CMOS Image Sensor Dynamic Range via Column Exposure Segmentation
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Solution Overview
Problem
Conventional high dynamic range CMOS image sensors require increased cost and buffer memory to support extended dynamic range, limiting their effectiveness in accurately reproducing natural light intensity variations.
Innovation Solution
The implementation of a periodic sequence of column exposure times in a CMOS image sensor, allowing pixel data from adjacent pixels with different exposure times to be combined within a single line, enabling color interpolation with a conventional 3-line image buffer and extending the dynamic range without increasing memory requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional high dynamic range CMOS image sensors use extended dynamic range with color interpolation, then dynamic range is improved, but line image buffer memory requirements increase and cost increases
Solution Approach 1:
The pixel array is divided into multiple columns, each with different exposure times. By segmenting the columns into groups (e.g., odd columns with one exposure time, even columns with another exposure time), the patent enables different exposure strategies for different spatial locations, allowing extended dynamic range without requiring increased buffer memory for color interpolation
Solution Approach 2:
The patent merges pixel data from adjacent pixels of different exposure times within the same line buffer. By combining short exposure and long exposure data horizontally within the line buffer, the system achieves extended dynamic range while maintaining the same buffer size, as the combined data fits within the existing buffer capacity
2Illumination intensity
If conventional high dynamic range CMOS image sensors use extended dynamic range with color interpolation, then dynamic range is improved, but hardware cost increases
Solution Approach 1:
The line image buffer is designed to serve dual purposes: conventional color interpolation mode and extended dynamic range mode. By making the buffer multi-functional, the same hardware infrastructure supports both operating modes without requiring additional expensive hardware components, thereby reducing overall system cost while maintaining extended dynamic range capability
3Illumination intensity
If column exposure times are varied in a periodic sequence, then extended dynamic range is achieved with reduced buffer memory, but processing complexity increases
Solution Approach 1:
Columns are assigned exposure times in a periodic sequence (e.g., odd columns use one exposure time, even columns use another). This periodic pattern creates a predictable, repeating structure that simplifies the processing logic compared to arbitrary exposure time assignments, as the same processing rules can be applied repeatedly across different column pairs
Solution Approach 2:
The patent changes the exposure time parameter across different columns in a systematic way. By varying this single parameter (exposure time) across columns while keeping other parameters constant, the system achieves extended dynamic range with relatively simple processing, as only one parameter needs to be tracked and adjusted rather than multiple complex parameters
Data Source
AI summary
An image sensor has an array of pixels organized into a row and column format. Pixels are read out in a line-by-line sequence and buffered in a line image buffer. An extended dynamic range is supported by varying a column exposure time according to a periodic sequence. As a result, the pixel exposure times vary within each row. A high dynamic range is generated by combining pixel data of adjacent pixels within the same row that are of the same filter type but having different exposure times. Color interpolation is performed on the combined line data.