The present invention relates to a method in a diffractive color system according to the preamble of the appended independent claim 1, which color system specifies visual color effects, target colors, which are formed by mixing together two or more diffractively produced primary colors. In addition, the invention relates to a diffractive color system implementing said method according to the appended independent claim 14. The invention further relates to a diffractive component producing a mixed target color according to the preamble of the appended independent claim 17. The invention also relates to a product comprising one or more diffractive color effects according to the appended claim 33.
In general, the invention relates to applying diffractive elements in producing colors, in which case conventional effects produced by means of printing inks can in certain applications be replaced with diffractively produced colors creating a more effective visual effect.
BACKGROUND OF THE INVENTION
Colors are of great importance in the way of life of the modern human being. Color is an important factor in the production of various materials and a very central factor in the commercial success of many products. For example, the colors used in packing materials have a very significant function in invoking the interest of consumers and in recognizing brands and trademarks. Colors, for example, help a consumer to find brand name products they are already familiar with among other competing products.
When developing color production methods, the aim is thus to provide very brilliant and exact color effects, which must also be reproducible on different materials and in different processes. Brilliant refers herein to, for example, that the color is very pure, exactly of the desired hue, and bright.
In the conventional so-called subtractive color systems colors are formed by mixing colorants or pigments in certain proportions, in which case a surface treated with this kind of colorants reflects the desired color. This type of subtractive and thus light-absorption-based mixing used on printed matter does not, however, in a known manner provide as brilliant and bright colors as the so-called additive mixing, in which light typically representing three primary colors is directly mixed together. Additive color formation is utilized, for example, in cathode ray tubes, in which the primary colors mixed together in a RGB system are red (R), green (G) and blue (B). In the subtractive color systems used with printed matter, the so-called CMYK system is generally used, in which the primary colors are cyan (C), purple (M), yellow (Y) and black (K).
It is known as such that the color spectrum, i.e. the so-called color gamut formed by the primary colors used in subtractive mixing is smaller than the colors achieved with additive mixing.
From prior art are also known such subtractive printing ink systems, in which more than four primary colors are used to provide a wider color spectrum. One such color system based on six primary colors is described in the U.S. Pat. No. 5,734,800.
Also, it is known as such in additive color systems to utilize more than three primary colors in order to achieve a better color fidelity. From prior art are these days known the so-called multi-color primary displays, in which in contrast with a conventional RGB system, for example, six primary colors are used.
In packing materials color formation has, however, conventionally been based almost solely on subtractive mixing of primary colors for the obvious reason that this type of colors can be easily produced in practice by means of printing methods. The tendency for more impressive color effects has, however, lead to that various hologram-based methods have been developed, in which the colors are produced by means of diffractive elements. By means of the hologram effects, the packing materials are provided with the desired brilliancy and they can, in addition, be used to show the originality of the product, for example, because the implementation of holograms is clearly more demanding than normal printing technique, which thus complicates the production of product copies.
U.S. Pat. No. 5,797,632 discloses a solution, in which a color image is produced on the surface of a substrate by printing ink on the surface, to which ink functioning as a medium are further formed three different color halftone images. These halftone images are formed to the printing ink as diffractive elements reflecting three different primary colors, which diffractive elements produce from said three primary colors a color image based on additive color mixing. The printing ink can be heat-setting, photopolymeric or some other thermoplastic ink (see U.S. Pat. No. 5,797,632 column 6 lines 63 to 67).
Even though the above-mentioned patent U.S. Pat. No. 5,797,632 presents a solution that enables the production of holographic effects that are more brilliant than prior art by means of printing technique on, for example the surface of a packing material, the color spectrum implemented by means of it is, however, still too limited to meet the present and ever-growing needs of, for example, product designers.
As a clear deficiency in the solutions according to prior art can also be noticed that thus far no proper tools have existed either, by means of which tools the color hues of standardized color coordinates, such as the CIE 1931 color coordinates (Commission Internationale de l'Eclairage) could be produced in a controlled manner by means of diffractive components by using additive color mixing. This prevents the wide and effective use of diffractively produced color effects, for example, when designing and producing product packages.
BRIEF DESCRIPTION AND THE MOST SIGNIFICANT ADVANTAGES OF THE INVENTION
The purpose of the present invention is to provide a new solution, which enables the diffractive production of colors comprising a wider color spectrum than previously. Further, by means of the invention, a color specified by means of any standardized color coordinates, for example the CIE 1931, or a color system specified specifically in relation to such coordinates, for example Pantone®, can be produced accurately by means of diffractive components. One purpose of the invention is to specify a new kind of diffractive color system, by means of which, for example, a graphic designer designing product packings can communicate both with the customer and the parties involved in producing the product packing. Related to this, a central target is also to determine the ways in which information on the colors contained in the color system and on the diffractive components implementing them can be transferred between different parties.
To attain these purposes, the method according to the invention is primarily characterized in what is presented in the characterizing part of the appended independent claim 1. The diffractive color system according to the invention is, in turn, primarily characterized in what is presented in the characterizing part of the appended independent claim 14. Further, the diffractive component according to the invention is primarily characterized in what is presented in the characterizing part of the appended independent claim 17. The characterizing features of the product containing one or more diffractive color effects according to the invention are, in turn, presented in the appended claim 33. The other, dependent claims present some preferred embodiments of the invention.
The basis of the invention is the insight that it is possible to produce very bright and pure primary colors with diffractive gratings by taking into account in the grating design those illumination conditions in which the colors produced by the gratings will be examined. A central feature of the invention is related to the selection of the wavelengths and the number of primary colors in a completely new and inventive manner, which manner enables the implementation of a wider color spectrum than previously in each individual application. In addition, when aiming for an application-specific, accurate color reproduction, attention is now also paid to the spectral characteristics of the grating substrate and the possible other background material. The reproduction of colors produced on different materials is a central feature, which is required in order to reproduce the colors connected to brands in an exactly correct manner and to affect consumers as efficiently as possible.
According to the invention, the desired target color is produced by additively mixing together primary colors, which each are produced with an elementary grating optimized for the primary color in question. The primary colors mixed together, typically three different colors, are selected according to the invention from an application-specific or a color-specific wider primary color candidate group, in which case in different applications and when producing different target colors, it is possible, if required, to use different combinations of primary colors. By selecting from the primary color candidate group the most suitable primary colors application-specifically for producing the color hue in question, it is possible to achieve a significantly wider color spectrum than in conventional color systems, in which the additively mixed primary colors are finalized in advance without a more specific application-specific or target color -specific optimization. In color space, the primary colors are located on the edges of the reproduced color spectrum, i.e. gamut area, and by mixing them it is possible to form mixed target colors, which are located on the area limited by the primary colors in the color space.
According to the invention, the primary colors and the characteristics of the elementary gratings used in producing them are selected in such a manner that they produce the desired exact primary colors particularly in the application-specific illumination and by taking into account, when required, the color of the substrate material and/or other background separately.
In an embodiment of the invention, the primary color candidates are fitted to the spectrum peaks occurring in the spectrum of the light emitted by a fluorescent lamp. For each primary color candidate is designed an appropriate standardized elementary grating comprising e.g. a specific grating profile and period, of which are then selected for use the typically three different primary colors/elementary gratings required for each application situation and/or target color. The additive mixing of the selected primary colors in the desired proportion is achieved by controlling the mutual area ratio of the standardized elementary gratings reproducing them. In other words, in all those situations in which the colors are desired to be reproduced in a fluorescent lamp illumination, according to the invention there are thus, for example, four primary color candidates (which correspond to the four spectral peaks occurring in the fluorescent light) and their corresponding standardized elementary gratings available. These four primary color candidates can cover a specific color area, i.e. color spectrum in the color space, as will become more apparent in the following. In order to reproduce the target color hue at a certain location of the color space, for example three primary colors are selected from the primary color candidates, and by additively mixing them, i.e. by controlling the area ratios of their corresponding elementary gratings, the hue in question is produced.
A basic area unit producing the mixed color and consisting of elementary gratings producing different primary colors, i.e. a virtual color pixel, can create a structure of the elementary gratings formed for example by pixelation in a spotted or banded manner. The pixelation of the basic area unit can be implemented, for example, as a banded horizontal or vertical structure, as will become apparent later. By forming these basic area units side by side, it is possible to produce the desired homogenous color over a larger area, in which case all the basic area units are similar to each other, or, for example, a figure, image, or text formed of rastered halftone images, or some other non-homogenous effect. In the lafter case a certain part of the basic area units forms, for example, one of the halftone images, in other words, reproduces a certain hue while the other basic area units reproduce one or more further hues. The final observable effect is formed as a combined effect of these halftone images.
The grating structure assembly formed by adjacent basic area units, in which structure the different basic area units can be arranged to produce the mutually same mixed hue or alternatively, different basic area units can produce different hues, is typically formed, for example, on a printing block or the like manufactured of nickel. By using this kind of a printing block or plate, the grating structure can advantageously by embossing (imprinting) be further transferred onto plastic, paper, paperboard or other suitable material as areas wide enough in order to be able to use said materials, for example, in printed products or as packing material. Preferably the embossing is performed as a roll-to-roll process or by sheet printing.
Thanks to the above-mentioned elementary gratings, which are standardized by their characteristics and intended for a certain illumination condition, it is possible to specify an exact diffractive color system according to the invention, by means of which it is possible to easily implement any color specified by means of standardized, for example CIE 1931 color coordinates, because when the characteristics of standardized elementary gratings and the primary colors produced by them are specifically known, it is possible to specify exact mixing ratios for the selected primary colors in order to produce the desired color. The desired figure can now be reproduced in the desired colors by rastering/pixelating the image to the basic area units, in each of which basic area units the elementary gratings produce the desired mixed color to the basic area unit in question.
With the color production method according to the invention, exact and controlled color mixtures are achieved for a selected viewing angle. This is very important e.g. in producing brands and trademarks. Thus, the invention enables the large-scale production of exact diffractive colors e.g. in graphic and packing industry. The invention also provides means, which can be used to transmit information on the colors of the diffractive color chart exactly and reliably between e.g. the customer, designer and the product manufacturer in such a manner that the colors are reproduced in the desired manner in the finished product.
The invention is not limited solely to applications utilizing fluorescent lamp illumination or other light sources comprising a discrete spectrum, but the primary color candidates (and respective elementary gratings) can also be implemented, for example, for an incandescent lamp with a continuous spectrum and for natural light illumination. However, light sources comprising a discrete spectrum, such as fluorescent tubes, semiconductor emitters (light diodes, semiconductor lasers), or conventional laser illumination (for example gas or crystal lasers) typically provide, however, a significantly better luminance in practice, i.e. brightness, in comparison to light sources with continuous spectra.
A central parameter to be optimized when implementing the color system according to the invention is the luminance of the produced color effect. Luminance, i.e. the perceived surface brightness of a target is dependent on both the spectral power of the radiation reflected by the target and the spectral sensitivity of the eye. The factors affecting the maximization of the luminance are discussed more closely in connection with the following examples.
In the following, the invention will be discussed more in detail by using selected examples, by means of which the invention, its advantages and different embodiments will become more apparent for a man skilled in the art.
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