FR2660822A1 - Camera with double image acquisition producing images with very high dynamic range - Google Patents

Abstract

The present invention relates to a camera with a very high dynamic range, that is to say one which is very resistant to dazzling, including a primary image sensor (5), a secondary image information source (10) corresponding to the same image as that taken up by the primary image sensor (5) but with a much lower sensitivity, and a means of combining the signals originating from the primary image sensor (5) and from the image information source (10). Several embodiments presented, with an image memory and with a secondary image sensor, with different optical diagrams and electronic circuit diagrams.

Description

 The present invention relates to a very high dynamic range camera tolerant to significant differences in brightness in the perceived image.

 Its applications are mainly in shooting in uncontrolled outdoor lighting, welding robotics, for example.

 The devices known to date, such as tube cameras or charge transfer device tolerate very dull glare and have a dynamic ratio of the strongest illuminations on the weakest illumination simultaneously and correctly perceived, very low, of the order of one hundred.

 Other devices having an image sensor and one or more passive screens optically placed in front of the image sensor and controlled by it have a higher dynamic but exhibit significant image instability. In addition, they have a limited image quality and a response time of the order of a few tens of milliseconds.

 The present invention intends to remedy these drawbacks by restoring a stable image and a high dynamic, which may be greater than one thousand.

 To do this, the device that is the subject of the present invention comprises an objective and a primary image sensor placed in the plane of focus of the objective and a second source of image information corresponding to the same image as that sensed by the primary image sensor but with a sensitivity different from that of said sensor and a means for combining image information from said source and said sensor.

 The combination of this information, by addition or weighted average, makes it possible to form a video signal corresponding to a scale of sensitivity or extended dynamics.

 The image information source is either a second image sensor perceiving the same image as the first image sensor with less sensitivity, or an image memory combined with a means for cyclically varying the sensitivity of the primary image sensor.

 Various optical and electronic schemes are proposed in the following description, by way of examples.

 The following description, made for explanatory and non-limiting purposes with reference to the accompanying drawings, provides a better understanding of the advantages, aims and features of the present invention.

 In this description only image sensors of the charge transfer type are shown for explanatory purposes. Any other type of image sensor will therefore be in accordance with the spirit of the invention.

 Figure 1 shows a sectional view of a first embodiment of the device according to the invention having two image sensors and an optical image recovery.

 FIG. 2 represents an electronic circuit that can connect to the devices presented with reference to FIG. 1.

 FIG. 3 represents a sectional view of another device according to the invention comprising an image sensor with an alternative sensibility and image memory.

 In FIG. 1 are represented in a case B partially represented, on an optical axis A, successively, an objective 1, a transparent material strip 2 supporting a multi-layer treatment 3 and inclined with respect to the optical axis A, a primary image sensor 5 a control and control circuit 6 of the primary image sensor 5. On an optical axis A '> reflection of the optical axis A in the plate 2, there is successively a field lens 7, an objective 8, a mirror 9 and an image sensor 10. The sensors 5 and 10 and the circuit 6 comprise video signal connectors 11 and control connectors 12 of the sensors 5 and 10. Finally, a combination circuit of video signals 15 connects the connectors 1 1 of the sensors 5 and 10 to the connector 11 of the circuit 6.

 Objective 1 is of known type. It is here integrated in the box B.

 The blade 2 is a single blade with parallel faces treated by a known antireflection treatment 3 on its rear face. The field lens 7 is placed in the plane of focus of the image reflected by the blade 2 on its front face. Combined with the objective 8 and the mirror 9, its function is to form on the sensor 10 the same image that is formed without reflection on the sensor 5, but with a much lower brightness.

 The control connectors 12 of the sensors 5 and 10 are connected to the control connectors of the circuit 6 so that these sensors 5 and 10 are controlled synchronously and identically.

 The circuit 6 is of a known type used in charge transfer camera cameras, also called DTC or CCD. In particular in these cameras, the circuit 6 is directly connected to the primary image sensor 5.

 The video signal output connectors 11 of the sensors 5 and 10 are connected to the video signal combination circuit 15. The output of this circuit is connected to the video signal input connector 11 in the electronic circuit 6.

 The circuit 15 shown here in the simplest version can perform a weighted average of the signals from the connectors 1 1 of the sensors 5 and 10 or an addition of these signals as a function of the resistance values that compose it. If several connectors 1 1 exist on the sensors 5 and I 10, corresponding to the output of different signals representative of the captured image, several circuits 1 5 will be used in the device.

 The operation of the device is as follows. Since the two sensors 5 and 10 capture different illumination ranges of a given scene, the glare of the sensor 1 0 is avoided.

 For example, if the sensor 5 has a dynamic enabling it to correctly and simultaneously render the illuminances between 1 and 100 lux, the sensor 10 will be optically illuminated or electronically closed so as to correctly and simultaneously render the illuminances between 10 and 1,000 luxs. A spot illumination of 1,000 lux is correctly perceived by the sensor 10. Illumination of 1,000 lux does not cause scattering of electrical charges on the surface of the scattering sensor characteristic of glare. Indeed, the effects of glare, commonly known as blooming and smearing appear in the response curve of an image sensor that long after the saturation of the output signal.

 The addition of two non-glare signals then gives a representative image of simultaneous and correctly perceived illumination over a range of 1 to 1,000 lux.

 This first version of the device has the main advantage of using existing components and systems.

 It should be noted that, alternatively, the signals and control connections of the electronic shutter of the sensors may be different so as to adapt the sensitivity of these sensors.

 Another means of adapting these sensitivities may also be the addition of a diaphragm in the lens 8 or a filter on the optical axis from the blade 2 to the sensor 10.

 It should be noted that complementary electronic circuits, such as automatic gain control, can thus be compatible with the device. However, and alternatively it is possible to add an electronic circuit automatically controlling the sensitivities of the two sensors 5 and 10 according to the dynamics of the received image.

 It should also be noted that the sensors 5 and 10 may be matricial or linear.

 FIG. 2 represents an electronic circuit for adding signals representing images captured by three image sensors comprising optical threshold compensation. this electronic circuit is preferably adapted to the embodiments of the device comprising three image sensors receiving the same images at different sensitivities.

 In FIG. 2 there is a Look-Up Table or LUT circuit or data matching table 50, three analog-digital converters 51, three shaping circuits 52, a synchronization signal extraction circuit 53, a LUT charging circuit 54, a synchronization circuit 55, a synchronization signal input connector 56, an image signal output connector 58, a signal input connector 59 from the sensor 5, a signal input connector 60 from the sensor 10 and a signal input connector 61 of a third sensor sensing the same image as the other two sensors 5 and 10.

 The LUT shown here is adapted to provide analog video signals from digital video signals. This LUT is loaded with information by the circuit 54 comprising a permanent memory.

The video data digitized by the digitizers 51 indicates to the
LUT addresses. The output signals of the LUT correspond to the information initially loaded at these addresses.

 Its realization presents no difficulty. Its operation is as follows: it combines the digital values from the three image sensors in such a way that the most sensitive image sensor provides the signals of smaller amplitudes, the least sensitive image sensor provides the signals higher amplitudes.

 In a variant, an identical circuit but not including a LUT will make it possible to obtain a digital output, the least significant bits corresponding to the most sensitive sensor, that is to say to weaker illuminations.

 FIG. 3 shows a third embodiment of the device in which a single sensor alternately has two different sensitivities, one weak and the other high, and in which the images picked up according to different sensitivities are stored during the duration of one shot and read for the duration of the next image so as to create two signal sources representative of images, the one immediate and the other decalled in time the duration of the taking of an image said signals being processed as previously described with respect to the preceding figures.

 FIG. 3 therefore shows, in a case B partially shown, on an optical axis A an objective 1, an image sensor 25 having a video signal output connector 1 1, a signal input connector 19, electronic shutter and control connectors 12, and outside the optical axis A, an electronic shutter signal generation circuit 18, an image memory 20, a control circuit 6 of the image sensor 25 and a video signal combining circuit.

 The electronic shutter signal generation circuit 1 8 is adapted to alternately control shots for a given duration and shooting for a much shorter time, for example equal to the first divided by the dynamics of the sensor. Its implementation does not pose any particular problem to those skilled in the art.

 This control is performed on the connector 19 of the sensor 25, intended for this purpose and which is common on the image sensors of consumer camcorders.

 The image memory 20 is adapted to contain at least one image.

It is written and read simultaneously during the output of video signals on the connector 11 so that it functions globally as a FI FIFO component, ie first outputting the information that was written therein. first and retaining the information for the duration of an image pickup cycle by the sensor 25.

The images entering and leaving this memory 20 are thus synchronized, one having been taken according to a high sensitivity of the sensor 25 the other having been taken according to a low sensitivity of the sensor 25.

 These images correspond permanently to different sensitivities of the sensor 25 and can be processed in the same way as the images from the sensors 5 and 10 in the embodiments presented with reference to FIGS. 1 and 2.

 The realization of the image memory circuit 20 is of known type, in particular in the image processing cards.

 One of the advantages of this embodiment is that it makes it possible to use retro-focus objectives, ie having optical elements very close to the surface of the sensor 25.

 Another advantage is that this embodiment does not require precise mechanical and optical adjustment.

 In one variant, the images can be taken at a frequency twice that of the output and an additional memory can be written at a frequency twice that of reading, as in certain image-embedding circuits, such that two images taken quickly or combined into an image that is displayed or displayed more slowly.

 For example, the images may be taken at a rate of forty frames per second, stored at that speed after combination as described with reference to Figure 3, and replayed and displayed at a rate of twenty frames per second.

 It should be noted that this can work on the frames as well as on the complete images according to the standard used. Finally, line by line, the signals can be slowed in this way before the treatment presented with reference to FIG.

 The memory circuits making it possible to carry out these processes are of known type, in particular for the production of image-embedding circuits.

 As a variant of all the proposed embodiments, the circuit 15 may comprise a look-up table, or LUT, that is to say a value mapping table.

 Such a LUT may, in addition, be given at its output and in parallel flat screen control signals, compensation of the optical attenuation produced by this screen, and combination of the image signals.

 Any combination of the elements of the two embodiments proposed to perform similar functions remain in accordance with the spirit of the invention.

Claims (7)

1) Shooting device having at least one lens  (1) and a primary image sensor (5.25) placed in the focal plane of the lens (1), characterized in that it has a corresponding second image information source (10, 20). at the same image as that picked up by the primary image sensor (5.25) but with a sensitivity different from that of the primary image sensor (5.25) and in that it comprises a means of combination (15) information from said source (10,20) and the primary image sensor (5,25). 2) Device according to claim 1 characterized in that the second source of image information is a secondary image sensor (10) optically placed in parallel with the primary image sensor (5) and having a lower sensitivity than that of the primary image sensor (5). 3) Device according to claim 2 characterized in that it comprises an image recovery means (2,7,8,9) forming the same image on the secondary image sensor (10) and on the sensor of primary image (5), the image formed on the secondary image sensor (10) being less bright than that formed on the primary image sensor (5). 4) Device according to claim i characterized in that the source of image information is an image memory (20) read and written simultaneously, the writing from the primary image sensor (25), and in that that the sensitivity of the primary image sensor (25) is alternately high and low such that the signals from the image memory (20) and the primary image sensor (25) correspond to successive shots made by the image sensor (25) with different sensitivities. 5) Device according to claim 4 characterized in that it comprises an electronic control means (18) of the sensitivity of the primary image sensor (25). 6) Device according to one of claims 4 or 5 characterized in that it comprises a memory and in that the image sensor (10) operates at a high frequency and in that said memory is written at the frequency sensor operation and read at a lower display frequency. 7) Device according to one of the preceding claims characterized in that it comprises a correspondence table (50) performing the combination of the signals from the primary image sensor (5.25) and the information source of pictures (10,20).