Printing device, printing method, and program

Abstract

To provide a printing technique that enables a printing medium having a plurality of different color development layers laminated thereon to properly develop colors using a plurality of heater elements.SOLUTION: A printing device 40 is provided with a plurality of heater elements 34 that apply heating energy to a printing medium 10 in which a plurality of color development layers 14, 16 and 18, which are applied with different heating energy to develop colors different from each other, are laminated. Further the printing device 40 is provided with obtaining means 46 that obtains respective heating characteristics of the plurality of heater elements, and generating means 401 that generates printing data for making the plurality of heater elements 34 generate heating energy on the basis of image data corresponding to pixels, on the basis of respective color developing / heating characteristics and heating characteristics of the plurality of color development layers. Driving control means 405 makes the plurality of heater elements 34 respectively generate heating energy on the basis of printing data generated by the generating means 401.SELECTED DRAWING: Figure 11

Description

Technical Field

[0006] , , ,

[0001] The present disclosure relates to a printing technique for forming an image by heating a printing medium in which a plurality of color - forming layers that form different colors are laminated, using a heating element. Conventional techniques

[0002] Conventionally, thermal printing that performs color printing using a printing medium such as thermal paper or an ink ribbon is known. Regarding such thermal printing, in Patent Document 1, based on the thermal and mechanical variations of a plurality of heating elements arranged in one line in a thermal transfer printing apparatus, a technique for reducing the density unevenness of a printed image by correcting the energy applied to the heating elements is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in Patent Document 1, regardless of the color of the ink region to be heated, the energy applied to each heating element is corrected with a correction value according to the variations of the heating elements. Therefore, even if the heat generation amount of the heating elements is corrected by the correction technique disclosed in Patent Document 1 for a printing medium in which a plurality of color - forming layers having different color - forming heating characteristics are laminated, each color - forming layer cannot be properly colored.

[0005] An object of the present disclosure is to provide a printing technique capable of properly coloring a printing medium in which a plurality of different color - forming layers are laminated, using a plurality of heating elements.

Means for Solving the Problems

[0006] This disclosure relates to a printing apparatus comprising a plurality of heating elements for applying heating energy to a printing medium having a plurality of color-developing layers laminated together, each producing different colors when different heating energies are applied, the apparatus comprising: a generation means for generating printing data for generating the heating energy in the heating elements based on image data corresponding to pixels; and an acquisition means for acquiring the heating characteristics of each of the plurality of heating elements, wherein the generation means generates the printing data corresponding to the image data based on the color-developing heating characteristics and the heating characteristics of the color-developing layers. [Effects of the Invention]

[0007] According to this disclosure, it becomes possible to properly color a printing medium having multiple different color-developing layers laminated on it using multiple heating elements. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows the structure of the printing medium used in this embodiment. [Figure 2] This is a diagram illustrating the color development conditions for the first printing medium. [Figure 3] (a) and (b) are diagrams illustrating the print head. [Figure 4] This is an internal configuration diagram of the printing apparatus in the first embodiment. [Figure 5] This is a block diagram illustrating the control configuration in a printing system. [Figure 6] This is a flowchart illustrating the process of providing printing services. [Figure 7] This figure shows an example of a heating pulse in the first embodiment. [Figure 8] This is a flowchart showing the process for creating density unevenness correction values. [Figure 9] This is a partially enlarged view showing an example of a detected image in the first embodiment. [Figure 10] This figure shows the heating pulses before and after correction in the first embodiment. [Figure 11]This is a flowchart showing the image forming process in the first embodiment. [Figure 12] This is a flowchart showing the image formation process in the second embodiment. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described in detail below with reference to the attached drawings. Note that the following embodiments are not intended to limit the scope of the claims of this disclosure, and not all combinations of features described in these embodiments are necessarily essential to the solutions of this disclosure.

[0010] (First Embodiment) <Print media> Figure 1 shows the structure of the printing medium used in this embodiment. The printing medium 10 is constructed by sequentially laminating a third image forming layer 18, a second spacer layer 17, a second image forming layer 16, a first spacer layer 15, a first image forming layer 14, and a protective layer 13 on a substrate 12. The side with the protective layer 13 (upper side in Figure 1) is the surface, and is the side that the print head, described later, contacts and the formed image is observed on.

[0011] The substrate 12 is a light-reflecting white layer, and the protective layer 13 is a transparent layer. The first image-forming layer (first color-developing layer) 14, the second image-forming layer (second color-developing layer) 16, and the third image-forming layer (third color-developing layer) 18 are basically colorless and transparent, but each is activated at a specific temperature and develops a different color (yellow, magenta, cyan).

[0012] The first spacer layer 15 and the second spacer layer 17 are layers for controlling the diffusion of heat applied to the protective layer 13, and the thickness of each is adjusted according to the rate at which heat diffuses and the activation temperatures of the three image-forming layers.

[0013] The time until the temperature applied to the surface reaches the lower image forming layer depends on the thickness of the spacer layer, and the applied heat dissipates along with diffusion. Therefore, for example, by applying heat higher than the activation temperature of the upper and lower image forming layers to the surface of the printing medium for a short time, only the upper image forming layer can be activated and the lower image forming layer can be prevented from being activated. Also, by applying a temperature higher than the activation temperature of the lower image forming layer and lower than the activation temperature of the upper image forming layer for a long time, the lower image forming layer can be activated without activating the upper image forming layer. That is, by adjusting parameters such as the temperature (heating temperature) of the heat applied to the surface of the protective layer 13 and the application time according to the image data, the first image forming layer 14, the second image forming layer 16, and the third image forming layer 18 can be individually activated and the coloring can be adjusted.

[0014] And in the printing medium after the image is formed in this way, the light incident from the protective layer 13 passes through the spacer layer and the non-activated image forming layer, and is reflected by the activated image forming layer or the substrate 12. Therefore, when the printing medium 10 is visually observed from the surface side, the observer can visually recognize the color corresponding to the combination of the light reflected by the individual image forming layers and recognize it as an image.

[0015] The colors (color materials) developed by the three image forming layers are not particularly limited. Hereinafter, as the first printing medium, a case where the first image forming layer 14 contains a yellow color material, the second image forming layer 16 contains a magenta color material, and the third image forming layer 18 contains a cyan color material will be described, but the configuration of the printing medium applicable to the present disclosure is not limited thereto.

[0016] Generally, in a printing medium used for forming a full-color image, as described above, the first image forming layer 14, the second image forming layer 16, and the third image forming layer 18 are configured to develop yellow, magenta, and cyan, respectively. However, the order of the colors (lamination order) of each image forming layer and the combination of colors to be developed in the printing medium 10 applicable to the present disclosure are not limited to the example shown in FIG. 1. Further, in the example shown in FIG. 1, image forming layers (color developing layers) corresponding to three colors are provided, but image forming layers corresponding to more colors or fewer colors may be provided. In FIG. 1, the thicknesses of each image forming layer are the same, but image forming layers having different thicknesses may be provided according to the color (colorant).

[0017] Also, the thicknesses of the spacer layers 15 and 17 provided between each of the image forming layers 14, 16, and 18 can be appropriately set according to the color developing heating characteristics of each of the image forming layers 14, 16, and 18, the heat conduction characteristics and heat diffusion rate of each of the spacer layers 15, 17, etc. Each spacer layer may be formed of the same material or different materials. Since the spacer layer functions to control heat diffusion within the printing medium 10, when the first spacer layer 15 and the second spacer layer 17 are formed of the same material, it is preferable to form the second spacer layer 17 to be four times or more thicker.

[0018] Also, the three image forming layers (first to third image forming layers) 14, 16, 18 in the printing medium 10 shown in FIG. 1 are arranged on the same side of the base material 12, but some image forming layers may be arranged on the opposite side of the base material 12.

[0019] Note that heating of the printing medium 10 is preferably performed using a print head that applies heat to the printing medium, but other methods may be used. For example, it is also possible to use a print head using other known heating means such as a modulated light source (means such as a laser).

[0020] <Color developing heating characteristics> FIG. 2 is a diagram for explaining the color development conditions of the first printing medium. In the figure, the horizontal axis represents the time for heating the surface of the printing medium 10 (heating time), and the vertical axis represents the temperature for heating (heating temperature). And the combinations of heating time and heating temperature at which the first image forming layer 14 containing a yellow (Y) coloring material, the second image forming layer 16 containing a magenta (M) coloring material, and the third image forming layer 18 containing a cyan (C) coloring material are activated are shown as regions 21, 22, and 23.

[0021] As shown in FIG. 2, the yellow layer, which is the first image forming layer 14, develops color when a temperature of Ta3 or higher is applied for t1 or more. The magenta layer, which is the second image forming layer 16, develops color when a temperature of Ta2 (<Ta3) or higher is applied for t2 (>t1) or more. The cyan layer, which is the third image forming layer 18, develops color when a temperature of Ta1 (<Ta2<Ta3) or higher is applied for t3 (>t2>t1) or more.

[0022] For example, for a region where only yellow is to be developed, a temperature of Ta3 or higher may be applied for t1 or more and t2 or less. For a region where only magenta is to be developed, a temperature of Ta2 or higher and Ta3 or lower may be applied for t2 or more and t3 or less. For a region where only cyan is to be developed, a temperature of Ta1 or higher and Ta2 or lower may be applied for t3 or more. Thus, by individually controlling the color development of each color element, it becomes possible to represent a color space by a combination of yellow, magenta, and cyan.

[0023] Ta1, Ta2, and Ta3 are values ​​adjusted by the materials contained in each image-forming layer, but generally, it is preferable to set them within a range of approximately 90°C to approximately 300°C with appropriate intervals (temperature differences). For example, Ta1 should be set to the lowest possible temperature so as not to activate during shipping and storage, and is preferably around 100°C. On the other hand, Ta3 should be at a temperature such that the second and third image-forming layers 15 and 18 located below it do not activate due to short-term thermal diffusion, and is preferably around 200°C. Ta2 should be at a temperature such that it does not reach Ta1 or Ta3 even if some temperature changes occur, and is preferably around 140°C to 180°C.

[0024] Furthermore, even when heating energy is applied to the corresponding region of each image-forming layer, the density of the color formed will differ depending on the position within that region. For example, when heating energy is applied to the second image-forming layer 16 within region 22, even with the same heating time, applying a temperature closer to Ta3 will result in a higher density image being formed than applying a temperature closer to Ta2.

[0025] <Print Head> Figures 3(a) and 3(b) are diagrams illustrating the print head 30 used in this embodiment. Figure 3(a) is a side view showing the state in which printing is being performed on the printing medium 10, and Figure 3(b) is a top view showing the surface on which the print head 30 comes into contact with the printing medium 10.

[0026] As shown in Figure 3(a), a glaze 32 and a convex glaze 33 made of the same material as the glaze 32 are provided on one side of the substrate 31 of the print head 30. A heating element 34 is positioned at the most protruding part of the convex glaze 33. Preferably, a protective film (not shown) is provided to cover the surfaces of the glaze 32, the convex glaze 33, and the heating element 34 to protect them. Note that the convex glaze 33 is not an essential component, and the heating element 34 may be positioned on a flat glaze 32. A heat sink 35 is provided on the other side of the substrate 31, and the entire print head is cooled by the use of a fan.

[0027] The x-direction shown in Figure 3 corresponds to the width direction of the printing medium 10, and the printing medium 10 is transported at a predetermined speed in the y-direction, which intersects (orthogonal in this example) the x-direction, while in contact with the convex glaze 33 and heating element 34 of the print head 30.

[0028] In the print head 30, the glaze 32 and the convex glaze 33 extend in the x-direction for a distance sufficient to cover the width of the printing medium 10, as shown in Figure 3(b), and a plurality of heating elements 34 are substantially linearly arranged along the x-direction (first direction) in the convex glaze 33. In this embodiment, the length of each heating element 34 in the x-direction is set to approximately 40 μm, and the length in the y-direction is set to approximately 120 μm. When the printing medium 10 is transported as shown in Figure 3(b), the printing medium 10 comes into contact with the convex glaze 33 containing the heating elements 34 for a length of approximately 200 microns or more.

[0029] Each heating element arranged in the print head generates heat when current is supplied, and this heat is transferred to the printing medium 10. The printing medium is transported while receiving heat from the resistance of the print head 30, and the applied heat causes each image forming layer to develop color. As a result, an image is formed line by line along the arrangement direction of the heating elements 34. In this embodiment, an infrared imaging method is employed in which the heating elements 34, as heat sources, irradiate the recording medium with infrared rays to heat the printing medium, but other methods or heat sources may be used.

[0030] The time during which heat is applied to the printing medium 10 by the print head 30 is typically in the range of approximately 0.001 milliseconds to approximately 100 milliseconds per line of the image. The upper limit of the heat application time is set by the printing speed, while the lower limit of the heat application time is determined by the constraints of the electronic circuit (not shown).

[0031] The size of one pixel area in the printing medium 10 is determined in the x-direction by the size of the heating element 34, and in the y-direction by the size of the heating element 34 and the transport speed of the printing medium 10. Therefore, the size of one pixel area is not particularly limited, but generally it is 100 to 600 dpi (dots / inch) in both the x and y directions. The size of the x-direction and y-direction areas of one pixel area may be different. In this embodiment, the area is assumed to be approximately 40 μm in both the x and y directions. That is, in the printing medium 10, individual pixels are arranged at a density of approximately 600 dpi (dots / inch).

[0032] <Printing device> Figure 4 is an internal configuration diagram of the printing apparatus according to this embodiment. In the figure, the x-direction is the width direction of the printing medium 10, the y-direction is the transport direction of the printing medium 10, and the z-direction is the vertical direction. The printing apparatus 40 is equipped with a print head 30, a holding unit 41, transport rollers 42, a platen 43, an outlet 44, a temperature sensor 45, a camera (acquisition means) 46, an imaging button 47, a battery 48, etc. The printing medium 10 before printing is stored in the holding unit 41. At this time, the multiple printing media 10 are stacked with their surfaces (the side with the protective layer 13 in Figure 1) facing upwards (+z direction).

[0033] When a print job is received, the transport rollers 42, which act as transport means, rotate to transport the printing medium 10 located at the bottom layer in the y direction. This sends the printing medium 10 to the printing section where the print head 30 and platen 43 are located. In the printing section, the convex glaze 33 of the print head 30 contacts the surface (top surface) of the transported printing medium 10, and the platen 43 supports the printing medium 10 from below during printing. The heating element 34 is driven according to the print data, and the printing medium 10 develops color in accordance with the heat applied by the heating element 34. After printing by the print head 30, the printing medium 10 is discharged from the discharge port 44.

[0034] Temperature sensors 45 are provided around the nip portion of the print head 30 and platen 43 to detect the temperature supplied by the print head 30. The temperature detected by the temperature sensors 45 may be, for example, the temperature of the heat-generating element 34 of the print head 30, or the surface temperature of the printing medium 10. Multiple temperature sensors 45 are arranged along the width direction of the print head 30, allowing measurement across the entire width of the recording medium 10. The transport speed of the printing medium 10 is controlled according to the image formation speed and the resolution during image formation. For example, when forming a high-resolution image, the transport speed is controlled to be slower than when forming a low-resolution image. When prioritizing printing speed, the transport speed is increased and the resolution is reduced.

[0035] <System Configuration> Figure 5 shows an example of the overall system configuration in this embodiment. As shown in Figure 5, the system according to this embodiment includes the printing device 40 shown in Figure 4 and a smartphone 50 as the host device for the printing device 40. The host device can be a personal computer, a tablet terminal, or a digital camera, in addition to the smartphone 50.

[0036] The smartphone 50 includes a CPU (Central Processing Unit) 501, RAM (Read Only Memory) 502, and HDD (Hard Disk Drive) 503. Furthermore, the smartphone 50 includes a communication interface 504, an input interface 505, a display device interface 506, a camera 507, and the like. These components are connected to each other via an internal bus, enabling communication between them.

[0037] The CPU 501 executes processing according to the programs and various data stored in the HDD 503 and RAM 502. RAM 502 is volatile storage that temporarily holds programs and data. HDD 503 is non-volatile storage that also holds programs and data. Camera 507 is a device that can capture images through user operation, and the captured image data is stored in HDD 503.

[0038] Communication I / F 504 is an interface that manages communication with external devices, and here it controls the transmission and reception of data between the printer 40 and the external device. For data transmission and reception, wired connections such as USB, or wireless connections such as Bluetooth® or WiFi® can be used. Input device I / F 505 is an interface that controls HID (Human Interface Device) such as a touch panel, and accepts user input. Display device I / F 506 controls the display on a display device (not shown) that displays captured images, image data, etc.

[0039] The printing apparatus 40 includes a CPU 401, RAM 402, ROM 403, communication I / F 404, head controller 405, camera controller 406, image processing accelerator 407, etc. Furthermore, these components are connected to each other via an internal bus so that they can communicate with one another. The CPU 401 transfers programs and various data held in ROM 403 and RAM 402 to a predetermined memory area of ​​RAM 402 and executes processing according to the embodiments described later, according to those programs and data. RAM 402 is volatile storage and temporarily holds programs and data transferred by the CPU 401, etc., as described above. ROM 403 is non-volatile storage and holds table data and programs used in the processing described later.

[0040] The communication interface 404 is an interface that manages communication with external devices, and in this case, it controls the transmission and reception of data with the smartphone 50. The head controller 405 acts as a drive control means that performs heating operations on the print head 30 shown in Figure 3 based on the print data. That is, the head controller 405 reads control parameters and print data from a predetermined address in the RAM 402. Then, when the CPU 401 writes the control parameters and print data to the predetermined address in the RAM 402, processing by the head controller 405 begins, and the heating operation of the print head 30 is performed.

[0041] The camera controller 406 controls the operation of the camera 46 shown in Figure 4. Specifically, when the user presses the image capture button 47, the camera controller 406 issues an image capture command to the camera 46, and the camera 46, upon receiving the command, takes an image. The captured image is temporarily stored in the RAM 402.

[0042] When printing captured images or other data, the head controller 405 starts processing and controls the heating operation of the print head 30 on the printing medium. The image processing accelerator 407 is hardware-based and can perform predetermined image processing at high speed.

[0043] When performing image processing, the CPU 401 first writes the parameters and data necessary for image processing to a predetermined address in the RAM 402. In response, the image processing accelerator 407 is activated and starts the predetermined image processing. In this disclosure, the image processing accelerator 407 is not necessarily an essential element. Depending on the specifications of the printing device 40, the CPU 401 can also perform the table parameter creation process and image processing described later.

[0044] Furthermore, the temperature sensor 45 detects the ambient temperature of the heating element 34 of the print head 30 and provides the detection result as temperature information to the CPU 401, etc. Based on predetermined acquired information, including the temperature information, the CPU 401 performs various processes to control the heat generation of each heating element 34 of the print head 30. Details of the processes and controls performed by the CPU 401 will be described later.

[0045] In this embodiment, a system configuration is illustrated in which two independent devices, namely a printing device 40 and a smartphone 50, are connected in a communicative manner. However, this system configuration can also be realized within a single device. Furthermore, the above system configuration can be realized within a device in which the printing device 40 and an imaging device (not shown) are integrated.

[0046] <Printing Service> Figure 6 is a flowchart showing a series of processing steps in the printing service provision process, where dashed arrows indicate data transmission and reception. In Figure 6, processes S601 to S605 are executed in the smartphone 50, and processes S611 to S616 are executed in the printing device 40. These processes are performed by the CPUs provided in each device. Specifically, in the host device, the smartphone 50, the CPU 501 performs processes S601 to S605 by reading and executing programs stored in the HDD 503 and RAM 52. In the printing device 40, the CPU 401 performs processes S611 to S616 by reading and executing programs stored in the ROM 403 and RAM 402. Note that dashed arrows in the figure indicate data transmission and reception.

[0047] When the power is turned on, the printing device 40 first confirms in S611 that it is ready to print, and once it is confirmed that it is ready to print, it enters a standby state.

[0048] Meanwhile, the smartphone 50 performs the Print Service Discovery on S601. This Print Service Discovery includes searching for peripheral devices according to user input, or periodically searching for printing devices that are ready to provide the Print Service. The smartphone 50 may also perform query processing when it connects to the printing device 40.

[0049] In S612, when the printing device 40 receives a print service Discovery from the smartphone 50, it responds by notifying that it is a device capable of providing print services.

[0050] In S602, if the smartphone 50 receives a notification from the printing device 40 that it can provide printing services, it requests printable information from the printing device 40.

[0051] In S613, the printing device 40 notifies the smartphone 50 of information about the printing services it can provide in response to a request for printable information from the smartphone 50.

[0052] Upon receiving print-ready information from the printer 40, the smartphone 50 generates a user interface for creating a print job based on the print-ready information in S603. Specifically, based on the print-ready information from the printer 40, it displays information such as the print image, print size, printable paper size, etc., along with information indicating appropriate options, on the display (not shown). It then accepts settings from the user via an input device (not shown), such as a touch panel. After this, in S604, the smartphone 50 issues a print job based on the settings information received from the user and sends it to the printer 40.

[0053] In S614, the printing device 40 receives a print job from the smartphone 50. The printing device 40 then analyzes the received print job and executes it (S615). Details of the processing corresponding to the print job (printing process) will be described later.

[0054] Once the printing process is complete, the printing device 40 sends a print completion notification to the smartphone 50 in S616. This completes the processing on the printing device 40 side, and it enters a standby state.

[0055] Meanwhile, the smartphone 50 receives the print job completion notification information from the S605, displays the notification information on its screen, and communicates it to the user. With this, the processing on the smartphone 50 side is complete.

[0056] In the above explanation, various types of information transmission were illustrated using a so-called Pull-type communication method, in which the smartphone 50 makes a request to the printing device 40, and the printing device 40 responds to that request. However, the communication method between the smartphone 50 and the printing device 40 is not limited to Pull-type communication. It is also possible to use a so-called Push-type communication method, in which the printing device 40 proactively sends messages to one or more smartphones 50 on the network.

[0057] <Print head control> The heating control of the print head 30 performed in this embodiment will be described below.

[0058] Figure 7 shows the heating signals applied to one heating element 34 of the print head to produce color for one pixel on the printing medium 10. Figure 7 shows the heating signals for producing color for each of the following pixels: yellow (Y), magenta (M), cyan (C), red (R), green (G), blue (B), and black (K). Each heating signal consists of a pulse signal sequence containing multiple heating pulse signals (voltage pulses). In Figure 7, the horizontal axis represents time, and the vertical axis represents the voltage of the heating signal.

[0059] In Figure 7, the heating signal that forms one pixel has a time corresponding to 52 intervals (intervals a to Z), and a predetermined number of heating pulse signals are contained within these 52 intervals. The pulse width (time) of one heating pulse signal is set within the time corresponding to one interval. When the length of one interval is Δt0, the time required to form one pixel is Δt0 × 52. In other words, the coloring of one pixel takes the time of 52 cycles of the heating pulse, and the coloring is controlled by a pulse signal train consisting of multiple heating pulse signals contained within this time.

[0060] The heating pulse signal changes between two voltage values: High and Low (ON and OFF). In the following description, the state when the heating pulse is ON is referred to as pulse ON, and the state when the heating pulse is OFF. When the voltage of the heating pulse signal is High, heating is performed by the heating element 34, and when the voltage of the heating pulse signal is Low, heating is not performed by the heating element 34. Therefore, the color development on the printing medium 10 is controlled by controlling the number of pulse ONs included in the heating signal for each color. In this embodiment, all heating pulse signals applied in sections a to Z have the same pulse width and the same voltage.

[0061] When activating (color-developing) the yellow (Y) color-developing layer in the printing medium 10, it is necessary to perform heating that satisfies the color-developing conditions shown in region 21 of FIG. 2. Therefore, heating pulses are generated in each of intervals a to j. That is, pulse ON and pulse OFF are repeatedly generated in intervals a to j. Also, when developing magenta (M), it is necessary to satisfy the color-developing conditions shown in region 22 shown in FIG. 2, and therefore, pulse ON and pulse OFF are repeatedly generated in intervals a to y. Similarly, when developing cyan (C), in order to satisfy the color-developing conditions of region 23 shown in FIG. 2, pulse ON and pulse OFF are repeatedly generated in intervals a to W. Thus, by interposing pulse OFF during the pulse ON period, it is possible to suppress the temperature of the printing medium 10 from rising above the target temperature. That is, by controlling the pulse ON time and the pulse OFF time, it becomes possible to maintain the target temperature. In this embodiment, the cycle of pulse ON is constant, but it is also possible to make the cycle of pulse ON different.

[0062] Summarizing the above, the relationship between the intervals a to Z shown in FIG. 7 and the heating times t1 to t3 and heating temperatures Ta1 to Ta3 shown in FIG. 2 is as follows.

[0063] That is, the heating time required to exceed the activation temperature shown in FIG. 2 is t2 > heating time of Y (intervals a to j) > t1 t3 > heating time of M (intervals a to y) > t2 heating time of C (intervals a to W) > t3 This is the case. Therefore, the relative relationship of the heating times required for color development of Y, M, and C respectively is heating time of Y < heating time of M < heating time of C This is the case. As described above, the color development of Y, M, and C respectively occurs in the first to third image forming layers 14, 16, and 18.

[0064] The heating energy (heat quantity) applied to the printing medium 10 by the print head 30 is conducted to the glaze 32 (and convex glaze 33), substrate 31, heat sink 35, etc. of the print head 30 shown in Figure 3 during the interval time (pulse OFF time) of each heating signal. Furthermore, the heat quantity conducted into the printing medium 10 propagates to the surrounding areas such as the platen 43 shown in Figure 4. Therefore, the temperature of the printing medium 10 decreases during the interval time. As a result, when the heating energy (heat quantity) applied to the printing medium 10 is the same, the peak temperatures in each image forming layer 14, 16, and 18 are: First image-forming layer 14 > Second image-forming layer 16 > Third image-forming layer 18 Therefore, in order to produce color in each of the image forming layers 14, 16, and 18, it is necessary to control the print head 30 so that the peak temperature of each image forming layer has the following relationship. Peak temperature of image forming layer 14(Y) > Ta3 Ta3 > Peak temperature of the second image-forming layer 16(M) > Ta2 Ta2 > Peak temperature of the third image-forming layer 18(C) > Ta1

[0065] By controlling the print head 30 so that the peak temperatures of each image forming layer have the relationship described above, the Y, M, and C colors can be produced independently.

[0066] Next, the heating pulse signal for forming Nth-order color pixels will be described. Here, Nth-order color refers to a color formed by combining N different colors. In this embodiment, secondary or tertiary color pixels are formed by causing two or three of the first, second, and third image forming layers, 14, 16, and 18 contained in the printing medium 10 to develop color at the same pixel position. In this embodiment, the secondary colors formed are red (R), green (G), and blue (B), and the tertiary color is black (K).

[0067] When forming a red (R) pixel, the heating pulse signal sequence shown in (R) of Figure 7 is applied to the heating element 34. This causes yellow (Y) and magenta (M) to be emitted in that order, and a secondary color red (R) pixel can be formed.

[0068] Furthermore, when forming a green (G) pixel, the heating pulse signal sequence shown in Figure 7(G) is applied to the heating element 34 to produce yellow (Y) and cyan (C) in that order. Similarly, when forming a blue (B) pixel as shown in Figure 7, the heating pulse signal sequence shown in Figure 7(B) is applied to the heating element 34 to produce magenta (M) and cyan (C) in that order. Also, when forming a black (K) pixel as shown in Figure 7, the heating pulse signal sequence shown in Figure 7(K) is applied to the heating element 34 to produce yellow (Y), magenta (M), and cyan (C) in that order. This results in the formation of a black (K) pixel, which is a combination of the three colors.

[0069] <Calculation flow for density unevenness correction value> Figure 8 is a flowchart showing the process flow for calculating the density unevenness correction value according to this embodiment, where dashed arrows indicate data transmission and reception. In Figure 8, processes S801 to S804 are executed in the smartphone 50, and processes S811 to S815 are executed in the printing device 40. These processes are performed by the CPU provided in each device. Specifically, in the host device, the smartphone 50, the CPU 501 performs processes S801 to S804 by reading and executing programs stored in the HDD 503 and RAM 502. In the printing device 40, the CPU 401 performs processes S811 to S815 by reading and executing programs stored in the ROM 403 and RAM 402.

[0070] When the user inputs an instruction to correct density unevenness, the smartphone 50 sends an instruction to the printing device 40 in S8011 to create a density unevenness correction value. When the printing device 40 receives the density unevenness correction instruction from the smartphone 50, it forms an image on the printing medium 10 for detecting the heat generation characteristics of the heat generation elements 34 (S811). This image for detecting the heat generation characteristics of the heat generation elements 34 is an image for detecting the variation in the heat generation characteristics of the multiple heat generation elements 34 provided on the print head 30, and its image data is stored in the ROM of the printing device 40. Hereinafter, this image will be referred to as the detection image, and the image data representing the detection image will be referred to as the detection image data. This detection image will be explained later with reference to Figure 9. When the printing process of the detection image is completed, the printing device 40 sends a print completion notification to the smartphone 50 (S812) and enters a standby state.

[0071] In S811, an example was described in which the printing device 40 reads and prints the detection image data stored in the ROM 403, but the system is not limited to this. Alternatively, the detection image data stored in the HDD 503 of the smartphone 50 may be sent to the printing device 40, and the printing device 40 may print the received detection image.

[0072] In S802, the smartphone 50 receives a print completion notification sent from the printing device 40 and displays the received print completion notification on its display. Furthermore, the smartphone 50 displays a message on its display instructing the camera 46 of the printing device 40 to capture the detected image formed on the printing medium 10, prompting the user to capture the detected image (S803).

[0073] Following the message displayed on the smartphone 50, when the user presses the imaging button 47 on the printing device 40, the printing device 40 captures a detection image formed on the printing medium 10 using the camera 46 (S813). Subsequently, in S814, the CPU 401 of the printing device 40 analyzes the detection image captured by the camera 46, calculates a density unevenness correction value, and creates a correction table for density unevenness correction. The created density unevenness correction table is stored in the RAM 402. Details of the calculation of the density unevenness correction value and the creation of the correction table will be described later. After this, the printing device 40 sends a notification to the smartphone 50 that the correction table has been created and enters a standby state (S815).

[0074] In S804, the smartphone 50 displays a notification on its screen indicating that the correction table has been completed, received from the printing device 40. This display allows the user to recognize that it is now possible to print an image with density unevenness correction applied. With this, the process of creating the density unevenness correction value and correction table is completed.

[0075] In the flowchart above, an example is shown where the detection image is captured by the camera 46 of the printing device 40, and the density unevenness correction value is calculated by the CPU (correction means) 401 of the printing device 40. However, it is also possible to perform the processes of capturing the detection image and calculating the density unevenness correction value on the smartphone 50 side. For example, the detection image may be captured by the camera 507 of the smartphone 50, the density unevenness correction value calculated by the CPU 501 of the smartphone 50 may be transferred to the printing device 40, and the printing device 40 may create a correction table based on the received correction value and store it in the RAM 402.

[0076] <Detected image> Next, the detection image formed in this embodiment will be described. Figure 9 is a partially enlarged view showing an example of a detection image 1001 printed on the printing medium 10. In the figure, the y direction is the transport direction of the printing medium (width direction of the printing medium), and the x direction is perpendicular to the transport direction of the printing medium 10. Multiple heating elements 34 of the print head 30 that prints on the printing medium 10 are arranged along the x direction.

[0077] The detection image 1001 shown in Figure 9 is an image printed to detect the heat generation characteristics of the heat generation element 34, and consists of a mark 1002 and analysis regions 1003 to 1008.

[0078] Multiple marks 1002 are printed along the width direction (x direction) of the printing medium at predetermined intervals. These multiple marks 1002 form an image used to identify the position of the heating element 34. Preferably, the multiple marks 1002 are formed by primarily coloring the first image forming layer 14, which develops color in the shortest heating time. These marks enable high-precision correspondence between the heating element 34 and the detection image when reading the printed detection image.

[0079] Analysis region 1003 is formed by high-density yellow (Y): (R,G,B) = (255,255,0). Analysis region 1004 is printed with low-density yellow (Y): (R,G,B) = (255,255,128). In other words, both analysis regions 1003 and 1004 are regions where the first image forming layer 14 is mainly colored and printed, and are regions for detecting the color heating characteristics of the first image forming layer 14 and the heat heating characteristics of the heating element 34.

[0080] Similarly, analysis region 1005 prints high-density magenta (M): (R,G,B) = (255,0,255). Analysis region 1006 prints low-density magenta (M): (R,G,B) = (255,128,255). These two analysis regions 1005 and 1006 are primarily for detecting the heat-generating color heating characteristics of the second image-forming layer 16 and the heat-generating characteristics of the heating element 34.

[0081] Analysis region 1007 is high-concentration cyanide (C):(R,G,B)=(0,255,255), and analysis region 1008 is low-concentration cyanide (C)(R,G,B)=(128,255,255). These images are primarily used to detect the characteristics of the third image-forming layer 18.

[0082] In this embodiment, an example of printing representative two gradations in each of the image forming layers 14, 16, and 18 has been described, but the number of gradations in the area to be printed may be three or more.

[0083] The detected image 1001 is formed on the recording member 10, photographed with a camera, and the number of pulse ONs is adjusted for each heating element 34 so as to suppress density unevenness in the direction (x direction) in which the heating elements 34 are arranged.

[0084] FIG. 10 shows an example in which the number of pulse ONs of the heating pulse signal is adjusted when printing with the heating element 34 having the lowest applied voltage. In FIG. 9, a configuration example of the corrected heating pulse signal (second heating signal) corresponding to the color to be colored in one pixel of the printing medium 10 and the heating pulse signal before correction (first heating signal) is shown as in FIG. 7. The voltage applied to the heating element 34 is V', and the relationship is V' < V. Here, as an example, V / V' = about 1.1.

[0085] FIG. 10 shows a high-density heating pulse signal and a low-density heating pulse signal as representative examples of the heating pulse signals of each color. That is, in order from the top of FIG. 10, Heating pulse signal (first heating signal) before density unevenness correction of high-density yellow (Y) Heating pulse signal (second heating signal) after density unevenness correction of high-density yellow (Y) Heating pulse signal (first heating signal) before density unevenness correction of low-density yellow (Y) Heating pulse signal (second heating signal) after density unevenness correction of low-density yellow (Y) Heating pulse signal (first heating signal) before density unevenness correction of high-density magenta (M) Heating pulse signal (second heating signal) after density unevenness correction of high-density magenta (M) Heating pulse signal (first heating signal) before density unevenness correction of low-density magenta (M) Heating pulse signal (second heating signal) after density unevenness correction of low-density magenta (M) Heating pulse signal (first heating signal) before density unevenness correction of high-density cyan (C) Heat pulse signal (second heating signal) after correction of concentration unevenness of high-concentration cyanide (C). Heat pulse signal (first heating signal) before correction of concentration unevenness of low-concentration cyanide (C) Heat pulse signal (second heating signal) after correction for uneven concentration of low-concentration cyanide (C). This is shown.

[0086] The heating pulse signal of high-density yellow (Y) before density unevenness correction, shown in Figure 10, has a lower voltage than the heating pulse signal of yellow (Y) shown in Figure 7. Therefore, although the number of pulses ON is the same as the heating pulse signal shown in Figure 7, the image density on the printing material 10 is lighter. For this reason, the heating pulse signal of high-density yellow (Y) after density unevenness correction, shown in Figure 9, has an increased number of pulses ON so that it obtains approximately the same density as the heating pulse signal of yellow (Y) shown in Figure 7.

[0087] Similarly, the heating pulse signal of high-density magenta (M) shown in Figure 10 before density unevenness correction has a lower voltage than the heating pulse signal of yellow (M) shown in Figure 7. Therefore, even if the number of pulse ONs is the same, the image density on the printing material 10 is lighter. For this reason, the heating pulse signal of high-density magenta (M) shown in Figure 10 after density unevenness correction has an increased number of pulse ONs so that it obtains approximately the same density as the heating pulse signal of magenta (M) shown in Figure 7.

[0088] Furthermore, the heating pulse signal of high-density cyan (C) before density unevenness correction shown in Figure 10 has a lower voltage than the heating pulse signal of cyan shown in Figure 7, so even if the number of pulse ONs is the same, the image density on the printing material 10 is lighter. For this reason, the heating pulse signal of high-density cyan (C) after density unevenness correction shown in Figure 11 has an increased number of pulse ONs so that approximately the same density as the heating pulse signal of cyan (C) shown in Figure 7 is obtained.

[0089] Furthermore, as shown in Figure 10, the heating pulse signal for yellow (Y) has a more frequent pulse ON interval compared to magenta (M) and cyan (C). Therefore, it is not possible to increase the number of pulse ONs in section a to section j to obtain approximately the same density as the heating pulse signal shown in Figure 7. In other words, the required heat flux cannot be obtained by the heating time in section a to section j. Therefore, in the example shown in Figure 10, a correction is made to increase the print density by widening the section, such as section a to section m, and increasing the number of pulse ONs.

[0090] On the other hand, for magenta (M) and cyan (C), there is a wide pulse interval between pulse ONs. Therefore, a correction is performed to increase the number of pulse ONs and thus the heat flux within the same interval (heating time) as the heating pulse signal shown in Figure 7. As a result, printing with approximately the same density as the heating pulse signal shown in Figure 7 is possible even for magenta (M) and cyan (C).

[0091] Furthermore, in the example shown in Figure 10, for yellow (Y), the number of pulse ONs in the heating pulse signal before density unevenness correction for high-concentration yellow (Y) is 10, while the number of pulse ONs in the heating pulse signal after density unevenness correction is 13. In other words, the number of pulse ONs after correction is increased by 1.3 times compared to the number of pulse ONs before correction. On the other hand, the rate of decrease in voltage V' relative to voltage V is approximately 1.1, indicating that the rate of increase in the number of pulse ONs is greater than the rate of decrease in voltage.

[0092] Furthermore, for magenta (M), the number of pulse ONs in the heating pulse signal before density unevenness correction for high-density magenta (M) is 7, while the number of pulse ONs in the heating pulse signal after density unevenness correction for high-density magenta (M) is 8. In other words, the increase in the number of pulse ONs due to correction is 1.1, which is approximately the same as the decrease in voltage V' relative to voltage V (approximately 1.1).

[0093] Similarly, for cyanide (C), the number of pulse ONs in the heating pulse signal before correction for density unevenness of high-concentration cyanide (C) was 9, while the number of pulse ONs in the heating pulse signal after correction for high-concentration cyanide (C) was 11, meaning the increase in the number of pulse ONs due to correction was 1.1. Therefore, in cyanide (C) as well, the increase in the number of pulse ONs due to correction is approximately the same as the decrease in voltage V' relative to voltage V (approximately 1.1).

[0094] Thus, yellow (Y), which cannot increase the number of ON pulses during the same heating time as the uncorrected heating pulse signal, exhibits a larger rate of change in the number of ON pulses (i.e., heating energy) compared to magenta (M) and cyan (C).

[0095] Furthermore, the number of pulse ONs in the heating pulse signal before density unevenness correction for low-concentration yellow (Y) was 5, while the number of pulse ONs in the heating pulse signal after density unevenness correction for low-concentration yellow (Y) was 6. The percentage increase in the number of pulse ONs due to correction was 1.2. In other words, the rate of change in the number of pulse ONs due to correction (density unevenness correction value) is larger for high-concentration yellow (Y) than for low-concentration yellow (Y).

[0096] As described above, for each of the yellow (Y), magenta (M), and cyan (C) colors, the rate of change in the number of pulses ON is calculated for each gradation, and the results are used as the respective density unevenness correction values. The target density used in calculating the density unevenness correction value may be set to the density printed with the heating element 34 whose applied voltage is closest to the center value among the multiple heating elements 34, or it may be set to the density printed with the heating element 34 with the lowest applied voltage.

[0097] In order to produce cyan (C), magenta (M), and yellow (Y) at the desired density, the heating energy generated by each heating element 34 must be corrected by the density unevenness correction value described above. In this embodiment, density unevenness correction values ​​that correct the c, m, and y data, which represent the number of pulses and pulse width of the heating pulse signal applied to each heating element 34, are created as 1D_LUTs and stored in the printing device 40. Specifically, 1D_LUT_C for correcting c data, 1D_LUT_M for correcting m data, and 1D_LUT_Y for correcting y data are created for each heating element 34 and stored in the ROM 403 of the printing device 40. This allows for proper correction of the heating energy of each gradation of c, m, and y data. Since the Nth order color is a combination of yellow (Y), magenta (M), and cyan (C), the respective density unevenness correction values ​​for yellow (Y), magenta (M), and cyan (C) are applied.

[0098] Furthermore, Figure 10 shows an example of correcting the heating pulse signal of a heating element 34 with a lower applied voltage than average. In this example, the number of pulse ONs in the heating pulse signal is increased during the correction. However, when correcting a heating element 34 with a higher applied voltage than average, the correction would involve decreasing the number of pulse ONs in the heating pulse signal.

[0099] <Image Processing> Figure 11 is a flowchart showing the image processing flow in this embodiment. The processing performed in each step of Figure 11 is performed in step S615 of the flowchart in Figure 6. The processing shown in Figure 11 is realized, for example, by the CPU 401 of the printing device 40 reading and executing programs and data contained in the ROM 403, etc. That is, in this embodiment, the CPU 401 functions as a generation means for generating heating signals, which are print data. Note that some of the functions shown in Figure 11 can also be performed by an ASIC such as an image processing accelerator 407.

[0100] In S1101, CPU401 acquires the image data from the print job received in S614 in Figure 6. Here, we will explain assuming that the image data is acquired page by page.

[0101] In S1102, the CPU 401 performs a decoding process on the compressed or encoded image data. This process is omitted if the image data is not compressed or encoded. The decoding process converts the image data into RGB data. Examples of RGB data types include standard image data such as sRGB and Adobe® RGB. In this embodiment, the image data has 8 bits of information for each color and has a value range of "0" to "255", but it may also be image data composed of 16 bits of information or information with other numbers of bits.

[0102] In S1103, the CPU 401 performs color correction processing on the image data. Note that color correction processing can also be performed on the smartphone 50. However, when performing color correction to match the printing device 40, it is preferable to perform it within the printing device 40, as in this example. The image data after color correction processing is RGB data, but at this point, it takes the form of RGB specific to the printing device 40, so-called device RGB.

[0103] In S1104, CPU401 performs brightness density conversion on image data using a 3D lookup table. In a typical thermal printing device, for example, the following conversion is performed using the RGB data of the image data. C=255-R M=255-G Y=255-B

[0104] On the other hand, in the case of pulse control according to this embodiment, for example, the control parameters for magenta (M) when it is composed as a single color are different from the control parameters for magenta that constitutes the secondary color red (R). Therefore, in order to set both individually, it is preferable to perform brightness density conversion using the three-dimensional lookup table shown below.

[0105] In this embodiment, brightness density conversion is performed using the following 3D lookup table. In the function 3D_LUT[R][G][B][N] of the following 3D lookup table, the variables R, G, and B are input values ​​of RGB data, respectively, and the variable N specifies one of the output C, M, or Y. Here, it is assumed that 0, 1, and 2 are specified for C, M, and Y, respectively. C=3D_LUT[R][G][B][0] M=3D_LUT[R][G][B][1] Y=3D_LUT[R][G][B][2]

[0106] The above 3D_LUT consists of 5,033,1648 data tables arranged in a 256 × 256 × 256 × 3 grid. Each data point corresponds to the pulse width applied in each of the intervals a to Z shown in Figure 7. To reduce the amount of data in the lookup table, for example, the number of grids can be reduced from 256 to 17, using a 17 × 17 × 17 × 3 grid of 14,739 data tables, and the values ​​between grids can be calculated by interpolation. In addition to 17 grids, it is also possible to set a suitable number of grids as appropriate, such as 16 grids, 9 grids, or 8 grids. As for the interpolation method, any known method such as tetrahedral interpolation may be used. In this embodiment, the 3D lookup table is predetermined and stored in the ROM 403 of the printing device 40.

[0107] By using the three-dimensional lookup table described above, the control parameters for each of the yellow (Y), magenta (M), and cyan (C) components that make up each print color can be set individually. In other words, it becomes possible to independently set the control parameters for each of the secondary colors: yellow (Y) and magenta (M) that make up red (R), cyan (C) and yellow (Y) that make up green (G), and magenta (M) and cyan (C) that make up blue (B). Similarly, it becomes possible to independently set the control parameters for each of the yellow (Y), magenta (M), and cyan (C) components that make up black (K). This allows for more precise control of color development and contributes to improved color reproduction.

[0108] In S1105, the CPU 401 performs output correction on the converted image data. First, the CPU 401 uses a conversion table corresponding to each print color to indicate the number of ONs and pulse ON intervals of the heating pulse signal corresponding to the C, M, and Y values. This conversion table (conversion formula) is predetermined and stored in the ROM 403 of the printing device 40. c=1D_LUT[C] m=1D_LUT[M] y = 1D_LUT[Y]

[0109] By correcting the number of pulse ONs and the interval between pulse ONs, as indicated by c, m, and y, it becomes possible to modulate the color intensity in the printing medium 10, thereby achieving a density corresponding to the desired gradation.

[0110] Furthermore, the CPU 401 modulates the heating pulse according to the temperature of the printing medium 10 or print head 30 obtained by the temperature sensor 45. Specifically, as the temperature detected by the temperature sensor 45 increases, the CPU controls the number of pulses ON in the heating pulse used to reach the activation temperature to decrease. This process can be carried out using known methods. In addition, the temperature of the printing medium 10 can be obtained by means other than the temperature sensor 45. For example, it can be obtained by estimating the temperature of the printing medium 10 or print head 30 in a smartphone 50 or a printing device 40, and the number of pulses ON in the heating pulse signal may be controlled based on the obtained estimated temperature. The method for estimating this temperature is not particularly limited, and known methods can be used.

[0111] In S1106, the CPU 401 performs a derivation process to convert (derive) the c, m, and y data generated in S1105 into c', m', and y' data as density unevenness correction values ​​using the following conversion table created for each heating element 34. That is, the CPU 401 converts (derives) the number of pulses ON and the interval between pulses ON, indicated by the c, m, and y data, into the number of pulses ON and the interval between pulses ON, indicated by the c', m', and y' data. c'=1D_LUT_C[c] m'=1D_LUT_M[m] y'=1D_LUT_Y[y]

[0112] Subsequently, the CPU 401 controls the print head 30 via the head controller 405 based on the number of pulses ON and the pulse ON interval derived in S1107 by referring to the above conversion table. At this time, heating pulse signals for yellow (Y), magenta (M), and cyan (C), respectively, which are controlled based on density unevenness correction values, are applied to each heating element 34 to heat each pixel area of ​​the printing medium 10. This makes it possible to produce the desired color in each pixel area on the printing medium 10.

[0113] In S1108, CPU 401 determines whether printing of one page is complete. If it is complete (YES in S1108), this processing flow is terminated and the process proceeds to the next page or to the process in S616 in Figure 6. If printing of one page is not complete (NO in S1108), the process proceeds to S1101 and the image formation process for that page continues.

[0114] As described above, in this embodiment, density unevenness correction is performed according to the heating characteristics of each heating element 34 of the print head 30 and the color development heating characteristics of each image forming layer 14, 16, 18 of the printing medium 10, making it possible to form a high-quality image on a printing medium in which multiple image forming layers are stacked.

[0115] <Second Embodiment> In the first embodiment described above, as shown in Figure 11, an example was explained in which the c data, m data, and y data were independently corrected by applying a 1D_LUT to the density unevenness correction values ​​for cyan (C), magenta (M), and yellow (Y), respectively. When forming a single-color pixel on the printing medium 10, as shown in Figure 10, the heating pulse signal can be contained within the heating time (interval a~Z) specified for forming one pixel. However, when forming pixels of the Nth order color, there is a possibility that the heating pulse signal will not be contained within the heating time. In particular, when forming pixels of the Nth order color, if the pulse ON signal of the heating pulse signal is corrected by independently increasing the pulse ON signal for each color, the heating pulse signals of each color are applied sequentially to the printing medium. For this reason, there is a possibility that the heating pulse signals for all colors necessary to form the Nth order color will not be contained within the heating time.

[0116] Therefore, in this embodiment, the c data, m data, and y data are corrected by applying 3D_DLUT. The following explanation will be given with reference to Figure 11. Note that in Figure 11, steps S1101 to S1105 and S1107 to S1108 are the same as the processes described in the first embodiment, so their explanation will be omitted.

[0117] In the density unevenness correction process of the first embodiment described above, the number of pulse ONs of the heating pulse signal of the heating element 34 with the lowest applied voltage is increased, which may cause the heating pulse signal to exceed the heating time. Therefore, in this embodiment, the heating element 34 with the lowest heating voltage is used as the reference heating element 34. Furthermore, a 3D_LUT_ combining c, m, and y data is used to perform correction to suppress density unevenness. If the heating pulse signal does not fall within the interval a to Z in this combination of c, m, and y data, the correction change rate (change rate of pulse ONs) of the c data with the longest heating time is reduced in the c, m, and y data so that the heating pulse signal falls within the heating pulse time.

[0118] In this way, correction values ​​corresponding to all combinations of c, m, and y data are calculated for the reference heating element 34 and stored in the 3D_LUT. For other heating elements 34 with higher applied voltages, correction values ​​are calculated so that approximately the same heating energy as the reference heating element 34 is obtained and stored in the 3D_LUT. In this way, a 3D_LUT is created for each heating element 34 and stored in the ROM 403.

[0119] In S1106, the c, m, and y data are converted to c', m', and y' data according to the heat generation characteristics of each heat generation element 34 using the following conversion table created for each heat generation element 34. c'=3D_LUT[c][m][y][0] m'=3D_LUT[c][m][y][1] y'=3D_LUT[c][m][y][2]

[0120] The above 3D_LUT may be a data table of 5,033,1648 elements (256 x 256 x 256 x 3), or it may be set to an appropriate number of grids, such as 17 grids, 16 grids, 9 grids, or 8 grids. The data corresponding to each grid is a value that corrects the c, m, and y data. Any known method, such as tetrahedral interpolation, may be used for interpolating the data between grids. In this embodiment, the 3D lookup table is predetermined and stored in the ROM 403 of the printing device 40. By using the above 3D lookup table, the c, m, and y data can be corrected with dependencies, making it possible to fit the heating pulse signals of each color within the heating time (interval a to Z) of one pixel.

[0121] (Third embodiment) Next, a third embodiment of this disclosure will be described. This embodiment also has the configuration shown in Figures 3 to 5 and performs printing on the printing medium 10 shown in Figure 1. The following description will focus on the differences from the first embodiment.

[0122] In the above embodiment, as shown in Figure 8, an example was shown in which the heating pulse signal converted to c, m, and y data was corrected. In contrast, in this embodiment, density unevenness is corrected by correcting the pixel values ​​RGB.

[0123] The image forming process performed in this embodiment will be described below with reference to the flowchart in Figure 12. Note that steps S1201 to S1203 and S1205 to S1208 shown in Figure 12 are the same as steps S1101 to S1103, S1105, S1107, and S1108 shown in Figure 11, and therefore, a redundant explanation with the first embodiment will be omitted.

[0124] In this embodiment as well, in the calculation process for density unevenness correction values, the heating element 34 with the lowest applied voltage is used as the reference heating element as an example, and the color that will be produced is calculated based on the heating characteristics of the reference heating element 34 and the c, m, and y data converted from the RGB data, similar to the first embodiment. This calculation is performed for 256 × 256 × 256 = 16,777,216 combinations of RGB data, and these colors are used as target colors. Similarly, for the other heating elements 34, the color that will be produced is calculated based on the heating element characteristics and the c, m, and y data converted from the RGB data, for all RGB combinations.

[0125] Next, for the other heating elements 34, a correspondence is made between all RGB combinations (16,777,216 possible combinations) and the RGB combination that produces approximately the same color as the reference heating element 34, and this is stored as a 3D_LUT. This 3D_LUT is created for each heating element 34. The 3D_LUT may be a data table of 256 × 256 × 256 × 3, resulting in 50,331,648 data points, or a suitable number of grids may be set as appropriate, such as 17 grids, 16 grids, 9 grids, or 8 grids. For interpolation of values ​​between grids, known methods such as tetrahedral interpolation may be used.

[0126] In the density unevenness correction process performed in S1304 of this embodiment, instead of correcting the c data, m data, and y data as in the density unevenness correction process performed in S1106 of the first embodiment, the pixel values ​​RGB are corrected. This is where this embodiment differs from the first embodiment. The pixel values ​​RGB are converted using the following conversion table created for each heating element 34. R'=3D_LUT[R][G][B][0] G'=3D_LUT[R][G][B][1] B'=3D_LUT[R][G][B][2]

[0127] As described above, in this embodiment, by correcting the image value RGB according to the heating characteristics of each heating element 34 of the print head 30 and the color heating characteristics of each image forming layer 14, 16, 18 of the print medium 10, density unevenness due to variations in the heating characteristics of the heating elements 34 can be reduced.

[0128] <Other Embodiments> In the above embodiment, an example was shown in which the process of deriving density unevenness correction values ​​and creating correction tables is performed by the CPU 401 of the printing device 40. However, these processes can also be performed by the host device, the smartphone 50. For example, the printing device 40 may transmit the heat generation characteristics of each heat generation element 34, and the CPU 501 of the smartphone 50 may derive density unevenness correction values ​​or correction tables based on these heat generation characteristics. In this case, the burden on the printing device 40 can be reduced by transmitting the obtained density unevenness correction values ​​or correction tables to the printing device 40 and having it hold them.

[0129] Furthermore, this disclosure can also be implemented by supplying a program that implements one or more of the above embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be implemented by a circuit (e.g., an ASIC) that implements one or more of the functions.

[0130] This disclosure includes the following configurations, methods, and programs.

[0131] (Composition 1) A printing apparatus comprising multiple heating elements for applying heating energy to a printing medium having multiple color-developing layers that produce different colors from each other when different heating energies are applied, An acquisition means for acquiring the heat generation characteristics of each of the multiple heat generation elements, A generation means for generating print data for generating heating energy in each of the multiple heating elements based on image data corresponding to pixels, based on the color heating characteristics and heating characteristics of each of the multiple color layers, A printing apparatus characterized by comprising a drive control means for generating heating energy in each of the plurality of heating elements based on the print data.

[0132] (Configuration 2) The printing apparatus according to configuration 1, characterized in that the acquisition means reads the density of a monochrome detection image formed on the printing medium by a plurality of heating elements, and acquires the heating characteristics of each of the plurality of heating elements based on the read density.

[0133] (Composition 3) The printing apparatus according to configuration 1 or 2, characterized in that the heat generation characteristic represents the amount of heat energy generated by the heating element in response to predetermined print data.

[0134] (Composition 4) The printing apparatus according to any one of configurations 1 to 3, characterized in that the generating means includes a correction means that generates a second heating signal by correcting a predetermined first heating signal based on the color heating characteristics of each of the multiple color layers according to the heating characteristics of each of the multiple heating elements, and outputs the second heating signal as print data.

[0135] (Composition 5) The printing apparatus according to configuration 4, characterized in that the correction means corrects the second heating signal such that the ratio of the heating energy generated by the heating element due to the first heating signal to the heating energy generated by the heating element due to the second heating signal increases as the density to be developed on the printing medium increases.

[0136] (Composition 6) The printing apparatus according to configuration 4 or 5, wherein the generating means uses a table provided with a correction value that is corrected according to the heating characteristics of the heating element for each of the three color layers corresponding to each pixel of the printing medium, and corrects the first heating signal that generates heating energy to be applied to each of the three color layers corresponding to each pixel of the printing medium to generate the second heating signal.

[0137] (Composition 7) The heating element generates the heating energy by applying a voltage, The first heating signal and the second heating signal are composed of a plurality of voltage pulses that apply voltage to the heating element. The printing apparatus according to any one of configurations 4 to 6, characterized in that the correction means generates the second heating signal by correcting at least one of the number of pulses and the pulse interval of the voltage pulses constituting the first heating signal according to the heating characteristics.

[0138] (Composition 8) The printing apparatus according to configuration 7, characterized in that the pulse width and number of pulses of the voltage pulses define the heating temperature and heating time at which the printing medium is heated by the heating element.

[0139] (Composition 9) The printing apparatus according to configuration 7 or 8, characterized in that the correction means increases the number of pulses of the voltage pulse constituting the second heating signal for heating elements with a lower amount of heating energy among the plurality of heating elements.

[0140] (Composition 10) The printing apparatus according to any one of configurations 7 to 9, characterized in that the correction means corrects the first heating signal using a correction table defined for each gradation value of a plurality of colors corresponding to the color layer, for correcting at least one of the number of pulses and the pulse interval of the voltage pulses constituting the first heating signal.

[0141] (Composition 11) The printing apparatus according to configuration 1, characterized in that the generation means changes the pixel values ​​of the image data in order to suppress density unevenness.

[0142] (Composition 12) The printing apparatus according to any one of configurations 1 to 11, characterized in that the printing medium includes a first color-developing layer that produces yellow, a second color-developing layer that produces cyan, and a third color-developing layer that produces magenta.

[0143] (Composition 13) The printing apparatus according to configuration 12, characterized in that the printing medium has the first color-developing layer, the second color-developing layer, and the third color-developing layer sequentially laminated on it, starting from the side to which the heating energy is applied by the heating element.

[0144] (Composition 14) The printing apparatus according to configuration 2, characterized in that the detected image includes at least one region among the plurality of color-developing layers that is printed when the heating time by the heating element is shorter than a predetermined time and the heating temperature is above a predetermined temperature, and one region that is printed when the heating time by the heating element is above the predetermined time and the heating temperature by the heating element is below the predetermined temperature.

[0145] (Composition 15) A printing apparatus according to any one of configurations 1 to 13, characterized in that it includes a transport means for transporting the printing medium in a direction intersecting the direction in which the plurality of heating elements are arranged.

[0146] (Method 1) A printing method for printing an image on a printing medium having multiple color-developing layers that produce different colors when different heating energies are applied, by applying the heating energy using multiple heating elements, A step of acquiring the heat generation characteristics of each of the multiple heat generation elements, A generation step of generating print data for generating heating energy in each of the multiple heating elements based on image data corresponding to pixels, based on the color heating characteristics and heating characteristics of each of the multiple color layers, A printing method characterized by comprising a drive control step of generating heating energy in each of the plurality of heating elements based on the print data.

[0147] (Program 1) A program that causes a computer to perform each step described in Method 1. [Explanation of Symbols]

[0148] 10 Print media 14. First Image Forming Layer 16. Second Image Forming Layer 18. Third Image Forming Layer 34 Heating element 40 Printing device 46 Cameras 401 CPU

Claims

1. A printing apparatus comprising a plurality of heating elements for applying heating energy to a printing medium in which a plurality of color-developing layers that develop different colors by being applied with different heating energies are laminated, an acquisition means for acquiring the heating characteristics of each of the plurality of heating elements, a generation means for generating print data for generating the heating energy in each of the plurality of heating elements based on image data corresponding to pixels, based on the color-developing heating characteristics and the heating characteristics of each of the plurality of color-developing layers, and a drive control means for generating the heating energy in each of the plurality of heating elements based on the print data, wherein the heating characteristics represent the amount of heat of the heating energy generated by the heating element for predetermined print data. The printing apparatus is characterized by this.

2. The printing apparatus according to claim 1, wherein the acquisition means reads the density of a single-color detection image formed on the printing medium by the plurality of heating elements, and acquires the heating characteristics of each of the plurality of heating elements based on the read density.

3. The printing apparatus according to claim 1, wherein the generation means includes a correction means for generating a second heating signal by correcting a predetermined first heating signal according to the heating characteristics of each of the plurality of heating elements based on the color-developing heating characteristics of each of the plurality of color-developing layers, and outputting the second heating signal as the print data.

4. The printing apparatus according to claim 3, wherein the correction means corrects the second heating signal so that the ratio of the heating energy generated by the heating element by the first heating signal to the heating energy generated by the heating element by the second heating signal becomes larger as the density to be color-developed on the printing medium is larger.

5. The printing apparatus according to claim 3 or 4, wherein the generation means uses a table provided with correction values for performing correction according to the heating characteristics of the heating element for each combination of the three heating energies applied to each of the three color-developing layers corresponding to the same pixel, and corrects the first heating signal for generating the heating energy to be applied to each of the three color-developing layers corresponding to each pixel of the printing medium, thereby generating the second heating signal.

6. The heating element generates the heating energy by applying a voltage, The first heating signal and the second heating signal are composed of a plurality of voltage pulses for applying a voltage to the heating element. The printing apparatus according to claim 3, wherein the correction means generates the second heating signal by correcting at least one of the number of pulses and the pulse interval of the voltage pulses constituting the first heating signal according to the heat generation characteristics.

7. The printing apparatus according to claim 6, wherein the pulse width and the number of pulses of the voltage pulse define a heating temperature and a heating time at which the printing medium is heated by the heating element.

8. The printing apparatus according to claim 6 or 7, wherein the correction means increases the number of pulses of the voltage pulses constituting the second heating signal for the heating element having less heat quantity of the heating energy among the plurality of heating elements.

9. The printing apparatus according to claim 6, wherein the correction means corrects the first heating signal using a correction table in which correction values for correcting at least one of the number of pulses and the pulse interval of the voltage pulses constituting the first heating signal are determined for each gradation value of a plurality of colors corresponding to the color developing layer.

10. The printing apparatus according to claim 1, wherein the generation means changes the pixel value of the image data in order to suppress density unevenness.

11. The printing apparatus according to claim 1, wherein the printing medium includes a first color developing layer that develops yellow, a second color developing layer that develops cyan, and a third color developing layer that develops magenta.

12. The printing apparatus according to claim 11, wherein the first color developing layer, the second color developing layer, and the third color developing layer are sequentially laminated on the printing medium from the side to which the heating energy is applied by the heating element.

13. The printing apparatus according to claim 2, wherein the detected image includes at least a region printed when the heating time by the heating element is shorter than a predetermined time and the heating temperature is equal to or higher than a predetermined temperature among the plurality of color developing layers, and a region printed when the heating time by the heating element is equal to or longer than the predetermined time and the heating temperature by the heating element is equal to or lower than the predetermined temperature.

14. The printing apparatus according to claim 1, further comprising a conveying means for conveying the printing medium in a direction intersecting the direction in which the plurality of heating elements are arranged.

15. A printing method for printing an image by applying heating energy to a printing medium in which a plurality of color - developing layers that develop different colors by being applied with different heating energies are laminated, comprising: an acquisition step of acquiring the heat - generating characteristics of each of the plurality of heating elements; a generation step of generating print data for generating the heating energy for each of the plurality of heating elements based on image data corresponding to pixels, based on the color - developing heating characteristics and the heat - generating characteristics of each of the plurality of color - developing layers; a drive control step of generating the heating energy for each of the plurality of heating elements based on the print data. The heat - generating characteristics represent the amount of heat of the heating energy generated by the heating element for a predetermined print data. The printing method is characterized by this.

16. A program for causing a computer to execute each step described in Claim 15.

Images