OLED Image Display Dithering for Low-Luminance Color Uniformity
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Solution Overview
Problem
Existing two-dimensional image display devices using OLEDs face issues with luminance and color unevenness, particularly noticeable on low luminance levels, due to variations in threshold voltage of driving TFTs, which affect image quality.
Innovation Solution
Implementing dithering techniques, including temporal and spatial dithering, to drive OLEDs at luminance levels above a threshold, and adjusting this threshold based on image type and total luminance, while avoiding low luminance levels to improve image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If OLEDs are driven at low luminance levels, then energy consumption is reduced, but luminance and color unevenness increases due to threshold voltage variation of driving TFTs
Solution Approach 1:
The patent divides the gray scale range into multiple segments: a first gray scale range (lower than threshold voltage) and a second gray scale range (higher than threshold voltage). By segmenting the operating range and applying different driving methods to each segment, the patent resolves the contradiction between low energy consumption and uniform image quality.
Solution Approach 2:
The patent changes the driving parameter (gray scale level) based on the threshold voltage of the driving TFT. When threshold voltage varies, the system adjusts the gray scale level dynamically - using higher gray scale levels for pixels with higher threshold voltage to maintain uniform luminance, thus resolving the unevenness problem while managing energy consumption.
2Use of energy by moving object
If dithering is applied to achieve low luminance levels, then energy consumption is reduced, but image quality deteriorates due to visible dithering patterns
Solution Approach 1:
The patent applies dithering selectively only in specific regions where the gray scale level is below the threshold voltage, rather than uniformly across the entire display. This local application of dithering reduces its visual impact and maintains image quality in regions where it is not needed, while still achieving energy savings in the low luminance regions.
Solution Approach 2:
The patent dynamically adjusts the gray scale level based on the threshold voltage of the driving TFT. When threshold voltage changes, the system updates the gray scale level in real-time, making the dithering pattern adaptive rather than static. This dynamic adjustment reduces the visibility of dithering artifacts and improves overall image quality.
3Manufacturing precision
If threshold voltage of driving TFTs is compensated, then luminance uniformity is improved, but device complexity increases
Solution Approach 1:
The patent employs a self-service mechanism where the display device automatically measures its own threshold voltage and performs compensation without requiring external calibration equipment or complex external circuits. The system uses built-in functionality to detect threshold voltage variations and adjust gray scale levels accordingly, simplifying the overall device architecture.
Solution Approach 2:
The patent implements a feedback mechanism where the measured threshold voltage is used to adjust the gray scale level in real-time. This closed-loop control system continuously monitors threshold voltage variations and compensates for them by adjusting the driving parameters, achieving luminance uniformity without requiring complex pre-compensation circuits.
Data Source
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AI summary
A method for displaying an image on an image displaying device is provided. The image displaying device comprises a plurality of pixels including light emitting elements. The method includes steps of: comparing gray scale level of an image signal for the light emitting element with given threshold level; and when the gray scale level is higher than the threshold level, driving the light emitting element by a driving signal corresponding to the gray scale level, and when the gray scale level is lower than the threshold level, driving the light emitting element by a dithering driving signal including a driving signal corresponding to the threshold level.