JPH02277663A - Density controlling method of thermal transfer printer - Google Patents

Abstract

PURPOSE:To obtain an image of good quality in a wide range of density by supplying power to a thermal head every predetermined pitch in the region where the density of pixels is thick, while supplying power to said thermal head at least at two different positions within a predetermined pitch in the region where the density of pixels is thin. CONSTITUTION:A platen roller 1 is rotated by a pulse motor. It is so arranged that the platen roller 1 forwards a recording paper 4 by two pulses. The density of pixels of signals sent to a heat generating element 5 is detected. For example, when the density of pixels is not smaller than 40%, the heat generating element 5 is allowed to generate heat once every two pulses of the pulse motor, so that pixels of one line are formed on the recording paper 4. In the case where the density of pixels is not higher than 40%, the heat generating element 5 is allowed to generate heat once by one pulse of the pulse motor, forming pixels of one line onto the recording paper 4. Subsequently, the heat generating element 5 is allowed to generate heat once by the next pulse by the same amount of energy, forming pixels of the one line on the recording paper 4.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention relates to a density control method for a thermal transfer printer that controls the density of pixels formed on recording paper by a thermal transfer printer, and particularly to a method for controlling the density of pixels formed on recording paper by a thermal transfer printer. The present invention relates to a density control method for a thermal transfer printer.

(Prior Art) In recent years, color video printers that convert video signals into color prints using thermal transfer printers have been commercialized. In particular, with the development of electronic still cameras, it has become possible to obtain color prints equivalent to silver halide photographs. In this case, delicate gradation is required to express in complete color, and for this purpose it is most suitable to use a sublimation type thermal transfer printer (hereinafter simply referred to as a printer).

The configuration of this printer is shown in FIGS. 6 and 7.

In FIG. 6, the outer periphery of the platen roller 1 has a roller 1
A line type thermal head 2 is provided along the rotation axis direction of the platen roller 1.
An ink sheet 3 and recording paper 4 are stacked and sandwiched between them. Further, the platen roller 1 is rotationally driven by a pulse motor (not shown), and supplies the ink sheet 3 and recording paper 4 held between the thermal head 2 and the recording paper 4 at a predetermined pitch in the direction shown by arrow A. As shown in FIG. 7, the thermal head 2 has a large number of heating elements 5 arranged in a straight line in the axial direction of the platen roller 1 at a pitch of usually 6 dots/mm. Similarly, the paper feed pitch p for feeding the recording paper 4 by the pulse motor is normally 6 dots/mm.

In the printer configured as described above, a current is simultaneously applied to each of the n heating elements 5 in the axial direction by a signal from a signal source, and heat is generated in accordance with the gradation of the pixel. Then, using this heat, the ink is applied to the ink sheet 3 and the ink is applied to the recording paper 4.
Transfer on top. At this time, in the ink sheet 3 using sublimation dye, by changing the amount of energy generated by the heating element 5, it is possible to change the density of the transferred pixels and produce gradation characteristics. In this way, one line of image is formed on the recording paper.

Next, the platen roller 1 is rotated by one pitch by the pulse motor, and the above-mentioned operation is repeated to obtain the next one line of image. is formed. When forming a color image, three colors of yellow, magenta, and cyan are used. For example, a color image can be obtained by forming one screen with yellow and then superimposing the next color.

When forming an image as described above, for example, if the predetermined pitch p of paper feeding is 6 dots/mm, that is, 0.167
In the case of mm/dot, conventionally, after one line of printing was completed, the recording paper was advanced 0.167 mm to form the next line of pixels.On the other hand, the length of the transferred pixels was It changes in accordance with changes in the energy emitted from each heating element 5 of the thermal head 2 in order to obtain the desired temperature. According to the results obtained from experiments, this change in length is 30% to 70% of the length of the heating element 5. Therefore, when the length of the heating element 5 is 0.3 m, the length of one transferred pixel is 0.09 mm to 0.21 mm. As a result, in the low concentration region 6 shown in FIG. 8, that is, the region where the energy emitted from the heating element 5 is small, the adjacent length a in the direction of the arrow A is shown in an enlarged view in FIG.
Length m between pixel 7 = 0.09mm = 0.077
A blank portion 8 of mm is generated. For this reason, there is a problem in that the image formed on the recording paper 4 becomes rough and the image quality deteriorates.

As a means to solve this problem, it is possible to increase the length of the heating element 5 so that the pixels 7 adjacent to each other in the direction of the arrow A in the low concentration region 6 overlap. Pixel 10 of length b in high concentration region 9 shown in
However, as shown in an enlarged view in FIG. 10, they overlap over a wide range of length n, resulting in a sticky image, making it impossible to obtain a good image.

(Problems to be Solved by the Invention) As described above, according to the conventional printer density control method, if the length of the heating element is short, blank areas will occur between pixels in the low density area, resulting in a rough image. Furthermore, if the heating element is made longer, the overlapping range of pixels in the high-density region becomes wider and the image becomes sticky. As a result, there is a problem in that the image quality deteriorates even in the case of A deviation.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a density control method for a printer that can obtain high-quality images in a wide density range using a simple method.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention uses a thermal transfer printer having a thermal head in which a large number of heating elements are arranged in a straight line. In a density control method for a thermal transfer printer, which controls the density of an image formed on a recording paper that is fed at a predetermined pitch in a direction perpendicular to the thermal head, a region of high density of pixels forming the image is provided. In this case, the thermal head is energized once at each of the predetermined pitches, and in areas with low pixel density, the thermal head is energized at least two same positions shifted within the range of the predetermined pitch. be.

(Function) According to the above method, by appropriately setting the feeding pitch of the recording paper and the length of the heating element, overlapping of pixels in high density areas can be minimized, and blank areas between pixels in low density areas can be minimized. occurrence can be minimized.

(Embodiment) Hereinafter, an embodiment of the printer density control method according to the present invention will be described with reference to the drawings.

An embodiment of the present invention is shown in FIGS. 1 and 2. FIG.

Note that the printer used in this embodiment is the same as that shown in FIGS. 6 and 7, so a description thereof will be omitted.

When the platen roller 1 is rotationally driven by a pulse motor, the platen roller 1 rotates the recording paper 4 by 0.16 pulses.
Make sure to feed it 7 mm. In addition, the pixel density of the signal sent to the heating element 5 is detected, and if the pixel density is 40% or more, the heating element element is activated once every two pulses of the pulse motor. 5 to generate heat,
Pixels for one line are formed on the recording paper 4. When the pixel density is 40% or less, one pulse of the pulse motor causes the heating element 5 to generate heat to form one line of pixels on the recording paper 4, and then the next pulse also generates the same amount of energy. The heating element 5 is made to generate heat once with
Form pixels for a line. That is, the recording paper 4 is 0.
While being sent for 167 m+s, one line of pixels is formed in the high density area, and two lines of pixels of the same density are formed in the low density area.

Adjacent pixels 11a and 11 in the low concentration area are shown in FIG.
An example of an overlapping state with b is shown. Here, the heating element 5
The length of the transferred pixel is 0.3m1n, and the length of the transferred pixel is 30% to 70% according to the density, that is, 0.09mm to 0.
．． 21 mm, and the paper feeding pitch p by two pulses of the pulse motor is 0.16711a11. In the low density area, the pixel length a is 0.09 mm, and the paper feed pitch 1/2p by one pulse is 0.0835 mm, so the length m of the overlapping portion of adjacent pixels 11a and 11b is 0.
．． It becomes 0065mm. That is, pixels 11a, 1
No blank space occurs between 1b, and a smooth image can be obtained.

FIG. 2 shows an example of an overlapping state of pixels 12a and 12b in a high concentration region. If the setting conditions in this case are the same as in the case of the low density area, the pixel length b is 0.21
mm, so the adjacent pixel 12a.

121), the length n of the overlapping portion is 0.043 mm. Therefore, the length n of the overlapping portion of pixels 21a and 21b
is relatively small and can produce good images without roughness.

Note that the supply of energy to the thermal head 2 is controlled by the energization time, so the energization time may be shorter in the low concentration region, and in the case of 40% concentration, it is 40% longer than the maximum concentration.
% of the current application time is sufficient, and the method according to this embodiment does not increase the printing time. Furthermore, the pulse motor is controlled electrically, and the thermal head 2 is easily controlled for each pulse using conventional techniques, so a description thereof will be omitted.

According to this embodiment, it is possible to prevent the occurrence of blank areas in low-density areas and wide overlap of pixels in high-density areas, and it is possible to increase the smoothness of images and obtain good image quality.

In the above embodiment, the case where the image has shading in the paper feeding direction of the recording paper 4 has been explained, but as shown in FIGS. 3 to 5, there is a case where the image has shading in the direction perpendicular to the paper feeding direction. The present invention can also be applied to. That is, for example, if the left side of the figure is a high concentration area and the right side is a low concentration area, the heating element 5 on the left side of the thermal head 2 is energized once every two pulses of the pulse motor to generate heat, and the heating element 5 on the right side is energized once for every two pulses of the pulse motor. By energizing the heating element 5 once per pulse to generate heat, it is possible to obtain the same functions and effects as in the embodiment described above. In addition, Figures 3, 4 and 5
Portions equivalent to those shown in FIG. 8, FIG. 1, and FIG. 2 are designated by the same reference numerals.

The present invention can also be applied to the case where a color image is formed on recording paper by a printer.

[Effects of the Invention] As explained above, according to the present invention, when an image is formed on recording paper by a thermal transfer printer, it is possible to prevent the occurrence of stickiness of the image in high density areas and roughness of the image in low density areas. You can obtain smooth and good image quality.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the configuration of pixels in a low concentration area formed according to an embodiment of the present invention, FIG. 2 is a plan view showing the configuration of pixels in a high concentration area, and FIG. FIGS. 4 and 5 are plan views showing images according to other embodiments; FIGS. 4 and 5 are plan views showing pixel configurations in low-density areas and high-density areas, respectively; and FIG. 6 is a perspective view showing the configuration of a thermal transfer printer. Fig. 7 is a perspective view showing the thermal head shown in Fig. 6, Fig. 8 is a plan view showing a conventional image, and Figs. FIG. 3 is a plan view showing the configuration of a pixel. 2...Thermal head 4...Recording paper 5...Heating element 6...
Low density area, 7.10.11.12...pixel 9
... High concentration area agent Patent attorney Norihiro Chika Yudo Hiroki Uji Figure Figure Figure

Claims (1)

[Claims] A thermal transfer printer having a thermal head in which a large number of heating elements are arranged in a straight line controls the density of an image formed on recording paper that is fed at a predetermined pitch in a direction perpendicular to the thermal head. In the density control method for a thermal transfer printer, in an area where pixels forming the image have a high density, the thermal head is energized once at each of the predetermined pitches; A density control method for a thermal transfer printer, characterized in that the thermal head is energized at least twice in different positions.