Plenoptic imaging device with a virtual intermediate image
A plenoptic imaging device for forming an image of the light field of an object, includes a sample holder suitable for holding the object; a main optical assembly, arranged to focus rays of the light field of the object, at a distance z 0 , referred to as the object distance, from the sample holder, which distance is smaller than an object focal distance f 1 from the main optical assembly so as to form an intermediate optical image (I v ) of the object in an intermediate image plane at a distance z 1 from the optical assembly; an assembly for sampling the light field, which assembly is suitable for acquiring spatiodirectional information on the rays forming the virtual image and for forming the image of the light field.
1 . A plenoptic imaging device for forming an image of the light field of an object (O), comprising:
a sample holder (SH) configured to hold said object,
a main optical assembly (LP), arranged to focus rays of the light field of said object, at a distance z o called the object distance from the sample holder less than an object focal distance f 1 of said main optical assembly, so as to form an intermediate virtual image (I v ) of said object in an intermediate image plane at a distance z 1 from said optical assembly,
a light-field-sampling assembly (LFS) configured to acquire spatio-directional information of the rays forming the virtual image and to form said image of the light field, said light-field-sampling assembly comprising:
a matrix-array photodetector (Det)
a microlens array (ML) arranged at a distance a from the intermediate image plane, the photodetector being arranged at a distance b from the microlens array, each microlens being of diameter d 2 and having a focal length f 2 and being configured to form a micro-image (μ l ) of a respective portion of the virtual image of the object on a respective segment of the photodetector, each said segment comprising a plurality of pixels, the micro-images forming said image of the light field,
wherein an image numerical aperture NA im,Lp of the main optical assembly is less than or equal to an image numerical aperture NA im,ML of each microlens.
2 . The device as claimed in claim 1 , wherein the photodetector is in a plane that is conjugated with the intermediate image plane by the microlens array.
3 . The device as claimed in claim 1 , wherein
d
1
z
1
+
a
+
b
=
d
2
b
,
with d 1 the diameter of the aperture of the main optical assembly.
4 . The device as claimed in claim 1 , wherein a distance c between the microlens array and the main optical assembly is greater than said distance z 1 .
5 . The device as claimed in claim 1 , comprising a processor configured to implement a refocusing algorithm allowing a depth image or a 3D image of the object to be reconstructed from said image of the light field.
6 . The device as claimed in claim 1 , wherein the main optical assembly and the microlens array are configured for X-rays.
7 . The device as claimed in claim 6 , wherein the main optical assembly is a photon sieve.
8 . The device as claimed in claim 6 , comprising an X-ray source irradiating said object so as to form said light field of the object.
9 . A method of use of a plenoptic imaging device, comprising a main optical assembly (LP) and a light-field-sampling assembly (LFS), according to claim 1 , said method comprising the following steps:
A. placing said device so that a distance zo called the object distance between an object to be imaged and said main optical assembly is less than an object focal length f 1 of said main optical assembly so as to form an intermediate virtual image (I v ),
B. acquiring, with the light-field-sampling assembly, spatio-directional information of the rays forming the virtual image in order to form an image of the light field of the object.