Vignetted-aperture correction for spectral cameras with integrated thin-film Fabry–Perot filters

Goossens, Thomas; Geelen, Bert; Lambrechts, Andy; Hoof, Chris Van

doi:10.1364/ao.58.001789

Cited by 12 publications

(15 citation statements)

References 16 publications

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“…The pupil walking effect was observed on the pupil plane. It is induced by spherical aberration of imaging optics and is a common effect in wide angle lenses [31][32][33][34]. The lens combination (L1, L2, and L3 lenses) was designed for the wide angle fundus image thus pupil walking was observed.…”

Section: Discussionmentioning

confidence: 99%

Light color efficiency-balanced trans-palpebral illumination for widefield fundus photography of the retina and choroid

Son

Toslak

et al. 2022

Preprint

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A wide-field fundus camera, which can selectively evaluate the retina and choroid, is desirable for better detection and treatment evaluation of eye diseases. Trans-palpebral illumination has been demonstrated for wide-field fundus photography, but its application for true-color retinal imaging is challenging due to the light efficiency delivered through the eyelid and sclera is highly wavelength dependent. This study is to test the feasibility of true-color retinal imaging using efficiency-balanced visible light illumination, and to validate multiple spectral imaging (MSI) of the choroid. 530 nm, 625 nm, 780 nm and 970 nm light emission diodes (LED)s are used to quantitatively evaluate the spectral efficiency of the trans-palpebral illumination. In comparison with 530 nm illumination, the 625 nm, 780 nm and 970 nm light efficiencies are 30.25, 523.05, and 1238.35 times higher. The light efficiency-balanced 530 nm and 625 nm illumination control can be used to produce true-color retinal image with contrast enhancement. The 780 nm light image enhances the visibility of choroidal vasculature, and the 970 nm image is predominated by large veins in the choroid. Without the need of pharmacological pupillary dilation, a 140° eye-angle field of view (FOV) is demonstrated in a snapshot fundus image. In coordination with a fixation target, the FOV can be readily expanded over the equator of the eye to visualize vortex ampullas.

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Section: Discussionmentioning

confidence: 99%

Light color efficiency-balanced trans-palpebral illumination for widefield fundus photography of the retina and choroid

Son

Toslak

et al. 2022

Preprint

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show abstract

“…A generalized model and practical method to estimate model parameters and a correction of undesired shifts in measured spectra for the common case of vignetted aperture is proposed in [15] . The most important cause for the angle dependence of the camera system under investigation is identified as the functionality of Fabry-Pérot filters on Filter-on-Chip CMOS sensor systems.…”

Section: Discussionmentioning

confidence: 99%

Measurement principle and arrangement for the determination of spectral channel-specific angle dependencies for multispectral resolving filter-on-chip CMOS cameras

Dittrich

Bichra

Pfützenreuter

et al. 2019

Photonics and Education in Measurement Science 2019

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Filter-On-Chip CMOS sensor equipped cameras are a convenient, reliable and affordable approach for the parallel acquisition of spatial and spectral information. The combination of pixel-arranged spectral filter matrices on CMOS sensors increases their integration density and system complexity by several times compared to standard RGB cameras. Due to their system design, these cameras have an increased spectral crosstalk and specific dependencies from the angle of radiation. The paper will show how to develop and set up a measurement arrangement for the characterization of the channel specific spectral sensitivities under different angles of radiation. These characterizations are necessary to develop a more robust model for the camera pixel-value correction to ensure the comparability and reproducibility of the measured values. Therefore, a measurement setup to investigate the influence of the angle of incident radiation on filter-on-chip CMOS sensors was developed. After initial investigations with a setup in which the camera was simply rotated and investigations with a lens and changed f-number confirmed that the angle influence results in a measurable difference in the sensor response, a new measurement arrangement was developed to investigate this behavior more precisely. The developed measurement arrangement allows multispectral resolving image sensors to be radiated with collimated light at reproducible angles of incidence and with adjustable wavelengths. By comparing the measured values with illuminances measured using a calibrated photodiode in the same setup and with the same parameters, it is possible to evaluate the angle dependence based on quantum efficiency curves according to the EMVA 1288 standard. The investigations carried out, the developed principles and the realized semi-automatic measurement arrangement will be shown and explained to characterize the capabilities of multispectral resolving filter-on-chip CMOS sensor equipped cameras for applications in industry and biomedicine.

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“…Thus, a large number of filter curves are incorporated into the signal of a pixel, whose measurement would take a lot of time. Goossens et al 14,15 presented a mathematical method that takes into account the shift of the filter curves for each angle within the numerical aperture such that not all angles must be measured. However, the presented method does not consider crosstalk between the individual channels.…”

Section: Oblique Incidence Of Light On the Sensormentioning

confidence: 99%

Detailed characterization of a mosaic based hyperspectral snapshot imager

et al. 2020

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Some widely used optical measurement systems require a scan in wavelength or in one spatial dimension to measure the topography in all three dimensions. Novel hyperspectral sensors based on an extended Bayer pattern have a high potential to solve this issue as they can measure three dimensions in a single shot. This paper presents a detailed examination of a hyperspectral sensor including a description of the measurement setup. The evaluated sensor (Ximea MQ022HG-IM-SM5X5-NIR) offers 25 channels based on Fabry-Pérot filters. The setup illuminates the sensor with discrete wavelengths under a specified angle of incidence. This allows characterization of the spatial and angular response of every channel of each macropixel of the tested sensor on the illumination. The results of the characterization form the basis for a spectral reconstruction of the signal, which is essential to obtain an accurate spectral image. It turned out that irregularities of the signal response for the individual filters are present across the whole sensor.

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Vignetted-aperture correction for spectral cameras with integrated thin-film Fabry–Perot filters

Cited by 12 publications

References 16 publications

Light color efficiency-balanced trans-palpebral illumination for widefield fundus photography of the retina and choroid

Light color efficiency-balanced trans-palpebral illumination for widefield fundus photography of the retina and choroid

Measurement principle and arrangement for the determination of spectral channel-specific angle dependencies for multispectral resolving filter-on-chip CMOS cameras

Detailed characterization of a mosaic based hyperspectral snapshot imager

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