# US 2017/0287667 A1 · Bimode image acquisition device with photocathode

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- Number: US 2017/0287667 A1
- Document ID: US20170287667A1
- Status: Published application
- Kind: A1
- Application number: 15/512,253
- Filed: 2015-09-22
- Published: 2017-10-05
- Earliest claimed: 2014-09-22
- Assignees: Photonis France
- Applicants: Photonis France
- Inventors: Damien Letexier; Franck Robert; Geoffroy Deltel
- Web page: https://patentgrep.com/patent/US20170287667A1

## CPC

- H01J 31/56: for converting or amplifying images in two or more colours
- H01J 31/508: {Multistage converters}
- H01J 2231/50026: Infrared
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)

## Abstract

Image acquisition device comprising a photocathode, converting an incident flux of photons into a flux of electrons, a sensor, and a processor. The device according to the invention comprises a matrix of elementary filters, each associated with at least one pixel of the sensor, the matrix being disposed upstream of the photocathode. The matrix comprises primary color filters, and transparent filters, termed panchromatic filters. The processor is configured to: calculate a quantity, termed a useful quantity (F), for determining whether at least one zone of the sensor is in conditions of weak or strong illumination, the useful quantity being representative of a mean surface flux of photons or of electrons which is detected on a set of panchromatic pixels of the sensor; forming, only if the zone is in conditions of strong illumination, an image of the zone on the basis of the primary color pixels of this zone.

## Claims

### Claim 1

Image acquisition device (100; 400; 500) comprising:
a photocathode (110; 410; 510), configured to convert an incident flux of photons into a flux of electrons;
a sensor (130; 430; 530) composed of a matrix of elements named pixels; and
processing means (140; 440; 540);
wherein:
the device (100; 400; 500) comprises a matrix (120; 420; 520) of elementary filters, each associated with at least one pixel of the sensor, said matrix being located upstream from the photocathode, such that an initial flux of photons passes through said matrix before reaching the photocathode;
the matrix comprises primary color filters (R, G, B; Ye, Ma, Cy), a primary color filter not transmitting a part of the visible spectrum complementary to said primary color, and filters transmitting the entire visible spectrum, named panchromatic filters (W); and
the processing means (140; 440; 540) are configured to:
calculate a quantity, termed a useful quantity (F), for determining whether at least one zone of the sensor is under conditions of weak or strong illumination, the useful quantity being representative of a mean surface flux of photons or electrons detected on a set of pixels named panchromatic pixels of the sensor, each panchromatic pixel being associated with a panchromatic filter (W);
forming, only if said zone is under conditions of strong illumination, a color image of said zone on the basis of the pixels in this zone associated with primary color pixels.

### Claim 2 (depends on 1)

Device (400; 500) according to claim 1, wherein the photocathode (420; 520) is located inside a vacuum chamber (450; 550), and in that the matrix of elementary filters (420; 520) is located on an input window (451, 551) of said vacuum chamber.

### Claim 3 (depends on 1)

Device (500) according to claim 1, wherein the photocathode (520) is located inside a vacuum chamber (550) closed by a bundle of optical fibers (552), and in that each elementary filter of the matrix of elementary filters (510) is deposited on one end of an optical fiber of said bundle (552).

### Claim 4 (depends on 1)

Device (400) according to claim 1, wherein the sensor (430) is a photosensitive sensor, in that the processing means (440) are configured to calculate a quantity representative of a mean surface flux of photons, and in that the device also comprises:
multiplication means (461) configured to receive the flux of electrons emitted by the photocathode, and supply a secondary flux of electrons in response; and
a phosphor screen (462), configured to receive the secondary flux of electrons and supply a flux of photons in response, named the useful flux of photons, the sensor (430) being arranged to receive said useful flux of photons.

### Claim 5 (depends on 1)

Device (400) according to claim 1, wherein the sensor (530) is a sensor sensitive to electrons, configured to receive the flux of electrons emitted by the photocathode, and in that the processing means (540) are configured to calculate a quantity representative of a mean surface flux of electrons.

### Claim 6 (depends on 1)

Device (100; 400; 500) according to claim 1, wherein the panchromatic filters represent 75% of the elementary filters.

### Claim 7 (depends on 6)

Device (100; 400; 500) according to claim 6, wherein the matrix of elementary filters (110; 410; 510) is generated by the periodic two-dimensional repetition of the following pattern:
M
=
{
R
W
G
W
W
W
W
W
G
W
B
W
W
W
W
W
}
in which R, G, B represent the primary color filters red, green and blue respectively and W represents a panchromatic filter, the pattern being defined except for an R, G, B permutation.

### Claim 8 (depends on 6)

Device (100; 400; 500) according to claim 6, wherein the matrix of elementary filters (110; 410; 510) is generated by the periodic two-dimensional repetition of the following pattern:
M
=
{
Ye
W
Ma
W
W
W
W
W
Ma
W
Cy
W
W
W
W
W
}
in which Ye, Ma, Cy represent the primary color filters yellow, magenta and cyan respectively, and W represents a panchromatic filter, the pattern being defined except for a Ye, Ma, Cy permutation.

### Claim 9 (depends on 1)

Image acquisition device (100; 400; 500) according to claim 1, wherein the processing means are configured to:
determine that said zone has weak illumination, if the useful quantity (F) is less than a first threshold, and
determine that said zone has strong illumination, if the useful quantity (F) is more than a second threshold, the second threshold being higher than the first threshold.

### Claim 10 (depends on 9)

Device (100; 400; 500) according to claim 9, wherein if the useful quantity (F) is between the first and second thresholds, the processing means are configured to combine a monochrome image and the color image of said zone, the monochrome image of said zone being obtained from the panchromatic pixels of this zone.

### Claim 11 (depends on 1)

Image acquisition device (100; 400; 500) according to claim 1, wherein the processing means are configured to:
form a monochrome image from the complete set of panchromatic pixels of the sensor;
segment this monochrome image into homogeneous regions; and
for each zone of the sensor associated with a homogeneous region, calculate the corresponding useful quantity independently to determine if said zone is under weak or strong illumination conditions.

### Claim 12 (depends on 1)

Image acquisition device (100; 400; 500) according to claim 1, wherein the matrix of elementary filters (110; 410; 510) also includes infrared (IR) filters that do not transmit the visible part of the spectrum, wherein each infrared filter is associated with least one sensor pixel named infrared pixel.

### Claim 13 (depends on 12)

Image acquisition device (100; 400; 500) according to claim 12, wherein, when a zone is under weak illumination conditions, the processing means are configured to:
compare a predetermined infrared threshold (FIR th) and a quantity named the secondary quantity (FIR), representative of a mean surface flux of photons or electrons detected by the infrared pixels of this zone;
when said secondary quantity is higher than the predetermined infrared threshold, superpose a monochrome image obtained from the panchromatic pixels of this zone and a false color image obtained from the infrared pixels of this zone.

### Claim 14 (depends on 12)

Image acquisition device (100; 400; 500) according to claim 12, wherein, when a zone is under weak illumination conditions, the processing means are configured to:
starting from the infrared pixels in this zone, identify sub-zones of this zone, which detect a mean surface flux of photons or electrons homogeneous in the infrared spectrum;
for each sub-zone thus identified, compare a predetermined infrared threshold (FIR th) and a quantity named the secondary quantity (FIR), representative of a mean surface flux of photons or electrons detected by the infrared pixels of this sub-zone;
when said secondary quantity is higher than the predetermined infrared threshold, superpose a monochrome image obtained from the panchromatic pixels of this sub-zone and a false color image obtained from the infrared pixels in this sub-zone.

### Claim 15 (depends on 1)

Image acquisition device (100; 400; 500) according to claim 1, wherein the matrix (120; 420; 520) of elementary filters consists of an image projected by an optical projection system.

### Claim 16

Image formation method, implemented in a device (100; 400; 500) comprising a photocathode (120; 420; 520) configured to convert an incident flux of photons into an flux of electrons, and a sensor (130; 430; 530), including the following steps:
filter an initial flux of photons to supply said incident flux of photons, this filtering making use of a matrix of elementary filters (110; 410; 510) including primary color filters (R, G, B; Ye, Ma, Cy), a primary color filter not transmitting a part of the visible spectrum complementary to said primary color, and filters transmitting the entire visible spectrum, named panchromatic filters (W);
calculate a quantity, termed a useful quantity (F), for determining whether at least one zone of the sensor is under conditions of weak or strong illumination, the useful quantity being representative of a mean surface flux of photons or electrons detected on a set of pixels named panchromatic pixels of the sensor, each panchromatic pixel being associated with a panchromatic filter (W);
form, only if said zone is under conditions of strong illumination, a color image of said zone on the basis of the pixels in this zone associated with primary color filters (R, G, B; Ye, Ma, Cy).