Gamma Adjustment Error Diffusion Electrophoretic Displays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electrophoretic display devices face challenges in achieving precise control over reflectance due to a non-linear relationship between grey scale input and optical response, leading to undesirable non-uniformities and poor match to the target reflectance vs. input level curve, known as the gamma curve, especially in the middle grey zone.
Innovation Solution
An image processing method that utilizes error diffusion to correct the error between reflectance and desired gamma by determining true grey level values from optical response curves and integer pulse numbers, allowing for improved display quality with a limited number of pulses, and compensating for batch variations, temperature changes, and aging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the bandwidth of pulse-width modulation is increased to have more steps between off and on, then reflectance can be controlled more precisely, but hardware complexity increases and costs rise
Solution Approach 1:
The patent creates a virtual expanded grey scale by mapping limited physical pulse levels to multiple virtual grey levels through error diffusion dithering. Instead of physically generating more pulse steps, the system copies the effect of fine-grained control through statistical distribution of errors across multiple pixels, achieving the appearance of higher precision without the hardware complexity.
Solution Approach 2:
The patent transforms the control parameter from direct pulse width modulation to error diffusion dithering with virtual grey level mapping. By changing how the limited pulse levels are interpreted and distributed across pixels, the system achieves effective higher precision control without modifying the physical pulse generation hardware.
2Measurement precision
If shorter pulse widths are used to control reflectance more precisely, then gamma curve matching improves, but the number of available pulses between off and on states decreases
Solution Approach 1:
The patent transitions from controlling reflectance through temporal pulse width variation to spatial error distribution across multiple pixels. By adding the spatial dimension of error diffusion, the system can achieve fine reflectance control even with limited temporal pulse steps, effectively trading temporal resolution for spatial distribution.
Solution Approach 2:
The patent introduces error diffusion dithering as an intermediary process between the limited pulse inputs and the desired reflectance output. This intermediary layer distributes quantization errors across neighboring pixels, creating the perception of intermediate grey levels that don't physically exist in the pulse sequence.
3Device complexity
If a limited number of pulses is used between off and on states, then hardware complexity is reduced, but it becomes difficult to obtain the desired reflectance and match the gamma curve
Solution Approach 1:
The patent creates virtual grey scale levels by copying the visual effect of multiple pulse steps through error diffusion. The limited physical pulse levels are mapped to expanded virtual grey levels, where the error from each quantization is diffused to neighboring pixels, creating the appearance of smooth gamma curve matching without requiring numerous physical pulse steps.
Solution Approach 2:
The patent changes the approach from direct pulse-count-based grey scale control to error diffusion-based virtual grey scale control. This parameter transformation allows the system to achieve accurate gamma curve matching with minimal hardware complexity by processing the limited pulse inputs through an error diffusion algorithm.
Data Source
AI summary
Embodiments are directed to image processing methods to improve display quality while using a limited number of pulses and to correct the error between the reflectance and the desired gamma. The complexity of the hardware used for driving a display device may then be reduced to minimum. In addition, in various embodiments the method can also be used to compensate for the change of an optical response curve due to batch variation, temperature change, photo-exposure or aging of the display device.