The invention relates to a method for production of an image recording and/or reproduction device comprising an optical image recording and/or reproduction system, an image sensor and/or generator and/or a synchronisation system, said image being processed for improvement by digital image processing means.
The invention is particularly aimed at optimising the aperture of the optical system of an image recording and/or reproduction device.
The invention also relates to a device obtained by such a method for production.
The known techniques for design or for production of such image recording and/or reproduction devices, such as digital or argentic cameras, video projectors or image projectors, consist of initially choosing the properties of the material elements of the device, in particular the optical image system for visualisation or projection, the image recorder or generator and the synchronisation system. Subsequently, where necessary, provision is made for the means for digitally processing images in order to correct defects of at least one of the material elements of the device.
In particular, to design a device's optical system, the first step is to establish a schedule of technical specifications, that is to say the bulk, the focal ranges, the aperture ranges, the field image, the performances expressed either in spot size or in MTF (modulation transfer function) values, and the cost are specified. From this schedule of technical specifications, a type of optical system is selected and, using a software tool of optical calculations, such as the “Zemax” tool, the parameters of this system are selected which best correspond to the schedule of specifications. This definition of the optical system is done interactively. In general, an optical system is designed in a way which presents the best central image quality and, usually, the quality of the image edge is of an inferior quality.
Furthermore, the usual techniques are such that the optical system is designed in such a way as to obtain a determined level of distortion, of vignetting and of blur, in order that the optical system can be compared to other optical systems.
Moreover, for digital photographic devices, the characteristics of the sensor, namely: the pixel quality, the pixel area, the number of pixels, the microlens matrix, the anti-aliasing filters, the pixel geometry and the disposition of pixels are also selected.
The usual technique consists of selecting the sensor of an image recording device independently of the other elements of the device and, particularly, of the image processing system.
An image sensor or generating device also usually comprise one or several synchronisation systems such as an exposure system and/or a focusing system “autofocus”
Thereby, to specify an exposure system which controls the aperture and exposure time, and possibly the sensor gain, the means of measuring are determined, in particular the image zones on which the exposure will be measured as well as the affected weight of each zone.
For a focusing system, the number and the position of image zones which will be used when focusing are determined. Settings are also specified, for example, a motor speed setting.
In all cases, these specifications are applied regardless of the presence of a digital means of image processing.
The invention derives from an observation that these classical techniques for the design and creation of devices do not permit that full advantage can be taken of the possibilities offered by the means for digitally processing images.
Thereby, the invention concerns, generally, a method for production of an image recording and/or reproduction device comprising an optical image recording and/or reproduction system, an image sensor and/or generator and/or a synchronisation system, said image being processed for improvement by digital image processing means;
A method in which parameters of the optical system and/or the image generator and/or the synchronisation system are determined or selected from the capacities of the digital image processing means. The production costs are thus minimised and/or the production of the image recording and/or reproduction device is optimised.
It is noted that the deliberate degradation of the distortion characteristics of an optical system in favour of the correction of other aberrations, the distortion being corrected using a system for digital image processing is already known. With such an optical system, which relaxes the constraints of distortion, provision can be made for a lower number of surfaces and, therefore, a reduction in costs. Alternatively, performance can be increased without increasing the total cost. It is equally possible to obtain systems with a wider angle.
But the current technology neither demonstrates nor suggests satisfactory solutions to the diverse problems which are resolved by the invention, in particular:
Thereby, according to the first of these aspects, the invention concerns a method for production of an image recording and/or reproduction device comprising an optical image recording and/or reproduction system, an image sensor and/or generator and/or a synchronisation system, said image being processed for improvement by digital image processing means,
In one embodiment, the method is such that the digital image processing means further include, in the known way, the means for distortion correction.
Generally, it is noted that even though the method according to the invention calls upon the means for distortion correction, it concerns the production of a device in which at least one parameter of the optical image recording and/or reproduction system and/or the synchronisation system based on the capacities of the digital image processing means other than the correction of distortion is determined or chosen.
In one embodiment, for which provision is made for the means of both blur and vignetting correction, in relation to a classic optic the vignetting and the central clarity are degraded in order to obtain, in terms of overall consistence of quality, a superior aperture.
In one embodiment, which can be used independently of the first aspect of the invention mentioned herewith, the optical system is of a variable focal length, furthermore the method is such that:
The digital image processing means include the means for correction of lateral chromatic aberrations and/or of blur, and/or of vignetting, and/or of noise and/or of parallax compensation, and
According to yet another of its aspects, which can be employed independently from the other aspects mentioned herewith, the invention concerns a said method of embodiment of an image recording and/or reproduction device comprising an optical image recording and/or reproduction system, an image sensor and/or generator and/or a synchronisation system, said image being processed for improvement by digital image processing means,
The method being such that at least one parameter of the image sensor and/or generator and/or of the synchronisation system from the capacities of the digital image processing means, is determined or chosen.
Significations of the diverse terms employed are hereby defined:
The term digital image processing means refers, for example, to a software programme and/or a component and/or equipment and/or a system permitting the modification of an image.
Digital image processing means can be completely or partially integral to the device, as in the following examples:
In the case where the digital image processing means are integral to the device, in practice the device corrects its own fault.
When using a set of devices, for example a fax with a scanner and a printer, the user can, however, use only part of the set of devices, for example, if the fax can also be used as a stand alone printer; in this case, the digital means for image processing must each correct their own faults.
The digital means for image processing can be totally or partially integral to a computer, for example in the following way:
In the case where the digital image processing means are integral to a computer, in practice the digital image processing means are compatible with multiple devices, and at least one device in a set of devices can vary from one image to another.
In one embodiment, the levels of performances of the optical system and/or the image sensor and/or generator, and/or the synchronisation system are adjusted, in particular the average performance levels, in terms of the performance of digital image processing means.
Thereby, the overall level of performances being dictated by the part of the device which presents the weakest level of performance, a priori the level of performance is fixed according to the capacities of the digital image processing means and the optical system, the image sensor or generator and/or the synchronisation system are chosen which have inferior performances but which can meet the levels determined by the digital image processing means.
The performances of a device are in particular, its cost, its dimensions, the minimum quantity of light it can receive or emit, the quality of the image and the technical qualities of the optic, of the sensor and the synchronisation. The performances of the digital image processing means are the limits of its capacity and its means.
According to one embodiment:
The capacities of the digital image processing means are, for example, defined in the following way:
The compensation of the parallax is the maximum value of the parallax which can be corrected by the digital image processing means. This value is, for example expressed in the number of pixels. It is noted that when the focal distance varies, the position of the optic centre can change and thus cause a change in the parallax. The parallax is the variation of the position of the optic centre which intervenes when the focal distance varies.
Clarity is measured, for example, in values which are denominated as BXU which is a measurement of the surface of the blur spot, as is described in the published article in the “Proceedings of IEEE, International Conference of Image Processing, Singapore 2004”, entitled “uniqueness of Blur Measure” by Jerome BUZI and Frederic GUICHARD.
In simple terms, the blur of an optical system is measured in the image, called “impulsive response”, from an infinitely small point situated in the plane of sharp focus. The BXU parameter is the variation of the impulsive response (that is to say its average surface). The processing capacities can be limited to a maximum value of BXU.
The digital image processing means can be specified for the distinctive correction of the various causes of lack of clarity, in particular, to take into account the symmetry of blur spots. For example, an astigmatic blur spot presents two axes of perpendicular symmetry, whilst a “comma” type blur spot presents only one perpendicular axis.
Vignetting is the variation in light in the field of image. For example, the maximum authorised percentage of vignetting in the image is specified.
The noise is specified, for example in its gap type, its shape, the dimensions of the noise spot as well as its coloration.
The moiré phenomena appear in spatial high frequencies. They are corrected using anti-aliasing filters. The digital image processing means are specified by the anti-aliasing filter parameters.
It should be noted that anti-aliasing filtering can be carried out, either by optical or digital means.
For the contrast, the digital image processing means are specified by the minimum value of the amplitude of variations in contrast which can be improved.
Concerning the optical system parameters, it should be remembered that decentering is an optical system property which allows for the correction of perspective effects.
Concerning the image sensor and/or generator: the term “quality of pixels” refers to the sensitivity, the yield and the image noise produced by each pixel, as well as the group of colours which can be captured and/or feasibly reproduced. The dynamics of the capturable signals by the pixels also constitutes one of their qualities.
For the synchronisation system which allows for automatic focusing, it is noted that focusing can be effected in different ways, in particular, by controlling the position of mobile elements of the optical system or by controlling the geometry of the deformable optical elements.
In one embodiment, at least one parameter of the image sensor or generator is determined or chosen, in particular the dimensions, using the digital image processing means which comprise the means to reduce noise. It is therefore, possible to obtain a given level of noise for a given quantity of light, whilst reducing the cost of the sensor.
It is noted that the classic technique for the design of an image sensor and/or generating device consists of choosing an optical system and a sensor or generator and, subsequently, reducing the noise but within the limits of the available calculating power.
In one embodiment, taking into account the capacities of the digital image processing means, the characteristics of the optical system and device are firstly determined, in particular the dimensions, the blur, the characteristics of colour, contrast, noise, details, secondly the characteristics of the optic are determined taking into account the capacities of the image processing, as well as the characteristics of the image sensor or generator, in particular the number of pixels.
In one embodiment, the optical system is preferably of a fixed focal length and its aperture is optimised for taking into account the digital image processing means which comprise the means for correction of blur, in particular variable in accordance with the position in the field of image, and/or the means for correcting the vignetting and/or the means for correcting distortions.
It is thereby possible to maximise the aperture of the optical system. In relation to an image recording device which has no means for correction, it is also possible to use:
In one embodiment, the device includes a synchronisation system which notably permits control of focusing, and the digital image processing means comprise the means for correction of blur and/or the means for correction for the depth of field, the parameters of the optical system, in particular the position of the image plane function of the focusing distance and/or of the focal distance, are determined or chosen in such a way as to ensure that the clarity of images is noticeably homogeneous in the image field.
Thereby, maximum clarity is not necessarily sought before digital processing in the image zone which serves as the focus. In this case, in one embodiment, the focusing point is practically independent from the image serving as the focal point whereas normally, because of the variable curving in the field of image the focusing distance varies with the focusing zone.
Thereby, the measurement of the focusing takes into account the ulterior correction. For example the measurement takes into account the position in the field and of the level of correction of blur function of the position in the field. It is not sought therefore to obtain maximum clarity for the brut measurement as with a classic device but for the measurement which has been corrected in this way.
The setting for focusing also takes into account the capacities of correction. A certain level of blur is acceptable which depends on the focal distance and the known capacities for correction, and maximum clarity is not sought during focusing as with a typical device.
The maximum level of blur in the field is therefore lower, and the minimum level in the field can be higher than in a typical device and is adapted to the capacities of the means for processing the image.
The variation in the blur level when the focal length varies without changing the focal point can therefore be greater than in a classic device, which permits the simplification of the optic and, therefore, a reduction of costs, since the synchronisation system of the focusing can take into account the focal distance and adapt the focusing when the focal distance varies.
In one embodiment, the device comprises an exposure synchronisation system and the exposure parameters of this synchronisation system are determined or chosen by taking into account the capacity for correction of the correction algorithms of noise and/or contrast and/or movement blur being part of the digital image processing means, for example to obtain, after correction, a given level in terms of noise, contrast and blur.
When noise is corrected, it is possible, for the same quality of image, to call for a higher sensitivity in relation to a situation where noise correction is not called for.
Thereby, the measurement of exposure taking into account the capacities for ulterior correction, which, for example, diminish noise by four, it is possible to set a shorter exposure time in order to avoid movement blur and/or set a higher sensor gain to enable shots in low light or to reduce the aperture and increase the field depth. In other words, the advantages are greater latitude of choice of exposure parameters. In brief, in relation to existing systems, shorter exposure times, apertures which are more closed and greater gains in the quantity of light given in the scene can be chosen.
When contrast is corrected, it is possible, for the same quality of image, to call for a lower sensitivity in relation to a situation where contrast correction is not called for.
When contrast is corrected, the exposure measurement taking into account the ulterior capacities for correction, can call for a lower sensor gain for those images which have dark zones than for those which do not have them, in the sense that the parts which are in the dark zones are correctable by the contrast correction algorithms at the cost of an increase in noise.
According to one embodiment:
Thereby, with the digital image processing means carrying out corrections a priori and/or appropriate compensations, it is possible to optimise, in particular by minimising, the number of optical elements of the optical system, it is possible to optimise the nature of the materials of the optical system, to reduce the cost and to optimise the treatment of optical surfaces. The colour of the materials of the optical system can be chosen at will, in as much as the means for correcting colours are prescribed. Assembly tolerances can be relaxed. The variation values admitted by the parallax in accordance with the focal distance can be increased, and it is also possible to relax the focusing characteristics.
The possibility of compensating the variations of the parallax constitute an important advantage for video devices, both amateur and professional (or other animated image recording devices) since, in these applications, it is important to keep a quasi constant parallax when the focal distance or the focusing varies in such that movement interference of the image is undetectable to the eye.
With the invention, conversely to usual optics, a variation of the parallax is permitted which is compensated by the digital processing means.
Furthermore, it is known that a zoom type objective permits variable focal distances whilst conserving, for diverse focal distances, the same focusing. A zoom type objective is, therefore, relatively onerous since it must respect this constraint of having to keep the focus for a diverse value of focal distances. The invention, in allowing the relaxing of focusing characteristics, permits the production of a less onerous zoom with the same performances, the focusing characteristics being compensated by the digital image processing means. In other words, the zoom can be produced at a cost which can be close to that of a “varifocal” objective, that is to say of an objective which does not require the maintaining of focusing when the focal distance varies.
According to one embodiment, the dimensions of the device are determined according to the capacities of the digital image processing means.
Notably, it is possible to minimise the bulk of the device. In particular, the sensor can be of reduced dimensions. It is possible to reduce the size of pixels, within the limits of the capacities of the digital image processing means for correcting the faults resulting from a smaller size of pixel and in particular the resulting increase of noise. Also, it is possible to reduce the size of pixels and increase the aperture of the optic within the limits of the capacities of the digital image processing means for correcting the faults resulting from an increase in the aperture of the optic and notably the resulting increase in blur. In the same way, it is possible to minimise the bulk of the optical system by making provision for a number of lenses which render the bulk inferior to the focal distance, on condition that the digital image processing means are prescribed for correcting the faults resulting from there being a large number of optical elements. The dimensions of the synchronisation system can also be reduced, the digital image processing means permitting, for example the minimising of the displacement of the optical elements of the optical system and therefore energy consumption, which brings about a reduction of the electrical energy volume of powering batteries as well as the synchronisation motors.
In one embodiment, the digital image processing means are at least partially included in the image recording and/or reproduction device.
The digital image processing means can also be at least partially separate from the image recording and/or reproduction device as in the case, for example, as explained herewith, where the digital image processing means are in a computer.
According to one embodiment, the choosing of parameters of the optical system consists of selecting the optical system from amongst pre-existing systems. It is also possible to choose the parameters of the sensor or generator by selecting the sensor or generator from amongst pre-existing systems.
For example, it is possible to choose simple pre-existing optical systems, in particular with a minimum number of lenses and, therefore, less onerous, the digital image processing means compensating for the faults which bring about the simplicity of the optical system.
In one embodiment, the digital image processing means comprise the means for acting upon the lack of clarity of the optical system and/or the image sensor and/or the generator and these means are such that they permit the production of an image recording and/or reproduction device which does not have a synchronisation system permitting focusing.
In other words, it is not necessary to displace or deform the optical elements to achieve focus if the means for correction of clarity can obtain a sufficiently clear image without means of focusing.
For example, if a fixed focal image recording device can obtain clear images of 80 cm to infinity, this device being without an automatic focusing system, and where using a sensor which has a greater number of pixels whilst conserving the same qualities of clarity (of 80 cm to infinity), without calling upon an automatic focusing system, provision is made for the digital image processing means which reduce the size of the blur spot in order to achieve the required result. As a further example, it is possible to produce, starting from digital image processing means which reduce the size of the blur spot, a recording device with a wider aperture, for example by going from 2.8 to 1.4, whilst conserving the same depth of field.
According to one embodiment: an overall schedule of specifications is defined for the device, as is, correlatively, notably in an interactive way, a schedule of specifications for the optical system and/or a schedule of specifications for the image sensor and/or generator and/or a schedule of specifications for the synchronisation system, and an overall schedule of specifications for the digital image processing means,
In order that the transfer of performances of the schedule of specifications of the optical system, and/or the schedule of specifications of the image sensor and/or generator, and/or the schedule of specifications of the synchronisation system to the schedule of specifications of the digital image processing means is possible, and/or in order that the method permits the reduction of production costs for the device.
The term schedule of specifications for a device, or of one of its components, or the digital image processing means refers to the group of technical specifications which the device, its components or the digital image processing means must conform to.
In one embodiment, the image recording and/or reproduction device comprises a synchronisation system and at least one parameter of the image sensor and/or generator and/or of the synchronisation system is chosen from amongst the capacities of the digital image processing means.
In one embodiment, the optical system is a zoom lens.
In one embodiment:
In one embodiment, at least one parameter is determined or chosen of the image sensor or generator relative to the dimensions of the sensor or generator, the digital image processing means comprising the means for reducing noise permitting the minimisation of the dimensions of the image sensor or generator.
In one embodiment in which the device comprises an synchronisation system, at least one parameter of the optical system, in particular the position of the image plane function of the focusing distance and/or of the focal distance, is determined or chosen in such a way as to ensure that the clarity of images is noticeably homogeneous in the image field, the synchronisation system taking into account the position of the image plane function of the focusing distance and/or of the focal distance.
In one embodiment for which the device comprises a synchronisation system, at least one parameter of the synchronisation system, in particular the exposure parameters, is determined or chosen taking into account the capacity for correction of the correcting algorithms of noise and/or contrast and/or movement blur being part of the digital image processing means.
In one embodiment, the digital image processing means comprise the means for acting upon the lack of clarity of the optical system and/or the image sensor and/or generator, these means being such that they permit the production of image recording and/or reproduction devices which do not have a focusing synchronisation system.
In one embodiment, the dimensions of the device are determined according to the capacities of the digital image processing means.
In one embodiment, the digital image processing means are at least partially included in the image recording and/or reproduction device.
In one embodiment the digital image processing means are at least partially separate from the image recording and/or reproduction device.
In one embodiment, the optical system is selected from amongst pre-existing optical systems.
In one embodiment, the sensor or generator is selected from amongst pre-existing optical systems.
In one embodiment, the digital image processing means comprise a means for improving the quality of the image by acting on at least one of the parameters of the group comprising: the vignetting of the optical system and/or of the image sensor and/or generator, the lack of clarity of the optical system and/or of the image sensor and/or generator, the noise, the moiré phenomena, and/or the contrast.
In one embodiment, at least one parameter is determined or chosen of the optical system from the group comprising: the number of optical elements of the system, the nature of the materials constituting the optical elements of the optical system, the cost of the materials of the optical system, the treatment of optical surfaces, the assembly tolerances, the values of the parallax according to the focal distance, the characteristics of the aperture, the mechanisms of the aperture, the possible focal range, the focusing characteristics, the focusing mechanisms, the anti-aliasing filters, including, the depth of field, the characteristics linking the focal distance and the focusing, the geometric distortions, the chromatic aberrations, the decentering, the vignetting, the clarity characteristics.
The invention also concerns an image recording and/or reproduction device obtained by the method of production defined herewith.
Other characteristics and advantages of the invention appear with the descriptions of some of the embodying modes, this being done by reference to the drawings annexed herewith on which:
a and 4b form the group of diagrams showing the adjustments used in the frame of the invention,
a to 6d are diagrams showing the properties of an optical system of a device according to the invention and of a classic device, and
a and 7b are schemas showing an example of the selection of an optical system for a device according to the invention.
Such a device, for example for image recording, includes, in part, an optical system 22, notably of one or several optical elements such as lenses, destined to form an image on a sensor 24.
Although the examples mainly concern a sensor 24 of an electronic type, this sensor can be of another type, for example a photographic film in the case of an “argentic” device.
Such a device also comprises a synchronisation system 26 acting on the optical system 22 and/or on the sensor 24 in order to focus so that the image plane is found in the sensor 24, and/or so that the quantity of light received in the sensor is optimised by the exposure settings and/or the aperture, and/or so that the colours obtained are true, by using the synchronisation of white balance.
Finally, the device includes digital image processing means 28.
Alternatively, the digital image processing means are separate from the device 20. It is also possible to allow for a part of the digital image processing means inside the device 20 and a part outside.
Digital processing of the image is done after images have been recorded by the recorder 24.
A reproduction device presents an analogous structure to an image recording device. In place of a sensor 24, there is an image generator 24′ receiving the digital image processing means 28′ and supplying the images to an optical system 22′, such as an optical projection system.
In the following, for the clarity of the exposure, reference is only taken from image recording devices.
The invention consists of the capacities of the digital image processing means 28, 28′ for determining or choosing the parameters of an optical system 22, 22′, and/or of an image sensor and/or generator 24, 24′ and/or of a synchronisation system 26.
The diagram in
Starting from these performance levels that can be obtained with the digital image processing means, the levels of performance can be chosen for each of the components of the device which are before processing, considerably inferior to the performance levels obtained after the application of the digital image processing means. In this way it is observed that the performance levels of the optical system can be established at level 30′, the performance levels of the sensor and of the synchronisation system can be established at levels, respectively 32′ and 34′.
In these conditions, in the absence of digital image processing, the level of performances of the device will be at the lowest level, for example level 36′ corresponds to the lowest level 30′ for the optical system.
The digital image processing means are preferably those which are described in the following documents:
“Method and system for producing formatted information related to defects of appliances in a set of appliances and formatted information destined for image processing means”.
These digital image processing means permit the improvement of the image quality by acting on at least one of the following parameters:
This defect is illustrated by
Depth of field: when the optical system is focused on a selected object plane, the images of this plane remain clear as well as the images of the objects close to this plane. “Depth of field” refers to the distance between the nearest object plane and the object the furthest away which remain clear in the image.
As is represented in
A description of an embodiment permitting uniformity of clarity in the field of image is described in relation to
It is firstly noted that the image surface of an object plane does not constitute a perfect plane but a curves known as a field curve. This curve varies according to diverse parameters including the focal distance and the focusing. Thereby, the position of the image plane 50 depends on the zone on which the focusing is carried out. In the example represented on
To simplify the focus synchronisation system, the image plane is in a position 58, intermediately between positions 54 (corresponding to a focus on a zone close to the edge of the image), and 50 (corresponding to a focus on a zone in the centre of the image). The union of the digital image processing means 28 with the focus synchronisation 26, permits the limitation of movement of the plane 58 for focusing, which reduces energy consumption by the synchronisation system and permits a reduction in volume of its components.
Represented on the diagram in
b is an analogous diagram of that which is in 5a showing the synchronisation properties of a device produced according to the invention, starting from the hypothesis that the digital image processing means permit the correction of blur up to a BXU value equal to 4. The curve represented on this diagram in
In one embodiment, the digital image processing means include the means for improving clarity which negate the need for a synchronisation of focusing.
As a comparable example, the diagrams in
The classic device is a digital photographic device integral with a mobile phone having a VGA sensor, that is to say a resolution of 640×480 without a focusing system.
The classic device has an aperture of 2.8 whereas the device obtained with the method according to the invention has an aperture of 1.4.
a, which corresponds to the classic device is a diagram on which the abscissa represents the percentage of the field of image, the origin corresponding to the centre of the image. The ordinate represents the vignetting V.
In the schema of
c is a diagram in which the ordinate represents the blur, expressed in BXU, according to the field of image (the abscissa) for a classic device. In this classic device, the blur characteristic is 1.5 at the centre and 4 at the edge of the image.
The diagram in
In other words, surprisingly, a degraded optic was chosen concerning the clarity at the centre, whereas it is possible to obtain the same results only with a classic device, with, what is more, a larger aperture. It is also to be noted that at the edges, the optic of the device according to the invention represents an analogous quality to that of the classic optic, this result can be obtained because of the degradation of the vignetting in comparison to a classic optic.
The diagrams in
In the example represented in
The optic represented by the schema in
The choice of an optical system is based on the fact that the correction algorithm of the modulation transfer function is effective from a value of 0.3. In these conditions, it is observed that with the optic in
In other words, with a correcting algorithm, the optic represented in
Number | Date | Country | Kind |
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0550163 | Jan 2005 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR06/50022 | 1/18/2006 | WO | 00 | 9/17/2007 |