ES2669819B1 - Procedure and lighting selection system on polychrome surfaces, and application device - Google Patents

Description

DESCRIPTION

Procedure and lighting selection system on polychrome surfaces, and application device

SECTOR OF THE TECHNIQUE

The present invention relates to a method of selection of lighting, space-spectrally, in objects with surfaces of differentiated color such as happens in commerce and in the elements of cultural heritage: handbags, textiles, ceramics, shoes, paintings, paintings and works of art in general: cave paintings, frescoes, scrolls, etc. In the case of elements of shops and commerce, the objective is the creation of lighting effects, such as highlighting the contrast, changing the color, etc. These effects can be static or dynamic, such as making the logo of the brand appear and disappear. In the case of objects of cultural heritage the objective will preferably be the minimization of damage, which is applicable when it is required to illuminate in an optimal way an artistic or cultural work sensitive to excessive lighting. It is part of the lighting and conservation sectors of the Cultural Heritage.

More specifically, the invention relates to a system that allows illuminating a work or object of special interest with an intensity distribution that adjusts spatially and spectrally based on the required parameters, such as: spatial and spectral distribution of reflectances and absorbances of the object , chromatic reproducibility, temperature variations, observer perception, improvement of contrast, improvement of visibility, decrease of damage or deterioration of the object, simulation of different natural or artificial lighting conditions, etc.

STATE OF THE ART

In the field of cultural heritage conservation, the commitment between lighting and conservation is particularly relevant:

The lighting of works of art poses a complex problem. On the one hand, it is necessary to resort to an adequate lighting that allows the public a correct chromatic perception of them and on the other, the basic rules of conservation make it essential to reduce as much as possible the damage caused to the works by the radiation to which they are subjected. These two needs, antagonistic in principle, can be reconciled.

On the other hand, the complexity of the problem is exacerbated when we consider the immense variety of possible works of art to be illuminated: paintings made with different materials and under different supports, textiles of very different nature, paper, photographic supports, incunabula, parchments, stones or rocks of different characteristics, different types of wood decorated with different materials, works in which the polychromy predominates and others less rich in tonal distributions, etc.

This very large casuistry prevents reaching a solution that, in general, is applicable in all circumstances. In return, it is possible to propose a protocol for action to be followed more or less systematically.

Previous work has already raised incipient solutions to the problem of the lighting of cave paintings. The solutions provided in these works were based on the arguable criterion proposed by Miller (Miller, JV, "Evaluating fading characteristic of light sources", Nouvir Research Co., Pasadena (1993).) According to this criterion the illuminant that produces less damage A material is one whose spectral distribution coincides with the spectral reflectance curve of the illuminated object, taking into account the complexity and variety of the processes of interaction of radiation with matter, this statement should be validated for each material in particular.

In the patent US 8246229 B2 the possibility of illuminating a painting by means of a special frame is presented. This system is only applicable to frames mounted on a wall and does not include any type of adjustment (neither spatial nor spectral) of the lighting to adapt it to the specific characteristics of the work.

In EP 2528481 A1 a method for controlling a light source whose color is adjustable is presented. The invention focuses on the possibility of adjusting different color parameters (saturation, color temperature), but does not contemplate the possibility of adjusting locally or adapting to the specific characteristics or requirements of the object to be illuminated.

Patent EP 2528481 A1 refers to a method for controlling the color of a light source, focusing on the possibility of adjusting different chromatic variables (saturation, color temperature), but it does not have the possibility of spatial adjustments or adaptation to the characteristics or specific requirements of the object to be illuminated.

In the article "Innovative Optimized Lighting Systems for Works of Arts" published in the minutes of the first conference of "Color and Light in Architecture 2010", a method to illuminate works of art that predicts what source of light will be able to guarantee the same perception of color that would be achieved with a reference source. The method focuses exclusively on the optimization of the chromatic variables of lighting, increasing the contrast, improving the visibility of certain details of the work.

In 1986 Lafontaine proposed the use of color slides to restore works of art that had yellowed due to the action of light. Lafontaine, R.H. 1986. "Seeing through a yellow varnish: a compensating illumination system." Studies in Conservation 31 (3): 97-102 In this case, the slides exerted a global color correction on the whole work and bathed it with a white light and yellowish uniform.

Jens Stenger in "Conservation of a room: A treatment proposal for Mark Rothko's Harvard Murals", Studies in Conservation, vol 0, n ° 0, pp1-14, proposes a point-to-point color correction system in which the lighting is It does point by point, but the color calculation system only takes into account the image perceived by a digital camera, which is compared with an objective image obtained from original slides of the works.

They are also relevant:

Cuttle et al, "Damage to Museum objects Due to Light Exposure" Lighting Res. Technol., 28 (1), pp. 1-9, Jan. 1996. [-2]

Cuttle et al, "Lighting Works of Art for Exhibition and Conservation " Lighting Res. Technol., 20 (2), pp. 43-53, Feb. 1988.

BRIEF EXPLANATION OF THE INVENTION

The invention consists in a method of lighting selection on polychrome surfaces of heritage or commerce or in any other space in which one wishes get the same effect, for example in an office or public space. Can be illuminated handbags, accessories of all kinds, clothing, fabrics, decorative objects, paintings, paintings and works of art of museums, etc., a system to execute it and a lighting device resulting from the procedure, according to the claims.

The procedure and the system allow to select the spectral distribution of frequencies to optimize a series of criteria, mainly the chromatic or luminous contrast, or the damage that can be perceived or produced to the work. For its part, the device allows a point-to-point object to be illuminated with a beam of light whose temporal, spatial and chromatic variation has been adjusted in such a way as to optimize or meet the specific criteria required by the specialists responsible for lighting and / or conservation of the work.

The system can be adjusted and / or optimized according to the characteristics of the work (such as shape, location in space, spatial distribution of reflectances and absorbances, characteristics of the materials of the work), conservation requirements (total temperature variations or relative, maximum radiation per unit area, presence of aggressive chemical compounds (CO2, O2, ...) minimization of functional factors that quantify the damage in the work), exposure requirements (improvement of contrast, improvement of the general perception by the observer, highlighting particular details of the work, simulation of specific lighting conditions, or others). This adjustment will allow radiating each point of the work with the optimal spectral distribution and energy quantity to achieve the proposed objectives in each case, and vary the lighting over time as the situation of the work and its environment is detected.

In particular, the procedure for selecting lighting in paintings, paintings and works of art from museums and other sensitive cultural heritage comprises the stages of:

- Define lighting criteria and parameterize the criteria according to the wavelength. These can be defined before or after the next stage, and in particular they can be checked at any time of enlightenment.

- Perform the measurement of the spectral reflectance p (X) at each point of the artistic or cultural work as a function of the wavelength.

- Select the spectral distribution of frequencies point to point that optimizes the criteria. The optimization will be done with maximization or minimization of the different criteria, considering a variable specific weight, or even through exponential relationships.

Preferably, one of the lighting criteria will be to minimize radiation damage to the work. A second possible criterion is to minimize the color contrast between that perceived and that existing in the original conditions of creation (torchlight or candlelight, natural light of high latitudes or tropical, etc.) as determined historically or at the discretion of the person in charge of The exhibition.

The system that will execute the procedure must comprise a light source, a point-to-point reflected spectrum detector system, and a microprocessor or the like. If the light source can not vary its wavelength, passband filters can be arranged to select the frequencies under study (emission and reception of the reflected light)

The detector system may comprise at least one CCD camera, while the light source will preferably be a plurality of monochrome LEDs.

The result of this procedure will be a lighting device that illuminates with a spectral distribution thus obtained and that obtains the optimum illumination, point to point, of each part of the object or of the work comprising the polychrome surface.

Given an object displayed in a shop window or a shelf inside a store, you can make the object appear consecutively with the color range corresponding to its color as it would be perceived if it were illuminated by direct sunlight, or the shadow of an umbrella on a sunny day, or well illuminated with a source of incandescent light. This series of illuminations would allow the client to appreciate and evaluate with a better knowledge the qualities of the object he intends to acquire.

Another use of the system can be as a means of claiming the attention of passers-by in a certain area. The previous color change, which can be accompanied by a digital change of decoration and setting can capture the attention of passersby. Likewise, a certain logo can be made to appear or disappear from the surface of objects following an established frequency that can be in consonance with a musical rhythm. This effect can being extended to all or part of the object, effects could be produced that even camouflage the object with its surroundings, altering the background of the environment and the object itself to make it appear and disappear. Spectrally selective point-to-point lighting can cause certain textures and volumes of the object to appear and stand out or be hidden and go unnoticed. The range of possibilities that the system opens, thanks to the controlled and calculated alteration of the color of the surface of the objects, is practically unlimited and is in the hands of the designers and publicists.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, the following figures are included.

Figure 1: schematic representation of an example of a spectral measurement device.

Figure 2: an embodiment of a second example of a measuring device.

Figure 3: example of reflectance measured at a point (i, j).

Figure 4: A and B, graphic representation of two functional examples as well as the spectral distribution of the obtained illuminants.

MODES FOR CARRYING OUT THE INVENTION

The following is a brief description of an embodiment of the invention, as an illustrative and non-limiting example thereof.

At the beginning of the procedure, a cultural or conservation choice must be made, which sets the criteria to be applied in the process. For example, you can prioritize that the reproduction of it resembles as much as possible when the author made it, or that the perceived color gamut is maximum, or that the work suffers minimal deterioration, or any other it is considered opportune. The selection does not affect the stages of the procedure to be applied, although it does affect the operations carried out in it. These criteria must be translated into objective and measurable optical parameters; For example, the resemblance to the original work can be set with the minimum distance in CIELAB units between the chromatic coordinates of the work and a certain objective. (target), or the damage as the minimization of the units of relative damage in accordance with the ICD 157 standard. Since several criteria and objectives usually intervene, these must be prioritized using specific weights that highlight or cancel each of the parameters in accordance with the importance placed on it by those responsible for the exhibition, museum or entity responsible for the work. With this information, we will proceed to the generation of a functional operative that can be applied automatically in the optimization programs of the spectral distribution adapted to each point. The functional can be varied if an increase in deterioration is observed, for specific cases (taking photographs or videos) without it being necessary to repeat all the stages of the procedure.

The method of the invention starts with a measurement of the spectral reflectance, that is, how the light is reflected at each point of the work (1) to be illuminated as a function of the wavelength. Both the damage that occurs in a sample and the color that it presents under a certain illuminant depend on its spectral reflectance. To design an adequate illuminant, the first information that we must have on the sample to illuminate is its spectral reflectance p (X) at each point of the work. The spatial accuracy of such information will depend on the observation conditions or the capacity of the projection system.

Therefore, the system must contain a spectral measurement device that allows obtaining a multispectral image of the work or area to be illuminated, a light projector that allows the spectral distribution of the radiation to vary from point to point and a processor of the information that calculates what is the spectral distribution and amount of energy necessary to reach the selected objectives with the maximum possible precision. Therefore, the system must consist of at least the following components (figure 1):

Light source (2)

Detector system (3) of the reflected spectrum point to point.

Filters (4) passband of selection of the frequencies under study (emission and reception of reflected light).

Microprocessor (5) or another type of programmable logic unit.

When it is desired to consider damage to the work as a priority, it must be parameterized according to the wavelength (X), for example as defined by the CIE (International Commission on Illumination) or explained in more detail in the article (Santiago Mayorga Pinilla, Daniel Vázquez, Antonio Álvarez FernándezBalbuena, Carmen Muro, Javier Muñoz "Spectral damage model for lighted museum paintings: Oil, acrylic and Gouache", Journal of Cultural Heritage, 2016) that is incorporated into this application by reference.

The damage to the work of art depends on the energy absorbed and is a function of the energy absorbed and the sensitivity of the material (constant for all wavelengths). Since transmittance is generally assumed to be zero, although it may not be the case in some works of art with transparent elements, the energy absorbed at each point is a function of the material's reflectance at each point and for each wavelength.

Now we consider the contrast of the motif, whose spectral reflectance at a point P ( ^{¡, j} ), where the indices (i, j) indicate the position of the pixel in the image, is p ^c (X). Yes

we define as ^d ( ⁽ ! ^a -1 ⁾ ), the distance in the chromatic space, for example in the CIELab system, which exists between the point (i, j) illuminated by an ideal illuminant, here called as a, and the calculated illuminant . The objective from the point of view of chromatic reproduction is to obtain an illuminant that has the minimum possible value of d .

Figure 2 shows an example of the system incorporating a detector system (3) formed by a CCD camera (charge coupled device) used for the geometric registration between the image of the light source (2) and through a few filters (4) Spectral allows the acquisition of information about the spectral reflectance, and the image of the work (1) of art. The acquisition of multispectral information is done through a specific system for this task that could be unique for several devices since it can work independently. The lighting is carried out point by point to be able to perfectly identify each illuminated point and the reflectance of it, without contamination of the adjacent ones.

If what is interesting is to highlight a certain area of the work that is on a background of spectral reflectance p ^p (X) should highlight as much as possible the subject highlighted against the background. To do this we would introduce a new magnitude d (ca) p, which we will call "color contrast", which we define as the distance in a space of adequate color representation between the color stimulus associated with the motif and the one that presents the background when both are illuminated with an illuminant a.

In a similar way, we can define other magnitudes that are relevant in each particular case. Suppose we identify a total of n significant magnitudes, which we will call M1, M2, ..., Mn (M1 = Dmg and M2 = d ) a) p .... Mn = ...).

These magnitudes will be maximized or minimized according to the design criteria initially defined, which will imply a hierarchy that prioritizes them and gives them a specific weight with which a functional F = F (M1, M2, Mn) is created. The maximization or minimization of this function will provide at the end the optimum spectral distribution of the optimum illuminant for each point of the work.

Application example.

In an exemplary case such as the lighting of a rock painting, a light source (2) is used, consisting of three LED devices (red, green and blue, designated respectively with the subscripts 1,2 and 3). Its spectral distribution is

3

S (A) = ^ K ^j L ^j (A) (Eq. 1)

j = 1

where L ^j (A) is the spectral irradiance distribution of the j-th Led. The parameters that determine the optimization of the illuminant are the constants Kj to be determined at the end of the process.

The spectral reflectances of the pigment and the stone that forms the bottom are measured at each point, with the necessary precision, p ^c (A) and ^{p p} (A) respectively.

The first magnitude to be considered, the damage (M ¹ = Dmg), is obtained by introducing the spectral distribution (Eq. 1) in the expression of the damage. The second magnitude is the color contrast (M ² = d (ca p).) In the lighting of cave paintings, it is desirable that the color presented by the illuminated object be as similar as possible to that perceived by the original authors. they observed their work under the lighting of a torch, we can consider that the closest color to the original would be the one obtained when illuminating with the distribution of a black body at the temperature Ta = 1850 K. Taking into account this fact, we define a third magnitude: the distance, between the color stimulus perceived by illuminating the painting with the torch and that perceived when illuminating it with the aforementioned spectral distribution, that is, to design the illuminant we have introduced n = 3 magnitudes (M ³ = da).

The applied design criteria will be, in order of importance, to minimize the damage, then highlight the painting with respect to the background (maximize the contrast d (ca) p) and finally, the color obtained by the pigment will be as close as possible to the primitive (minimize gives).

If priority multiples are given to each quantity, a linear function is obtained. If greater importance is given to reducing damage and maximizing contrast, a quadratic dependence of the magnitudes Dmg and d (ca) p can be given and the importance of the distance given by a square root can be reduced.

The minimization of these functional (the contrast is with negative value) will provide two sets of values for the constants Kj in the expression (Ec 1), thus obtaining two different illuminants.

Other functionalities are possible, for example by combining linear and exponential parts, or any other suitable operation according to the criteria considered.

From this expression the damage can be calculated, while the distances ^d c ^(a- p ^> and da are calculated in the CIELAB space as any expert in colorimetry can perform.

In order to analyze the functional, take one of the constants of (Ec 1) as the unit (for example K ³ ) and calculate the functional ones for the different values of K ¹ and K ² . Figure 4A shows the graphs obtained (Ec 2 left, Ec 3 right). The solution to minimization when an illuminance level of 40 lx is imposed is shown in figure 4B, which represents the spectral distribution of the illuminants obtained by minimizing functional 1 (left) and 2 (right))

In the first case, the color obtained for the pigment is practically the same as that obtained by illuminating with a torch (da = 3.3) and the contrast between the pigment and the stone is appreciable ( ^d c ^(a -p ⁾ = 11.5). The second illuminant has a much more greenish tone. In this case the color stimulus obtained for the pigment differs substantially from that which would be obtained by illuminating with a torch (da = 23.8) and the

contrast is greater than with the first illuminant ( ^d c ^(a -p ⁾ = 15.9). The damage that occurs on the painting is very similar in both cases. Obviously, these two illuminants would provide effects on the perception of color very different from each other, but both are valid to illuminate the painting under study. The choice of one or the other depends on the end user of the lighting system.

Claims (6)

1- Procedure for selecting lighting on polychrome surfaces, characterized in that it comprises the steps of: - define lighting criteria and parameterize the criteria according to the wavelength; - perform the measurement of the spectral reflectance p (X) at each point of the polychrome surface as a function of the wavelength; - select the frequency spectral distribution that optimizes the criteria at each point of the work (1). 2- The method according to claim 1, wherein the lighting criteria comprise minimizing radiation damage to the polychrome surface. 3- Procedure, according to claim 1, wherein the lighting criteria include minimizing the color contrast between the perceived and the existing in the original conditions of creation. 4- Procedure, according to claim 1, wherein the criteria of the illumination comprise the change of the luminous or chromatic contrast of certain parts of the object. 5. - Procedure, according to claim 1, wherein the lighting criteria comprise the creation of dynamic effects that can draw the attention of the observers. 6. - Method according to claim 1, wherein the lighting criteria comprise the development of different lighting scenes in different conditions that allow the observer to appreciate different qualities of the object such as highlighting the texture or reproducing the color under different lighting conditions. illumination. 7- System for executing the lighting selection method according to any of claims 1 to 6, comprising a light source (2), a detector system (3) of the reflected spectrum point-to-point, and a microprocessor (5) or Similary. 8- System, according to claim 7, wherein the detector system (3) comprises at least one CCD or CMOS camera. 9- System, according to claim 7, wherein the light source is a plurality of monochrome LEDs. 10- System, according to claim 7, which has filters (4) passband selection of the frequencies under study. 11 - Lighting device comprising at least one light source characterized by illuminating point to point with the spectral distribution obtained by the method of any of claims 1 to 6 by applying coefficients to several different light sources or the application of filters bandpass