Perceptual Color Brightness Addressed in New Version of SEMI D61
By Seungmin Lee and Su Young Kim, Samsung Display and Natalie Shim, SEMI Korea
SEMI D61, Test Method of Perceptual Angle for OLED Displays, was recently published in July 2023. Developed by the Perceptual Image Quality Task Force of the Flat Panel Display Korea Technical Committee Chapter, this Test Method encompasses an evaluation of perceptual angles, which can check the color viewing angle characteristics of the display. It does this by calculating the display color volume and comparing the rate value between on-axis and off-axis color volume data.
This revision not only incorporates the latest calculation method of color volume, but also introduces the new concept of “Experienced luminance (brightness),” which can capture the impact of display luminance and color. Furthermore, this revision enables the calculation of the perceptual angle associated with “Experienced luminance (brightness).”
In recent years, display products featuring wide color gamut properties have become available, and a diverse range of video content is being consumed. Consequently, the luminance values measured by devices may not comprehensively capture the intricate experiences of viewing actual display content. Notably, color significantly impacts the perceived brightness, and this concept of brightness level is addressed in SEMI D61, which is also called average picture brightness (APB).
The perception of brightness in individuals varies depending on the color type and saturation level, a phenomenon known as the H-K effect, which was discovered by German physicists Helmholtz and Kohlrausch in 1860. APB is calculated based on this H-K effect.
Research into the application of the H-K effect to enhance display picture quality is being actively conducted in the display industry. The APB which is reflected in SEMI D61 represents a significant concept because it opens up the possibility of solving the limitations of brightness measurement, which has been expressed traditionally using luminance values.
As wide color and deep luminance expression (HDR) properties gain growing importance, the concept of APB that aligns with human perception is anticipated to bring about significant changes in designing, developing, and evaluating the displays in the future. Moreover, it is expected to make a valuable contribution to enhancing the overall perceived characteristics of displays.
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September 14, 2023