JPH0564904A - Thermal transfer printer - Google Patents

Abstract

PURPOSE:To make a halftone print without degrading resolution by a printer wherein transfer dots whose sizes are different are arranged regularly, optional dots are made to grow to an area of 1/(NXM) or more stepwise in a matrix of NXM dots, and dots other than the optional dots are made to be optional dots in a bridged state. CONSTITUTION:Image data 31 for a plurality of lines are sample in a matrix state of NXM (integer of M>1, N>1) dots. A gamma conversion means 34 for performing gamma conversion of each dot of NXM dots and outputting printing data is provided. Here, the gamma conversion means 34 makes optional dots grow to an area of 1/(NXM) or more stepwise in the matrix of the NXM dots from a low density to a middle density. From the middle density to a high density, dots other than the optional dots are made to grow in the matrix of the NXM dots in a state that the dots are always bridged with the optional dots.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention arranges at least one or more heat generating resistance elements on the surface of a substrate and selectively heats the heat generating resistance elements corresponding to print data to generate ink on an ink sheet or ink ribbon. The present invention relates to a gradation control technique suitable for a thermal transfer printer in which dots are melted to form dots on a recording sheet.

[0002]

2. Description of the Related Art Thermal transfer printers use ink sheets or ribbons in which wax containing pigment is applied to a polymer film and supply signals based on pixel data to a thermal head in which minute heating resistance elements are integrated on a substrate. By doing so, the ink in the minute area is melted to form dots on the recording paper.

Such a thermal transfer printer is widely used in the field of full-color printing, which requires high-density dot formation, because it is easy to form a heating resistance element that is a dot-forming element in a minute size.

By the way, when full-color printing is performed by a printer, usually three colors of three primary colors of yellow, magenta, and cyan, or four colors of the three primary colors and black are superposed. Here, in order to give gradation representation to each color, a matrix consisting of N × M (M> 1, N> 1) segments is configured as one pixel, and each heating resistor element corresponding to each segment generates heat. Binary transfer is performed with or without. That is, N × M gradation expression is possible. For example, FIG. 12 partially shows the arrangement of conductive dots in the case where the matrix is composed of 4 × 4 segments and 16 gradations are expressed per color. (A) is 1/16 gradation,
(B) is 4/16 gradation, (c) is 8/16 gradation, (c)
Is an expression of 14/16 gradation.

[0005]

However, if the conventional gradation expression method is adopted, the matrix must be expanded as the number of expressed gradations is increased (16 gradations per color is 4 × 4, If there are 64 gradations, 8 × 8), and eventually the resolution decreases and the image quality deteriorates. This is one of the conventional thermal transfer printers
This is because the gradation expression for each dot is difficult and the binary transfer is forced. The reason will be described based on FIG.

When the maximum resolution of the thermal head is maintained and area gradation is performed simultaneously for each dot, 1 in (a)
With / 16 gradation, the transfer to the recording paper is not stable and the shapes are also different. As a result, the feeling of looseness is emphasized.
At (4/16) gradation of (b), the adhesive force to the recording paper is stable,
Since the distance from the adjacent dot is also appropriately separated, the reproducibility of each dot is improved and a clear gradation expression can be performed. However, next, in the case of 8/16 gradation shown in (c), the distance from the adjacent dot becomes short, and an irregular dot bridge is generated due to the influence. Here, too, the dot reproducibility is poor, so that the feeling of blurring is emphasized and the image quality is impaired. 14/16 of (d)
In gradation, all the adjacent dots are stably bridged, so that the transfer is relatively stable.

As described above, when the area gradation is performed at the maximum resolution of the head, the transfer instability at the low gradation and the dot bridge at the halftone can stably reproduce the reproduction even if the number of gradations is large. Limited to 4 or less.

Therefore, an object of the present invention is to provide a thermal transfer printer capable of multi-gradation expression without holding the dot matrix to a minimum and expanding the dot matrix size by the expression gradation number, that is, without lowering the resolution. Is to provide.

[0009]

A thermal head having at least one heating resistance element arranged therein, a means for conveying a recording paper and an ink sheet at a predetermined pitch, and input image data. Means for continuously extracting pixel data for a plurality of lines, means for sampling the image data for the plurality of lines in a matrix of N × M (M> 1, N> 1 integer) dots, and N × M (M>
1, an integer of N> 1) γ conversion means for performing γ conversion on each dot and outputting printing data;
The converting means gradually changes 1 / (N × M) arbitrary dots in a matrix of N × M dots from low density to medium density.
And growing in a matrix of N × M dots from the medium density to the high density, the growth of dots other than the arbitrary dots is carried out in a state of being always bridged with the arbitrary dots.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will now be described based on the illustrated embodiments.

FIG. 1 shows a thermal transfer printer according to an embodiment of the present invention. The printer mechanism uses a stacker 2 stocking recording paper 1 to pick up one recording paper by a pickup roller 3. A paper feed mechanism 4 that pulls out and conveys the recording paper 1 and the ink sheet 9 at a constant speed, a thermal head 6 that is pressed against the platen 5 during recording, and a printed recording paper. The stacker 2 includes a transport roller 8 for returning the stacker 2 again, a stock roller 10 for supplying an ink ribbon 9, and a take-up roller 11.

As shown in FIG. 2, the thermal head 6 has heating elements 14, 1 on the surface of the substrate 13 at a constant pitch.
4, 14 ... Are formed in a row, and lead wires 15, 15, 15 ..., 16, 16, 16 ...
It is constructed by pulling out. FIG. 3 shows an embodiment of the above-mentioned control circuit, in which reference numeral 17 is a microcomputer constituting the central part of the control device, and C
An external device such as a personal computer via a PU 18, a ROM 19 storing a control program and a data processing program described later, and a RAM 20 forming a data processing buffer and a frame memory, and a thermal device such as a personal computer via interfaces 21 and 22. It is connected to the head drive circuit 23 and the motor drive circuit 24.

The thermal head drive circuit 23 supplies electric energy corresponding to the density data output from the interface 22, for example, densities B1, B2, B as shown in FIG.
3, B4, ... Bn corresponding to times T1, T2, T3, T4,
.. are supplied to the respective heating resistance elements 14, 14, 14, ... Of the thermal transfer thermal head 6.

The motor drive circuit 24 is also configured to output a drive pulse to the motor so that the rotation direction and rotation speed correspond to the command output from the interface 22.

FIG. 5 shows an embodiment represented by the function performed by the above-mentioned microcomputer 17 which is necessary for performing color recording by making use of the above-mentioned basic recording function. Is an image memory for storing image data output from the external recording device, and is configured to store a predetermined amount of image data for each color output from the external device, for example, for one page. An image data reading unit 31 extracts the image data stored in the image memory 30 by moving the pixel data for N lines (an integer of N ≧ 2) by N lines and outputs the extracted pixel data to the line buffer 32. It is a thing. A sampling means 33 samples N digits (N ≧ 2 integers), that is, N × N dots, in the main scanning direction from the pixel data stored in the line buffer 32, and outputs the samples to the γ conversion means 34 described later. It is a thing.

Reference numeral 34 denotes the above-mentioned γ conversion means, which is a density of the pixel data (hereinafter referred to as conversion recording data) so that the pixel data from the sampling means 33 can function as a filter and a recording density setting means. Is specified), data defining the relationship between the density of pixel data and print conversion data is stored.

The present printer expresses the area gradation, that is, the density is expressed by the size of the dot area corresponding to the density data. According to the pixel data shown in FIG.
A first example of a process of growing a dot area represented by a plurality of conversion characteristic functions γ set to 4 will be described. Assuming that the dot represented by the conversion characteristic function γ1 is D1, D1 becomes a substantially linear shape with the maximum value of Rb which is slightly shorter than the dot radius Ra corresponding to the head resolution from 0 to low density to medium density area. The dot radius Rb is increased to maintain the dot radius Rb from the medium density region to the high density region, and at the highest density, the dot radius Rd is slightly longer than the dot radius Ra / 2.

When the dots represented by the conversion characteristic functions γ2 and γ3 are D2 and D3, D2 and D3 are not transferred from the low density to the middle density area, and the dot radius is from the middle density to the high density area.
It has a characteristic that the dot radius Rc, which is shorter than Ra and Rb, increases linearly with the maximum value, and the dot radius Rd is slightly longer than the dot radius Ra / 2 at the maximum density.

Assuming that the dot represented by the conversion characteristic function γ4 is D4, D4 is not transferred from the low density area to the high density area, and has a dot radius Ra / 2 which is 1/2 of the head resolution near the maximum density. It has characteristics.

FIG. 7 shows a second embodiment of the growth process of the dot area represented by a plurality of conversion characteristic functions γ set in the γ conversion means 34 according to the pixel data.
Here, the dot represented by the conversion characteristic function γ1 is D1
Then, D1 increases from 0 in a low density to medium density area in a substantially linear manner with the maximum value being Rb which is slightly shorter than the dot radius Ra corresponding to the head resolution, and the dot radius Rb from the middle density to high density area. Keep the dot radius Ra / 2 at maximum density
It has a characteristic that the dot radius Rd is slightly longer than that.

If the dot expressed by the conversion characteristic function γ2 is D2, D2 is not transferred from the low density to the first half of the medium density area, and the dot radius R from the first half of the middle density to the high density area.
It has a characteristic that the dot radius Rc, which is shorter than a and Rb, increases linearly with the maximum value, and the dot radius Rd is slightly longer than the dot radius Ra / 2 at the maximum density.

Assuming that the dot represented by the conversion characteristic function γ3 is D3, D3 is not transferred from the low density to medium density area (higher density side than D2), and the dots are distributed from the middle density to high density area while following D2. Dot radius Rc shorter than radius Ra and Rb
It has a characteristic that the dot radius Rd increases linearly with the maximum value, and the dot radius Rd is slightly longer than the dot radius Ra / 2 at the maximum density.

Assuming that the dot represented by the conversion characteristic function γ4 is D4, D4 is not transferred from the low density region to the high density region and has a dot radius Ra / 2 which is 1/2 of the head resolution near the maximum density. It has the characteristics to

Examples of application of the above conversion characteristic function to actual recording are shown in FIGS. 8, 9 and 10.

FIG. 8 is common to the first and second embodiments, and is a matrix pattern for expressing 32 gradations per color in a 2 × 2 matrix, that is, D1, D2, D3, D.
The arrangement of 4 is shown.

FIG. 9 uses the matrix pattern of FIG. 8 and uses (a), (b),
(C) and (d) The dot growth process at four locations and a part of the gradation expression are shown. (A) is 8/32 gradation, (b) is 1
6/32 gradation, (c) 24/32 gradation, (d) 31
/ 32 gradations.

FIG. 10 uses the matrix pattern of FIG. 8 and, in the second embodiment of FIG. 7, (a), (b),
Parts (c) and (d) of the gradation expression at four locations are shown.
(A) is 8/32 gradation, (b) is 16/32 gradation,
(C) shows 24/32 gradations, and (d) shows 31/32 gradations.

Even if the positions of D2 and D3 are interchanged, the effect of the present invention is not impaired. Further, even if the arrangement is changed without breaking the relative positional relationship of each dot in the 2 × 2 matrix, the effect of the present invention is not impaired.

According to the first and second embodiments, when the dots of D1, D2, D3, and D4 are bridged to the dot of D1 when the dots of D1, D2, D3, and D4 start to be transferred, the abrupt density increases. Jumps are suppressed as much as possible.

Further, since different conversion characteristic functions for different print data are applied to the same image data, the mutual interference of the heating elements forming the adjacent dots is reduced, and the gradation which is faithful to the input print data is reduced. It is possible to form transfer dots exhibiting the characteristics.

FIG. 11 shows the recording result of the gradation characteristic per color according to the present invention. A smooth gradation characteristic without density jump was demonstrated from low gradation to high gradation.

[0032]

As described above, according to the present invention,
A thermal head in which at least one or more heat generating resistance elements are arranged, a means for conveying a recording paper and an ink sheet at a predetermined pitch, and pixel data forming input image data are continuously provided for a plurality of lines. To extract the image data of the plurality of lines into N × M (M> 1,
A means for sampling in a matrix of N> 1 integer) dots, and a [gamma] conversion for performing [gamma] conversion on each of N * M (M> 1, N> 1 integer) dots to output print data. Means and the γ conversion means stepwise 1 / (N × M) an arbitrary dot in a matrix of N × M dots
Since it has been grown to an area equal to or larger than the area and the growth of the dots other than the arbitrary dot in the matrix of N × M dots is always performed in a state of being bridged with the arbitrary dot,
As a result, it is possible to provide a thermal transfer printer capable of expressing smooth multi-gradation without density jump without lowering the resolution as compared with the conventional apparatus.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a thermal transfer printing apparatus of the present invention.

FIG. 2 is a front view showing an example of a print head used in the present invention in a state in which a coating layer on the surface is removed and an electrode portion is exposed.

3 is a block diagram showing an embodiment of a control device in the device shown in FIG.

FIG. 4 is a diagram showing signals from a thermal transfer type print head drive circuit in the apparatus shown in FIG.

5 is a block diagram showing functions to be performed by a microcomputer in the apparatus shown in FIG.

FIG. 6 is a diagram showing a first embodiment of a function used in the present invention.

FIG. 7 is a diagram showing a second embodiment of the function used in the present invention.

FIG. 8 is a diagram showing an embodiment of a dot matrix pattern according to the present invention.

FIG. 9 is a diagram showing an example of a dot growth process and gradation expression according to the first embodiment of the function used in the present invention.

FIG. 10 is a diagram showing an example of a dot growth process and gradation expression according to a second embodiment of the function used in the present invention.

FIG. 11 is a diagram showing a recording result of gradation characteristics per color according to the present invention.

FIG. 12 is a diagram showing a grayscale expression method in a conventional technique.

FIG. 13 is a diagram showing details of problems in the conventional technique.

[Explanation of symbols]

 2 Stacker 3 Pick-up roller 4 Paper feed mechanism 5 Platen 6 Thermal transfer print head 9 Ink sheet 12 Circuit board 14, 14 Heating resistor element 15, 16 Lead wire 17 Microcomputer

[Procedure amendment]

[Submission date] July 9, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] Figure 9

[Correction method] Change

[Correction content]

[Figure 9]

Claims (1)

[Claims] 1. A thermal head in which at least one or more heat generating resistance elements are arranged, a means for transporting a recording paper and an ink sheet at a predetermined pitch, and pixel data forming input image data. A unit for continuously extracting a plurality of lines and N × M image data for the plurality of lines.
Means for sampling in a matrix of (M> 1, N> 1) dots, and γ conversion for each dot of N × M (M> 1, N> 1) dots for printing data. And a γ-converting means for outputting any dot in a matrix of N × M dots from a low density to a medium density stepwise to an area of 1 / (N × M) or more. A thermal transfer printer characterized in that, from medium density to high density, dots other than the arbitrary dots are grown in a matrix of N × M dots in a state of being always bridged with the arbitrary dots.