Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/46—Colour picture communication systems
  • H04N1/48—Picture signal generators
  • H04N1/482—Picture signal generators using the same detector device sequentially for different colour components
  • H04N1/484—Picture signal generators using the same detector device sequentially for different colour components with sequential colour illumination of the original
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T11/00—2D [Two Dimensional] image generation
  • G06T11/003—Reconstruction from projections, e.g. tomography
  • G06T11/006—Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0202—Mechanical elements; Supports for optical elements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/0272—Handheld
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/12—Generating the spectrum; Monochromators
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/30—Measuring the intensity of spectral lines directly on the spectrum itself
  • G01J3/36—Investigating two or more bands of a spectrum by separate detectors
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T7/00—Image analysis
  • G06T7/90—Determination of colour characteristics
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/2803—Investigating the spectrum using photoelectric array detector
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
  • G01J3/50—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors
  • G01J3/501—Colorimeters using spectrally-selective light sources, e.g. LEDs
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/10—Image acquisition modality
  • G06T2207/10016—Video; Image sequence
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/10—Image acquisition modality
  • G06T2207/10024—Color image
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2211/00—Image generation
  • G06T2211/40—Computed tomography
  • G06T2211/416—Exact reconstruction

Definitions

• a method of reconstructing an image including an exact color image, associated computer program, device and system
• the present invention relates to a method for reconstructing an image, in particular an exact color image, the image being a matrix and representative of a static scene under predetermined light conditions.
• the present invention also relates to a computer program comprising software instructions which, when executed by a computer, implement such a method of reconstructing an image, in particular an exact color image.
• the present invention also relates to a device for reconstructing an image, in particular an exact color image and a system for reconstructing an image, in particular an exact color image comprising at least one such device.
• the spectral distribution of an illumination corresponding to such predetermined light conditions is a function of the wavelength A, denoted for example D e 5 (A) for the reference illuminant of the Des- type.
• (j, j) of the image are, for example, expressed in the following form, in the presence of a predetermined illumination of a Lambertian surface of reflectance p i; (A), for example corresponding to the reference illuminant of type D 6 5, and denoted D è 5 (A): where K is a constant of proportionality and where the domain of integration is the visible spectrum corresponding to the wavelengths in vacuum from 380nm to 780nm.
• the spectral sensitivities of an electronic image sensor (s) such as a sensor embedded within a camera are in practice different from the spectral sensitivities defined by the CIE XYZ standard.
• the colors are generally expressed in a space called RGB for Red Green Blue (in English CIE RGB for Red Green Blue).
• the lighting is also different from the theoretical reference illuminant considered.
• a light signal received at the pixel (i, j) of the image obtained by an onboard sensor within a camera with spectral responses ( r ( ⁇ ), î7 ( ⁇ 3r ⁇ ( ⁇ )) during illumination E ⁇ zl) of a Lambertian surface of reflectance p i; (/ l) is then rather generally expressed as the following:
• ⁇ i . 'j . 3 ⁇ 4 "3 ⁇ 4 ) (3 ⁇ 4 ⁇ 3 ⁇ 4 ⁇ " ( 2 ) .
• the invention relates to a method for reconstructing an image, in particular an exact color image, the image being a matrix and representative of a static scene under predetermined light conditions, the method comprising the following steps:
• each image of said plurality being captured using distinct lighting from one image to another, - digital reconstruction of said matrix image, in a reconstruction space suitable for a predetermined range of wavelengths, in particular the CIE XYZ color space, the reconstruction space being distinct from a native spectral space of the image sensor (s), by determining, for each pixel of said matrix image, the spectral components, in particular the colorimetric components of the CIE XYZ color space, by weighted combination of the spectral components of the native spectral space of the image sensor (s) ), in particular colorimetric components of the native colorimetric space of the image sensor (s), photometrically adjusted and associated with the same pixel of each image of said plurality of captured images, the weighting of each spectral component of the spectral space native of the adjusted image sensor (s), in particular of each color component of the native color space of the adjusted image sensor (s), being obtained by resolution of a system of linear
• the method of reconstructing an exact color image comprises one or more of the following characteristics, taken in isolation or in any technically possible combination:
• the method further comprises a preliminary step of selecting each lighting to be applied during said acquisition step to acquire respectively each image of said plurality of images of said scene captured by the image sensor (s), 'set of selected lights being able to scan an entire predetermined light spectrum while respecting a predetermined spectral decorrelation criterion between each pair of lights of said set;
• each lighting corresponds to a source of light of predetermined wavelength, in particular a source of colored light, or is obtained by applying at least one filter of predetermined wavelength, in particular a colored filter, combined with a source white light, the transmittances of each filter, in particular of each colored filter, selected being at least partially decorrelated according to a criterion of different dominant wavelength two by two and / or at least partially separate passband two by two;
• the method further comprises, after implementation of the preliminary selection step, a step of spectral characterization of each lighting; - The method further comprises a prior step of acquiring information on spectral sensitivities of the image sensor (s);
• the method further comprises a step of obtaining the matrix representative of both the spectral responses of the sensor of image (s) and of the spectral distribution of each illumination respectively used during the acquisition of each associated image of said plurality;
• the method further comprises a step of adjusting the exposure of said reconstructed matrix image by applying a digital gain suitable for making the luminance of said reconstructed matrix image identical to the average luminance of the scene.
• the method further comprises a step of converting said reconstructed matrix image, obtained in a reconstruction space suitable for a predetermined range of wavelengths, in particular the CIE XYZ color space, into another predetermined conversion space, in particular a predetermined color space, distinct at the same time:
• the method further comprises a step of exporting said reconstructed raster image or said constructed raster image in a predetermined file format.
• the invention also relates to a computer program comprising software instructions which, when executed by a computer, implement a method of reconstructing an exact color image as defined above.
• the subject of the invention is also a device for reconstructing an image, in particular an exact color image, the image being a matrix and representative of a static scene under predetermined light conditions, the device being suitable for implementing the following steps:
• the reconstruction space being distinct from a native spectral space of the image sensor (s), by determining, for each pixel of said matrix image, the spectral components, in particular the colorimetric components of the CIE XYZ color space, by weighted combination of the spectral components of the native spectral space of the sensor image (s), in particular colorimetric components of the native color space of the image sensor (s), photometrically adjusted and associated with the same pixel of each image of said plurality of captured images, the weighting of each spectral component of the native spectral space of the adjusted image sensor (s), in particular of each colorimetric component of the native color space of the adjusted image sensor (s), being obtained by solving a system of linear equations of which the matrix writing has at least for parameters: a matrix of predetermined value associated with the predetermined light conditions, a matrix representative of both the spectral response of the im
• the subject of the invention is also a system for reconstructing an image, in particular an exact color image, the image being a matrix and representative of a static scene under predetermined light conditions, the system comprising at least the aforementioned device.
• an image sensor (s) suitable for capturing a plurality of images and a lighting system suitable for applying a distinct lighting during each image capture of said plurality, each lighting corresponds to a light source of length of predetermined wave, in particular a colored light source, or is obtained by applying at least one filter of predetermined wavelength, in particular a colored filter, combined with a white light source, the transmittances of each filter, in particular of each colored filter, selected being at least partially decorrelated according to a criterion of different dominant wavelength two by two and / or at least partially disjoint two to two passband of them.
• said au at least one filter of predetermined wavelength, in particular a colored filter is placed between said white light source and the target scene of the image to be captured, or placed between said target scene of the image to be captured and the sensor d 'image (s).
• FIG. 1 is a schematic representation of a system for reconstructing an image, in particular an exact image in color
• FIG. 2 is a flowchart of an example of a method for reconstructing an image, in particular an exact color image
• FIG. 3 is a perspective representation in front view of the rear shell of a computer provided with an example of image capture module (s);
• FIG. 4 is a perspective representation of the shell of Figure 3 seen from behind;
• FIG. 5 is a perspective representation of part of the image capture module (s) of Figure 3,
• FIG. 6 is a perspective representation in front view of the rear shell of a computer provided with another example of image capture module (s);
• FIG. 7 is a perspective representation of the shell of Figure 6 seen from behind
• FIG. 8 is a perspective representation of part of the image capture module (s) of FIG. 6.
• a system 10 for reconstructing an image, in particular an exact image in color, is represented in FIG. 1.
• exact color image is understood to mean a theoretical image perfectly reproducing the colors of a static scene S under predetermined light conditions.
• Such a static scene S corresponds in particular to a scene associated with the high-quality photograph of a product or object O, also known under the name of “pack shot”, used to present the product in a catalog, on a website or even in a quality control process within a company.
• such a static scene S corresponds to a shooting scene in the medical field, in particular dental, in order to obtain the real shades of the dentition of the patients for the manufacture of dental prostheses by a remote prosthetist, or even dermatological for the evaluation of spots or moles.
• the system 10 for reconstructing an image, in particular an exact color image comprises an electronic device 12 for reconstructing an image, in particular an exact color image, the image being a matrix and representative of the perfectly static scene S under predetermined light conditions, an image sensor (s) C embedded within a camera, within a digital camera or even within a mobile terminal such as a smartphone ( from English smartphone) or a digital multimedia tablet with touchscreen, stationary in particular fixed on a stand or tripod, suitable for capturing a plurality of images and, where appropriate, a lighting system suitable for applying a distinct light during each image capture of said plurality, each light corresponding to a source of light (ie flash), for example colored not shown, or being for example obtained by application of at least one colored filter F combined with a source of white light (ie very wide spectral band) to illuminate the scene or the object at measuring, the white light being identical for each image capture of said plurality.
• an image sensor (s) C embedded within a camera, within a digital camera or even within a mobile terminal such as a smartphone ( from
• each colored filter F applied corresponds to a conventional colored filter or to a colored filter with a more or less wide filtration band and not only to a colored filter with a narrow filtration band such as a colored band-pass filter or to a colored filter. a colored low-pass or high-pass filter.
• the spectrum covered by the reconstruction system 10 is the least common between the image sensor (s) C and the light source used (ie colored according to a first embodiment or white according to a second embodiment. as indicated above).
• the present method is implemented with a CMOS sensor can measure from ultraviolet to infrared.
• Such a description can easily be transposed to any other image reconstruction associated with spectral sensitivities all or part outside the visible spectrum such as the ultraviolet or even infrared spectrum, in particular for image reconstruction, commonly referred to as a "false color” image, for technical imagery such as astronomical imagery, satellite imagery, medical imagery, or mining prospecting, and this using a reconstruction space adapted to the range of wavelengths of the non-visible spectrum considered and / or to the desired application, for example a “false-color” reconstruction space distinct from the CIE XYZ color space associated with the visible spectrum.
• said at least one colored filter when the light is obtained by applying at least one colored filter combined with a white light source as illustrated in FIG. 1, said at least one colored filter is placed between said white light source and the target scene of the image to be captured as shown in the figure 1 or, in a manner not shown, placed between the image sensor (s) and said target scene of the image to be captured.
• the native color space of the image sensor (s) is considered to be an RGB color space.
• the electronic device 12 for reconstructing an exact image in color comprises an acquisition module 14 configured to acquire the plurality of images of said scene S captured by the immobile image sensor (s) C. , each image of said plurality being captured by applying a distinct light from one image to another, each light corresponding to a colored light source not shown, or being obtained by applying at least one colored F filter combined with a white light source.
• the electronic device 12 further comprises a module 16 for digitally reconstructing said matrix image, in the CIE XYZ color space, by determining, for each pixel of said matrix image, the XYZ color components, by weighted combination of the colorimetric components of the 'native color space of the image sensor (s) of the camera, for example RGB colorimetric components or more generally colorimetric components supplied by the channels of the camera capable of being monochrome or multispectral, etc., associated with the same pixel and adjusted "photometrically", the photometric adjustment being the combination of the application of a mathematical conversion function reducing the colorimetric components supplied to values taking into account the exposure parameters of the image and the metadata of the image sensor.
• a module 16 for digitally reconstructing said matrix image, in the CIE XYZ color space, by determining, for each pixel of said matrix image, the XYZ color components, by weighted combination of the colorimetric components of the 'native color space of the image sensor (s) of the camera, for example RGB colori
• image (s) such as ISO, exposure time, aperture, linearity function or even the level of black of the sensor, taking into account the possible ambient lighting of the scene, for example by applying a subtraction of the colorimetric components supplied to the colorimetric components obtained during the acquisition of an image without applying any additional light.
• This technique of eliminating the possible ambient lighting of the scene is applicable for an unknown and constant ambient lighting only between the shooting with additional flash and the shooting without flash (before and / or after each color flash with a very short time in practice).
• the weighting of each colorimetric component of the native colorimetric space of the image sensor (s), in particular RGB, photometrically adjusted is obtained by solving a system of linear equations whose matrix writing has at least for parameters: a matrix of predetermined value associated with predetermined light conditions, a matrix representative both of the spectral response of the image sensor (s) and of the spectral distribution of each illumination respectively applied during the acquisition of each associated image of said plurality .
• M j the matrix representative both of the real spectral response of the image sensor (s) and of the real spectral distribution of each illumination respectively applied at the level of the pixel (i, j) during the acquisition of each image and defined as follows: with m the number of wavelengths after discretization according to the wavelength of equation (4),
• Ti j the theoretical matrix resulting from equation (5) as defined as follows: a change of reference illuminant, for example to go from D 65 to D 50 being therefore, according to the example described, taken into account mathematically directly within the theoretical matrix T ij , and W ij the matrix defined as next :
• Equation (5) amounts to W ij being the solution of the system of linear equations illustrated by the following matrix writing:
• MI WI Tu (9) with at least one predetermined theoretical value associated with the predetermined light conditions corresponding to the values of the theoretical matrix T j , a matrix M j representative of both the spectral response of the image sensor (s) and of the spectral distribution of each lighting respectively applied during the acquisition of each image.
• the electronic device 12 for reconstructing an exact color image comprises only the acquisition module 14 and the reconstruction module 16, the reconstruction module 16 receiving and / or storing the weighting of each colorimetric component of the native color space of the image sensor (s), including RGB, photometrically adjusted obtained beforehand by a computer external to the device for reconstructing an exact image in color.
• the electronic reconstruction device 12 comprises additional modules allowing an autonomous calculation (ie without dependence on an external computer) of the weighting obtained by solving the problem. system of linear equations whose matrix writing is illustrated by equation (9) above.
• such a selection module 18 is for example suitable for selecting lightings each produced by means of a colored filter, each lighting being produced by means of a colored filter, the spectral transmittance of which varies from one lighting to another. , the transmittances of each selected colored filter being at least partially decorrelated according to a criterion of a different dominant wavelength two by two and / or at least partially separate two by two passband, an overlap of the spectral passbands of the colored filters being possible but without being significant.
• the electronic reconstruction device 12 further comprises a characterization module 20 configured to characterize (ie measure) each selected lighting.
• a characterization module 20 is in particular activated only once per set of selected lights, for example at the installation of the image capture studio (s), and / or even activated periodically, for example according to an annual periodicity. following the installation of the image capture studio (s).
• Such a characterization module 20 is for example composed on the one hand of one or more measuring instruments such as a spectrometer or a luxmeter, and on the other hand of a software part for controlling this or these instruments and / or storage and processing of characterization data provided by one of these instruments or by their combination.
• the electronic reconstruction device 12 further comprises a module 22 for obtaining (ie acquiring) information on the spectral sensitivity of the image sensor (s) C.
• a module d 'obtaining 22 is in particular activated only once per set of selected lights, or else activated periodically, for example according to an annual periodicity.
• Such an obtaining module 22 is for example composed on the one hand of a measuring instrument configured to measure the spectral sensitivities information of the image sensor (s) C, and on the other hand of a software part of control of this instrument and / or storage and processing of the measurements provided by this instrument.
• the electronic reconstruction device 12 further comprises a calculation module 24 configured to obtain, from the prior characterization of each illumination and from the spectral sensitivities information of the sensor.
• image (s) C the matrix M i; representative both of the spectral response of the image sensor (s) and of the spectral distribution of each illumination respectively applied during the acquisition of each image to be combined to reconstruct the exact image in color.
• the electronic reconstruction device 12 further comprises a resolution module 26 configured to construct and solve the system of linear equations whose matrix writing is illustrated by equation (9) .
• the system of linear equations whose matrix writing is illustrated by equation (9) is also suitable for being simplified by the resolution module 26 by considering in particular that the theoretical spectral distribution of the lighting, for example corresponding to the reference illuminant of type D 65 , being constant, 7 ⁇ can also be expressed in the following form:
• the values t are therefore selected to obtain the desired image rendering, so that the weighting solution is then independent of the position of the single pixel (i, j) for any the image and then noted W.
• MW gT (13) where y is a constant to be determined and able to define whether the image reconstructed subsequently is correctly exposed or not.
• the resolution module 26 is suitable for using a Tikhonov regularization.
• the matrix M i; of equation (6) is poorly conditioned, and to improve the resolution of equation (12) the use of a Tikhonov regularization is proposed according to the example described in order to limit the norm of each vector of the matrix W and therefore prevent certain coefficients from obtaining values that are too high suitable for increasing the uncertainty when solving the system of linear equations.
• Equation (12) is then suitable for taking the following form: where D is a diagonal matrix and has a proper regularization coefficient to be determined empirically.
• the resolution module 26 is therefore configured to deliver, after obtaining by resolution of the system of linear equations, the weighting of each colorimetric component of the native color space of the image sensor (s), in particular RGB, photometrically adjusted to the module 16 for digital reconstruction of the exact color matrix image obtained in the CIE XYZ space.
• the electronic device 12 for reconstructing an exact color image also comprises an adjustment module 28 configured to adjust the exposure of said reconstructed matrix image by applying a digital gain capable of rendering the luminance of said image. reconstructed matrix image identical to the average luminance of the scene.
• a gain of the reconstructed image can be parameterized according to the image reproduction needs / wishes, or can be calculated according to a reference image of said scene S captured by the image sensor (s) under classic white light.
• the electronic device 12 for reconstructing an exact color image also comprises a conversion module 30 configured to convert said reconstructed matrix image obtained in the XYZ color space (ie CIE XYZ also called CIE 1931) into another. predetermined color space and at the same time distinct from said XYZ color space and distinct from the color space, for example RGB, native to the image sensor (s) (ie the color space directly resulting from the design of the image sensor ( s) and therefore specific to it).
• XYZ color space ie CIE XYZ also called CIE 1931
• the electronic device 12 for reconstructing an exact image in color also comprises an export module 31 configured to export said reconstructed raster image in a predetermined file format (eg JPG, DNG, TIFF, etc.) for storing said matrix image.
• a predetermined file format eg JPG, DNG, TIFF, etc.
• the device 12 for reconstructing an exact image in color comprises an information processing unit 32, formed for example of a memory 34 associated with a processor 36 such as a data processor.
• a processor 36 such as a data processor.
• CPU Central Processing Unit
• GPU Graphics Processing Unit
• the acquisition module 14, the digital reconstruction module 16, the selection module 18, optionally the characterization module 20, optionally the obtaining module 22, the calculation module 24, the resolution module 26, the adjustment module 28, the conversion module 30 and the export module 31 are each implemented, at least in part, in the form of software executable by the processor 36.
• the memory 34 of the information processing unit 32 is then able to store an acquisition software, a digital reconstruction software, a selection software, a characterization software, an acquisition software, a calculation software. , resolution software, adjustment software, conversion software, and export software.
• the processor 36 is then able to execute the acquisition software, the digital reconstruction software, the selection software, the characterization software, the obtaining software, the calculation software, the resolution software, the analysis software. 'adjustment, conversion software and export software.
• the acquisition module 14, the digital reconstruction module 16, the selection module 18, the characterization module 20, the obtaining module 22, the calculation module 24, the resolution module 26, the adjustment module 28, the conversion module 30 and the export module 31 are each produced, at least in part, in the form of a programmable logic component, such as an FPGA (standing for Field Programmable Gâte Array), or in the form of a dedicated integrated circuit, such as an ASIC (Application Specifies Integrated Circuit).
• a programmable logic component such as an FPGA (standing for Field Programmable Gâte Array)
• ASIC Application Specifies Integrated Circuit
• the computer readable medium is, for example, a medium capable of storing electronic instructions and of being coupled to a bus of a computer system.
• the readable medium is an optical disc, a magneto-optical disc, a ROM memory, a RAM memory, any type of non-volatile memory (for example EPROM, EEPROM, FLASH, NVRAM), a magnetic card or an optical card.
• a computer program including software instructions is then stored on the readable medium.
• the electronic device 12 comprises the sets of modules 14, 16, 18, 20, 22, 24, 26, 28, 30 and 31 above.
• the electronic device 12 comprises the modules 14 and 16 and part of the modules 18, 20, 22, 24, 26, 28, 30 and 31, the modules not included in the electronic device 12 being either external or then not integrated because they are optional and not retained for the embodiment intermediary considered.
• the electronic device 12 is external to the camera or to the digital camera comprising the image sensor (s) C and in particular integrated within a computer, but according to another embodiment. , not shown, the electronic device 12, in particular software, is directly embedded within the camera or the digital camera comprising the image sensor (s).
• FIG. 2 shows a flowchart of a method 40 for reconstructing an exact color image according to the second embodiment illustrated. by figure 1.
• Such a step 42 is optional and implemented upstream during the hardware design of the system for reconstructing a raster image according to the example described by selecting the predetermined light conditions to be applied such as the LEDs or filters to be used to form the lighting system and selected from an existing catalog.
• the electronic device 12 via the aforementioned characterization module 20, actually characterizes each light. in particular by measurement by means of a luxmeter.
• the electronic device 12 via the aforementioned obtaining module 22, acquires the information of actual spectral sensitivities of the image sensor (s) C.
• the electronic device 12 via the resolution module 26, constructs and solves the system of linear equations whose matrix writing is illustrated by equation (9), or else by equation (12 ) or else by equation (13) or even by equation (14) depending on the resolution capacities of the module 26 and the applicable calculation assumptions as explained previously.
• the electronic device 12 via the acquisition module 14, acquires the plurality of images of said scene S captured by the same still image sensor (s) C, each image of said plurality being captured by applying distinct lighting from one image to another
• acquisition the fact that the module 14 receives, from the camera or the digital camera, the images captured by the same immobile image sensor (s) C on board within the camera or the digital camera. 'digital camera.
• the electronic device 12 via the reconstruction module 16, constructs (ie reconstructs) the exact color image by determining, for each pixel of said matrix image, the colorimetric components XYZ, by weighted combination of the components.
• colorimetric values of the native colorimetric space of the image sensor (s) for example RGB colorimetric components, photometrically adjusted and associated with the same pixel of each image of said plurality of captured images.
• the electronic device 12 via the adjustment module 28, adjusts the exposure of said reconstructed matrix image by applying a digital gain suitable for making the luminance of said reconstructed matrix image identical to the average luminance from the scene.
• a gain of the reconstructed image can in particular be configured according to the needs / wishes for restitution of the image, or can be calculated according to a reference image of said scene S captured by the image sensor (s) under light. classic white.
• the electronic device 12 via the conversion module 30, converts said reconstructed matrix image obtained in the XYZ color space into another predetermined color space and both distinct from said XYZ color space and distinct from l color space, including RGB, native to the image sensor (s).
• step 60 the electronic device 12, via the export module 31, exports said reconstructed raster image in a predetermined file format.
• the electronic device 12 is thus an instrument for colorimetric measurement of the surface / texture of flat or volume objects.
• Such a faithful reconstruction of real colors furthermore allows an application to the simulation of such colors to virtually evaluate, for example, whether the color of a product / object is in agreement with that of other products / object or of the complexion of persons (s ).
• the present method does not require any knowledge of reflectance, gloss, texture, etc. of the objects of the scene S captured by image.
• Such a reconstruction is characterized by a low computation time associated with the combination of the images.
• such a reconstruction is suitable for being implemented for any reference illuminant, a change in reference illuminant being taken into account within the weighting resulting from the resolution of the aforementioned system of linear equations and applied according to the process, without requiring additional image capture (s).
• a change of reference illuminant only affects the combination of images without requiring additional shooting.
• Illuminants of the D series of illuminants representing natural daylight.
• Illuminants of the D 5 o, D 55 , D 65 , and D75 type are in particular advantageously envisaged.
• the method of reconstructing an image can also be implemented with different reconstruction devices 12.
• a first implementation is previously proposed with a set of a camera and a series of colored flashes, for example produced by colored light-emitting diodes.
• the reconstruction device 12 can then be qualified according to the portmanteau word "spectrophone" since the reconstruction device 12 makes it possible to benefit from both the functionalities of a telephone and of a spectrometer.
• a second implementation by a set of a camera, relatively powerful exterior lighting and a series of filters has also been described.
• external lighting is obtained, for example, by a light booth or by the use of flashes in a photo studio.
• the set of filters is positioned in front of the camera, for example a filter wheel is used.
• Another example of implementation of the method for reconstructing an image is an implementation by an assembly comprising a camera, external lighting.
• relatively powerful and a group of cameras are also possible.
• exterior lighting is obtained, for example, by a light booth or by the use of flashes from a photo studio.
• FIGS. 3 to 5 show an example of a camera and of a group of cameras arranged in an image capture module 104 itself arranged on a computer. More precisely, FIG. 3 is a schematic view of the shell of the computer seen from the front, FIG. 4 is a schematic view of the shell of the computer seen from behind and FIG. 5 is a view of a detail of the device. image capture module (s).
• the shell 100 of the computer of Figures 3 to 5 has a shell (rear) with a front face 101 and a rear face 102.
• the front face 101 is provided with the image capture module 104.
• the image capture module 104 has two parts 106 and 108.
• the first part 106 is the optical part while the second part 108 is the mechanical part for holding the optical part.
• the first part 106 has the form of a ring defining peripheral openings 110 and a central opening 112.
• the number of peripheral openings 106 in Figure 5 is 8 in number.
• the peripheral openings 106 are arranged in a circle centered on the central opening 112.
• the central opening 112 is through as shown in the three figures 3 to 5.
• the second part 108 has a substantially parallelepipedal shape, the first part 106 being positioned at one of the sums of the parallelepiped.
• the image capture module 104 includes a central camera 114 and 7 satellite cameras 116.
• the whole of the central camera 114 and the 7 satellite cameras 106 form the image sensor (s) C.
• the central camera 114 is part of the native acquisition module of the smartphone while the 7 satellite cameras 116 are added compared to the native acquisition module of the smartphone.
• the central camera 114 is positioned opposite the central opening 112. In particular, this implies that the field of the central camera 114 is not obscured by the edges of the central opening 112.
• each satellite camera 116 is positioned facing a respective peripheral opening 110.
• One of the peripheral openings 110 is positioned opposite another sensor of the native acquisition module of the computer.
• a different color filter is positioned in front of each satellite camera 116. Further, the size of the satellite cameras 116 is smaller than that of the central camera 114, so that each satellite camera 116 can be referred to as a "mini camera”.
• the satellite cameras 116 have the same dimensions.
• Figures 6 to 8 correspond to another embodiment in which the image capture module 104 has an L-shape and the additional cameras 116 are arranged in an L.
• central opening 112 is rectangular in shape, which does not obscure the native acquisition module of the smartphone.
• a device for maintaining in position such as a foot of the image capture module (s) 104.
• each flash of light being emitted by a source and having a known illumination in a range of wavelengths
• the step of solving the equation comprising: - the calculation of solution points of the equation,
• the equation is an overdetermined equation from which is extracted a plurality of sub-equations to be solved, said sub-equations forming an over-determined system to be solved and according to which solving the equation involves solving each sub-equations to obtain a plurality of solution reflectances and calculating the average of the plurality of solution reflectances to obtain the object reflectance.
• the step of solving the equation also comprises the use of a second approximation according to which the interpolation function determines the points of stability of the equation and according to which the points of stability are used in the step of solving the equation, the points of stability being the points of the interpolation function for which the solution is less sensitive to instabilities.
• the step of solving the equation also comprises the use of a third approximation according to which the illumination of the external illuminant at the instant of emission of a flash of light is equal to the illumination of the external illuminant at a previous instant, the third approximation being used during the step of solving the equation, the method comprising a step of taking a reference image by collection of the wave reflected by the object to form at least one image on a sensor in the absence of flash emitted by the source the step of solving the equation comprising an operation of subtracting a reference equation for obtain a simplified equation, the reference equation being obtained from the reference image.
• the source and the sensor are placed on the same device.
• a plurality of flashes of light are emitted, each flash having a maximum illumination in wavelength, the collection step being implemented for each flash of light emitted and at least two flashes of light have a remote maximum illumination of at least 20 nanometers.
• the second approximation is used during the step of solving the equation and in which the interpolation function is a weighted combination of basis functions sealed by a finite number of interpolation points, including cubic splines, each interpolation point being a point of stability of the equation.
• a plurality of flashes of light are emitted, each flash having a maximum illumination in wavelength, the collection step being implemented for each flash of light emitted, and the interpolation points satisfy at least the following property: the number of interpolation points is equal to the number of flashes.
• the method further comprises the steps of estimating a time interval of variation of the illumination of the external illuminant and, from the time interval of estimated variation, determination of the frequency at which the step of taking a reference image is to be repeated so that the third approximation remains valid
• the method further comprises a step of adjusting the exposure of said reconstructed matrix image by using a calibration test pattern, as can be done in particular in the field of spectroscopy.
• the method allows from a sequence of photos with flashes to be replaced with a perfect standard illuminant by calculation. and a standard eye.
• the illuminant is any type of illuminant such as a D50, D65 or A illuminant.
• the standard eye corresponds, for example, to the CIE 1931 2 ° or CIE 1960 10 ° standards. This visible example immediately extends to other spectral bands, for example an illuminant and a standard eye in IR

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• 2020
  • 2020-05-28 FR FR2005664A patent/FR3110994B1/fr active Active
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