The present invention relates to a device for taking 360° panoramic images.

The taking of images in particular sectors, such as for example video surveillance or environmental monitoring, necessitates the use of lens assemblies with a wide field of view.

In particular, in such sectors the use of devices for taking 360° panoramic images is widespread.

Some conventional types of device are capable of instantly capturing images with a relatively limited field of view, i.e. with greatly reduced azimuth and elevation angles.

The azimuth angle is the angle of view of the lens assembly taken along the horizon and has values comprised between 0° and 360°. The elevation angle is the angle along the perpendicular, and is from 0° to +90° or to -90° with respect to the horizon.

In order to obtain a panoramic image of a given scene, devices with a limited field of view are mounted on supports with 360° scanning mechanisms, for taking images of the surrounding space with a series of exposures, and the images obtained during the scan are placed side by side in the sequence of exposures to form a mosaic of adjacent photographs.

Since these photographs are taken at different times, the resulting panoramic image does not correspond to a recording of the surrounding space made at a single moment in time.

Alternatively, a plurality of such devices are mounted on fixed supports so as to cover an overall azimuth angle of 360°.

This solution makes it possible to capture the images to be placed side by side at the same instant, but, however, it is economically unfeasible for the simultaneous use of a plurality of devices.

Other conventional types of systems are constituted by lens assemblies which, having a reduced focal length, provide a wide angle of view and which represent, therefore, the category of wide-angle optics.

One particular type of lens assembly with wide-angle optics is the so- called fisheye, which is capable of taking the scene with an azimuth of 360° and a maximum elevation of +90°, but which, however, has the drawback of providing a very distorted image.

In recent years various devices have been developed for obtaining lens assemblies capable of taking the scene with an azimuth of 360° and an elevation that exceeds 90°, by using specially-shaped mirrors which are capable of capturing light rays originating from under the horizon.

Such devices typically produce a circular image on the focal plane, with a hole in the center, and the greater the (absolute) value of the elevation under the horizon, the smaller the image will be.

In fact, the size of the circular image depends on the focal length of the optical system, and the relative size, i.e. the size of the inner radius of the hole with respect to the outer radius of the circular image, depends on the choice of maximum elevation (absolute value) that the user wishes to obtain.

The most modern solutions developed for this type of device adopt a catadioptric system in order to capture the light rays originating from angles with an elevation of up to values comprised between -60° and +45°, and an optical system with a plurality of lenses in order to dimension the field of view on the focal plane and correct optical aberrations.

In particular, US Patent no. 6373642 discloses a device with a catadioptric system which is constituted by a refractive transparent lens, with a substantially vertical axis of revolution, which has a concave surface and a reflective convex surface. The catadioptric system is capable of capturing 360° of light from the surrounding panoramic scene and reflecting it in a lens assembly with a plurality of lenses, which is arranged in a downward region, in order to dimension the field of view on the focal plane and correct the optical aberrations.

According to such patent, the anchoring of the catadioptric system to the lens assembly occurs by way of an intermediate lens which is glued to the catadioptric system on one side and to the support of the lens assembly on the other side.

Since the intermediate lens is interposed between the lens assembly and the catadioptric system, from a construction viewpoint, the resulting alignment of the two components depends on the precision with which it is positioned.

In fact, if such alignment, i.e. the coincidence of the optical axis of the catadioptric system with the optical axis of the lens assembly, is not precise within a few hundredths of a degree, these devices using an intermediate lens have the drawback of providing a deformed circular image, with the hole off- center, and of low quality because it is affected by aberration.

In particular, whereas the deformation of the image is due only to the skewing of the optical axes of the catadioptric system and of the lens assembly, the deterioration of the quality of the image, i.e. the introduction of optical aberrations, is due not only to the skewing but also to the fact that the two surfaces of the catadioptric system may not be concentric.

Moreover, the adhesive bonding of the intermediate lens requires later maintenance for realignment of the optical axes.

The aim of the present invention is to solve the above-mentioned drawbacks, by providing a device that is capable of taking panoramic images of a higher quality than the devices known today.

Within this aim, an object of the invention is to provide a device that is less sensitive to the effects of skewing of the optical axes.

Another object of the invention is to provide a device that does not require tedious maintenance for realignment of the lens assembly.

This aim and these and other objects which will become more apparent hereinafter are all achieved by a device for taking 360° panoramic images, characterized in that it comprises:

- at least one catadioptric system, which is constituted by a transparent spherical lens and has a convex surface and a reflective concave surface, which are perfectly concentric,

- at least one lens assembly, which has a substantially cylindrical shape and is arranged so that the optical axis passes through the center of curvature of said spherical lens, said lens assembly being integrally connected to said catadioptric system at said convex surface by means of a sleeve which connects said lens assembly to said catadioptric system,

- at least one image sensor for digital processing of the acquired images.

Further characteristics and advantages of the invention will become more apparent from the description of a preferred, but not exclusive, embodiment of the device according to the invention, which is illustrated by way of non-limiting example in the accompanying drawings wherein:

- Figure 1 is a side view of the device according to the invention;

- Figure 2 is an enlarged detail of the device according to the invention, in the view seen in Figure 1 ;

- Figure 3 is a perspective view of the catadioptric system.

With reference to the figures, the device according to the invention, generally designated by the reference numeral 10, comprises a catadioptric system 1 1, which is constituted by a transparent spherical lens (with center of curvature 16) and has a convex surface 12 and a reflective concave surface 13, which are perfectly concentric.

As can be seen in Figure 2, the curvature of the convex surface 12 is identified by the first radius 20 of the spherical lens, and the curvature of the concave surface 13 is identified by the second radius 21.

Moreover, the concave surface 13 is rendered reflective by way of the application of a covering which is adapted to give it such properties.

With respect to the drawings that illustrate it, the catadioptric system 1 1 is arranged so that the optical axis is substantially vertical.

The device 10 moreover comprises a lens assembly 14, which has a substantially cylindrical shape and is arranged so that the optical axis 15 passes through the center of curvature 16 of the spherical lens, and which contains an optical system of lenses to dimension the field of view on the focal plane and correct optical aberrations.

The lens assembly 14 is rendered integral with the catadioptric system

1 1 at the convex surface 12 by means of a sleeve 17 that connects it to the catadioptric system 1 1 and is followed, at the opposite end, by an image sensor 18 for digital processing of the acquired images.

Conveniently, the sleeve 17 is connected to the catadioptric system 1 1 with its upper end 17a (with respect to the drawings that illustrate it), which is opposite to the lower end 17b which is for coupling, along the optical axis

15, to the lens assembly 14.

More specifically, the sleeve 17 is rendered integral with the catadioptric system 1 1 by being inserted with its upper end 17a into a complementarily shaped groove 19 which is formed on the convex surface

12.

Such groove 19 has a circular shape which is centered on the optical axis 15 that passes through the center of curvature 16.

Preferably, the sleeve 17 is rendered integral with the catadioptric system 1 1 by insertion and adhesive bonding.

Either or both of the sleeve 17 and the lens assembly 14 are preferably made of metallic material.

The dimensions of the catadioptric system 1 1 and of the diameter of the lens assembly 14 are such that the light rays are capable of passing with the lower elevation angle 22 approximately 60° below the horizon and with the upper elevation angle 23 approximately 45° above the horizon. The overall field of view in elevation is indicated by the angle 24 of approximately 105° and the device 10 reproduces the scene in a panoramic image 25 which is circular in shape and has a hole at its center.

Figure 1 shows some objects in the panoramic scene and their reproduction on the panoramic image 25. The object 26, at elevation 23, is focalized at point 26a of the panoramic image 25, the object 27 on the horizon is focalized at point 27a and lastly the object 28 at elevation 22 under the horizon is focalized at point 28a.

The operation of the device according to the invention when taking panoramic images is as follows.

The catadioptric system 1 1 captures the light rays from all azimuth angles, i.e. from 0° to 360°, and refracts them, with passage through the convex surface 12, thus directing them toward the concave surface 13 from which they are reflected in the direction of the lens assembly 14.

The rays pass through the sleeve 17 to reach the lens assembly 14, where the optical system of lenses directs them onto the focal plane of the image sensor 18 to produce a panoramic image 25 of the surrounding space.

In the example shown, the image of the object 26 is focalized at point 26a on the outer rim of the panoramic image 25 and, similarly, the images of the objects 27 and 28 are reproduced respectively at points 27a and 28a.

It should be noted that the catadioptric system, since it has concentric spherical surfaces, does not have a preferential optical axis and this can therefore coincide, in every direction, with the optical axis of the lens assembly. In this manner, skewing between the catadioptric system and the lens assembly does not introduce optical aberrations, thus rendering the quality of the image more stable because it is less sensitive to the thermal and mechanical variations that are encountered during use of the device and to the distortions induced by possible thermal stresses owing to contact between the metal of the sleeve and the glass of the catadioptric system.

This contrivance therefore reduces maintenance operations for realigning the lens assembly with the catadioptric system and enables an assembly of the device according to less stringent alignment tolerances, thus lowering the costs of assembly.

In practice it has been found that the invention fully achieves the intended aim and objects, by providing a device that is capable of reproducing images unaffected by aberrations since it is not influenced by skewing between the optical axis of the catadioptric system and the optical axis of the lens assembly.

The invention, thus conceived, is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements.

In practice the materials employed, provided they are compatible with the specific use, and the contingent dimensions and shapes, may be any according to requirements and to the state of the art.

The disclosures in Italian Patent Application No. PD201 1A000320 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, such reference signs have been inserted for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.