_ Long-term Repeatability
- Summary of Observer Performance Test
- Observer Variability on Color Matching
- Effect of Field Size on Color Matching
- Effect of Display Spectral Characteristics on Color Matching
- Summary of Color Matching Experiment
The color matching was performed by adjusting CIELAB a*, b* to make the color of the reference and test screen look the same. As shown in Table 3-3 and Table 3-4, a total of 81 metameric pairs were collected in the color matching experiment. For data analysis, the color matching result was represented with color coordinates and the color difference to show the variation between observers.
The color matching ability was checked by expressing color coordinates and calculating a color difference between the reference and test displays. The yellow dot represents test displays that the participants match during the 1st trial of color matching experiment and the green dot represents test displays during the 2nd trial of the experiment. The yellow dot represents test displays participants corresponding to the 1st day of the color matching experiment and the green triangle represents test displays while the 2nd day of the experiment.
For the color test types, the color difference (△𝑢′10𝑣′10) of the multicolor was higher than that of the white color matching experiment in most participants. The FOV impact was analyzed by calculating the color difference between 2 degrees and 4 degrees of the FOV color matching result of the test screens. As shown in the figures, the color matching result is slightly different depending on the FOV.
It was confirmed that inter-observer variability existed and the color matching results were varied depending on the field size and display spectral characteristics.
Color Difference Experiment
- Introduction
- Experimental Settings
- Psychophysical Experimental Method
- Experimental Results .1 Data Analysis Method
- Individual Result of Color Difference Experiment
- Average Result of Color Difference Experiment
- Summary of Color Difference Experiment
The color change experiment was performed with different colors using two different types of screens. To check how people visually view the different colors that were matched during the color matching experiment, the same participants as the color matching experiment were recruited into the color change experiment. Since the color coordinates of the screen change over time, there was a difference between the participant's adapted color and the stimuli of the color change experiment.
As the participant felt that the color difference between the reference and test colors was large, a score close to 5 was given. Also, they ignored the luminance difference between the displays and considered the luminance to be the same when evaluating the color difference. For each participant, an attempt was made to analyze the relationship between their color matching scores and the color change of the test colors they rated.
First, by assessing the color difference for the colors that people matched in the color matching experiment, it was assessed how the matched color was perceived by someone other than me. Therefore, it was confirmed how the color change was perceived when looking at the same coordinates as a reference. As shown in Figure 4-2, the result of the color change experiment is expressed in the CIE xy color space.
The yellow diamond represents stimuli participants responded to the color difference below 2.5, as to some extent acceptable. The red broken line means the color matched by each observer in the color matching experiment. The color difference evaluated by each participant was averaged and it was shown in number next to stimuli.
The red solid line means the color matched by each observer in the color matching experiment. However, people rated the color difference as low for colors similar to their color match. However, people responded that the color difference was large for the colors located far from the average color matching result.
Color Matching Function Performance Test
- Introduction
- Color Prediction Process
In the previous chapter, it was confirmed that the currently used CIE 1931 2°, CIE 1964 10° color matching functions do not represent color matching data well. Therefore, in this chapter, a performance test of the color matching function was conducted to see if there is a color matching function that can predict colors without performing a color matching test for all colors. It was performed by a color prediction procedure using four color matching test functions for all color matching experiments performed.
The input values for color prediction are the reference and test color spectrum, the main maximum RGB spectrum of the test screen, and the test color matching functions. If the color matching function shows the visual characteristics of people well, the matching data and the prediction data should overlap with each other and the color difference between them is small.
Calculation of the tristimulus values in the reference display
Calculation of the R scalar in the test display
Calculation of predicted spectrum using R scalar
- Color Matching Function Performance Test Result
- Conclusion and Discussion
- Conclusion
- Application & Future work
The color difference was calculated between the test display and the predicted color using four test color matching functions. This means that the new color matching function that represents the human visual characteristics is needed. This means that this color matching function can represent the color matching for most of them.
In conclusion, the need for a new color matching function was found to perfectly predict the color matching data. A color matching experiment and a color difference experiment were conducted with a total of six types of displays in a dark room. In the color matching experiment, the color matching dataset was obtained and the metamerism of the observer was analyzed from different points of view.
Color matching variation between observers was analyzed by the color difference between matching averages and individual matching data. Furthermore, showing that the color difference for observer variability is 0.0032 △ 𝑢′10𝑣′10, which was three times larger compared to individual repeatability, it also showed that the color matching results are different for each individual. The color difference for FOV influence was 0.0035 △𝑢′10𝑣′10, about twice that of individual repeatability, so the result showed that color matching was different depending on the field size.
Finally, the effect of screen characteristics on color adaptation was analyzed by the color difference between reference and test screens. Therefore, a new color matching function is needed, which unifies reference color, matching colors and color rated as a low color difference. In the color matching function performance test, the color prediction using four test CMFs was performed.
However, it was found that the Asano 151 lms-CMF alone cannot predict human color matching data. Therefore, a need was identified for a new color matching function to fully predict color matching data without color matching for all colors. In this study, a color matching experiment and a 2 degree and 4 degree color difference experiment were conducted on simple patches.
Basic chromaticity diagram with physiological axes – Part 2: Spectral light efficiency functions and chromaticity diagrams (Vol. CIE.
