3D Camera Calibration Using Orientation-Sensitive Pattern

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Solution Overview

Problem

Conventional three-dimensional calibration methods for imaging systems, particularly in scanning bound documents, face challenges when camera fields of view do not overlap significantly, limiting the visibility of the calibration pattern and requiring tedious and potentially damaging procedures.

Innovation Solution

An orientation and position sensitive calibration pattern is used, comprising unique sub-areas that can be partially imaged by each camera, allowing for the determination of coordinate pairs and optimization to construct a three-dimensional camera calibration model without requiring the entire pattern to be visible within the cameras' fields of view.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional calibration schemes require the calibration pattern to be completely visible within all camera images, then calibration accuracy can be maintained, but the calibration becomes extremely difficult to satisfy when camera fields of view do not overlap significantly

Engineering Contradiction:

Improvecalibration accuracyVSAvoidcalibration feasibility

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The calibration pattern is divided into multiple sub-areas, where each sub-area contains a unique configuration of features and orientation/position markers. This segmentation allows different cameras to capture different sub-areas rather than requiring all cameras to see the entire pattern simultaneously, resolving the contradiction between maintaining calibration accuracy and enabling calibration when fields of view do not overlap.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each sub-area of the calibration pattern is designed with locally unique features and orientation/position markers that enable identification and calibration without requiring global visibility of the entire pattern. This local quality approach allows each camera to perform calibration based on its own field of view containing a single unique sub-area.

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If flat-bed platen scanners apply force to the spine or binding region to ensure documents are within depth of focus, then image quality improves, but the spine region of the document can be damaged

Engineering Contradiction:

Improveimage qualityVSAvoiddocument damage

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

Instead of applying force to the bound document to make it conform to the scanner (traditional approach), the system inverts the approach by scanning the document in its natural face-up position without applying stress to the binding region. The calibration system adapts to the document's natural state rather than forcing the document into a predetermined scanning configuration.

Inventive Principle:

Principle #13The other way round (Inversion)

3Productivity

If flat-bed platen scanners require documents to be lifted and repositioned after each page scan, then complete document scanning is achieved, but the process becomes tedious and time-consuming

Engineering Contradiction:

Improvescanning completenessVSAvoidscanning time

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The system performs preliminary calibration by capturing images of the calibration pattern with unique sub-areas and orientation/position markers before scanning the actual document pages. This preliminary calibration establishes the geometric model and distortion parameters, enabling subsequent document pages to be scanned and automatically corrected without manual repositioning or adjustment for each page.

Inventive Principle:

Principle #10Preliminary action

4Object-affected harmful factors

If platen-less scanners scan documents in face-up position without additional stress to binding region, then document damage is reduced, but three-dimensional calibration becomes more difficult when camera fields of view do not overlap

Engineering Contradiction:

Improvedocument stressVSAvoidcalibration complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The calibration system changes the parameters of the calibration pattern by incorporating orientation/position markers and unique feature configurations in each sub-area. This parameter change allows the calibration to work with partial pattern visibility and non-overlapping fields of view, reducing calibration complexity for platen-less scanners while maintaining document stress reduction.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7623274B1Three-dimensional calibration using orientation and position sensitive calibration pattern

Publication Date: 2009.11.24 GOOGLE LLC

AI summary

Systems and methods using an orientation/position-sensitive calibration pattern for three-dimensional calibration of an imaging system, such as one used in a process for scanning documents are disclosed. The method generally includes positioning the pattern on a support, capturing images using cameras to be calibrated, each image containing at least a unique orientation and position sensitive sub-area of the pattern, determining a set of coordinate pairs of corresponding points in the image and the pattern for each image utilizing image data and pattern information, and performing optimization utilizing the sets of coordinate pairs to calibrate relative position, orientation, zoom, and/or lens distortion, etc. of each camera so as to construct a three-dimensional camera calibration model. The pattern is generally comprised of overlapping sub-areas of a minimum portion of the pattern.