JPH0548656B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to thermal transfer recording, and particularly to a thermal transfer halftone recording system suitable for recording grayscale images and its control circuit. [Background of the Invention] The conventional thermal transfer halftone recording method is introduced in a document entitled "Thermal Transfer Color Recording" by Mr. Iwamoto in the Journal of the Institute of Image Electronics Engineers, Vol. 12, No. 4 (1981). . Figure 2 shows an outline of the thermal transfer recording method. When the resistance heating element 12 of the thermal head 11 is energized, it is possible to heat a minute area, and when the transfer film 13 consisting of the base film 13a coated with the transfer material 13b is locally heated, the transfer material 13b in that area is heated. is transferred onto the recording paper 14. FIG. 3 shows a conventional resistance heating element. A current-carrying conductor 1 is used at both ends of the resistance heating element 2. When the transfer material 13b corresponding to the area indicated by the broken line in the figure is transferred onto the recording paper 14 by energizing each of the resistance heating elements 2, for example, if the transfer material 13b has black dots, the entire surface is black. Therefore, below, the area indicated by the broken line will be described as the filling transfer area of each resistance heating element. An example of recording a halftone image using conventional thermal transfer recording is a method using a sublimable dye as a transfer material, as introduced in the above-mentioned document entitled "Thermal Transfer Color Recording." Since this thermal transfer recording uses the sublimation phenomenon of dye for transfer, a huge amount of energy must be supplied during recording, and due to the heat resistance of the resistive heating element on the thermal head, the area equivalent to one filled transfer area is Since recording takes a long time of 10 to 20 milliseconds, it has been difficult to shorten the recording time. However, this method can record 32 or more levels of shading. On the other hand, methods using meltable solid ink as a transfer material use the melting phenomenon of the solid ink for transfer, so the energy required during recording is relatively small, and the recording process corresponds to one filled transfer area. It is only necessary to spend 2 to 5 milliseconds for the recording, which shortens the recording time. However, since the energy required for recording is small, even if the amount of energy supplied to the resistance heating element is changed, it is not possible to delicately control the recording area transferred and recorded by one resistance heating element or the amount of transfer material transferred. had some difficult drawbacks. Third
FIG. 4 shows the relationship between the input energy to the conventional thermal head shown in the figure and the recording density. The recording density is given by the following formula, the closer to 0.0 is white, and the recording density = Iog ₁₀ (amount of reflected light from the perfect reflector (pure white) / amount of reflected light from the recording surface) The larger the number, the darker the recording. It is. In order to record a grayscale image, it is necessary that the recording density rises gradually with respect to the input energy, and that the variation in recording density is small, and the characteristics shown in FIG. 4 do not satisfy this requirement. In order to demonstrate this characteristic, in thermal transfer recording methods that use meltable solid ink as a transfer material, in the case of meltable solid ink with black dots, a density pattern method is used that records shading by recording only the white color that is not transferred and the black dots that are transferred. It is used to record halftone images. FIG. 5 shows an example of gradation expression using the density pattern method. The area to be transferred and recorded by one resistance heating element is hereinafter referred to as a recording point. In the density pattern method, shading is expressed by whether or not each of m×n recording points, which is composed of m recording points horizontally and n recording points vertically, is transferred or recorded. Here, m and n
is an integer greater than or equal to 2. In the example shown in Figure 5, m and n are each set to 4, and there are 16 recording points in total with 17 levels of shading (cases in which all recording points are not transferred and cases in which all recording points are transferred are not shown). can be selected. However, when this density pattern method is used, as the number of gradations, that is, the number of gradations increases, it is necessary to increase the number of recording points required to express the shading.
When the number of gradations is n, the number p of recording points required to express the number of gradations is given by the following equation. p=n-1 The number of recorded points is l in the horizontal direction and l in the vertical direction.
Since it is composed of l recording points, the following equation holds true. l=√−1 Here, the arrangement density of resistance heating elements is γ (pieces/mm)
If a thermal head is used, the effective pixel density d (pixels/mm), which is the unit of one piece of grayscale information to be recorded, is given by the following equation. d=γ√−1 For example, if you try to obtain 17 gradations using a thermal head with 8 resistance heating elements per 1 mm, γ
By substituting =8 and n=17 into the above formula, d=2,
The effective pixel density is 2 (pixels/mm). FIG. 6 shows the relationship between the number of gradations and the effective pixel density in the case where shading is expressed by the density pattern method using a heat sensitive head having a resistance heating element array density of 8 (pieces/mm). To express halftones, at least 17 gradations are required, so the effective pixel density is 2.
(pixels/mm), and the stored image becomes a rough image. [Object of the Invention] An object of the present invention is to improve the drawbacks of the prior art and provide a high-speed, high-definition halftone recording system using thermal transfer and its control circuit. [Summary of the Invention] It has been found that the minimum reproducible transfer recording area of one resistance heating element is approximately the area of the resistance heating element when meltable solid ink is used as the transfer material. Using this property, if the area of the resistance heating element is made sufficiently smaller than the filling transfer area (hereinafter referred to as the minimum resistance heating element area), then by using this resistance heating element, By controlling the input energy to the resistance heating element, it is possible to transfer and record from an area that is approximately the same as the area of the minimum resistance heating element, which is sufficiently small, to a filled transfer area by controlling the input energy to the resistance heating element. From the minimum resistance heating element area to the filling transfer area,
Transfer recording has a high recording density and is important as information on the image.The shading of this high recording density can be expressed for each resistive heating element, so the transferred image is created by the arrangement of the resistive heating elements on the thermal head. It has high definition, which is the same as density. On the other hand, for light recorded densities that are too dark to be expressed even with a transfer recording area that is approximately the same as the area of the minimum resistance heating element, the light recorded density portion is not very important as information, and the actual pixel density This method takes advantage of the fact that recorded images do not appear rough even when the image quality decreases. That is, by using the minimum resistance heating element area or a larger transfer recording area and thinning out the transfer recording at a certain recording point among several recording points, similar to the density pattern method described above, a light recording density can be expressed. I can do it. [Embodiments of the Invention] FIG. 1 shows an example of recording density characteristics by the thermal transfer halftone recording method according to the present invention. The density gradation has 32 steps, and when the input density is between 4 and 31, the recording density is adjusted by controlling the input energy to the resistance heating element. On the other hand, when the input density is between 1 and 3, a light recording density is properly expressed by recording one of the two recording points with an appropriate input energy. This example is a characteristic example using a thermal head in which the minimum resistance heating element area is 50% of the filling transfer area.
The recording density is 0.3 (corresponding to an input density of 4) when transfer recording is performed at the minimum recording point at which transfer recording can be performed with good reproducibility. For input densities of 1 to 3, transfer recording is performed as shown in Table 1.

〔Effect of the invention〕

According to the present invention, in thermal transfer recording using meltable solid ink, it is possible to control the recording density gradation for each high-definition recording pixel on the high-density side, which is the same as the arrangement density of the resistive heating element on the thermal head, and also on the low-density side. Although the effective pixel density becomes coarser, the image quality is not affected, and smooth recording density control is possible by thinning out recording pixels, making it possible to beautifully reproduce halftone images and full-color images, which were previously difficult to do. effective. Also,
It allows for faster recording than sublimation dye thermal transfer,
Five times faster recording is also possible.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram of the thermal transfer halftone recording method according to the present invention, FIG. 2 is a sectional view explaining the principle of thermal transfer recording, and FIG. 3 is a front view showing a resistance heating element of a conventional thermal head. Fig. 4 is a characteristic diagram of thermal transfer recording using meltable solid ink, which is a conventional technique, Fig. 5 is a density pattern diagram explaining a density pattern method, which is a conventional technique, and Fig. 3 is a density pattern method, which is a conventional technique. 7 is a characteristic diagram of the thermal transfer intermediate recording method according to the present invention, and FIGS. 8 and 9 are characteristic diagrams of the present invention.
The figure is a top view showing the resistance heating element on the thermal head used in the present invention, Figure 10 is a characteristic diagram of the thermal transfer intermediate recording system according to the present invention, and Figures 11, 12, and 13 are according to the present invention. A circuit diagram of a control circuit used in the thermal transfer intermediate recording method, and FIG. 14 is a timing diagram of the circuit shown in FIG. 13. 1... Conductor, 2... Resistance heating element, 2'... Minimum resistance heating element area, 3... Concentration information input terminal, 4...
...Input energy selection circuit, 5...Input energy supply limiting circuit, 6...Thermal head output creation circuit, 7
... Output terminal, 11 ... Thermal head, 12 ... Resistance heating element, 13 ... Transfer film, 14 ... Recording paper.

Claims (1)

[Claims] 1. From a recording area that is sufficiently narrower than the filling transfer area,
By controlling the input energy, a thermal head consisting of a plurality of resistive heating elements can be used to perform stepwise recording from a recording area sufficiently narrower than the above-mentioned filling transfer area to almost filling transfer. When recording a recording density that can be expressed up to the area, the input energy is controlled for each resistance heating element, and when recording a low recording density that cannot be expressed even by using a recording area that is sufficiently narrower than the above-mentioned filling transfer area, A thermal transfer halftone recording method characterized in that it also uses control of the number of resistive heating elements that are not used for recording among a plurality of adjacent resistive heating elements. 2. In what is stated in claim 1,
A thermal transfer halftone recording method characterized in that the recording area is sufficiently narrower than the filling transfer area and is 0.15 to 0.5 times the filling transfer area. 3 The circuit for transmitting recording density information to the thermal head includes an input energy selection circuit that selects the magnitude of the input energy to the resistive heating element in multiple stages, and an input energy supply limit that regularly selects whether input energy is supplied or not. For high-density recording density information that can be expressed in a recording area larger than the recording area that is sufficiently narrower than the filling transfer area, the input energy supply limiting circuit is used as the supply side, and the input energy selection circuit selects the necessary energy. For low-density recording density information that cannot be expressed even with a recording area sufficiently narrower than the filling transfer area, the input energy selection circuit selects an appropriate energy, and the input energy supply limiting circuit regularly supplies the input energy. A thermal transfer halftone recording control circuit characterized by selecting supply and non-supply. 4 In what is stated in claim 3,
A thermal transfer halftone recording control circuit characterized in that one or more flip-flop circuits are used as an input energy supply limiting circuit.