Radiation Imaging Offset Correction for 1/f Noise
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Solution Overview
Problem
Radiation imaging apparatuses using large-area flat panel sensors with rectangular semiconductor substrates suffer from artifacts due to 1/f noise, which degrades image quality and dynamic range, particularly in low-frequency regions.
Innovation Solution
The apparatus employs a method to correct 1/f noise by generating a target value for offset correction, using multiplexers, D/A converters, and amplifiers to adjust offset values in real-time, thereby reducing noise artifacts and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large-area flat panel sensor is constructed by tiling multiple rectangular semiconductor substrates, then the imaging area can be enlarged beyond the size of a single silicon wafer, but 1/f noise from the substrates and readout circuits generates block artifacts that degrade image quality
Solution Approach 1:
The patent applies preliminary action by performing offset correction before actual image acquisition. A dark image is acquired without radiation exposure to measure the offset values generated by 1/f noise in each rectangular semiconductor substrate. These offset values are stored and subtracted from subsequent images, preventing block artifacts from appearing in the final images. This preliminary measurement and correction approach eliminates the harmful effect before it degrades image quality.
2Object-affected harmful factors
If offset correction is performed using dark images, then block artifacts from 1/f noise can be reduced, but the correction must be updated frequently to account for drift in offset values over time
Solution Approach 1:
The patent implements feedback by continuously monitoring offset values through periodic acquisition of dark images and updating the correction values accordingly. The system measures the offset values at regular intervals, compares them with stored reference values, and updates the correction data when drift is detected. This feedback mechanism ensures that block artifacts are consistently suppressed while adapting to temporal variations in the readout circuits and semiconductor substrates.
3Ease of operation
If readout circuits and A/D converters are used to process signals from photoelectric conversion elements, then digital image data can be obtained, but shot noise, thermal noise, and 1/f noise are generated in these circuits
Solution Approach 1:
The patent applies the taking out principle by separating the measurement of circuit noise from the measurement of actual signals. The offset correction process extracts and isolates the noise components generated by readout circuits and A/D converters by acquiring dark images without radiation exposure. These extracted offset values represent only the circuit-generated noise, which can then be subtracted from subsequent images containing both signal and noise, thereby removing the harmful noise components while preserving the useful signal.
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 effectively reduces artifacts caused by 1/f noise, enhancing the dynamic range and image quality of radiation imaging by adjusting offset values in real-time, even during readout operations.
Implementation Method 1
a large-area flat panel radiation imaging apparatus based on a 1x optical system using photoelectric conversion elements
Data Source
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AI summary
An image sensor driving apparatus extracts an image signal from an image sensor including a plurality of photoelectric conversion elements two-dimensionally arrayed, and includes a conversion unit which converts the image signal into digital data by performing offset correction for the image signal. The apparatus obtains digital data corresponding to a first sampling count by causing the conversion unit to process a reference voltage signal in accordance with a synchronization signal which determines an imaging frame rate, and obtains digital data corresponding to a second sampling count by causing the conversion unit to process a reference voltage signal every time extracting an image signal from a photoelectric conversion element group obtained by dividing a plurality of photoelectric conversion elements. The apparatus generates a correction value used for offset correction based on the obtained digital data corresponding to the first and second sampling counts.