Depth from Defocus Imaging Using Spatial Frequency Analysis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing depth from defocus (DFD) techniques face challenges in accurately measuring distance due to difficulties in distinguishing between lens focus blur and inherent image blur, and require either increased sensitivity or longer exposure times, which can introduce noise or reduce light, affecting measurement accuracy.
Innovation Solution
An imaging apparatus that captures images with varying focal positions, allowing for a broader focal range without stopping down the aperture, enabling stable distance measurement from a small number of images with uniform blur, and extending the depth of field for accurate distance calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a mask with a special structure is inserted into the aperture to create periodic zero points in the spatial frequency spectrum, then distance measurement accuracy is improved, but the amount of incident light decreases
Solution Approach 1:
The patent extracts the function of creating spectral nulls from the physical mask structure and implements it through digital signal processing. By removing the mask and using software-based spatial frequency analysis, the system maintains measurement accuracy while preserving light intensity.
Solution Approach 2:
The patent replaces the mechanical/optical mask structure with a computational approach. Instead of using physical components to manipulate light, the system uses digital image processing and spatial frequency spectrum analysis to achieve the same measurement objective without blocking light.
2Illumination intensity
If exposure time is increased to compensate for reduced light, then more light is captured, but subject blur increases and spectral components decrease
Solution Approach 1:
The patent extracts the distance measurement function from the temporal domain (requiring long exposure) and transfers it to the spatial frequency domain. By analyzing spatial frequency spectra of shorter exposure images, the system achieves accurate measurements without the blur that would result from prolonged exposure.
3Productivity
If the aperture is significantly stopped down to extend depth of field, then the reference image can be obtained from fewer images, but the amount of incident light decreases
Solution Approach 1:
The patent replaces the mechanical aperture stopping method with a computational approach. Instead of physically reducing the aperture to extend depth of field, the system uses digital image processing and spatial frequency analysis to achieve the same effect while maintaining light intensity.
4Illumination intensity
If sensitivity of the imaging device is increased to compensate for reduced light, then light capture is improved, but noise in the captured image increases
Solution Approach 1:
The patent extracts the measurement function from the intensity domain (requiring high sensitivity) and implements it in the spatial frequency domain. By analyzing spectral ratios rather than relying on high-sensitivity detection, the system achieves accurate measurements without amplifying image noise.
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 approach allows for accurate and stable distance measurement from a small number of images, reducing noise and maintaining light intensity, while extending the depth of field for a broader measurement range without the need for multiple images or significant aperture stopping.
Implementation Method 1
an imaging unit configured to capture an image of a subject
Implementation Method 2
a lens which collects light into the imaging device
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
An imaging apparatus (10) includes: an imaging unit (11); a focal range control unit (12) configured to cause the imaging unit (11) to capture a first image (31a) and a second image (31b) which have mutually different focal ranges, changing a focal position of the imaging unit (11); a reference image generation unit (13) configured to generate, using the first image (31a) and the second image (31b), a reference image (32) to be used as a blur standard; and a distance measurement unit (14) configured to measure a distance to the subject based on a difference in blur degrees between the reference image (32) and each of the first image (31a) and the second image (31b). The focal ranges of the first image (31a) and the second image (31b) are independent of each other, and an out-of-focus space is provided between the focal ranges.