JPH0240617A - Color image display method - Google Patents

Abstract

PURPOSE:To obtain desired color contrast by shifting the positions of the image of an image carrier and a color pattern corresponding to the image respectively in accordance with the incident angle of light transmitted almost linearly. CONSTITUTION:The color pattern 12 and the image carrier 10 which are aligned to each other are irradiated with the use of an optical system projecting the light of back lights having directivity in a diagonal direction. As a result, a color (indicated by R in the figure) which passes almost linearly through the transparent parts of the image carrier 10 does not come into the field of view, while colors (indicated by G and B in the figure) made incident on the scattering parts of the image carrier 10 are scattered so as to be viewed clearly as a color (a cyan color) of mixed scattered light. The dots of the color pattern 12 and positions where the transparent parts are formed on the image carrier 10 are shifted relatively to each other when viewed from a viewpoint, with respect to light made incident diagonally and almost linearly. Incident light is transmitted satisfactorily in a direction away from the viewpoint so that light transmitted through the color pattern 12 is not made incident on the scattering parts of the image carrier 10. The crosstalk of a transmissive color can be thereby prevented.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention receives an image signal output from a floppy disk, an optical disk, a magneto-optical memory medium, a computer, etc. or a facsimile signal or other image signal and outputs and displays an image. The present invention relates to image display methods, particularly to image display methods for outputting increasingly diverse color images.

[Conventional technology]

Traditionally, video output from TVs and VTRs, and output for interaction with computers, have been done using CRTs (cathode ray tubes) and T.
High-definition images of documents, graphics, and the like have been output and displayed on N (twisted nematic) liquid crystal display monitors, documents, graphics, etc., using WP (word processors), facsimiles, etc., as hard copies printed out on vapor machines.

Here, although a CRT outputs a beautiful image when outputting a moving image, the visibility of an image that remains stationary for a long period of time is reduced due to flicker and scan results due to insufficient resolution. Furthermore, although conventional liquid crystal displays such as the above-mentioned TN liquid crystal have achieved flatness, they have had issues such as the labor involved in manufacturing them, such as sandwiching the liquid crystal between glass substrates, and the screen being dark. . Furthermore, CRTs and TN liquid crystals have drawbacks such as the fact that beams and pixel voltages must be constantly accessed even while outputting still images as described above because they do not have a stable image memory.

On the other hand, images output to vapor are obtained as high-definition and stable memory images, but if you use a large number of them, it takes space to organize them, and it is also a waste of resources to dispose of large quantities. do not become.

Therefore, an image display method has been studied to construct a display device that can express high-definition images, which were previously only available as hard copies, with the same clarity as hard copies, and can be repeatedly displayed and erased. Various display systems using belt-like image carriers using methods such as electrophotographic recording and thermosensitive recording have been proposed. For example, JP-A-5
No. 7-171:180 proposes a method for forming color images using a thermal method.

[Problems to be Solved by the Invention] However, in the image display method of the prior art, it is necessary to arrange the color paint in a staggered pattern and precisely select the color paint portion with a heat-sensitive head. However, it has been difficult to put it into practical use because of the drawbacks such as the need for a means to do so. Therefore, in order to solve the above problems, the present inventors formed an image on an image carrier using differences in optical scattering states, prepared a color pattern separately from this, and combined the two into one unit. An application has already been filed for an image forming apparatus (Japanese Patent Application No. 62-336125). According to this, since the image carrier and the color pattern are separate, it is possible to easily obtain a flicker-free, high-definition color image. The image display principle of this device is as shown in FIG. 8, and the image is formed by the difference in optical scattering state by the polymer liquid crystal 21 of the image carrier 10, that is, the transparent state and the opaque state. When light is irradiated, the light passes through the image portion formed on the image carrier and further passes through the color pattern 12, so that a color image is displayed.

The present invention further improves the color display method that can be widely applied in the color display method having the above structure, and specifically, prevents crosstalk between display colors and enables clearer color display. The present invention provides a method.

[Means to solve the problem]

According to the present invention, there is provided a method of converting a color image into positional information, forming a transparent-opaque pattern on an image carrier, and displaying a color image by combining this with a color pattern. By displaying a color image in a state where the positions of the image and the corresponding color pattern are shifted according to the incident angle of the light that passes through each approximately straight line,
It is possible to prevent crosstalk of colors other than those displayed, and to obtain clear desired color contrast.

The basic configuration of color image display according to the present invention will be explained in detail below. In the present invention, a material exhibiting thermotropic liquid crystal properties is suitable as a material for forming a transparent-opaque pattern on a sheet. Examples of this include so-called side-chain polymer liquid crystals in which low-molecular liquid crystals with main chains of methacrylic acid polymers, siloxane polymers, etc. Main chain type polymer liquid crystal such as polyester or polyamide.

In addition, liquid crystal phases include smectic, nematic,
Those with cholesteric properties, those with other phases, and discotic liquid crystals are also used.

Furthermore, a polymer liquid crystal having a phase exhibiting "SmC" in which asymmetric carbon is introduced into the polymer liquid crystal and exhibiting ferroelectricity is also preferably used.

Specific examples of polymer liquid crystals will be illustrated below, but the present invention is not limited thereto.

M stomach = ia, oo.

4CH2-CH)n CH3 (CH2-(Jn) The optical anisotropy of the liquid crystal shown above changes depending on the temperature, temperature rise, and cooling rate, and the light transmission rate changes. The principle of image formation in the present invention utilizes this property of liquid crystal, and next, the principle process in the case where a polymer liquid crystal layer is provided on a transparent substrate will be explained using FIG.

In FIG. 7, ■ in the figure indicates a state of light scattering. If this is heated to T2 (Tiso = isotropic state transition temperature) or higher as shown in ■a using a heating means such as a thermal head or a laser, and then rapidly cooled, the light transmission becomes almost the same as in the isotropic state, as shown in ■ in the figure. The state is fixed. In this rapid cooling state, it is sufficient to naturally dissipate heat from the substrate into the air without using any particular cooling means. This isotropic state is Ts(
It is stable at room temperature or room temperature below Tg (glass transition temperature), and is also stable as an image memory.

After heating to 12 or more as in method ■a, the liquid crystal temperature T, #
72, for example, if it is held for one to several seconds, the scattering intensity increases again during this holding time, as shown in (b), and returns to the original scattering state (■) at room temperature, and this state becomes stable below T. Retained.

In addition, as shown in the figure, if the liquid crystal temperature is maintained between T and T2 for a period of about 10 milliseconds to 1 second, the intermediate transmission state can be maintained at room temperature in that part. It is also possible to use it as a gradation expression.

In other words, in this example, after heating isotropically, the transmittance or scattering intensity can be controlled by how long the liquid crystal temperature is maintained at room temperature. Can be held stably. Furthermore, the temperature when returning to the scattering state in the above is
It is faster if it is closer to T2 within the liquid crystal temperature, and if it is left at the liquid crystal temperature for a relatively long time, it will return to the scattering state of ■ regardless of the previous state, even if it is not heated to the isotropic state. It is possible.

Using a liquid crystal having the above-mentioned properties, a transparent part and a scattering part are formed according to a desired image by adjusting the heating conditions, and a color image is displayed by combining this with a color pattern and irradiating light. be able to.

Next, each component for actually displaying a color image will be described. First, the above-mentioned liquid crystal is coated on a substrate to create an image carrier. At this time, a solvent is used to coat the liquid crystal onto a transparent substrate such as glass or polyester that has been washed with alcohol. The coating properties can be adjusted, and the solvent used is dichloroethane, DMF, cyclohexane, etc., as well as tetrahydrofuran (THF), acetone, ethanol, other polar or non-polar solvents, or a mixture of these solvents. The material is selected depending on factors such as solubility with the polymeric liquid crystal used, the material of the substrate to which it is coated, wettability with the surface layer provided on the surface of the substrate, and film-forming properties.

In order to obtain a more beautiful image, the weight percent of liquid crystal to solvent should be such that after addition and stirring, a clear solution or viscous state is obtained. For example, when the polymeric liquid crystals represented by the structural formulas (I) to (rV) are dissolved alone in dichloroethane, the wt% concentration of the polymeric liquid crystals is 1.
At 0%, the solution is cloudy and micellar, but at a relatively high concentration of about 15% to 25%, a stable, transparent, viscous solution is obtained. This tendency is also observed in combinations with several other types of polymeric liquid crystals and solvents. After applying this transparent viscous solution to a well-cleaned substrate such as glass or polyester using an applicator, wire bar, or dipping, and maintaining it at the liquid crystal temperature, when similarly applied in the micellar form, In comparison, an optical scattering film with extremely high uniformity can be obtained.

In other words, stable optical scattering is achieved by dissolving the liquid crystal in a solvent and coating it on a substrate, and then maintaining the substrate at the liquid crystal temperature (75°C to 110°C) for a certain period of time during or after the solvent is volatilized. A film can be formed.

Among the liquid crystals, polymer liquid crystals as shown in the structural formulas (1) to (rV) are preferable, and the solvent used for coating may be a mixed solvent of a plurality of solvents or a mixture other than polymer liquid crystal materials. It is also possible to add pigment materials and other substances within a range that does not adversely affect the coating. The resulting film thickness is 20% by weight based on the weight of the polymer liquid crystal solvent in the coating agent.
%, it is about IO μm, and generally 2 to 15 μm.
It is.

By scanning the image carrier thus obtained with a thermal head, a desired character pattern can be fixed as a transparent portion. If this image carrier is placed on a black background with an optical density of 1.2, a clear display of black on a white background will be obtained.

Moreover, the above image can also be deleted. In other words, if the entire surface of the image carrier on which the above image is recorded is heated to about 120°C and then kept at about 105°C for a few seconds, the entire surface will return to its original white scattering state, and it will remain stable even if returned to room temperature. can be,
Record 1 can be displayed again. This phenomenon can be controlled by changing the state of the liquid crystal shown in FIG. 7 above.

On the other hand, if the image carrier on which the above image is recorded is guided over the color pattern and irradiated with a backlight or front light source, the color display image can be visually seen depending on the alignment of the color pattern and the image carrier.

The color pattern is generally used, for example, R (red), G (green), B at a pitch of 125 μm.
(Blue) can be used. The principle behind color display is as follows. The image portion, which is fixed as a transparent portion of the image carrier, is composed of dots with the same pitch as the pitch of the color pattern, and when these dots are aligned with the R of the color pattern, red light passes through and the G If the position is aligned with the green light, the green light will pass through, but if the colored light that has passed through the transparent part of the image carrier is viewed from a position away from the direction of the incident angle of the light, it will not enter the field of view and will be transmitted through the image carrier. The colored light that hits the scattering part of the body is scattered and can be clearly seen as scattered light. For example, R (red), B (blue), G (
When using a color pattern of green), if R passes through the transparent part, B and G scattered by the scattering part can be seen visually, but in reality, since the dots are sufficiently small, the color mixture of B and G, Visually visible as cyan. As a result, the entire image becomes one color display image. In the above description, light that is transmitted through the image carrier without being scattered is referred to as substantially straight-line transmitted light.

In the structure for color display described above, the color pattern and the image carrier are separate, so a normal thermal printer, fax, etc. can be used to draw the image on the image carrier, and positioning can also be done using the recording pitch. However, the unavoidable gap between the color pattern and the image carrier, the liquid crystal layer on the image carrier, etc. Due to the thickness of the color pattern and the thickness of the color pattern, it may happen that the pitch of the color pattern and the dots constituting the image do not match well with respect to light irradiation.

In other words, if the light passing through the color pattern and image carrier is incident perpendicularly to both, and the dot positions of both are perfectly matched, a beautiful color image will be displayed, but if the angle of incidence of light is perpendicular, If it deviates from the line, the pitch of the image dots and the color pattern will not align with the incident light due to the thickness of the color pattern, the thickness of the image carrier, and the gap between them, and the light will fall onto the scattering part of the image carrier. The scattered lights overlap at the boundary, causing so-called crosstalk and making it impossible to obtain clear color contrast.

Since images are generally viewed from the front, it is not appropriate to set the direction of the incident angle of light to be perpendicular, so the above phenomenon inevitably occurs. Roughly calculating the degree of crosstalk assuming a constant angle of incidence of light, the gap between the color pattern and the image carrier including the thickness is 1, the angle of incidence of light is θ, and the pitch of the pattern and the The deviation Δ from the dot is Δ=
It is approximately Ittanθ. If θ=30° 1=20μm, Δ= about 11.5μm, and the pitch is 125
Colors other than display colors will be mixed into about 9% of μm.

In the present invention, the above-mentioned crosstalk is solved by the positional relationship between the color pattern and the image carrier.

This will be explained in detail below with reference to the drawings.

FIG. 1 shows a color image displayed using an oblique incidence backlight (light source + oblique projection Fresnel lens), and is viewed directly. In this case, the color pattern is on the light source side and the image carrier is on the outside, forming a mirror image. The aligned color pattern and the image carrier are irradiated with an optical system that projects obliquely directional light onto a backlight. In this way, the color (R, red in the figure) that passes through the transparent part of the image carrier in a substantially straight line does not enter the field of view, and the color (G, red) that hits the scattering part of the image carrier does not enter the field of view.
, green, B, and blue) are scattered, and these scattered lights are clearly visible as a mixed color (cyan color).

Furthermore, in FIG. 1, with regard to light rays that are incident obliquely in a substantially straight line, each dot of the color pattern and the position where the transparent part of the image carrier is formed are relatively shifted when viewed from the viewpoint, so that the light that has passed through the color pattern is reflected in the image carrier. Crosstalk of transmitted colors can be prevented by preventing the incident light from entering the body scattering section and allowing the incident light to pass in a direction away from the viewpoint. On the other hand, if there is no shift as described above, part of the light that has passed through the color pattern will enter the scattering section of the image carrier, and part of the scattered light will become mixed colors.

Further, in addition to the configuration shown in FIG. 1, the same applies when the image carrier and the color pattern are arranged in reverse, as shown in FIG. That is, in FIG. 2, crosstalk is prevented by preventing the scattered light from hitting the dots of the color pattern that should be transmitted substantially straight. If the image carrier does not have a transparent part and has a scattering part all over, the image will be white. Note that even if the backlight optical system is used as an optical system that emits light almost vertically, rather than as the obliquely directional light described above, the same color as above can be seen visually by placing the viewpoint away from the front. can.

Furthermore, it is better to make the dots in the transparent part slightly larger than the dots in the corresponding color patterns.

A mirror image is formed in FIG. 1, and a normal image is formed in FIG. 2, because the surfaces of the liquid crystal layer of the image carrier are exactly opposite.

As mentioned above, in order to prevent the light that passes through the color pattern in a substantially straight line from hitting the scattering part of the image carrier, or to prevent the scattered light from hitting the dots of the color pattern that should pass through the color pattern in a straight line, it is necessary to The misalignment between the pattern and the image carrier must be appropriate. The degree of crosstalk is affected by the unevenness of the gap between the color pattern and the image carrier, the thickness of both, the incident angle of light, etc.

First, the partial unevenness of the gap between the color pattern and the image carrier is preferably about 50 μm or less, and if it is larger than 100 μm, it is inevitable that light other than the displayed color will enter the scattering portion. When the image carrier faces the light source and the color pattern is on the outside, scattered light enters the color pattern, so it is desirable that the gap be made slightly narrower than in the case of the opposite positional relationship. Although the gap can be adjusted to some extent by adjusting the thickness of the protective layer of the liquid crystal layer on the image carrier, the gap can be adjusted as appropriate depending on the structure of the color display device.

On the other hand, the thicknesses of the color pattern and the liquid crystal layer of the image carrier are usually about 0.1 to 5 μm and 3 to 15 μm, respectively.

Also, as a light source, both a backlight and a front light can be used, but in either case, a light source with directional light beams is preferable, and a Fresnel lens or the like is used to convert non-directional light from the light source into a directional light source. It is desirable that the The incident angle is preferably about 10° to 60° with respect to the color pattern or image carrier, and this range is effective in preventing crosstalk. If the light is incident at an angle greater than 80°, it will be difficult to prevent the occurrence of crosstalk even by adjusting the misalignment between the color pattern and the image carrier.

Within the range that satisfies the above conditions, the positional deviation between the color pattern and the image carrier is further adjusted within a range of about 1 to 100 μm. By setting the color pattern, the thickness of the image carrier liquid crystal layer, and the gap between them, the degree of crosstalk can be adjusted by adjusting the incident angle of light and the positional deviation between the two. In other words, the positional relationship between the color pattern and the image carrier is shifted according to the incident angle of the light that passes through the color pattern and the image carrier in a substantially straight line, but the degree of this shift depends on the air layer between the color pattern and the image carrier. Calculate the position of the color pattern and the image carrier from the incident angle of the light that passes in a straight line, assuming the thickness as the range described above (Δ
= n tan θ) is made slightly larger than the deviation caused by the deviation at the interface, taking into account refraction at the interface, etc., thereby making it possible to prevent crosstalk and obtain a clear image.

In the above configuration, especially when a front light is used, light refraction occurs appropriately at the interface between the air layer, which is a layer with a low refractive index, and the image carrier or color pattern, and as a result, scattering of the image carrier occurs. Appropriate scattering intensity can be obtained at some points, and substantially straight-line transmitted light is transmitted through a predetermined position.

Incidentally, as a method of forming an image on the image carrier, a normal thermal printer, FAX, etc. can be used. For example, when an image is formed by passing an image carrier through a thermal printer having a thermal head with a density of 8 dots per millimeter, a separate image processor in the thermal printer prints 3 dots at a distance of 2 dots from the thermal head. A stripe pattern is printed in which one dot is continuously turned on. If this is combined with a striped color pattern in which R (red), G (green), and B (blue) are sequentially formed at a pitch of 125 μm, and R is transmitted, the G and B lights will enter the scattering part and become G. The scattered light of B can be visually observed as cyan.

Note that the polymer liquid crystal shown above has sufficient heat resistance and strong film strength, so even if the polymer layer is directly rubbed and scanned with a thermal head, it is basically impossible to repeat image writing and erasing. Although there is no problem in image formation, if necessary, in order to further increase the strength, a protective layer of polyimide, aramid, etc. may be provided on the surface by lamination or the like, or a coating of fluororesin may be provided.

In addition, polymer liquid crystals have a large contrast between transparent parts and opaque parts (scattering parts), and the liquid crystal state changes quickly depending on temperature.
When this material is used as an image carrier, it is possible to form a clear image, and by shifting the alignment between the image carrier and the color pattern described above, the crosstalk prevention effect is further enhanced, and the desired excellent color can be obtained. It becomes possible to obtain contrast. Furthermore, it is also possible to obtain gradation display by varying the strength of the voltage applied to each dot by a thermal head or the like during drawing, or by changing the applied voltage pulse width.

As explained above, various display formats can be obtained by using the difference between the transparent part and the scattering part. Therefore, if various color images corresponding to the desired colors are recorded on the image carrier using a thermal head or laser heat, etc., as the difference between the transparent part and the scattering part whose colors are changed in position, this can be done. By combining this with a color pattern, it is possible to form a clear, full-color image.

(Example〕 Hereinafter, the present invention will be explained in further detail along with examples.

FIG. 3 is a block diagram of a display device for implementing the color image display method according to the present invention. The display device includes a recording section consisting of a thermal radar 11, a scattering plate image carrier belt, a color filter (color pattern), a Fresnel lens, a display section consisting of a backlight, a surface heater, an image erasing section consisting of a temperature sensor, a roller, It is composed of a conveyance section consisting of an image carrier belt.

The image carrier belt IO has a polymer liquid crystal Glass□ liquid crystal phase □1so represented by the following structural formula on a polyethylene terephthalate transparent substrate with a thickness of 50 μm.

was dissolved in dichloroethane to make a 20% solution, applied with a wire bar, and left in an oven at 90° C. for 15 minutes to form an endless white scattering layer. The thickness of the obtained liquid crystal layer was 8 μm.

The drive roller 17 is driven by a motor (not shown), and
All other means can be operated by mechanical components or electrical or electronic components (not shown).

First, when writing an image, the drive roller 17 is driven in the direction of the arrow, and when an image signal is output to the thermal head (multi-head) 11 using a facsimile signal from another facsimile machine, the image carrier belt 10 is An image-shaped transparent pattern is formed in the heated portion. Through this operation, the image-like transparent pattern for one page of A4 size is sequentially formed and then stopped at the display section 20.

4 to 6 show an example of an alignment detection method and its configuration for better matching the formed transparent pattern and each color of the color filter with the direction of the backlight beam. In this example, a photocoupler 23 provided in the color filter I2 is used to match the transparent pattern formed on the image bearing belt 10 and the color pattern of the color filter 12. As an example of this, as shown in Figure 4, the color background 12
A cutout 24 is made at the blue (B) position of the tip of the color pattern, and the light emitting element 25 and the light receiving element 2 are cut out.
A photocoupler 23 is provided so that the photocouplers 6 and 6 face each other. When viewed from the side, it looks like Figure 5. On the other hand, for the image carrier belt IO, the transparent part 27 is always formed at the timing when the blue (B) image part 28 should arrive immediately after the start of image writing during the movement of the image carrier belt IO (see FIG. 6). . Thereafter, the desired transparent pattern is formed by the thermal head 11 by a shift distance corresponding to the irradiation direction of the backlight beam with respect to each filter as shown in FIG. 110 μm is provided, and this is led to the display section 20, and the blue (B) at the beginning is written.
) comes to the position of the photocoupler 23, at this time the amount of light detected by the light emitting element 25 at the light receiving part becomes maximum, and this is fed back to the belt drive motor (not shown). By doing this, it is possible to stop at a predetermined position.

In this example, as a protective layer for the liquid crystal layer, 3.
A 5 μl aramid sheet was provided by lamination, the average gap between the color filter and the image carrier was 10 μm, and the average incident angle of light was 45°.

In the display section, due to the difference in scattering transparency of the image carrier,
In combination with the color filter provided in the display section, the second
A beautiful color image was displayed as shown in the figure and its explanation.

There was no change in this image even if it was left as it was for 100 days.

Next, the image is erased using a halogen lamp 14 and a roller 15.
a halogen roller 32 and a surface heater 13
After displaying a predetermined image, the driving roller 17 was again started to be driven in the direction of the arrow. At this time, the temperature of the halogen roller 32 is controlled to approximately 115° C., and the surface heater 13 is controlled to approximately 95° C. from the detection output of the temperature sensor 16. When the state of the image carrier belt 10 was observed in this way, when it passed through the halogen roller 32, almost the entire surface became transparent, and when it passed through the area heater 13, the entire surface became scattered white again. With this operation, the displayed image was completely erased, and a white scattered state was obtained again. Here, the width of the surface heater 13 used in the above-mentioned present configuration in the belt movement direction was approximately 40 mm, and the entire surface was set to be at least 74° C. or higher.

〔Effect of the invention〕

As explained above, by appropriately shifting the positions of the image carrier and the color pattern according to the incident angle of light, crosstalk other than display colors can be prevented and a clear desired color contrast can be obtained. Furthermore, according to this method, even when a high-contrast image is clearly viewed directly from the front, the above-mentioned crosstalk does not occur and excellent color display is possible.

The method of the present invention can also be applied to a conventional sheet in which a color filter and an image carrier are integrated.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a color display unit for explaining the color display method of the present invention. FIG. 2 is a color display unit for explaining the color display method of the present invention. FIG. 3 is a schematic diagram of a device whose positional relationship is opposite to that of FIG. 1, and FIG. 3 is a configuration diagram of a color display device used in an embodiment of the present invention. FIGS. 4 to 6 are explanatory diagrams of an alignment detection method.
Figure 4 is a diagram showing the color pattern, Figure 5 is a cross-sectional view,
FIG. 6 is a diagram showing an image carrier, FIG. 7 is a diagram showing the relationship between temperature and light transmittance in a liquid crystal according to the present invention, and FIG. 8 is a diagram showing the principle of a color display method. It is. 10 Image carrier 11 Thermal head 12 Color pattern (color filter) 13 Surface heater 14 Halogen lamp roller Temperature sensor drive roller Fresnel lens (diagonal direction) Background substrate Display section Night crystal layer Transparent substrate Photocoupler Cutout light emitting element Light receiving element Transparent section Image section Backlight incident light Halogen roller Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1. A method of converting a color image into positional information and forming a transparent-opaque pattern on an image carrier, and displaying a color image by combining this with a color pattern, the method comprising: 1. A color image display method, characterized in that the positions of a body image and a corresponding color pattern are shifted according to the incident angle of light transmitted in a substantially straight line. 2. The method according to claim 1, wherein the image on the image carrier is displayed by irradiating the image with a light directional backlight source means or front light source means. 3. The method according to claim 1, wherein the image carrier is made of polymeric liquid crystal.