Flash Control via Subject Area Brightness Difference
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Solution Overview
Problem
Imaging devices equipped with flash units often cause overexposure or underexposure due to incorrect ambient light measurement, as external sensors may not accurately represent the light conditions of the main subject within the frame.
Innovation Solution
The imaging device includes a flash unit, a signal extractor, a light-amount corrector, and a controller, which perform pre-emission and regular emission to calculate and adjust the flash amount based on brightness differences in divided areas of the image sensor, ensuring proper flash control according to the ambient light applied to the main subject.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the ambient-light amount is integrated with an external sensor covering the entire shooting frame or central part, then the flash emission can be terminated to prevent overexposure, but the ambient-light amount does not accurately indicate the light conditions of the main subject, causing overexposure or underexposure
Solution Approach 1:
The shooting frame is divided into multiple small areas, and the brightness difference is calculated for each divided area between non-emission and pre-emission images. This segmentation allows identification of the main subject area without relying on a single external sensor measurement that covers the entire frame or only the central part.
Solution Approach 2:
The invention focuses on measuring the brightness characteristics of specific local areas (small areas within the shooting frame) rather than using a uniform measurement across the entire frame. By selecting the small area with maximum brightness difference, the system adapts to the local lighting conditions of the main subject, ensuring accurate flash control for the actual subject area.
2Measurement precision
If the flash unit emits flash before regular shooting to perform pre-emission, then the brightness difference can be calculated to determine correct flash amount, but the shooting time is increased due to additional pre-emission process
Solution Approach 1:
A pre-emission is performed before the regular shooting to capture a pre-emission image. This preliminary action allows calculation of the brightness difference between the pre-emission image and the non-emission image, which is then used to determine the correct flash amount for the regular shooting, ensuring accurate exposure control.
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 solution accurately identifies the main subject's brightness area and adjusts the flash amount, preventing chroma clip and ensuring proper exposure, thereby improving image quality by aligning flash emission with the ambient light conditions.
Implementation Method 1
The flash unit emits a flash before regular shooting to perform pre-emission when the regular shooting is instructed. In addition, the flash unit emits the flash in synchronization with the regular shooting to perform regular emission.
Implementation Method 2
The imaging device has an image sensor for taking a subject image
Data Source
AI summary
Upon depression of a release button, pre-shooting is performed before regular shooting. In the pre-shooting, flash of a predetermined amount is emitted and exposure of an image sensor is performed. A shooting frame is divided into small areas. As to each of the small areas, subject brightness of pre-emission and subject brightness of non-emission are detected to calculate a difference between them. The small area having the maximum difference is selected as a main-subject area. The brightness of the non-emission of the selected small area, which is the brightness of an ambient light applied to the main subject, is set as reference brightness. A correction amount of the flash amount of the regular shooting corresponding to the reference brightness is derived with reference to an LUT. In the regular shooting, regular emission is performed during a regular-emission time corresponding to the collected flash amount.