Adaptive Exposure Compensation for Mobile Camera Luminance Stability

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Solution Overview

Problem

Existing mobile communication terminals take too long to achieve automatic exposure compensation and suffer from instability in reaching a target luminance value for camera images.

Innovation Solution

A mobile communication terminal and method that determine a convergent coefficient value based on the difference between the average luminance value of a current image frame and a target luminance value, and update the weight of an adaptive filter to quickly stabilize and adjust exposure for subsequent frames.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the aperture opening time is adjusted based on average luminance value threshold to control light amount for automatic exposure compensation, then the exposure can be adjusted, but the time required for compensation is too long and stability is degraded

Engineering Contradiction:

Improvestability of exposure compensationVSAvoidtime required for automatic exposure compensation

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies dynamics by making the convergent coefficient adaptive rather than fixed. The coefficient changes dynamically based on the current exposure state and error magnitude, allowing the system to converge faster when error is large and stabilize when接近 target, thus resolving the contradiction between speed and stability

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements feedback control by continuously monitoring the luminance error and adjusting the aperture opening time accordingly. The feedback loop uses the error signal to drive the convergence process, enabling the system to automatically correct exposure deviations while maintaining stability through controlled adjustment rates

Inventive Principle:

Principle #23Feedback

2Illumination intensity

If the aperture opening time is lengthened to increase light amount, then the image brightness is improved, but the compensation time increases

Engineering Contradiction:

Improveamount of light for imageVSAvoidcompensation time

Core Design Contradiction:

Illumination intensityVSLoss of time

Solution Approach 1:

The patent applies partial or excessive action by allowing the aperture opening time to temporarily exceed normal ranges during the convergence process when large corrections are needed. This enables faster compensation by making larger adjustments initially, then reducing to normal ranges as convergence approaches completion

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent changes parameters by dynamically adjusting both the aperture opening time and the convergent coefficient based on the current error state. This allows the system to optimize the balance between correction speed and stability by adapting parameters to the specific compensation stage

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7430371B2Mobile communications terminal for compensating automatic exposure of camera and method thereof

Publication Date: 2008.09.30 LG ELECTRONICS INC

AI summary

A method for compensating an automatic exposure of a camera in a mobile communication terminal. The method includes determining a presumptive error value based on an average luminance value of an input current image frame and a particular target luminance value, selecting a convergent coefficient value based on the determined presumptive error value, determining a weight value of an adaptive filter based on the determined convergent coefficient value, and determining an exposure value for a next image frame based on the selected weight value, the determined presumptive error value and the exposure value of the current image frame.