CMOS Image Sensor Phase Offset for Shutter Distortion
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Solution Overview
Problem
The use of color-separation optical systems in television cameras, which offset the axial positions of red and blue image capturing elements from green elements to account for chromatic aberration, can lead to modulation degree deterioration and focal plane shutter distortion, especially when combined with CMOS image capturing elements.
Innovation Solution
The image capturing method involves capturing images of blue, green, and red components at specific frame rates and synchronizing their vertical synchronization phases to ensure each center phase has approximately the same vertical synchronization phase, thereby reducing focal plane shutter distortion and widening the dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the axial position of red and blue image capturing elements is offset from the green image capturing element to account for chromatic aberration, then manufacturing of the zoom lens is simplified, but modulation degree of red and green deteriorates
Solution Approach 1:
The patent changes the timing parameters (frame rates and vertical synchronization phases) of image capture for different color components. By capturing blue at N multiple speed, green at M multiple speed, and red at M multiple speed, and then offsetting their vertical synchronization phases, the patent compensates for the axial position offset effects without requiring physical repositioning, thus maintaining both manufacturing simplicity and image quality
Solution Approach 2:
The patent replaces the mechanical/optical approach of physically offsetting image capturing elements axially with an electronic/timing approach. Instead of changing the physical positions of the CMOS sensors to account for chromatic aberration, the patent uses differential timing and phase offsetting in the image capture and processing pipeline to achieve the same compensatory effect, thereby avoiding the modulation degree deterioration caused by physical offset
2Device complexity
If CMOS image capturing elements with axial offset are used to simplify lens manufacturing, then device complexity is reduced, but focal plane shutter distortion occurs
Solution Approach 1:
The patent applies parameter changes by adjusting the vertical synchronization phases of different color components. Specifically, it offsets the vertical synchronization phase of blue and red components relative to green by approximately half a vertical synchronization period, which compensates for the focal plane shutter distortion caused by axial offset in CMOS sensors while maintaining the simplified device structure
Solution Approach 2:
The patent applies preliminary anti-action by pre-offsetting the vertical synchronization phases of the color components before image processing. This anticipatory phase offset counteracts the focal plane shutter distortion that would otherwise occur during normal operation, allowing the system to maintain low complexity while avoiding distortion artifacts
3Manufacturing precision
If vertical synchronization phases of different color components are synchronized, then image quality improves, but processing complexity increases
Solution Approach 1:
The patent uses periodic action by establishing regular patterns in the frame rate relationships between color components. By setting blue at N multiple speed and green/red at M multiple speed where M is N+1 or more, the system creates a periodic synchronization pattern that simplifies the phase offsetting process while maintaining image quality, as the periodic nature allows for predictable and systematic processing
Data Source
AI summary
A color-separation optical system for image capture includes three rolling shutter CMOS image capturing elements of B, G and R, respectively capturing: an image of B at the speed of an integer N multiple of the number of output picture frames, an image of G at the speed of an integer M multiple of N+1, and an image of R at the speed of the integer M multiple of N+1. The vertical synchronization phases of the captured image frames of B, G and R, are offset by approximately half the vertical synchronization period of an even multiple of speed such that the center phases of the captured image frames of B, G and R have approximately the same vertical synchronization phase. A picture to be output uses the vertical effective pictures of the captured image frames having approximately the same vertical synchronization phase.