Classifications

• • 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
• • 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
  • G01J3/462—Computing operations in or between colour spaces; Colour management systems
• • 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
  • G01J3/51—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using colour filters
• • 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
  • G01J3/51—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using colour filters
  • G01J3/513—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using colour filters having fixed filter-detector pairs
• • 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
  • G01J3/52—Measurement of colour; Colour measuring devices, e.g. colorimeters using colour charts
  • G01J3/524—Calibration of colorimeters
• • 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
  • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
  • H04N1/10—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces
  • H04N1/1013—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of at least a part of the main-scanning components
• • 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
  • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
  • H04N1/10—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces
  • H04N1/1013—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of at least a part of the main-scanning components
  • H04N1/1039—Movement of the main scanning components
  • H04N1/1043—Movement of the main scanning components of a sensor array
• • 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
  • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
  • H04N1/19—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using multi-element arrays
  • H04N1/191—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using multi-element arrays the array comprising a one-dimensional [1D] array
  • H04N1/192—Simultaneously or substantially simultaneously scanning picture elements on one main scanning line
  • H04N1/193—Simultaneously or substantially simultaneously scanning picture elements on one main scanning line using electrically scanned linear arrays, e.g. linear CCD arrays

Definitions

• Expanded gamut multispectral scanner including single-pass flatbed scanner
• the invention relates to the field of colorimetric analysis.
• the sensation of color results from the perception of a set of radiations of given wavelengths.
• spectral re fl ectance describes in the form of a continuous characteristic (spectrum) the distribution of the proportions of the different wavelengths over the extent of the visible range.
• This spectral reflectance can be determined directly from a spectrophotometer or a spectroradiometer, which are instruments equipped with a dispersive system such as a Newtonian prism making it possible to project on a sensor a selective band of wavelengths. .
• a spectrophotometer or a spectroradiometer which are instruments equipped with a dispersive system such as a Newtonian prism making it possible to project on a sensor a selective band of wavelengths. .
• these are complex and delicate devices to implement, which reserves them for laboratory and metrology applications.
• color analysis is done using three red, green and blue filters (RGB trichrome selection).
• RGB trichrome selection red, green and blue filters
• the color information resulting from this analysis can be described and stored as three (or six) coordinates defined in the CIE colorimetric system, and shown with respect to the CIE
• a colorimeter which is a measuring instrument provided with a sensor, a light source and a series of filters, generally four in number, making it possible to reproduce a standard observing torque CIE / standardized illuminant.
• CIE illuminant the colorimeter makes it possible to obtain coordinates in a color space of type CIEL * u * v, CIEL * a * b, XYZ, etc., colorimetric systems in themselves well known and abundantly referenced.
• a color acquisition system with RGB filters or a colorimeter gives only discrete values of color coordinates, three or six depending on the number of filters, and not a continuous spectrum of reflectance, the only representative of the physical reality at the origin of the perception of color.
• the knowledge of only three or six color coordinates does not make it possible to obtain a perfect characterization of a given color.
• Various methods (which will be explained below) have been proposed to reconstitute a spectral reflectance characteristic from coor ⁇ color data; for example, the so-called "interpolation" method allows to approximate a spectral reflectance on 30 points with the knowledge of only six color coordinates.
• the invention proposes a multispectral scanner of a known type, for example according to the aforementioned WO-A-00/25509, that is to say comprising: a linear photosensitive sensor, capable of analyzing a line the document in a transverse direction; a set of N optical filters pas ⁇ se-band, with N> 4, preferably N>6; illuminating means, capable of forming on the document a light band in the region ana ⁇ lysed by the sensor; and motor means, adapted to operate in a controlled manner a scan of the document in successive steps in a longitudinal direction.
• a linear photosensitive sensor capable of analyzing a line the document in a transverse direction
• a set of N optical filters pas ⁇ se-band with N> 4, preferably N>6
• illuminating means capable of forming on the document a light band in the region ana ⁇ lysed by the sensor
• motor means adapted to operate in a controlled manner a scan of the document in successive steps in a longitudinal direction.
• This scanner is capable of delivering, for each scanning step and for each pixel of the analyzed line, N corresponding quantized partial measurement values, each representative of the spectral re fl ectance of the document collected by the sensor through the one of the N respective filters.
• spectral reconstruction means of the image of the document operating according to a method of extrapolation with learning from colored samples of ré ⁇ ference, these means comprising: a memory storing a knowledge base formed from known spectral reflectance values of said reference samples; and a neural network, receiving at input, for each pixel, said N partial quantized measurement values and outputting at least one reconstructed quantized value, representative of the spectral reflectance of the corresponding pixel of the document.
• a bootstrap-type iterative resampling processing before application of these N measurement values in en ⁇ trea of the neural network.
• the invention can be implemented with a conventional RGB scanner mechanism, for example a conventional A3 or A4 flatbed scanner.
• the senor is an integrated component comprising N parallel lines of photosites with, for each line of photosites, one of the N optical filters bandpass associated with it, and the scanning on the éten ⁇ of the document is a scan operated in a single pass.
• the analysis of the document in a single pass avoids in particular the use of mechanical scanning systems of precision such as those of the prior systems, necessary to ensure the reproducibility of multiple passes.
• a multispectral flatbed scanner capable of covering 100% of the visible color spectrum - unlike conventional RGB scanners whose "gamut", ie the colorimetric domain reproduced, covers only 50 to 70% of this spectrum.
• spectrum - has a considerable advantage in a very large number of industrial and artistic applications, among which:
• Pantone in an image using a device as simple to use as a desktop scanner is a considerable advance for professionals in this field; the digitization of artist documents made for example at the aerodrome or other tools from inks or pigments that have difficulty entering the RGB gamut;
• colorimetric control in production lines for example in the field of printing, for the control at the output of rota ⁇ tive of the conformity of samples of the document actually imprinted with the original color selection sent to the printer ;
• the neural network of the spectral reconstruction means is preferably a multi-threshold network, able to receive the N measurement values as input, to apply a weighting peculiar to these N values and to output a plurality of elementary quantized quantized values, associated with corresponding spectral components of the reflectance of the pixel.
• the neural network may output a number N 'of quantized reconstructed elementary values greater than the number N of the measurement values, in particular a number N 1 of at least 15 values, preferably at least 15 values. 25 values, preferably 30 values, for a number N of measurement values equal to 6 or 7.
• FIG. 1 is a schematic view showing the configuration of the different mechanical elements of a single-pass flatbed scanner.
• Figure 2 illustrates the principle of spectral reconstruction using a neural network.
• FIG. 3 is a view of the integrated multispectral CCD sensor with partial enlargement showing the series of associated filters.
• FIG. 4 shows the transmittance curves of the different filters of the sensor of FIG.
• Fig. 5 is a representation of the chromaticity diagram in the CIE system showing the respective gamuts of different colorimetric analysis systems, relative to the extent of the visible color space.
• Figure 1 there is shown the general structure of a multispectral flatbed scanner, to which the invention can be advantageously applied.
• this type of scanner is not limiting, and the invention can be implemented with other analysis devices, for example the document reproduction chamber described in the WO-1.
• A-00/25509 where an image of the document is formed on an image plane scanned by a sensor driven by a micrometric system.
• the mechanics of a single-pass flat scanner, for example of the A4 or A3 office scanner type, are in themselves well known.
• This scanner 10 allows the analysis of a document 12 arranged flat against an analytical window 14, fixed.
• a first mobile unit 16 carries illuminating means 18 capable of illuminating a narrow transversal band of the document 12.
• the crew 16 is movable in linear translation in a direction perpendicular to the illuminated line of analysis, and there is provided a optical assembly capable of forming an image of this line on a fixed linear sensor 20, by means of mirrors 22, 24, 26 and an objective 28.
• the mirror 22 is integral with the mobile assembly 16, while the mirrors 24 and 26 are mounted on another movable element 30 whose position is adjustable, as well as the lens 28 mounted on a movable support 32 so as to vary the optical magnification factor.
• the sensor 20 is a multispectral sensor that typically delivers color signals in six distinct bands.
• This number of bands (six) is however not limiting of the invention; it only corresponds to the best compromise present. It will be understood simply that the number of bands is greater than the three bands of the RGB sensors, the inadequacies of which have been explained above, and less than the twelve or thirteen bands of the complex apparatus mentioned above and used, for example, in the field of museography, which because of their complexity do not allow a simple implementation, including a single-pass scanner.
• the use of a number of filters less than six, for example five filters, or even four filters only, is within the scope of the invention but of course with a qualitatively lower result.
• the problem of the invention essentially consists in reconstructing a reflectance spectrum from these six values, thus calculating intermediate values (so-called "reconstruction” operation), while reducing the interpolation noise to a minimum. added by this operation. This is a known problem for which many of its proposals have been formulated.
• a first method consists in characterizing all the elements of the acquisition and digitization chain of the image: spectral curve of the lighting device, spectral sensitivity of the sensor, respective transmittances of the used filters, transmit- tance of different elements of the optical system.
• a second method is only concerned with the response of the camera with respect to a perfect white reference.
• the camera After normalization with respect to the standard blank, the camera is considered as a sampler of the spectrum, a point of the spectral curve being for example measured every 40 nm in the visible range.
• the intermediate points of the spectrum are then reconsti ⁇ killed by an interpolation method, for example a cubic spline or Modified Discrete Sine Transform (MDST) method, so as to obtain a spectrum reconstituted by points spaced for example from 10 nm, 5 nm or 1 nm.
• an interpolation method for example a cubic spline or Modified Discrete Sine Transform (MDST) method
• This interpolation method has the advantage of requiring only knowledge of the response of the camera, with digital processing from conventional algorithms.
• the spectrum to be reconstructed is a spectrum whose profile is relatively smooth; in fact, the algorithms used to reconstruct the missing points do not make it possible to detect a narrow peak in the spectrum, which peak will be smoothed, and the information reconstituted deformed.
• a noise of im ⁇ important interpolation is superimposed, which degrades very quickly the performance of the method.
• the spectral analysis must be able to relate to complex spectra, for example those of pigments used in painting whose very specific spectrum pro ⁇ , if it is smoothed by the reconstruction algorithm, will be immediately perceived as deformed by an observer led to distinguish the subtle shades of colors and their substitution by an approaching color.
• the implementation of this technique with a suitable degree of fidelity in color reproduction involves a relatively high number of filters to give enough starting samples, typically eleven or thirteen filters, which limits its use. to relatively complex cameras and only allows not its realization in the form of a large-scale scanner, comprising for example a six-band analysis system only.
• the third method - to which the present invention relates - is called "indirect reconstruction" or "reconstruction by learning”.
• this method makes provision for the use of a standardized test pattern allowing, by extrapolation, to model a transfer func ⁇ tion between, on the one hand, the reference spectra measured on the test pattern for each of the samples and, d On the other hand, the response of the camera.
• the invention proposes a certain number of improvements to this known method of indirect reconstruction, in order to be able to determine the desired transfer function with performances far superior to what may have been possible. proposed up to now, and can also implement this method from information delivered by a sensor analyzing the spectrum on a reduced number of bands, typi ⁇ on only six bands (typical value, of course not limi ⁇ tative).
• the implementation of this method by the invention is shown diagrammatically in FIG. 2.
• the sensor 20 of the scanner is, as indicated above, typically a six-filter sensor, thus delivering for each pixel six values. quantified colorimetry. These six values are applied to a network of neurons 40 with six inputs and thirty outputs (assuming that it is desired to reconstitute the spectral reflectance over thirty points).
• the neural network 40 is associated with a memory 42 storing a con ⁇ born base formed from the known spectral reflectance values of a certain number of reference samples, advantageously chosen as a function of the desired application: for example For applications in the field of museography or illustration, a database made from the 300 main pigments used in pain ⁇ ture. This knowledge base will determine the various weights applied by the neural network.
• the neural network 40 may optionally be in the form of a specific digital signal processor integrated in the multi-spectral sensor 20.
• the sensor 20 used for the implementation of the invention is advantageously a built-in sensor such as that illustrated in FIG. 3, which is in the form of a bar comprising six (or possibly seven) lines of photosites, for example 10,000 or 12,000 photosites each, each of these lines being associated with a corresponding filter 51 to 56, tinted in the mass.
• the respective spectral responses 61 to 66 of these filters are illustrated in FIG. 4.
• the multispectral sensor 20 is combined with the scanner's mechanical and optical scanning system in the same manner as with the conventional tri-chromatic sensors of the prior art, and thus makes it possible to deliver simultaneously for each pixel of the document line.
• the invention provides with a sensor only six filters a gamut covering the entire visible range , allowing the reproduction of the most subtle color shades with a very high fidelity, and perfor ⁇ mances much higher than what could have been proposed so far with systems of analysis in hexachrome or a fortiori in trichromie.
• the problem is to find from the data thus determined (starting reference data and corresponding responses of the ca ⁇ mera) the corresponding transfer function, which is a matri ⁇ sky operator Q of dimension N x K such that
• This is a matrix that can be easily calculated by algorithms in them -known ones.
• the starting data used in the implementation of the indirect reconstruction are subjected to a ,. ..
• the bootstrap method is in itself known, for example from Efron B, Bootstrap Methods: Another Look at the Jacknife, Annals of Statistics, 7, pp. 1-26, 1979.
• This is a resampling computer technique for assigning precision measurements to statistical es ⁇ timations, by providing confidence intervals on the estimation of a population. statistical.
• a resampling of the data makes it possible to incorporate by statistical inference information contained in data related to its probabilistic distribution.
• the starting point of the invention consists in using this bootstrap statistical processing technique for the treatment of color signals, in order to improve the reconstruction of a spectral reference.
• the matrices R and C defined above are resampled by random selection of their columns, with a uniform probability distribution for this selection.
• the proposed algorithm forms a reconstruction operator Q from matrices obtained by resampling the matrices R and C defined above, and evaluates the distance between the initial Q pager and the resulting Q operator.
• Ci resample (C)
• the selection is operated in a non-random manner, in order to increase the precision of the method and to achieve a faster convergence towards the final operator.
• This improvement implements colorimetric video acquisition performed concurrently with the analysis of the reference color sample chart.
• a source of illumination combined with appropriate filters is used in this case to associate the standard observer with a standardized illuminator, it is possible to emulate the behavior of a colorimeter. and accurately obtain colorimetric coordinates in a single system.
• These colorimetric data can advantageously be delivered by a secondary sensor directly integrated with the scanner, delivering information simultaneously to the scanning of the document.
• the colorimetric video acquisition makes it possible to locate the most important color differences between the camera response and the corresponding colorimetric coordinates.
• the multispectral reconstruction by learning is implemented by means of a neural network.
• This aspect of the invention is preferably provided in combination with the bootstrap processing which has just been described, which constitutes a statistical engine advantageously applicable to the samples before their application to the neural network.
• These are, however, two distinct techniques that can be used independently of each other, although their combination obviously provides particularly advantageous results.
• Neural networks are generally defined as a network comprising a very large number of simple processors (neurons) connected together by communication paths (connections) conveying digital data coded in various ways, the neurons only being on the contrary. inputs applied by their respective connections.
• the neural networks can be represented in the form of a matrix with N inputs and N outputs, each of the output values being dependent on all the values of the N inputs as a function of weighting attributed to each neuron.
• the individual neurons are organized into subgroups, each of which carries out independent treatments, the result of which is transmitted to the following subgroup: there is thus propagation of the information within the neural network, with the possibility of apply the output values to previous subgroups (backpropagation).
• the weights of connections to neurons are adjusted by a set of data determined from prior learning.
• Knowledge of the network (learning) is thus stored in the various weights, which can be adapted during the course of treatment.
• the neural network will then present a behavior taking into account the parameters collected during this phase of apprentis ⁇ sage, which makes it suitable for some form of generalization from particular cases.
• a detailed study of this concept can be found in Bishop CM, Mixture Density Network, Neural Computing Research Group. Report NCRG / 4288, Aston University, United Kingdom, 1996.
• the learning phase consists in acquiring the multiple samples of the chart. Reference color samples (typically 250 to 300 samples) and store the data in a knowledge base containing the corresponding weights of all neurons in the network.
• the behavior of the network will thus integrate the con ⁇ birth of the spectral characteristics of the samples of the chart.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Mathematical Physics (AREA)
• Theoretical Computer Science (AREA)
• Color Image Communication Systems (AREA)
• Image Input (AREA)
• Spectrometry And Color Measurement (AREA)
• Facsimile Image Signal Circuits (AREA)
• Facsimile Heads (AREA)
• Facsimile Scanning Arrangements (AREA)

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  • 2004-06-07 FR FR0406098A patent/FR2871325B1/fr not_active Expired - Fee Related
• 2005
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  • 2005-05-30 JP JP2007526485A patent/JP2008524875A/ja active Pending
  • 2005-05-30 EP EP05772992A patent/EP1766957A1/de not_active Withdrawn
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