JP2012040741A - Heat transfer printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To print an image to make banding noise hardly conspicuous in a heat transfer printer.SOLUTION: The heat transfer printer can make the banding noise generated at the time of printing the image hardly conspicuous by controlling a gain in a predicted region where banding occurs.

Description

  The present invention relates to a thermal transfer printer that prints an image on paper.

  In various printing apparatuses such as an ink jet printer and a sublimation type thermal transfer printer, it is known that so-called banding occurs during printing. For example, in an ink jet printer, uneven production of ink nozzles is a major cause of banding noise. Ideally, all inkjet nozzles should be uniformly oriented in the same direction, but in reality, variations occur at the manufacturing stage, resulting in unevenness in the direction in which the ink scatters. Ending banding noise occurs.

  In order to suppress the occurrence of such banding noise, in Japanese Patent Laid-Open No. 2004-228561, a solid image test pattern is printed and density data is captured, and banding noise occurrence information is acquired and ink at the time of printing based on the occurrence information. The dot arrangement has been corrected.

JP 2008-93852 A

  In recent years, thermal transfer printers that can obtain printed matter equivalent to the quality of silver halide photographs are being used instead of ink jet printers. However, in the thermal transfer printer, banding noise is generated as in the case of the ink jet printer. However, the method of Patent Document 1 is a technique that can be applied only to an ink jet printer that uses an area gradation method that can correct the dot arrangement method during printing, and uses a density gradation method (applying to a thermal transfer printer) Impossible.

  In order to solve such a problem, an object of the present invention is to print an image so that banding noise is not noticeable in a thermal transfer printer.

In order to solve the above problems, the thermal transfer printer of the present invention is
A thermal transfer printer that prints an image by sequentially transferring inks of a plurality of colors on an ink sheet onto a printing sheet, and a gain unit that performs gain processing on a predetermined area of the image data, and a conveying unit that conveys the printing sheet Based on the gain amount calculated by the gain amount processing means, correction means for correcting the image data of the predetermined area of the image data, and based on the image data corrected by the correction means A thermal head for transferring ink on the printing sheet conveyed by the conveying means, a density acquisition means for acquiring a density value of the predetermined area in the image data, and acquired by the density acquisition means Depending on the density-dependent gain amount calculation means for calculating the gain amount depending on the density and the position of the predetermined area. A position dependent gain amount calculating means for calculating a gain amount to be performed, a random gain amount calculating means for calculating a random gain amount for each calculation, and the gain amount processing means, the density dependent gain amount calculating means, the position dependent gain The gain amount of the gain amount processing means is calculated from the gain amount calculated by the amount calculating means and the random gain amount calculating means.

  With the above-described configuration, the thermal transfer printer of the present invention can print an image so that banding noise is not noticeable.

1 is a conceptual diagram of a printing apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a hardware configuration for realizing a printing apparatus according to an embodiment of the present invention. It is the flowchart which showed the banding noise correction process which concerns on embodiment of this invention. It is the figure which showed the correction | amendment object area | region which concerns on embodiment of this invention. It is the figure which showed the density | concentration dependence gain table which concerns on embodiment of this invention. It is the figure which showed the position dependence gain table which concerns on embodiment of this invention.

  Hereinafter, the thermal transfer printer according to this embodiment will be described with reference to FIGS.

  The embodiment described below is an example as means for realizing the present invention, and should be appropriately modified or changed according to the configuration and various conditions of the apparatus to which the present invention is applied. It is not limited to the embodiment.

First, the print processing system block of the thermal transfer printer will be described with reference to FIG.
Reference numeral 201 denotes a card reader for setting various memory cards, which can read image data recorded on the memory card. A non-volatile memory (ROM) 202 stores in advance a program for controlling the printer, various parameter values necessary for printing, various table data to be described later, and the like. A system control unit 203 controls the entire printer, reads a program stored in the ROM 202, controls each block and performs arithmetic processing based on the read program, and controls the entire printer. Reference numeral 204 denotes a volatile memory (RAM), which holds image data read from the card reader 201 and holds temporary parameters. Reference numeral 205 denotes an image processing unit, which performs decompression processing of a JPEG image read from the card reader 201. In the present embodiment, the decompression process is conversion from the Jpeg format to the YUV format. Reference numeral 206 denotes a print image generation unit, 207 a banding noise correction unit, and 208 a print processing unit.

  The print processing unit 208 includes the thermal head 101 and a transport mechanism (such as transport path rollers 103 and 104). The print processing unit 208 in this embodiment employs a sublimation thermal transfer recording type thermal head 101, and an ink cartridge in which an ink sheet and printing paper are integrated is mounted on the printer. The printing paper is pulled out from the mounted ink cartridge, and the ink of the ink sheet is transferred onto the printing paper by the thermal head 101, thereby performing image printing processing. The ink sheet is coated with a plurality of colors of ink, and the yellow (Y), magenta (M), and cyan (C) ink layers and the overcoat (OP) layer are arranged in a size corresponding to the size of the printing paper. It is provided. After thermal transfer for each color, the printing paper is returned to the recording start position and conveyed, and sequentially transferred onto the paper. For this reason, the print image generation unit 206 converts the print data generated by the image processing unit 205 from the YUV format to the YMC format. The print processing unit prints an image by driving the thermal head based on the mYMC format data. The banding noise correction unit 207 performs banding noise correction described later on the Y, M, and C color data generated by the print image generation unit 206. The print processing unit 208 records the paper by sequentially transferring the Y, M, and C ink layers to the paper using the Y, M, and C color data after the banding noise correction generated by the banding noise correction unit 207. Repeat the return to the start position to print all colors.

An image display device 209 can select a menu image or a print image.
Reference numeral 210 denotes a UI operation unit, which includes up / down / left / right buttons for operating a menu screen displayed on the image display unit 208, a print button, and the like.

Here, generation of banding noise in the thermal transfer printer will be described with reference to FIG.
(The main cause of banding noise in a thermal transfer printer is a change in conveyance speed during paper feeding. FIG. 1A is a conceptual diagram showing the positional relationship between a thermal head of a thermal transfer printer, printing paper, and a paper feeding roller. It is.

  Reference numeral 101 denotes a thermal head for printing an image by applying heat to the ink ribbon by applying heat to the ink ribbon, and 103 and 104 are paper feed rollers for conveying the printing paper.

  (Generally, the thermal transfer printer does not move the position of the thermal head 101, and the paper feed rollers 103 and 104 convey the printing paper 102. While the printing paper is being conveyed, the heat generated in the thermal head 101 is arranged side by side. By controlling the voltage applied to the resistor to change the heat generation amount of the heating resistor, the heat applied to the ink ribbon is changed to express gradation.

  Here, as shown in FIG. 1B, when the end 105 of the printing paper 102 passes through the position where the printing paper contacts with the paper feeding roller 103 (the position of the line segment in the paper feeding roller in the figure), printing is performed. The conveyance speed may temporarily decrease due to the level difference of the paper 102. Due to the decrease in the conveyance speed, the heat applied to the ink ribbon by the thermal head 101 temporarily increases, banding noise occurs in the head direction (main scanning direction), and an image with a single line is printed. . That is, banding noise is generated at a position corresponding to the relative distance from the end 105 of the print sheet to the position where the print sheet contacts with the paper feed roller 103 to the heating resistor of the thermal head.

  Further, as shown in FIG. 1C, when using the printing paper 107 with the perforation 106, when the perforation 106 passes the paper feed roller 103, the conveyance speed is increased due to the step of the perforation 106. May temporarily decline. Due to the decrease in the conveyance speed, the heat applied to the ink ribbon by the thermal head 101 temporarily increases, banding noise occurs in the head direction (main scanning direction), and an image with a single line is printed. . Accordingly, banding noise occurs at a position corresponding to the distance from the perforation to the position where the printing paper contacts with the paper feed roller 103 to the heating resistor of the thermal head.

In this embodiment, in order to make such banding noise inconspicuous, the following banding noise correction process is performed.
The banding noise correction process according to this embodiment will be described in detail with reference to FIGS.

  This process is a process capable of making the banding noise streak inconspicuous to the user by performing a gain process on the image data corresponding to the predicted banding noise occurrence position caused by the decrease in the paper transport speed. . The generation position of the banding noise is uniquely determined by the relative positional relationship between the thermal head 101 and the paper feed roller 103 described with reference to FIG. However, it does not necessarily occur at the same position, and some variation occurs in the generation position due to various external factors. Examples of causes include, for example, the shape of the paper edge 105, variations in paper feed speed, and variations in relative positional relationship during manufacturing. Therefore, in the present embodiment, in consideration of the variation in the banding noise occurrence location measured in advance, the range indicated by CorrectHeight shown in FIG. 4 is set as the banding noise occurrence predicted position, and gain processing is performed on the print data for this range Do it. The range CorrectHeight is written in the ROM 202 in advance at the manufacturing stage. In the case of the perforated paper 106, the predicted banding noise occurrence position is determined in consideration of the distance from the edge of the paper to the perforated position.

  FIG. 3 is a block diagram showing the operation of the banding noise correction unit 207 for the Y (yellow) plane generated by the print image generation unit 206 and recorded in the RAM 204 when an image read from the card reader 201 is printed. It is.

First, in step 301, initialization processing of a pseudo random number used for calculation of a correction gain amount described later is performed.
Here, the random number calculation algorithm used in the present embodiment uses a so-called linear congruence method obtained by the following equation.
rand _{x + 1} = (rand _x × A + B)% C (Formula 1)
Here, A, B, and C are arbitrary coefficients, and a pseudo-random number rand _x of ₀ to C-1 can be calculated by determining an initial value rand ₀ in advance. Here, the subscript x of rand indicates a pseudo-random number obtained at the time of the x-th calculation. The initialization process in step 301 is that the system control unit 203 reads the pre-recorded initial value rand ₀ from the ROM 202. It is to start.

  In the subsequent step 302, the density value D [x, y] of the Y (yellow) plane to be corrected stored in the RAM 204 is acquired. Here, as shown in FIG. 4, x and y represent the pixel position in the thermal head direction on the Y (yellow) surface, and y represents the pixel position in the paper feed direction.

  In step 303, the density-dependent gain amount is calculated based on the density value D [x, y] acquired in step 302. As shown in FIG. 5, the density-dependent gain amount is stored in advance in the ROM 202 as a table for each of the Y, M, and C planes, and is calculated by the system control unit 203 reading the table, and the result is The data is temporarily stored in the RAM 204.

  This process is a process of calculating a gain amount for correcting the effect difference because the effect level of the banding noise correction according to the present embodiment differs depending on the density of the color to be printed. In the present embodiment, the gain amount is reduced because the effect of banding noise correction is more effective in the portion where the density of the C (cyan) plane is high.

  In step 304, the system control unit 203 calculates the pseudo random number gain amount using the above-described equation (1), and temporarily stores the result in the RAM 204.

  In step 305, the position-dependent gain table at the coordinates x and y of the image data is calculated by reading the position-dependent gain table stored in the ROM 202 and temporarily stored in the RAM 204.

  In the present embodiment, a position-dependent gain table having a horizontal 150 grid and a vertical 15 grid shown in FIG. Here, the X-axis in FIG. 6A indicates the pixel position in the thermal head direction (main scanning direction), and the Y-axis indicates the pixel position in which the correction start coordinate CollectStartY in FIG. Also, the black density change represents the gain amount change, and the black region has a higher gain amount, and the gain amount is lower as it becomes whiter.

  In FIG. 6B, Y [0], Y [7], and Y [14] indicate the change in gain amount in the X direction when Y = 0, Y = 7, and Y = 14 in FIG. A cross-sectional view is shown. X [0], X [50], and X [100] in FIG. 6C indicate the change in the gain amount in the Y direction when X = 0, X = 50, and X = 100 in FIG. A sectional view taken along the axis is shown. Thus, the change amount of the gain amount in the X-axis direction is about 20 pixel cycles, and the change amount of the gain amount in the Y-axis direction is about 1 pixel cycle. The most important point in this embodiment is that the gain amount period differs between the thermal head direction and the paper feed direction.

As shown in FIG. 1, in order to make the banding noise line extending in the thermal head direction inconspicuous,
Rather than performing gain processing of the same size in the thermal head direction and paper feed direction, applying gain processing that extends in the thermal head direction in this way makes the banding noise streaks properly divided by gain processing and less noticeable. It becomes possible. Here, the reason why the gain amount period in the thermal head direction is set to about 20 pixels is because the printing resolution of the printer used in this embodiment is 300 dpi. If the printing resolution is different, the period needs to be set to be different. There is.

In step 306, the density-dependent gain amount calculated in step 303 held in the ROM 202, the pseudo-random gain amount calculated in step 304, and the position-dependent gain amount calculated in step 305 are read. Then, the system control unit 203 calculates the gain amount Gain to be added to the density D [x, y] on the Y (yellow) plane based on the following equation stored in the ROM 202 in advance.
Gain = 256 + {Gain2 [x% tw, y% ty] + Gain3} × Gain1 [D [x, y]] / 16 (formula 2)
Gain1: Density-dependent gain amount Gain2: Position-dependent gain amount Gain3: Pseudorandom gain amount tw: Horizontal width of position-dependent gain amount th: Vertical width of position-dependent gain amount Here, density-dependent gain amount: Gain1 is the density of each surface It plays a role of adjusting the correction effect of the present embodiment which is different. Position-dependent gain amount: Gain2 plays a role of making banding noise inconspicuous by dividing the banding noise streak by giving image data the gain amount extending in the thermal head direction. The pseudo-random gain amount: Gain3 has an effect of reducing the periodic pattern of the position-dependent gain amount.

  Here, Gain2 and Gain3 must be adjusted so that the average gain amount of the gain amount Gain added to the density D [x, y] is 256. This is because if the average gain amount is higher than 0, it is understood that the print data is darker to the user's eyes, and conversely, if the average gain amount is lower, it is understood that the print data is thinner.

In step 307, the corrected density value D ′ [x, y] is calculated based on the following equation using the gain amount Gain calculated in step 306.
D ′ [x, y] = (D [x, y] × Gain) / 256 (Expression 3)
Here, D ′ [x, y] is clipped with a maximum of 255 and a minimum of 0.

  In step 308, the density value after correction is overwritten in the RAM 204, and in the subsequent step 309, it is determined whether or not processing has been performed for all predicted banding noise occurrence positions shown in FIG. That is, it is determined whether the processing has been performed for the entire thermal head direction (main scanning direction) or whether all the colors (Y, M, C) have been processed. If processing has not been performed for all predicted banding noise occurrence positions, the process returns to step 302. If the process has been performed for all the predicted banding noise occurrence positions, the process proceeds to step 310 and the process ends.

  As described above, by applying gain processing extending in the direction of the thermal head to the image data where the banding noise is expected to occur due to the change in the conveyance speed of the printing paper, the banding noise lines are divided to make it noticeable to the user's eyes. It becomes possible not to be.

  Here, in order to shorten the processing time, a table having a value equivalent to the gain amount calculated by Expression 2 may be stored in the ROM in advance.

  Further, the banding noise occurrence predicted position stored in advance in the ROM 202 is used as the correction processing target area of the present embodiment. However, since the variation of the occurrence position may shift with the passage of time, the user may be able to adjust the correction position to the UI operation unit 210 or the like.

  Further, although the correction process target range of the present embodiment is performed for all the thermal head directions of the printing paper shown in FIG. 3, the correction process for a part of the areas may be performed without performing all the areas.

  For example, some recent thermal transfer printers are equipped with a calendar printing function. If this process is applied to date letters and fine lines with high-frequency components of this calendar, the letters and lines will be blurred. It may be preferable from the viewpoint of the user not to perform the correction process, so the character portion of the calendar and the portion of the thin line may be excluded from the correction target region.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included.

  Also, when a software program that realizes the functions of the above-described embodiments is supplied from a recording medium directly to a system or apparatus having a computer that can execute the program using wired / wireless communication, and the program is executed Are also included in the present invention.

  Accordingly, the program code itself supplied and installed in the computer in order to implement the functional processing of the present invention by the computer also realizes the present invention. That is, the computer program itself for realizing the functional processing of the present invention is also included in the present invention.

  In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS.

201 Card reader 202 ROM
203 System control unit 204 RAM
205 Image Processing Unit 206 Print Image Generation Unit 207 Banding Noise Noise Correction Unit 208 Print Processing Unit 209 Screen Display Unit 210 UI Operation Unit

Claims (3)

A thermal transfer printer for printing an image by sequentially transferring a plurality of colors of ink on an ink sheet to a printing paper,
Conveying means for conveying printing paper;
Gain processing means for performing gain processing on a predetermined region of the image data;
A thermal head for transferring the ink of the ink sheet to the printing paper conveyed by the conveying unit based on the image data gain-processed by the gain processing unit;
Density-dependent gain calculating means for calculating a gain amount depending on density based on the density value of the predetermined region in the image data;
Position-dependent gain calculating means for calculating a gain amount depending on the position of the predetermined region;
Random number gain calculating means for calculating a gain amount based on a random number;
The gain processing means includes the gain amount calculated by the density dependent gain calculating means, the gain amount calculated by the position dependent gain calculating means, and the gain amount calculated by the random number gain calculating means. A thermal transfer printer, wherein a gain amount for performing gain processing is calculated by a processing means.   2. The thermal transfer printer according to claim 1, wherein the predetermined area is an area extending in a main scanning direction, which is determined based on a distance between the conveying unit and the thermal head. The image data has data for each color of the plurality of inks,
The thermal transfer printer according to claim 1, wherein the density-dependent gain calculating unit calculates a gain amount according to the color and density of ink.

Images