Aerial Camera Slit Shutter Distortion Correction
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Solution Overview
Problem
Aerial photographs taken with slit diaphragm shutters suffer from distortions due to varying exposure times of sensor lines caused by forward flight movement, leading to image blurring or motion blur, especially when the terrain has a varying height profile.
Innovation Solution
Assigning a relative flight altitude to each sensor line and determining a compensation factor based on flight speed, focal length, and current altitude to correct distortions line by line, using a digital 3D model of the terrain and measurement data from navigation and inertial sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a slit diaphragm shutter is used to reduce exposure time and minimize motion blur, then image blurring is reduced, but distortion occurs due to varying exposure times of individual sensor lines
Solution Approach 1:
The patent divides the image correction process into segment-specific operations, where each sensor line is corrected individually based on its own exposure time and drift characteristics. This segmentation allows precise compensation for the varying exposure times caused by the slit diaphragm shutter without introducing uniform distortion across the entire image.
Solution Approach 2:
The patent changes the exposure time parameter for each sensor line based on its position and the drift speed of the projected image. By adjusting the exposure time parameter individually for each line, the system compensates for the motion blur caused by forward flight movement while maintaining image sharpness.
2Reliability
If individual sensor lines are exposed at different times to reduce motion blur, then image blurring is reduced, but distortion occurs due to varying average exposure times
Solution Approach 1:
The patent implements a feedback mechanism where the actual exposure times of individual sensor lines are measured and used to calculate drift speed. This feedback information is then used to adjust the exposure time parameter for each line, creating a closed-loop system that compensates for motion blur while preventing distortion.
Solution Approach 2:
The patent makes the exposure time parameter dynamic rather than static, allowing it to vary for each sensor line based on real-time drift speed measurements. This dynamic adjustment enables the system to adapt to changing flight conditions and maintain image sharpness without introducing distortion.
3Reliability
If exposure time is shortened to reduce motion blur during forward flight, then image blurring is reduced, but image quality deteriorates due to insufficient light exposure
Solution Approach 1:
The patent changes the exposure time parameter dynamically for each sensor line based on its specific drift speed and position. This allows the system to use the minimum necessary exposure time for each line, reducing motion blur while maintaining sufficient light exposure for image quality through precise, individualized parameter optimization.
Data Source
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AI summary
The invention relates to a method for correcting a distortion in an aerial photograph (1) caused by a flight movement in the forward direction, the photograph being taken with an aerial camera (2) from a flying object (3). The aerial photograph (1) is captured by a surface sensor (4) of the aerial camera (2) having a plurality of photo-sensitive pixels (5), the sensor lines (6) of which sensor, in particular rows, are exposed at different, successive exposure times by means of a slit diaphragm shutter (7) which moves over a projected image, so that each individual sensor line (6) senses a strip of terrain (9) of the terrain (8) flow over at the different exposure times. According to the invention, a relative flight altitude, which is current in particular at the exposure time, above the strips of terrain (9) captured by the respective sensor line is assigned to the individual sensor lines (6). Furthermore, a compensation factor is separately determined for each of the individual sensor lines (6), wherein the factor depends on an air speed of the flying object (3), a focal length of the aerial camera (2) and the relative flight altitude assigned to the respective sensor line, and corrects the distortion in the aerial photograph (1) for the lines based on the respective compensation factor.