WO2005069600A1 - Dispositif et procede de reglage pour correction de valeurs de couleurs de donnees d'images numeriques - Google Patents

Dispositif et procede de reglage pour correction de valeurs de couleurs de donnees d'images numeriques Download PDF

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Publication number
WO2005069600A1
WO2005069600A1 PCT/EP2004/013216 EP2004013216W WO2005069600A1 WO 2005069600 A1 WO2005069600 A1 WO 2005069600A1 EP 2004013216 W EP2004013216 W EP 2004013216W WO 2005069600 A1 WO2005069600 A1 WO 2005069600A1
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WO
WIPO (PCT)
Prior art keywords
colour
values
colour values
primary
adjustment device
Prior art date
Application number
PCT/EP2004/013216
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English (en)
Inventor
Klaus Anderle
Original Assignee
Thomson Licensing
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson Licensing filed Critical Thomson Licensing
Publication of WO2005069600A1 publication Critical patent/WO2005069600A1/fr

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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
    • H04N1/56—Processing of colour picture signals
    • H04N1/60—Colour correction or control
    • H04N1/6002—Corrections within particular colour systems
    • H04N1/6008—Corrections within particular colour systems with primary colour signals, e.g. RGB or CMY(K)
    • 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
    • H04N1/56—Processing of colour picture signals
    • H04N1/60—Colour correction or control

Definitions

  • the invention relates to an adjustment device and to a method for the colour correction of digital image data.
  • a special case of subtractive colour mixing is the combination or superposition of optical filters.
  • the transmission of the filter combination is equal to the product of the respective transmissions of the individual filters, which is why the jargon also uses the term multiplicative colour mixing in this case.
  • This last-mentioned type of colour mixing is also critical for colour reproduction in the projection of colour films which have three different colour layers lying one above the other.
  • Figure 1 diagrammatically shows an example of the construction of a colour film 1 in cross section.
  • a layer carrier 2 carries three colour layers 3, 4, 5 having the primary colours red, green and blue, the red-sensitive colour layer 3 adjoining the layer carrier 2 and the blue-sensitive colour layer 5 forming the topmost colour layer.
  • a yellow filter 6 lies between the blue-sensitive and green-sensitive colour layers 5 and 4, respectively.
  • the individual layers are represented spaced apart in figure 1 but in reality they adjoin one another.
  • the intermediate layer for preventing interdiffusion of the green-sensitive and red-sensitive colourants is not taken into account here and is not illustrated in figure 1 since it has no influence on the colour behavior of the film which is essential to the present invention.
  • the colour coordinates are transformed for example by means of so-called look-up tables in which an input colour value is assigned an output colour value, thereby obtaining a conversion or transformation of the colour values.
  • the more extensive the table the greater the resolution of the conversion in the colour space. In practice this means that the colour conversion is all the more precise, the more extensive the table.
  • the content of the table depends on the parameters in accordance with which the colour conversion is intended to be carried out. These parameters are prescribed by the colourist or altered during the processing of the film material. A change in the parameters has the consequence that the output values of the table have to be recalculated on the basis of the new set of parameters.
  • a given computing power consequently limits the size of the table that can be made available as it were continuously to a colourist. Only in this case does the colourist see the effect of a parameter change without an appreciable delay on his screen, which facilitates his work.
  • the adjustment device for the correction of colour values of digital image data has a computing unit, which, in terms of program technology, is set up for calculating secondary colour values from primary colour values.
  • the primary colour values are related to the first representation means and the secondary colour values are related to a second representation means.
  • the adjustment device comprises a memory containing a table in which each primary colour value is assigned a secondary colour value.
  • an interpolation stage (36) is provided, which calculates by interpolation secondary colour values for such primary colour values which are not contained in the table.
  • the primary colour values may be divided into a first and a second group of colour values.
  • the first group of primary colour values preferably describes such points in the colour space for which a secondary colour value is stored in the table.
  • the second group of primary colour values describes such points in the colour space for which no secondary colour value is stored in the table.
  • the method according to the invention for the colour correction of digital image data assigned to a first representation means comprises the following steps:
  • Figure 1 diagrammatically shows the structure of a colour film in cross section
  • FIG. 2 shows the construction of a colourist' s workstation in greatly simplified form
  • Figure 3 shows the spectral density of the blue, green and red colour layers of a colour film
  • Figure 4 shows a flow chart of the method according to the invention.
  • Figure 5 shows an adjustment device according to the invention for the correction of colour values.
  • FIG 2 illustrates a colourist' s workstation in greatly simplified form.
  • a first copy is made from the film material originally exposed by the camera.
  • the copy is used to produce further prints which form the starting point for the postprocessing of the film.
  • such a print is inserted in a film scanner 11.
  • the photographic image information is converted into digital image data and fed to a device 12 for colour correction, which is usually operated by a colourist.
  • the colourist views the image to be processed on a monitor 13.
  • the colour representation on the monitor 13 is determined by colour values at the output of the colour correction device.
  • the colour values at the output of the colour correction device 12 are also forwarded as control commands or "Code Values" to a film exposer 14, which exposes the data onto an internegative film.
  • the content of the internegative film is then transferred to a positive film by means of a contact copy.
  • the positive film is symbolized by a film reel 16 in Figure 2.
  • the latter is projected onto a projection screen 18 by a film projector 17.
  • the colour representation of an image projected onto the projection screen 18 corresponds to the colour representation of the same image on the monitor 13.
  • a device 19 for adjusting the colour coordinates is connected between the colour correction device 12 and the monitor 13.
  • the adjustment device 19 converts the "Code Values" sent to the film exposer 14 into colour coordinates for the monitor 13.
  • the conversion has the aim of obtaining as far as possible identical colour representations on the monitor 13 and the projection screen 18, respectively.
  • the conversion method and the conversion device 19 are described in greater detail below.
  • Figure 3 illustrates spectral curves of in each case three colour filters of different density for the colours red, green and blue.
  • the density D is plotted on the ordinate and the wavelengths in nanometers (nm) are plotted on the abscissa.
  • Density curves for filters with different transmissions are plotted for each of the primary colours red, green and blue. It can clearly be seen that, for the density curves for the red filter, by way of example, appreciable secondary maxima occur in the blue spectral range around 400 n , and lead to a considerable absorption for the colour impression. The same applies to a lesser extent to the density curves of the green filters.
  • the density curves for the blue filters fall sharply in the wavelength range of between 440 nm and 380 nm only to rise again below 380 nm.
  • the density curves of the blue filters exhibit a more and more highly pronounced plateau in the green spectral range around 550 nanometers, the plateau projecting right into the red spectral range.
  • the absorption of a primary colour filter in spectral ranges other than the spectral range assigned to the respective primary colour is referred to as the "secondary density" of the density curve and results in colour shifts during the projection of colour films for example in the case of multiplicative colour mixing.
  • the film exposer 14 exposes with predetermined code values so-called "test patches” i.e. image windows with different colours and colour densities. This film material is then copied and produces the actual film.
  • the test patches are then measured by densitometers in order to determine the absorption of a colourant in specific wavelength windows.
  • the measurement characteristic of the densitometers is determined in accordance with DIN 4512 3 or a corresponding international standard. With densitometer measurements, the absorption of the colourants is ascertained not only in the primary maxima but also in the secondary maxima.
  • the values determined in this way form the basis for the subsequent transformation of the colour values which define the representation on the colourist' s monitor 13.
  • the transformed colour values are corrected colour values which define the illumination commands of the film exposer 14 and thus determine the subsequent colour representation on the projection screen 18.
  • the colour values or code values which control the film exposer 14 are "predistorted” in order to compensate for the "distorting" influence of the colourants of the film material used.
  • the invention commences at determination of the correction values. From the more precise consideration of the spectral density curves of the colour filters as shown in Figure 3, it is possible to derive further properties of the colourants which lead to colour shifts. However, these properties cannot be identified by means of the densitometer measurements used in practice. This is because conventional densitometers permit only an integral consideration of the absorption properties of the colourants. Upon more precise consideration of the spectral absorption curves, a shift in the primary maxima toward shorter wavelengths can be discerned for all primary colours as the density increases. This shift S is represented using the example of the primary maximum for red in Figure 3. Furthermore, the form of the density curves also changes as a function of the densities. It is exactly in this way that it is thus possible to determine and correspondingly describe the spectral influences of particular film treatments during the copying process and the development.
  • the invention therefore proposes measuring the test patches of the film materials using a spectrometer over the entire wavelength range and interpolating intermediate spectra from the spectra thus obtained. From the totality of the spectra, it is possible to derive, for the three primary colours, tables which put a colour value that determines the representation on the colourist' s monitor 13 into a relationship with a code value of the film exposer 14. A three-dimensional table is produced overall in this way.
  • the method according to the invention is described in greater detail below with reference to figure 4.
  • the starting point is formed by RGB colour values which are output from the colour correction device 12 to the monitor 13, on the one hand, and to the film exposer 14, on the other hand.
  • a so-called look-up table for the monitor LUT (M) is stored in the adjustment device 19, said table taking account of the reproduction properties of the monitor.
  • the film is exposed in the film exposer in accordance with these RGB values. Said film is then copied onto the material to be projected.
  • the colour patterns or patches generated in this way are measured spectrally in a step 22.
  • further intermediate spectra are calculated in a step 23.
  • the totality of the spectra generated in this way are convolved with the perception curves of a standard observer in a step 26 in order to generate colour coordinates X, Y, Z corresponding to the RGB values.
  • the colour coordinates X, Y, Z are finally linked with an "inverted" look-up table of the monitor LUT (M) ⁇ 1 in a step 27.
  • the influence of the film material on the colour reproduction can be derived from the differences between the colour values R, G, B and R' , G' , B' .
  • Further look-up tables are therefore generated from said differences and are stored in the adjustment device 19 and kept ready for application to the colour values RGB. What is achieved in this way is that the colour representation on the monitor 13 corresponds very well to the colour representation on the projection screen 18.
  • the volume of data increases correspondingly with the third power of the resolution; the number of calculations for generating these data rises with the third power of the resolution.
  • a large number of support points prevents a dynamic colour correction during the film processing.
  • "dynamic correction” means that the 3D look-up table is adapted to changed parameters input by the colourist at the colour correction device.
  • FIG. 5 diagrammatically illustrates an exemplary embodiment of the adjustment device 19 according to the invention for colour correction, which is shown only as a single block 19 in Figure 2.
  • a three-dimensional look-up table is calculated in a computer 31 and stored in a memory 32.
  • the resolution with which the computer was able to calculate the three-dimensional look-up table defines the number of "most significant bits" MSB.
  • the MSB describe the resolution in the colour space for which calculated support points are present in the table. All intermediate values in the table are determined by interpolation between the support points. All customary interpolation methods which are known in the prior art and prove to be suitable for the present purpose are taken into consideration for this.
  • the colour values R ⁇ n , Gj_ n , Bi n of incoming image data Dj .n are divided into two data streams by means of a data processing stage 33.
  • a first data stream contains colour values R MSB ⁇ G MSB , B MSB in the case of which all LSB are set to be equal to zero.
  • R MSB , G MSB , B MSB there is a complementary colour value R LSB , G LSB and B LSB , respectively, which contains the LSB of the complementary colour value and whose MSB are set to be equal to zero.
  • the information originally contained in each individual colour value R in , G ⁇ n and B ⁇ n is thus divided between two colour values, namely R MSB and R LSB ⁇ G M SB and G LS B ⁇ and B MSB and B LSB , respectively. All the colour values mentioned have the same bit length.
  • the colour values R MSB ⁇ G MSB and B MSB correspond to those points in the colour space for which support points have been calculated by the computer 31.
  • the complementary colour values R LSB , G LSB and B LSB correspond to points in the colour space that lie between the said support points.
  • the colour values R M SBA G M SB and B MS B are converted into corrected colour values R S B, G M SB and B MSB in accordance with the support points in the look-up table.
  • the intermediate values corresponding to the colour values R SBA G LSB and B LSB are interpolated between the support point values, so that corrected output colour values RO u t r G' out , B' out for all the input colour values Rj .n , G ⁇ n , B ⁇ n are available at the output of the interpolation stage 36.
  • the resolution of the look-up table is increased to the extent to which time for calculating further support points is available to the computer, so that the boundary of the MSB shifts further until the full resolution is ultimately attained in the colour space. If the colourist alters an input parameter of the colour correction, the calculation is repeated anew.
  • One advantage of the device according to the invention is that the colourist sees the result of a parameter change immediately on the screen 13, albeit only with a reduced resolution in the colour space which, however, generally suffices for the first editing cuts of the film material.
  • the immediate visibility facilitates the colourist' s work.

Abstract

L'invention concerne un dispositif de réglage destiné à la correction de valeurs de couleurs de données d'images numériques et comprenant une unité de calcul qui, en termes de technologie des programmes, est conçue pour calculer des valeurs de couleurs secondaires à partir de valeurs de couleurs primaires. Les valeurs de couleurs primaires sont associées à une première unité de représentation et les valeurs de couleurs secondaires sont associées à une seconde unité de représentation. Le dispositif de réglage comprend une mémoire contenant une table dans laquelle une valeur de couleur secondaire est attribuée à chaque valeur de couleur primaire. Un étage d'interpolation calcule par interpolation des valeurs de couleurs secondaires pour les valeurs de couleurs primaires qui ne sont pas contenues dans la table. En outre, l'invention concerne un procédé destiné à calculer une table d'attribution entre les valeurs de couleurs primaires et secondaires.
PCT/EP2004/013216 2004-01-08 2004-11-22 Dispositif et procede de reglage pour correction de valeurs de couleurs de donnees d'images numeriques WO2005069600A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102004001295.4 2004-01-08
DE200410001295 DE102004001295A1 (de) 2004-01-08 2004-01-08 Abgleichvorrichtung und Verfahren zur Farbkorrektur von digitalen Bilddaten

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WO2005069600A1 true WO2005069600A1 (fr) 2005-07-28

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012051486A1 (fr) * 2010-10-15 2012-04-19 Thomson Licensing Procédé et système permettant de produire une archive vidéo sur un film

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0497466A1 (fr) * 1991-01-23 1992-08-05 Crosfield Electronics Limited Améliorations apportées au traitement d'image en couleurs
US5377025A (en) * 1992-11-24 1994-12-27 Eastman Kodak Company Optimal color quantization for addressing multi-dimensional color calibration look-up-table
US5930388A (en) * 1996-10-24 1999-07-27 Sharp Kabuskiki Kaisha Color image processing apparatus

Family Cites Families (4)

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Publication number Priority date Publication date Assignee Title
JPS63159983A (ja) * 1986-12-23 1988-07-02 Dainippon Screen Mfg Co Ltd ルツクアツプテ−ブルデ−タの生成方法および装置
GB2275584B (en) * 1993-02-25 1997-05-14 Quantel Ltd An image processing system
DE19641822A1 (de) * 1996-10-10 1998-04-16 Hell Ag Linotype Verfahren zur Interpolation in einem n-dimensionalen Farbraum
US6705703B2 (en) * 2002-04-24 2004-03-16 Hewlett-Packard Development Company, L.P. Determination of control points for construction of first color space-to-second color space look-up table

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0497466A1 (fr) * 1991-01-23 1992-08-05 Crosfield Electronics Limited Améliorations apportées au traitement d'image en couleurs
US5377025A (en) * 1992-11-24 1994-12-27 Eastman Kodak Company Optimal color quantization for addressing multi-dimensional color calibration look-up-table
US5930388A (en) * 1996-10-24 1999-07-27 Sharp Kabuskiki Kaisha Color image processing apparatus

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012051486A1 (fr) * 2010-10-15 2012-04-19 Thomson Licensing Procédé et système permettant de produire une archive vidéo sur un film
WO2012051483A3 (fr) * 2010-10-15 2012-08-02 Thomson Licensing Procédé et système d'archivage de vidéo sur film

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