The field of the invention is in the field of imaging.
More particularly, the field of invention is that of imaging using a single matrix detector for estimating the distance of objects in an observed scene.
Said plénoptiques cameras have this function. The figure
1 shows the architecture of such a camera. In the various figures, it has adopted the following policies, the optics are represented by bold lines and light rays in fine lines. It essentially comprises a lens 1, a die 2 of microlenses 20 and a matrix sensor 3. The lens 1 comprises an exit pupil 4. Operation is as follows. The image of an object plane 5 is formed by means of the objective 1 in an intermediate plane 6. Each object point M, thus an image M 'in the intermediate plane. This intermediate plane is arranged in front of the matrix of microlenses 2 20 so that the image of the plane given by the microlenses 20 is done in the plane of the matrix detector 3. Thus, according to the lens aperture and the position of thej "in the detector plane. For example, in Figure 1, the point M 0 has as intermediate image point M ' 0 which gives as images on the detector the three points M" 0 i, M " 0 2 and M " 0 3 and the point M has the intermediate image the ΜΊ point which gives as images on the detector the triplet of points M" n, m " 12 and m" 13 . the position of the different images M of the detector allows to determine both the position of Mj object point and its distance from the objective.

For further information on plénoptiques cameras, see the US reference application 7,962,033 entitled "Methods and Apparatus for Full-Resolution Light Field Capture and Rendering" and US2013 / 0308035 entitled "Image Pickup Apparatus". Refer also to the publications entitled "The Focused Plenoptic Camera", A. and T. Lumdaine Gerogiev and "Single Lens 3D Camera with Extended Depth-of-Field", "PerwaB C. and L. Wietzke. Concerning

distance estimation methods of objects in a scene imaged by one or more optical systems include the publication "Depth resolution in three-dimensional images," Jung-Young Son, Oleksii Chemyshov, Chun Hae Lee Min- Chul Park and Sumio Yano. Opt. Soc. Am. A / Vol. 30, No. 5 / May 20.

Clearly we seek to achieve with this type of camera the best possible resolution both in the same object plane and depth. However, a depth resolution increases with the known methods is always accompanied by a loss in spatial resolution. In addition, the distance range within which it is possible to estimate the distance of the objects observed is fixed and defined by the lens parameters chosen. Figure 2 illustrates this problem. It is the uncertainty I on an estimated distance D Eaccording to said estimated distance for a given focal length lens. Thus, at an estimated distance of 200 meters is a measurement uncertainty of about 15 meters, which can be high. This uncertainty is related to the precision of the image processing method, that is to say the ability to estimate sub-pixelliques shifts between different images of the same point. The curve of Figure 2 is performed with a capability of estimating these offsets tenth of a pixel, which corresponds to a fairly common value. Terminals B I N F and B SUP of the curve represent the camera's depth of field to the lens focal length. In this case, the depth of field is between 30 meters and 300 meters. You can choose larger terminals, for example by changing the definition criterion for calculating the depth of field or the change by applying a defocusing to a focal value of the given objective but uncertainty remains high for some remote beaches.

To overcome this problem, different approaches have been explored. Thus, EP 2,244,484 entitled "Digital imaging method for synthetizing an image using data Recorded with a camera plenoptic" implements variable focal length microlens. We find this approach dabs the publication of the company Raytrix entitled "Single Lens 3D Camera with Extended Depth-of-Field, C. and L. PerwaB Wietzke". More recently, the publication entitled "An Electrically tunable plenoptic camera using a liquid crystal microlens array", Review of Scientific Instruments 86, 053101 (2015) has a plenoptic camera incorporating a microlens array of electrically controllable focal length. The disadvantage of these approaches is that they require sophisticated arrays of microlenses.

The optical system of the invention does not have these disadvantages and operates with a simple and identical microlens array. It is based on the following analysis.

If you change focal length, the previous curve varies. Thus, Figure 3 shows the uncertainty I on an estimated distance D Eaccording to said estimated distance for lenses of different focal lengths which are rated from 1 1 to 19. To give an order of magnitude, the focal lengths are between 30 and 200 millimeters. For a given object in the distance, there exists an optimal focal giving minimal measurement uncertainty. For example, for 50 meters, the optimal objective lens 18 and the measurement uncertainty with this goal does not exceed 1 meter. Thus, it can be determined for each target distance range for which the measurement uncertainty is minimal. With the above objectives, the ranges shown is obtained in Figure 4. For reasons of clarity, the shorter focal objectives Jan. 1, 12 and 13 are not shown in this figure, the beaches are very close together. Using either an optical but a series of different focal optics, we can significantly reduce the measurement uncertainty. Of course, we can not change lenses permanently. The proposed solution is to use a zoom objective, that is to say, a varifocal lens, operating continuously or discretely to allow for the most accurate estimate of the distance of objects in the scene adjusting the focal length.

More specifically, the invention relates to an optical system having a zoom type lens and an optical detection unit to estimate depth of said sensor array to depth estimation comprising a microlens array and an array detector, the matrix of microlenses being arranged so that the image of the back focal plane is focused by the microlens array in the plane of the matrix detector,

characterized in that said optical system includes means for calculating, for a first zoom ratio and for a given object, the estimated distance of the object and the measurement uncertainty of this estimate, based on said first focal and said estimated distance and the estimated distance being known, optimization means for determining at least a second zoom ratio which corresponds to a measurement uncertainty lower on this estimate.

Advantageously, the optimization means comprise an iterative loop for determining an optimum focal length which corresponds to the uncertainty of minimum extent on said estimation, each iteration comprising at least a focal length change, the calculation of the estimated distance corresponding to the new focus and the measurement uncertainty of this estimate.

Advantageously, the iterative loop is performed in a focal plane of the zoom constant or within a focal plane of the zoom variable.

Advantageously, the iterative loop is performed at opening of constant or variable zoom.

Advantageously, the zoom is a continuously variable focal length zoom or the zoom is a multifocal lens.

Advantageously, the optical detection unit to depth estimation is an infrared detection unit.

The invention will be better understood and other advantages will appear on reading the description which follows, given without limitation and from the appended figures among which:

1 shows a plenoptic camera with fixed focal length according to the prior art;

2 shows the measurement uncertainty on an estimated distance based on a distance to a plenoptic camera known fixed focal length;

Figure 3 shows the measurement uncertainty of an estimated distance based on the distance to a camera plenoptic including increasing focal objectives;

4 shows, for the previous objective, the minimum measurement uncertainty range depending on the distance;

Figures 5 and 6 show a plenoptic back according to the invention in two extreme configurations of focal length;

7 shows an enlarged view of the receiving part of the previous plenoptic zoom.

8 shows, for plenoptic zoom continuously variable focal length, the minimum measurement uncertainty based on the estimated distance.

The object of the invention is an optical system having a zoom type lens and an optical detection unit to estimate depth of said sensor array to depth estimation comprising a microlens array and an array detector, the matrix microlenses being arranged so that the image of the focal plane of the zoom is focused by the microlens array in the plane of the matrix detector.

To ensure proper operation of the depth estimation, it is necessary to know the distortion and field curvature zoom for different this zoom factor values.

There are two zoom categories. These are firstly the continuously variable focal length zoom lenses and also zooms known of multifocal goals. The invention applies to both categories.

For example, Figures 5 and 6 show a plenoptic Z zoom according to the invention in two extreme configurations of focal length. 7 shows an enlarged view of the receiving part of the previous plenoptic zoom.

This zoom Z includes two fixed lens groups denoted G1 and G2 and three lens groups D1, D2 and D3 mobile. The movement of these three lens groups in a determined movement can change both the zoom ratio and keep the development in its focal plane. Thus, Figure 5 shows the zoom in a long lens configuration and Figure 6 the zoom in a short focal configuration. The zoom ratio is about 7 in the case of this lens. Other zoom configurations are possible.

The zoom lens according to the invention being plenoptic, it comprises, where is a vector in the zoom detector, an optical detection unit to estimate depth of said sensor array to depth estimation comprising a microlens array and a MML DM matrix detector as seen in Figure 7 which shows an enlarged view of the circled portion of figures 5 and 6 above.

As stated previously, there are, for each estimated distance, focal zoom giving a minimum measurement uncertainty IMIN- This minimal measurement uncertainty based on the estimated distance D E is shown in Figure 8. This uncertainty depends terminals depth of field of the optical system. On this curve, the measurement uncertainty does not exceed 1 meter to 00 meters away. The zoom ratio changes along this curve. In the case of Figure 8, the focal length varies by a factor 8 between the bottom of the curve and the top of the curve. Zooming necessarily has a maximum focal length. Therefore, this curve has a linear appearance as it is possible to increase the focal length of the lens. When the focus reaches its maximum value,

When the user makes a measurement, he does not know, in principle, to estimate the distance and therefore he can not know a priori zoom the lens in its smallest measurement uncertainty at the distance. To this end, the optical system comprises:

- means for calculating, for a first zoom ratio and for a given object, the estimated distance of the object and the measurement uncertainty of this estimate, based on said first focal length and said estimated distance, and

- the estimated distance is known, optimization means for determining at least one second zoom ratio which is a measurement uncertainty of less than this estimate.

The average estimated distance calculation and measurement uncertainty at this distance are carried out according to conventional methods used in plénoptiques cameras, zoom the lens in and openness are known.

The first selected focal length can be, for example, the smaller zoom ratio, or its greater focus or an intermediate focal length. It is possible that this choice is arbitrary focal length, the object of which is to measure the distance is not within the depth of field range of the retaining focal length, in this case, we start the measurement with a focal more smaller or larger depending on the case until a first distance evaluation to initiate the distance estimation optimization process.

There are different techniques for performing the optimization of the measure. For example, optimization means comprise an iterative loop for determining an optimum focal length which corresponds to the uncertainty of minimum extent on said estimation, each iteration comprising at least a focal length change, the calculation of the estimated distance corresponding to the new focus and the measurement uncertainty of this estimate. One can thus quickly converge to the optimal focal length. This process can be automated, optimization means automatically adjusting the zoom ratio to achieve the desired accuracy.

This loop iterations may be performed in a focal plane of the zoom constant. It is also, in order to change terminals distances accessible to zoom, practicing a known defocusing and start the process of iterations with the new terminals and defined.

One can also work to open the zoom constant to facilitate distance calculation in the iteration loop. In this case, for a point in the object field, the number of microlenses ensuring the measurement remains constant. One can also work to open the variable zoom in order to improve the measurement uncertainty. In this case, for a point in the object field, the number of microlenses ensuring measurement increases with the opening.

CLAIMS
1. An optical system having a zoom type lens (Z) and an optical detection unit to estimate depth of said sensor array to depth estimation comprising a microlens array (ML) and a matrix detector (DM), the matrix microlenses being arranged so that the image of the focal plane of the zoom is focused by the microlens array in the plane of the matrix detector,

characterized in that said optical system includes means for calculating, for a first zoom ratio and for a given object, the estimated distance (D E ) of the object and the measurement uncertainty (I) of this estimate, according to said first focal length and said estimated distance and the estimated distance being known, optimization means for determining at least a second zoom ratio which corresponds to a measurement uncertainty lower on this estimate.

2. Optical system according to Claim 1, characterized in that the optimization means comprise an iterative loop for determining an optimum focal length which corresponds to the uncertainty of minimum extent on said estimation, each iteration comprising at least one change focal length, the calculation of the estimated range for the new focus and the measurement uncertainty of this estimate.

3. An optical system according to claim 2, characterized in that the iteration loop is performed in a focal plane of the zoom constant.

4. An optical system according to claim 2, characterized in that the iteration loop is performed in a focal plane of the zoom variable.

5. An optical system according to claim 2, characterized in that the iteration loop is performed to open the zoom constant.

6. Optical system according to Claim 2, characterized in that the iteration loop is performed to open the variable zoom.

7. Optical system according to one of the preceding claims, characterized in that the back is a continuously variable focus zoom.

8. Optical system according to one of claims 1 to 6, characterized in that the back is a multifocal lens.

9. Optical system according to one of the preceding claims, characterized in that the optical detection unit to depth estimation is an infrared detection unit.