Multispectral Camera Neutral Filter Exposure Compensation
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Solution Overview
Problem
In digital camera systems with multiple independent cameras, manufacturing-related deviations in shutter and sensor behavior lead to inconsistent exposure times and light quantities, causing color casts in multispectral images, which existing methods cannot precisely correct due to differences in color channels and light information.
Innovation Solution
A digital camera system with independent cameras equipped with separate planar digital sensors and color filter elements featuring neutral areas that allow uniform light transmission across all cameras, enabling precise compensation for exposure deviations during image processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple independent digital cameras with separate shutters and sensors are used to capture images in different spectral ranges, then the ability to record multispectral images is improved, but manufacturing-related deviations in shutter and sensor behavior cause inconsistent exposure times and light quantities, leading to color casts
Solution Approach 1:
A neutral density filter is introduced as an intermediary element in the optical path of each camera head. This filter has a neutral spectral transmission characteristic that allows precise measurement of actual light exposure without being influenced by the spectral sensitivity differences of the various color channels. The filter serves as a common reference that mediates between the different camera heads, enabling accurate determination of exposure time deviations that can then be compensated in image processing.
2Measurement precision
If position sensors are used to measure actual exposure times of individual camera heads, then rough measurements can be obtained, but the different amounts of light or image information caused by different color channels prevent precise estimates
Solution Approach 1:
The neutral density filter acts as an information mediator that provides a common reference signal across all camera heads. By measuring light exposure through this neutral filter, which has flat spectral transmission, the system obtains exposure time information that is independent of the varying spectral sensitivities of different color channels. This intermediary measurement allows precise determination of exposure deviations without being confounded by color channel differences.
3Stability of the object's composition
If the same amount of light or exposure time is required for all independent camera heads, then color balance can be maintained, but manufacturing tolerances cause deviations that lead to color casts in the multispectral image
Solution Approach 1:
The neutral density filter is installed in advance in each camera head's optical path, before image acquisition begins. This preliminary configuration ensures that during the actual multispectral imaging process, the exposure measurements can be taken simultaneously and consistently across all camera heads. The filter is positioned and configured beforehand to establish a common reference framework, allowing subsequent precise measurement and compensation of any exposure deviations without requiring adjustments during operation.
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
Ensures consistent light exposure across all cameras, allowing for accurate color balancing and reduction of color casts in multispectral images by using neutral areas for compensation calculations, thereby improving image quality.
Implementation Method 1
The neutral area of the color filter element advantageously allows light to pass through the required entire wavelength spectrum without modification or has a very high transmittance
Implementation Method 2
at least one in the direction of the input light, arranged in front of the at least one planar digital image sensor or upstream of the planar digital image sensor, corresponding to the respective narrow-band spectral range with at least one filter area
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a digital camera system (2) having at least two independent digital cameras (3.1-3.4), which capture image signals in different narrow-band spectral ranges, wherein each of the at least two independent digital cameras (3.1-3.4) comprises at least one separate two-dimensional digital image sensor (6), preferably a CCD sensor or a CMOS sensor, and at least one filter element (7.1-7.4) corresponding to the particular narrow-band spectral range connected upstream of the at least one two-dimensional digital image sensor (6) and having at least one filter region (7a.1-7a.4). The at least one colour filter element (7.1-7.4) additionally comprises at least one neutral region (7b), which is translucent in a spectral range that includes at least the different narrow-band spectral ranges of the at least two independent digital cameras (3.1-3.4), in particular in a panchromatic spectral range, and which is assigned to at least one specific neutral, in particular unused, pixel region (6b) of the associated at least one two-dimensional digital image sensor (6).