Why do you want to do “DC-like dimming”?
In the industry, OPPO is the first to use OLED screens. In November last year, we were concerned about the voice optimization for screen dimming: some users reflected that under low brightness, the OLED screen will turn on PWM dimming (240 HZ), and they feel uncomfortable .
OPPO has always been committed to a high-quality experience, so the ColorOS multimedia development team optimized the low-brightness PWM dimming of OLED screens, which we call “DC-like dimming.”
How ColorOS does “DC-like dimming”
The ColorOS multimedia development team has tried 4 solutions:
- Low brightness backlight smoothing algorithm
- PCC image mask
- Modify the PWM frequency
- Mask dimming + dither
However, the first three solutions will have a negative impact on the screen perception, such as:
- Screen color cast
- Uneven illumination
- Screen splash
- Gray scale deviation deterioration
After several rounds of testing, we finally selected the “mask dimming + dither” program . The solution calls the Snapdragon Display Engine layer mixer function inside the Qualcomm Snapdragon platform, which typically handles VR binocular image blending or handles the overlay of video and application interfaces.
The dedicated layer of the SDE mixer is the Dim Layer. The layer mixer is transparently mixed with other layers through the Dim Layer. Finally, the brightness of the entire image is effectively reduced, while retaining the effect similar to the DC dimming mode.
How is ColorOS “DC-like dimming” effect?
When ColorOS “DC-like dimming” is turned on, it can effectively reduce the fatigue of sensitive people due to low-frequency PWM dimming . In the process of productization, the ColorOS multimedia development team also encountered many problems, such as: color misalignment, flashing white light, unstable brightness values and other issues.
Therefore, from the architectural level , they made a large-scale modification of the Android backlight system ; and through a large number of data acquisition, thousands of debugging of the Y (content brightness) value, constantly exploring the relationship of color mapping.
Finally, three optimal value coefficients are obtained, which remaps the brightness and color of the screen content; and solves the ribbon by “dither” smoothing, and finally the techniques in the color, dynamic range, contrast, and color gradation. The indicators have passed the extremely stringent display testing of the ColorOS multimedia development team.
At the same time, the SDE mixer function is the built-in technology of the bottom layer of the Snapdragon platform, and the power consumption performance is also significantly better than that of the three-party interface, which ensures the user’s battery life experience.
In addition, we have been accelerating the promotion of screen suppliers, and hope to realize the “true global DC dimming” of hardware and software integration as soon as possible .
Which models can use ColorOS “DC-like dimming”
The OPPO Reno new mobile phone released on April 10 will be equipped with ColorOS DC dimming, and the Find X, R17 series, R15 series and other models are also planned to be debugged.