Guide to Testing Smartphone Performance – Display Panel Quality

In today’s fast-paced digital world, smartphones have seamlessly integrated into our daily lives. From communication to entertainment, we heavily rely on these devices to accomplish various tasks. With intense competition among smartphone manufacturers, the quality of the display has emerged as a vital determinant of overall performance. A good display panel is crucial for delivering an excellent user experience. Not only does it enhance the visual appeal of a smartphone, but it also plays a significant role in its functionality and efficiency.

Why Smartphone Display Panel Quality Matters

Smartphone display panel quality is crucial for a variety of reasons that collectively contribute to an enhanced user experience. The display serves as the primary interface, impacting aesthetics, functionality, and overall device satisfaction. A high-quality display ensures a positive first impression, facilitates smooth user interactions, and significantly improves the consumption of multimedia content, whether it’s for productivity, reading comfort, photography, or gaming. With consumers becoming more tech-savvy and demanding, smartphone manufacturers must prioritize the quality of their display panels to stay competitive in the market.

Evaluating Smartphone Display Panel Quality

When it comes to evaluating display panel performance, manufacturers must consider various parameters to ensure their readability, color accuracy, etc. Below is a brief overview of some of the commonly tested parameters.

• Chromaticity and luminance are fundamental parameters in display measurement. They play a crucial role in quantifying the color and brightness of a display. Chromaticity refers to the specific color characteristics of light emitted by a display, while luminance measures the intensity or brightness of that light. These parameters are calculated based on the XYZ tristimulus values, which are derived from the integration of the spectral power distribution (SPD) and the CIE color matching functions (CMF).
• Display contrast, expressed as a ratio, measures the difference between the luminance of the brightest white and the darkest black a screen can display. A high contrast ratio is important for better image quality, clarity, detail, and color accuracy.
• Color gamut refers to the entire range of colors that the display can reproduce within a specific color space. Common color spaces include sRGB and DCI-P3. Moreover, High Dynamic Range (HDR) content is frequently linked to a wider color gamut. The extended brightness levels in HDR require a broader spectrum of colors to complement the increased brightness and contrast levels.
• The Electro-Optical Transfer Function (EOTF) establishes the connection between the input signal (brightness levels in the source content) and the light emitted or displayed on the screen. Ensuring accuracy in the EOTF is crucial for maintaining the intended brightness and contrast levels of the displayed content, especially in the context of HDR.
• Display uniformity refers to the consistency of brightness and color across the entire screen. Achieving a uniform brightness and color output is crucial for providing users with a visually satisfying and immersive experience without distracting variations or inconsistencies.
• The viewing angle performance evaluates the changes in the colors and brightness levels of the smartphone display from different angles or orientations. In particular, Liquid Crystal Display (LCD) can experience color and brightness shifts when viewed from extreme angles. On the other hand, Organic Light-Emitting Diode (OLED) displays have relatively few issues with brightness consistency but can exhibit color shifts.
• Flicker pertains to quick and repetitive fluctuations in brightness, typically occurring at frequencies that are not easily noticeable to the naked eye. Various techniques can be employed to measure flicker in displays, with the contrast method and JEITA method being two notable approaches.
• Gamma correction plays a crucial role in display technology by fine-tuning the luminance or XYZ tristimulus values. This ensures that the display exhibits a linear response to the input signal. While the standard gamma value for most displays is 2.2, it’s important to note that various applications and display technologies may employ different gamma values.
• Mura is a term used to describe the non-uniformity in brightness, color, or pixel intensity across a screen. This phenomenon can manifest in various forms, such as patches or cloudiness. Mura can be attributed to several factors, including process flaws during assembly and optical bonding, impurity contamination, manufacturing defects, backlight non-uniformity, and inconsistent pixel response times.
• Screen reflectance measures the amount of light that reflects off a screen. Lower reflectance means less glare, better outdoor visibility, and an improved user experience in varying lighting conditions.

Apart from the mentioned factors, there are other display parameters that are also commonly assessed, including but not limited to defects like dead pixels. Accurate measurement and effective management of these parameters are vital to ensure the best possible display quality and user experience. It is recommended to test these parameters under various lighting conditions in order to replicate real-world scenarios as closely as possible.

Challenges in Evaluating Emissive Displays

Emissive displays, such as OLED, have become increasingly popular in smartphones. However, they present unique challenges for inspection when compared to LCDs. Unlike LCDs, each pixel in an emissive display is an independent emitter and its own light source. Typically, each emitter comprises subpixel elements of red, green, and blue diodes, which produce their own light independently. Consequently, such displays may exhibit non-uniform brightness and color output from pixel to pixel, resulting in non-uniformity across the display. Ensuring consistent brightness and color uniformity across the entire display requires measuring the luminance and chromaticity of each subpixel to calculate the correction coefficients for adjusting the input of each subpixel individually.

Measurement Solutions for Smartphone Display Panel Evaluation

Konica Minolta Sensing, a renowned provider of measurement solutions, offers a broad range of accurate and reliable instruments that enable the comprehensive evaluation of smartphone display panels. These instruments are widely trusted by experts within the industry for their precision and reliability. Notably, DXOMARK, a company specializing in evaluating and benchmarking various consumer electronics, particularly smartphones, cameras, and audio devices, relies on Konica Minolta Sensing’s range of test and measurement instruments for their display evaluations.

One standout example is the state-of-the-art Spectroradiometer CS-3000 Series, which consists of three different models. These models provide precise measurements of luminance, chromaticity, contrast, color gamut, gamma, spectral power distribution (SPD), viewing angle, and current-voltage-brightness (I-V-L) characterization.

Another noteworthy instrument is the Display Color Analyzer CA-410 series. It features a diverse selection of probes to cater to various measurement needs. This tool is excellent for measuring luminance, chromaticity, contrast, color gamut, gamma, and flicker of smartphone displays.

The ProMetric® I-Series Imaging Colorimeters are another set of instruments that are highly useful for evaluating smartphone displays. In addition to measuring luminance, chromaticity, contrast, and viewing angle, they can also measure uniformity and mura, including pixel-level analysis.

When evaluating screen reflectance, the Spectrophotometer CM-26d or Rhopoint IQ-S can provide reflectance curve data that is useful in the assessment of the quality of the screen’s reflective properties. Additionally, the Illuminance meter T-10A monitors the intensity of ambient lighting during evaluation.

Unsure about which display metrology instruments or measurement solutions would be the best fit for your specific requirements? Reach out to us now for a complimentary consultation and let our team of experts guide you towards the ideal display measurement solution that perfectly meets your needs.