Dichroic Filter Suppresses Infrared Reflections on Airlock Glass
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Solution Overview
Problem
The existing installations for detecting the uniqueness of a person in an airlock face challenges due to dazzling reflections from powerful infrared lighting on the protective glass, which reduce image readability and lead to errors in detecting single individuals, especially when the lighting is close to the camera and has a wide field, making it difficult to automatically verify the presence of a single person.
Innovation Solution
The integration of a dichroic filter between the video camera and the protective glass, along with a high-pass filter by absorption, selectively filters out angular reflections, and the optical axis is tilted downwards to facilitate detection, while the dichroic filter is positioned between the lighting means and the camera to suppress impactful reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If powerful infrared LED lighting is placed close to the video camera with a wide field, then good illumination of the viewed area is achieved, but dazzling reflections appear on the protective glass reducing image readability
Solution Approach 1:
A dichroic filter is introduced as an intermediary element between the protective glass and the video camera. This filter selectively transmits infrared wavelengths while blocking visible light reflections, thereby eliminating the harmful reflections on the protective glass while preserving the useful infrared illumination from the LEDs.
Solution Approach 2:
The optical properties of the system are modified by introducing a dichroic filter with specific wavelength-selective transmission characteristics. The filter's spectral parameters are chosen to transmit infrared wavelengths (where the LEDs operate) while blocking visible light reflections, thus changing the optical parameter spectrum to resolve the contradiction.
2Ease of operation
If the video camera objective is placed close to the protective glass, then the camera can be positioned for proper viewing, but reflections from the lighting appear in the camera field reducing image quality
Solution Approach 1:
The dichroic filter serves as a mediator between the camera and protective glass, allowing the camera to remain positioned close to the glass for ease of operation while the filter eliminates the harmful reflections that would otherwise degrade image quality.
3Object-affected harmful factors
If anti-reflective treatment is applied to the protective glass, then reflections are reduced, but the solution becomes too expensive for large or mechanically functional windows
Solution Approach 1:
Instead of expensive permanent anti-reflective coating on the protective glass, the invention uses a relatively inexpensive dichroic filter that can be easily installed and replaced. This filter provides the same reflection-reduction function at a lower manufacturing cost, especially for large or specialized windows.
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 effectively reduces or eliminates parasitic radiation, improving image quality and enabling accurate detection of a single person in the airlock without increasing costs or installation space, ensuring reliable uniqueness detection.
Implementation Method 1
a dichroic filter, for example of the multi-layer type, is provided substantially perpendicular to the optical axis X-X of the display device between the display device 2 and the protective glass 5
Implementation Method 2
a high-pass filter by absorption is provided integrated in the image display device
Implementation Method 3
reflections from the infrared lighting appear on the glass, reflections which may be in the field of the camera
Data Source
Figure 1
AI summary
The invention relates to an equipment for detecting the uniqueness of a person in a given volume in order to check that only one person at a time passes through a hatch for the optical recognition of a person outline, wherein said equipment comprises: an image visualisation device (2), lighting means (4) and a protection glass (5); characterised in that it comprises an absorption high-pass filter (7) provided on the trajectory of the optical axis (X-X); a dichroic filter (6) essentially perpendicular to the optical axis (X-X) of said visualisation device (2) and provided between the visualisation device (2) and the protection glass (5), said dichroic filter (6) being capable of displacement together with the visualisation device (2) relative to the protection glass (5), whereby the reflection generated by the LEDs on the protection glass (5) is selectively and angularly filtered.