Coded Focal Stack Imaging via Diffraction Grating
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Solution Overview
Problem
Conventional computational cameras face challenges in achieving high-resolution images and efficient depth mapping, with time-of-flight cameras requiring extensive modifications and light field cameras producing low-resolution images.
Innovation Solution
The method involves changing the focal surface within a single exposure time and per-pixel coding the sensor readout to obtain a modulation function, allowing for programmable non-planar, interleaved, and compressive focal stack imaging, which enables the recovery of full-resolution all-in-focus images and depth maps using sparsity coding and compressive sensing algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a time-of-flight camera is used to obtain three-dimensional images, then depth information can be measured, but extensive modification of sensor circuitry and on-board processing is required
Solution Approach 1:
The patent replaces the mechanical/electronic depth sensing mechanism of ToF cameras with an optical coding approach using a diffraction grating. Instead of modifying sensor circuitry to measure flight time, the system uses optical diffraction to encode depth information spatially, which is then decoded computationally. This substitution eliminates the need for complex sensor modifications while achieving depth measurement capability.
Solution Approach 2:
The patent introduces a diffraction grating as an intermediary optical element between the lens and sensor. This grating acts as a mediator that encodes depth information into spatial patterns in the captured image, allowing depth measurement without direct temporal measurement. The grating transforms the depth measurement problem from a temporal sensing challenge into a spatial encoding problem that can be solved with standard sensors.
2Adaptability or versatility
If a light field camera is used to reconstruct a three-dimensional focal stack, then post-capture refocusing is enabled, but only low resolution images are achieved
Solution Approach 1:
The patent adds a depth dimension to the traditional 2D image plane by using a diffraction grating to create a coded aperture pattern. This transforms the imaging system from capturing only 2D spatial information to capturing 3D information (x, y, depth) encoded in a single 2D image. The grating modulates light from different depths into distinct spatial patterns, enabling depth discrimination without sacrificing spatial resolution.
Solution Approach 2:
The patent applies per-pixel coding where different regions of the image sensor correspond to different depth ranges. The diffraction grating creates localized encoding patterns where specific pixel groups capture information from specific depth planes. This local differentiation allows the system to maintain high resolution while encoding depth information, as each pixel contributes to both spatial and depth information.
3Ease of operation
If a conventional camera is used to take images, then simple operation is achieved, but the user must carefully choose camera parameters and cannot achieve flexible depth control
Solution Approach 1:
The patent changes the optical parameters of the camera system by introducing a diffraction grating with specific line densities and patterns. This parameter modification enables the camera to capture coded depth information automatically. The grating's physical parameters (line spacing, orientation) are designed to encode depth ranges that correspond to typical photography scenarios, allowing the camera to operate automatically without user parameter selection while maintaining flexibility for different depth control needs.
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 flexible capture modes, higher-resolution image capture, and reduced computational resources, enabling the recovery of full-resolution all-in-focus images and depth maps from a single photograph.
Implementation Method 1
a diffraction grating is positioned in an optical path of a camera to modulate light from different depth planes into distinct spatial patterns in a captured image
Data Source
AI summary
A method and an apparatus for coded focal stack photographing are provided. The method includes: changing a focal surface within a single exposure time and per-pixel coding a sensor readout for each focal surface to obtain a modulation function M(y,z), where y⊂{y1,y2} is a two-dimensional spatial coordinate and z is a depth coordinate of a latent three-dimensional focal stack F(y,z); coding the latent three-dimensional focal stack F(y,z) into a two-dimensional sensor image I(y) by using the modulation function M(y,z); and achieving one or more of a programmable non-planar focal surface imaging, an interleaved focal stack imaging, and a compressive focal stack imaging, based on the modulation functions M(y,z) and the two-dimensional sensor image I(y).