Photon-Counting Pixel Sensitivity Control for Tone Gradation
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Solution Overview
Problem
High luminance in objects leads to a reduction in tone gradation in photoelectric conversion devices due to the short time required for photons to reach a predetermined threshold, resulting in coarse tone calculations.
Innovation Solution
A photoelectric conversion device with a sensitivity adjustment unit that controls the pulse period of the pulse generating circuit to adjust pixel sensitivity, prolonging the time to reach the threshold during high luminance conditions and increasing sensitivity during low luminance conditions, thereby maintaining tone gradation and improving signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the photon counter measures time until a predetermined number of photons is reached, then high dynamic range is achieved, but tone gradation deteriorates under high luminance conditions
Solution Approach 1:
The invention applies dynamics by making the measurement threshold variable rather than fixed. The threshold is dynamically adjusted based on the measured time: when the time to reach the predetermined photon count is short (indicating high luminance), the threshold is increased to extend the measurement range and maintain tone gradation. This dynamic adaptation resolves the contradiction between maintaining high dynamic range and preserving tone precision under varying luminance conditions.
Solution Approach 2:
The invention changes the parameter of the photon count threshold based on measurement results. By modifying the threshold parameter adaptively according to the measured time and luminance conditions, the system maintains optimal measurement precision across the full dynamic range, preventing tone degradation in high luminance scenarios while preserving the ability to measure both bright and dark regions.
2Speed
If the measurement time is short due to high luminance, then measurement speed is improved, but tone precision deteriorates
Solution Approach 1:
The invention changes the photon count threshold parameter based on the measured time. When measurement time is short (high luminance), the threshold is increased to maintain tone precision. This parameter adaptation allows the system to preserve measurement precision without sacrificing the speed advantage of short measurement times under high luminance conditions.
Solution Approach 2:
The invention implements feedback by using the measured time information to adjust the threshold parameter for subsequent measurements. The system feeds back the measurement results to modify the operating parameters, creating a closed-loop control that maintains tone precision while adapting to varying luminance conditions and measurement speeds.
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
The solution effectively suppresses the reduction in tone gradation and improves the signal-to-noise ratio by dynamically adjusting pixel sensitivity based on luminance levels, ensuring consistent image quality across varying light conditions.
Implementation Method 1
a photoelectric conversion element that outputs signals according to incident photons
Implementation Method 2
a photoelectric conversion element that outputs signals according to incident photons, using an avalanche photodiode
Data Source
AI summary
In order to achieve a photoelectric conversion device that enables suppressing the lowering in tone, a photoelectric conversion device has a pixel including a photoelectric conversion element that outputs a signal according to an incident photon; a photon counter that outputs a measured value according to the number of photons incident to the pixel, a time counter that measures a time until the measured value of the photon counter reaches a first threshold after the photon counter starts the measurement, and a sensitivity adjustment unit configured to perform a sensitivity change for the pixel during a time until the measured value of the photon counter reaches the first threshold after the photon counter starts the measurement.