Camera Exposure Control Using Shifted Brightness Detection
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Solution Overview
Problem
Digital still cameras face challenges in determining exposure values precisely and quickly, especially in low-light conditions, due to the limited dynamic range of image sensors and the delay caused by multiple photometry measurements for autofocus control, leading to time lags in shutter release.
Innovation Solution
An image pickup apparatus with an image sensor, an auxiliary illumination light source, and a brightness detector that performs initial brightness detection without auxiliary light and subsequent detection with auxiliary light, allowing for the determination of exposure values and autofocus control, using a shift in exposure values to ensure accurate and rapid exposure settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple photometry measurements are performed at different exposure values to measure object brightness with precision, then measurement precision is improved, but loss of time increases due to delay in shutter release
Solution Approach 1:
The patent performs preliminary brightness detection before autofocus control using a first exposure value, and then performs second brightness detection right before shutter release using a second exposure value that is shifted from the first. This preliminary action allows the system to prepare exposure settings in advance while still making final adjustments based on actual lighting conditions, thereby reducing shutter release time lag while maintaining measurement precision.
Solution Approach 2:
The patent changes the exposure value parameter from the first exposure value to the second exposure value (which is shifted by a predetermined amount) for the second brightness detection. This parameter change allows the system to adapt to actual lighting conditions more quickly, enabling precise brightness measurement with reduced time delay by using a shifted exposure value that better reflects current conditions.
2Measurement precision
If AF auxiliary light is applied to raise object brightness for better autofocus detection, then measurement precision is improved, but exposure value accuracy deteriorates due to brightness level changes
Solution Approach 1:
The patent performs the first brightness detection before AF auxiliary light is applied, using this information to determine the first exposure value. Then, right before shutter release, it performs a second brightness detection using a second exposure value that is shifted from the first. This preliminary detection allows the system to establish baseline exposure settings before auxiliary light affects the scene, ensuring exposure accuracy while still enabling good autofocus detection.
Solution Approach 2:
The patent introduces a shifted exposure value as an intermediary parameter between the first exposure value (determined before auxiliary light) and the actual exposure settings. This intermediary allows the system to account for the effect of AF auxiliary light on brightness without directly using the altered brightness values, thereby maintaining exposure value accuracy while still benefiting from improved autofocus detection precision.
3Productivity
If exposure value is determined using brightness level detected before AF control, then productivity is improved by reducing time lag, but measurement precision deteriorates in low-light conditions
Solution Approach 1:
The patent determines the first exposure value using brightness detected before AF control to enable fast shutter release. Then, it shifts this exposure value by a predetermined amount to create a second exposure value for the second brightness detection right before shutter release. This parameter shifting allows the system to maintain high productivity by using pre-determined exposure values while improving measurement precision in low-light conditions through the adjusted second exposure value that better captures actual lighting conditions at the moment of capture.
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
Enables precise and rapid determination of exposure values even in low-light conditions, reducing time lag between shutter release and image capture by controlling exposure and autofocus using shifted exposure values, ensuring proper lighting and focus.
Implementation Method 1
An object image is photographed by an image sensor, is converted into digital image data
Implementation Method 2
an illumination light source applies auxiliary light to the object
Data Source
AI summary
A digital still camera includes a lens system and an image sensor. The image sensor receives object light through the lens system to output an image signal of an object, wherein exposure control and autofocus control of the lens system are carried out according to the image signal. The image sensor photographs an image of the object after the exposure control and the autofocus control. Auxiliary light is applied to the object with an illumination light source for the autofocus control. A second exposure value is determined by use of a first exposure value determined according to object brightness measured while the illumination light source is inactive. Exposure is carried out to measure object brightness by use of the second exposure value while the auxiliary light is applied, for determining a third exposure value for use in the autofocus control with the auxiliary light.