Spatial Light Modulator Greyscale Resolution via Pulse Width Modulation
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Solution Overview
Problem
Current projection systems with spatial light modulators suffer from limited greyscale resolution due to the switching times of switchable elements, which is not sufficient for human perception, especially with nonlinear eye behavior and additional losses from other effects.
Innovation Solution
The method involves using multiple solid state light sources of different colors to illuminate a spatial light modulator, with pulse width modulation during illumination periods to increase greyscale resolution by controlling light pulses shorter than the switchable elements' switched-on time, and adjusting illumination periods for optimal power use and contrast enhancement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If pulse width modulation is used with switchable elements having limited switching times, then the system can operate with faster switching elements, but the greyscale resolution is reduced
Solution Approach 1:
The illumination period is segmented into multiple sub-periods, with light pulses of different durations assigned to different grey scale levels. This segmentation allows the system to achieve fine greyscale resolution by combining multiple pulse widths rather than relying on a single long pulse, thereby resolving the contradiction between switching speed and greyscale precision.
Solution Approach 2:
The system dynamically adjusts the duration of light pulses based on the required grey scale level. By varying pulse widths within the illumination period and using multiple pulses per colour component, the system adapts to different brightness requirements while maintaining fast switching operation, thus resolving the contradiction between speed and precision.
2Speed
If the shortest possible switched-on time of switchable elements is used, then switching speed is maximized, but the amount of light arriving at the screen is insufficient for adequate brightness
Solution Approach 1:
The system employs periodic illumination with multiple light pulses within each illumination period. By delivering multiple pulses rather than a single continuous pulse, the system accumulates sufficient light energy at the screen while maintaining fast switching between pulses, thus resolving the contradiction between switching speed and illumination intensity.
Solution Approach 2:
The system performs preliminary modulation of the light source intensity before the light reaches the spatial light modulator. By pre-adjusting the light pulse duration and intensity, the system ensures that each pulse delivers the optimal amount of light energy, accumulating sufficient brightness over multiple pulses while maintaining fast switching characteristics.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances greyscale and color resolution, reduces light losses, and minimizes artefacts, resulting in higher image quality and brightness with improved greyscale and color representation.
Implementation Method 1
said array is addressed such that the light is timely and spatially modulated to project one image onto the screen, said modulation being achieved by switching said switchable elements by means of pulse width modulation during one of said illumination periods
Implementation Method 2
projection system comprising several solid state light sources of different colour
Data Source
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AI summary
The present invention relates to a method of operating a projection system comprising several solid state light sources (2, 3, 4) of different colour 13, 14, 15) and at least one spatial light modulator (1) having an array of switchable elements. Said array is illuminated by at least one of said light sources (2, 3, 4) for several illumination periods and is addressed such that the light is timely and spatially modulated to project images onto a screen. In the present method said light sources (2, 3, 4) are controlled to emit light modulated in amplitude (15) and/or time (18) during said illumination periods of said array. With the present method an increased greyscale resolution of the projection system can be achieved.