Recording device and recording method

Abstract

To suppress erroneous color development of a pixel right behind a pixel recording an image with high density.SOLUTION: When a pixel right behind a target pixel does not develop color in a color development layer of a bottom layer, heat energy to be applied to the target pixel is reduced.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a recording apparatus and a recording method. [Background technology]

[0002] Until now, monochrome printing using thermal paper and color printing using ink ribbons have been widely used in recording with thermal printheads. Recently, color recording using paper with multiple color-forming layers has been proposed and has become popular as a simple method for printing photographs, etc. Each of the multiple color-forming layers requires different heating temperatures and heating times to develop color, and these differences are utilized to cause specific color-forming layers to develop color, thereby recording a color image (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2011-523914 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-described conventional example may cause erroneous color development. For example, if a pixel immediately following a high-density pixel of interest is one that does not cause the color development layer to develop color, heat applied to the pixel of interest may propagate to the pixel of interest, causing the color development layer corresponding to the immediately following pixel to develop color erroneously.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to suppress erroneous color development in pixels immediately following pixels that print a high-density image. [Means for solving the problem]

[0006] The present invention provides a recording device that heats a sheet-like recording medium having multiple color-forming layers superimposed thereon, each color forming a different color in response to heat, to cause a desired one of the multiple color-forming layers to color and form an image on the recording medium, the recording device comprising: a recording head having multiple heating elements arranged in a predetermined direction and that heats the recording medium based on image data; a first condition determination means that determines whether a first condition is satisfied, that is, a pixel immediately following the pixel of interest that is at the same position as the pixel of interest in the predetermined direction and that causes the color layer at the bottom of the recording medium to color; and a pulse control means that controls pulses to be applied to the recording head when forming the pixel of interest based on the determination result of the first condition determination means, wherein, when the value of the pixel of interest in the image data is a predetermined value and the first condition is not satisfied, the pulse control means controls the pulses so that the thermal energy applied by the recording head to the recording medium when forming the pixel of interest is smaller than when the value of the pixel of interest in the image data is the predetermined value and the first condition is satisfied. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress erroneous color development of pixels immediately following pixels that print a high-density image. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating the overall configuration of a recording apparatus according to a first embodiment. [Figure 2] FIG. 1 is a diagram illustrating the system configuration of a recording apparatus according to a first embodiment. [Figure 3] FIG. 2 is a diagram illustrating the configuration of a print head and a print medium during printing according to the first embodiment. [Figure 4] FIG. 2 is a diagram illustrating a layer structure of a recording medium according to the first embodiment. [Figure 5] FIG. 3 is a diagram illustrating the heating time and heating temperature for coloring each image forming layer of the recording medium according to the first embodiment. [Figure 6]6 is a flowchart showing the processing of the printing apparatus and the host PC when a print service is executed in the first embodiment. [Figure 7] 4A to 4C are diagrams illustrating pulses for producing each color in the first embodiment. [Figure 8] 3A to 3C are diagrams illustrating reference pixels and image patterns according to the first embodiment. [Figure 9] 10 is a flowchart of a print job execution process according to the first embodiment. [Figure 10] FIG. 2 is a diagram illustrating pulse control according to the first embodiment. [Figure 11] FIG. 4 is a diagram illustrating the temperature of the lowermost recording layer with respect to time in the first embodiment. [Figure 12] 4A and 4B are diagrams illustrating high-concentration pulse control based on thermal history in the first embodiment. [Figure 13] 4A and 4B are diagrams illustrating low-concentration pulse control based on thermal history in the first embodiment. [Figure 14] FIG. 10 is a diagram illustrating pulse control in the second embodiment. [Figure 15] FIG. 10 is a diagram illustrating pulse control in the third embodiment. [Figure 16] 13A and 13B are diagrams illustrating reference pixels and image patterns according to the fourth embodiment. [Figure 17] FIG. 10 is a diagram illustrating pulse control in the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] (First embodiment) Preferred embodiments of the present invention will be described more specifically and in detail below with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe multiple features, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0010] <Outline of the recording device (Figs. 1 to 3)> FIG. 1 is a side cross-sectional view showing the schematic configuration of a recording apparatus according to a typical embodiment of the present invention.

[0011] 1, the recording device 40 includes a recording head 30, a storage unit 41, a transport roller 42, a platen 43, and an outlet 44. The storage unit 41 can store a plurality of sheet-like recording media 10, and the recording media 10 can be replenished by opening and closing a cover (not shown). During printing, the recording medium 10 is transported to below the recording head 30 by the transport roller 42, and after an image is formed between the platen 43 and the recording head 30, it is discharged from the outlet 44, completing the printing.

[0012] Fig. 2 is a block diagram showing the control configuration of a recording system made up of the recording device and a host device connected to it shown in Fig. 1. As shown in Fig. 2, this recording system is made up of the recording device 40 shown in Fig. 1 and a personal computer (host PC) 50 as its host device.

[0013] The host PC 50 includes a CPU 501 , a RAM 502 , a HDD 503 , a data transfer interface (I / F) 504 , a keyboard / mouse interface (I / F) 505 , and a display interface (I / F) 506 .

[0014] The CPU 501 executes processing in accordance with programs stored in the HDD 503 and RAM 502. The RAM 502 is volatile storage and temporarily stores programs and data. The HDD 503 is nonvolatile storage and also stores programs and data. The data transfer I / F 504 controls the transmission and reception of data with the recording device 40. This data transmission and reception can be performed using a wired connection such as USB, IEEE1394, or LAN, or a wireless connection such as Bluetooth (registered trademark) or WiFi. The keyboard / mouse (registered trademark) I / F 505 is an interface that controls a UI (user interface) such as a keyboard or mouse, allowing the user to input information into the host PC. The display I / F 506 controls the display on a display (not shown).

[0015] On the other hand, the recording device 40 includes a CPU 401 , a RAM 402 , a ROM 403 , a data transfer interface (I / F) 404 , a head controller 405 , and an image processing accelerator 406 .

[0016] The CPU 401 executes the processes of each embodiment described below in accordance with programs stored in the ROM 403 and RAM 402. The RAM 402 is a volatile storage that temporarily stores programs and data. The ROM 403 is a non-volatile storage that stores table data and programs used in the processes of each embodiment described below. The data transfer I / F 404 controls data transmission and reception with the PC 50.

[0017] The head controller 405 controls the heating operation (described later) of the print head 30 based on the print data. Specifically, the head controller 405 is configured to read control parameters and print data from a predetermined address in the RAM 402. In other words, when the CPU 401 writes the control parameters and print data to a predetermined address in the RAM 402, the head controller 405 starts processing and performs the heating operation of the print head.

[0018] The image processing accelerator 406 is configured with hardware and executes image processing faster than the CPU 401. Specifically, the image processing accelerator 406 is configured to read parameters and data required for image processing from a predetermined address in the RAM 402. When the CPU 401 writes the parameters and data to a predetermined address in the RAM 402, the image processing accelerator 406 is activated and the predetermined image processing is executed.

[0019] The image processing accelerator 406 is not necessarily a necessary component, and the above table parameter creation process and image processing may be performed by the CPU 401 alone, depending on the specifications of the recording device.

[0020] <Outline of the recording head configuration (Fig. 3)> FIG. 3 is a side cross-sectional view showing the configuration of the recording head and the state of the contact area between the recording head and the recording medium.

[0021] The recording head 30 comprises a glaze 32 on a substrate 31. The glaze 32 may further comprise a "convex glaze" 33. The resistor 34 is disposed on the surface of the convex glaze 33 if present, or on the flat surface of the glaze 32 if not present. A protective film layer is preferably formed on the resistor 34, glaze 32, and convex glaze 33. The combination of the glaze 32 and convex glaze 33, which are generally made of the same material, is hereinafter referred to as the "recording head glaze." The thermistor 36 is disposed on the glaze 32 near the resistor 34.

[0022] The substrate 31 is in contact with a heat sink 35 and is cooled using a fan or other device. The recording medium 10 generally contacts the printhead glaze over a length substantially longer than the actual length of the heating resistor. The resistor 34 is an electrothermal transducer (heater or heating element) that generates heat when supplied with current. When the resistor 34 generates heat, the resistance value of a thermistor 36 located nearby changes, allowing the temperature near the thermistor to be estimated. However, the thermistor 36 cannot directly measure the temperature of the resistor 34, which corresponds to the printhead surface. Therefore, the temperature of the printhead surface can be estimated by experimentally correlating the temperature near the thermistor 36 with the temperature on the printhead surface. A typical resistor has a length of approximately 120 μm in the direction of transport of the recording medium 10, but the thermal contact area between the glaze and the recording medium in a typical printhead is 200 μm or more.

[0023] <Outline of recording principle (Figs. 4 and 5)> 4 is a cross-sectional view showing the structure of a sheet-like recording medium for use in image formation using infrared rays as a heat source. Recording medium 10 is also called an infrared imaging member because it is made up of multiple color-forming layers that are heated by heat rays (infrared rays) emitted from resistors 34 when an electric current is supplied to the resistors, as described in detail below, and these color-forming layers develop colors to form a full-color image. Therefore, in this sense, recording medium 10 will be referred to as an infrared imaging member in the following description.

[0024] 4, the thermal imaging member 10 includes a light-reflective substrate 12 on which are formed image-forming layers 14, 16, and 18, spacer layers 15 and 17, and an overcoat layer 13. The image-forming layers 14, 16, and 18 are typically yellow (Y), magenta (M), and cyan (C), respectively, in full-color printing, but may be other color combinations.

[0025] Each image-forming layer is initially colorless, but when heated to a specific temperature called the activation temperature, it becomes colored. The color order of the image-forming layers can be selected arbitrarily. One preferred color order is as described above. Another preferred order is when the three image-forming layers 14, 16, and 18 are cyan (C), magenta (M), and yellow (Y), respectively. Here, an example will be described in which the layers are configured in the above-described order of yellow (Y), magenta (M), and cyan (C).

[0026] Spacer layer 15 is preferably thinner than spacer layer 17, provided that the materials comprising both layers have substantially the same thermal diffusivity. The function of the spacer layer is to control heat diffusion within the thermal imaging member 10. Preferably, spacer layer 17, if composed of the same material as spacer layer 15, is at least four times thicker. All layers disposed on substrate 12 are substantially transparent prior to imaging. If substrate 12 is a reflective color (e.g., white), the color image formed in the thermal imaging member 10 is viewed through overcoat layer 13 against the reflective background provided by substrate 12. Because the layers disposed on substrate 12 are transparent, the combination of colors formed in each imaging layer is visible.

[0027] It should be noted that although the three imaging layers 14, 16, 18 of the thermal imaging member 10 are disposed on the same side of the substrate 12, some of the imaging layers may be disposed on opposite sides of the substrate 12.

[0028] The imaging layers 14, 16, 18 are processed at least in part independently by varying two adjustable parameters, temperature and time, which are adjustable to select the temperature of the recording head and the duration of time during which the thermal imaging member is heated to form an image in the desired imaging layer.

[0029] Here, each of the imaging layers 14, 16, and 18 is processed by heating while the recording head 30 is in contact with the top layer of the member, i.e., the overcoat layer 13 of the thermal imaging member 10. The activation temperature (Ta3) of imaging layer 14 (the third layer from the substrate 12 and the imaging layer closest to the surface of the thermal imaging member 10) is greater than the activation temperature (Ta2) of imaging layer 16, which in turn is greater than the activation temperature (Ta1) of imaging layer 18.

[0030] Heating of the image-forming layers at greater distances from the print head 30 is delayed by the time required for heat diffusion through the spacer layers to those layers. This heating delay ensures that the image-forming layers closer to the print head do not activate the image-forming layers below them, even though their activation temperatures are substantially higher than the activation temperatures of the lower-activation image-forming layers (layers further from the print head). Instead, they are allowed to heat above their activation temperatures. Thus, when processing the top image-forming layer 14, the print head 30 briefly heats to a relatively high temperature, which insufficiently heats either of the image-forming layers 16, 18, preventing them from activating.

[0031] To activate only the imaging layer closer to substrate 12 (in this case, imaging layer 16 or 18), heating is performed for a long enough period of time below the activation temperature of the imaging layer further from substrate 12. In this way, if the lower imaging layer is activated, the higher imaging layer is not activated.

[0032] Heating of the thermal imaging member 10 is preferably accomplished using the recording head 30, although any method of applying controlled heat to the thermal imaging member may be used, such as by using a modulated light source (e.g., a laser light source) or any other known means.

[0033] FIG. 5 is a diagram illustrating the heating temperature and time of the recording head required to process the three image forming layers shown in FIG.

[0034] In FIG. 5, the vertical axis represents the heating temperature on the surface of the infrared image member 10 that contacts the recording head 30, and the horizontal axis represents the heating time. Region 21 (where the recording head is at a relatively high temperature and for a relatively short heating time) provides imaging of the imaging layer 14, and region 22 (where the recording head is at an intermediate temperature and for an intermediate heating time) provides imaging of the imaging layer 16. Also, region 23 (where the recording head is at a relatively low temperature and for a relatively long heating time) provides imaging of the imaging layer 18. The time required for imaging the imaging layer 18 is substantially longer than the time required for imaging the imaging layer 14.

[0035] The activation temperature selected for the imaging layer is generally within the range of about 90°C to about 300°C. The activation temperature (Ta1) of the imaging layer 18 is preferably as low as possible and consistent with the thermal stability of the infrared image member during shipping and storage, preferably about 100°C or higher. The activation temperature (Ta3) of the imaging layer 14 is preferably consistently low with respect to the activation of the imaging layers 16 and 18 by heating through this layer without being activated by the heating method of this embodiment, preferably about 200°C or higher. The activation temperature (Ta2) of the imaging layer 16 is such that Ta1 < Ta2 < Ta3, preferably between about 140°C and about 180°C.

[0036] The recording head 30 used here includes a resistor array in which a plurality of resistors are linearly arranged so as to extend substantially over the entire width of the image (in a direction perpendicular to the conveyance direction of the infrared image member).

[0037] Note that the recording width of the recording head may be shorter than the width of the image. In such a case, the recording head is configured to be moved relative to the infrared image member 10 to process the entire width of the image or used in combination with other recording heads.

[0038] By supplying current to these resistors, heating pulses are provided while the thermal imaging member 10 is imaged while being transported in a direction perpendicular to the resistor array of the recording head. The time for which the thermal imaging member 10 is heated by the recording head 30 typically ranges from about 0.001 to about 100 milliseconds per line of the image. The upper limit is reasonably set based on the image printing time, while the lower limit is defined by the constraints of the electronic circuitry. The dot spacing of the formed image is typically in the range of 100 to 600 lines per inch in both the transport direction and the perpendicular direction of the thermal imaging member 10, although the spacing in each direction may be different.

[0039] The recording device described above is a type of thermal printer, and the recording method employed by this device is also called the ZINK (Zero Ink) method or Zero Ink technology (registered trademark).

[0040] <Recording system flowchart> Figure 6 is a flowchart showing the processing of the recording device 40 and host PC 50 when a conventional print service is executed in the above-mentioned recording system. In Figure 6, steps S601, S602, and S604-S606 show the processing of the host PC 50, and steps S611-S614 and S616-S617 show the processing of the recording device 40. Also, as shown in Figure 6, when a user desires to print, processing of the host PC 50 starts, and in response, processing of the recording device 40 starts. Therefore, in step S611, the recording device 40 confirms that it is capable of printing, starts the print service, and becomes ready to print (Ready).

[0041] In this state, when the host PC 50 executes print service discovery in step S601, the recording device 40 responds to that discovery in step S612, notifying the recording device 40 that it is a device that can provide print services. Next, in step S602, the host PC 50 obtains print capability information. Basically, the host PC 50 requests the print capability information from the recording device 40, and in response, in step S614, the recording device 40 notifies the recording device 40 of information about the print services it can provide.

[0042] Furthermore, the host PC 50 constructs a user interface for creating a print job based on the print capability information notified in step S604. Specifically, based on the print capability information of the recording device 40, appropriate options such as print size and printable paper size are displayed on the display and provided to the user. Next, in step S605, the host PC 50 issues a print job.

[0043] In response, the recording device 40 receives the print job in step S614 and executes the print job in step S616. When printing based on the print job is completed in the recording device 40, the recording device 40 notifies the host PC 50 of the completion of printing in step S617. The host PC 50 receives the print completion notification in step S606 and notifies the user of this.

[0044] When the print job is completed, the host PC 50 and the recording device 40 each complete a series of print service processes.

[0045] In the above explanation, various types of information transmission are explained using an example in which the host PC 50 makes a request to the recording device 40, and the recording device 40 responds to that request. However, communication between the host PC and the recording device is not limited to the so-called pull type, and may be the so-called push type in which the recording device 40 spontaneously sends information to the host PC 50 (and other host PCs) on the network.

[0046] <Pulse applied to the recording head> 7 shows an example of heating pulses applied to the recording head of a recording apparatus. In FIG. 7, timing p0 is the earliest in time, and the timing becomes later as one moves from left to right on the time axis.

[0047] The left side of Figure 7 shows the color to be developed, and the right side shows the corresponding heating pulse. For example, to develop yellow (Y), heating is performed once for Δt1 at timing p0 to achieve the heating temperature and heating time of region 21 in Figure 5. To develop magenta (M), heating is first performed once for a time shorter than Δt1 at timing p0 to achieve the heating temperature and heating time of region 22 in Figure 5. This heating is for preheating purposes and does not result in color development. Heating is performed a total of five times, at timing p1, which is Δt1 + Δt2 after p0, for a time of Δt3, with an interval of Δt4 between each heating. To develop cyan (C), heating is first performed once for a time shorter than Δt1 at timing p0 to achieve the heating temperature and heating time of region 23 in Figure 5. The heating time may be longer than M. This heating is for preheating purposes and does not result in color development. At timing p3, which is Δt1 + Δt2 + ((Δt3 + Δ4) × 4 + Δt3) + Δt5 from p0, heating for Δt6 is carried out a total of six times, with an interval of Δt7 between each heating. Heating time of Y = Δt1 Heating time of M = Δt3 × 4 + Δt3 Heating time of C = Δt6 × 5 + Δt6 The relative relationship of the heating time for each image forming layer is as follows: Heating time of Y < Heating time of M < Heating time of C Here, Y, M, and C refer to the image-forming layers 14, 16, and 18.

[0048] Furthermore, the heat applied by the recording head 30 is conducted to the glaze 32, substrate 31, and heat sink 35 of the recording head 30 during periods when the recording head 30 is not heated, such as pulse intervals Δt2, Δt4, Δt5, and Δt7, causing the temperature of the infrared imaging member 10 to drop. Similarly, the heat conducted to the infrared imaging member 10 is also transferred to the platen 43, etc., causing the temperature of the infrared imaging member 10 to drop accordingly. For the same amount of heat applied at the same temperature, the larger the interval, the greater the drop in temperature. The relationship between the peak temperature when only each image-forming layer is colored, depending on the heating time, heating interval, and heating time, is shown below. Peak temperature of Y>Ta3 Ta3>M peak temperature>Ta2 Ta2>C peak temperature>Ta1 By controlling in this way, it is possible to produce the colors Y, M, and C independently.

[0049] Next, a description will be given of the heating pulses that control the color development of the secondary colors R, G, and B and the tertiary color K.

[0050] In FIG. 7, the heating pulses for red (R) are controlled so that they develop in the order of yellow (Y) → magenta (M). In addition, in FIG. 7, the heating pulses for green (G) are controlled so that they develop in the order of yellow (Y) → cyan (C). Similarly, in FIG. 7, the heating pulses for blue (B) are controlled so that they develop in the order of magenta (M) → cyan (C). Finally, in FIG. 7, the heating pulses for black (K) are controlled so that they develop in the order of yellow (Y) → magenta (M) → cyan (C).

[0051] When developing R, the heating pulse for Y is the same as that for single-color Y development, Δt1, but the heating pulse for M development is one less than that for single-color M development. The reason for the fewer pulses is to prevent the C image-forming layer from reaching the color-developing temperature. When developing G, the heating pulse is an OR combination of a single-color Y pulse and a single-color C pulse. The temperature inside the recording medium is lowered between the heating pulses for Y and C to prevent M from developing. When developing B, a total of Δt6 heating pulses are executed 10 times at timing p0, with an interval of Δt7. By using more heating pulses than for single-color C, the M image-forming layer also reaches the color-developing temperature. When developing K, the heating pulse is an OR combination of a pulse for developing R and a single-color C pulse.

[0052] FIG. 8 is a diagram illustrating the pixels referenced to control the heating pulse in this embodiment. The arrow indicates the transport direction of the recording medium 10. In FIGS. 8(a) to 8(h), a pixel of interest is indicated by a circle in the transport direction, the three pixels immediately preceding it, and the pixel immediately following it are indicated by a double circle. Of the three pixels immediately preceding it, the shaded pixels indicate pixels that are colored black, showing a three-pixel black coloring pattern. The pixel at the tip of the arrow (the upper side of the figure) is the pixel that is printed first. In FIG. 8(a), all three pixels are colored, so the temperatures of the print head 30 and the recording medium 10 immediately before the start of printing of the pixel of interest are the highest among FIGS. 8(a) to 8(h). In FIG. 8(h), none of the three pixels are colored, so the temperatures of the print head 30 and the recording medium 10 immediately before the start of printing of the pixel of interest are the lowest among FIGS. 8(a) to 8(h). The closer the pixel that is colored black is to the pixel of interest, the higher the temperatures of the print head 30 and the recording medium 10 immediately before the start of printing of the pixel of interest. Therefore, the temperatures of the print head 30 and the recording medium 10 immediately before the pixel of interest increase in the order of Figures 8(a) to 8(h). The surface temperature of the print head 30 due to the heating pulses applied to the pixels before the pixel of interest is referred to as the thermal history. Alternatively, the temperature of each layer of the recording medium 10 may be referred to as the thermal history, or both the surface temperature of the print head 30 and the temperatures of each layer of the recording medium 10 may be referred to as the thermal history. Note that while the example described here references the three pixels immediately before the pixel of interest, the number of pixels is not limited to this. The surface temperature of the print head 30 immediately before the pixel of interest can be estimated by referencing a pixel one or more pixels before the pixel of interest. However, because the temperature fluctuates depending on the thermal history of multiple pixels before the pixel of interest, it is desirable to reference multiple pixels from the perspective of temperature estimation accuracy. Furthermore, because referencing too many pixels increases the processing load, it is advisable to set appropriate reference pixels through prior experiments. The surface temperature of the print head 30 for each pattern in Figures 8(a) to 8(h) is measured through prior experiments, and the correspondence between each pattern and the temperature of the print head 30 is stored in the ROM 403 of the recording device 40. 8(a) to 8(h), the surface temperature of the recording head 30 can be estimated. The temperatures of the image forming layers 14, 16, and 18 of the recording medium 10 may also be used as the thermal history.As with the recording head 30, the patterns shown in Figures 8(a)-(h) can be correlated with the temperature of each image-forming layer through prior experiments. Color development ultimately occurs when each image-forming layer is heated to a temperature that allows color development. Using the thermal history of each layer complicates control, but it also improves control accuracy. Furthermore, even with the same pulse, the temperature of each image-forming layer varies depending on the surface temperature of the recording head 30. Therefore, using both the recording head 30 and the recording medium 10 improves accuracy. The temperatures of the recording head 30 and the recording medium 10 can be measured during image recording, as described above, or simulated values ​​can be used. When using simulated values, the specific heat, density, and thermal conductivity of the materials constituting the recording head 30 and the recording medium 10, as well as the heat generation, pulse data, and size of the heaters in the recording head 30, are prepared as parameters. By substituting the prepared parameters into the heat conduction equation and solving the heat conduction equation for elapsed time and the transport direction, the simulated values ​​of each temperature described above can be obtained. 8(a) to 8(h) may be determined for the pixel values ​​to be determined without simulating the temperature. Therefore, the pixel value pattern may be used as the thermal history.

[0053] Figure 9 is a flowchart of the print job execution process in step S616 in Figure 6. In this process, heating pulses are generated by referencing the pixels shown in Figure 8, and printing is performed using the generated pulses. The flow will be explained below in the order of the steps in Figure 9. The process in Figure 9 is executed by the CPU in accordance with a program stored in ROM 403.

[0054] In step S901, the printing process in the print job execution in step S616 in FIG. 6 starts.

[0055] In step S902, the image data of the print job received in step S614 of FIG. 6 is input.

[0056] In step S903, if the image data has been compressed or encoded, a decoding process is performed.

[0057] In step S904, it is determined whether the pixel on line n, which is the pixel of interest in the image data, is a black image. Whether or not it is a black image that emits black can be determined from the R, G, and B of the input pixel data. This can be determined by defining a value range, such as determining that pixels with RGB values ​​of R=0 to r0, G=0 to g0, and B=0 to b0 are black. r0, g0, and b0 can be set according to the value range desired for black. If r0=0, g0=0, and b0=0, pixel data with R=0, G=0, and B=0 is determined to be black, and data with other values ​​is determined to be non-black. r0, g0, and b0 can be set to values ​​that make it highly likely that the pixel immediately following line n+1 immediately after heat propagation will emit a color erroneously. In this embodiment, pixels that emit black are considered to be pixels with a high probability of erroneous color generation. However, even if a pixel is not black, a pixel that emits a high density of C in the bottom layer may also be considered to be pixels with a high probability of erroneous color generation.

[0058] If it is not determined in step S904 that the pixels on line n are a black image, the pixels immediately following line n+1 will not erroneously color due to heat propagation, so in step S917 the head is controlled to record the image. At this time, line n is recorded using the pulses shown in Figure 7. If it is determined that the pixels on line n are a black image, there is a risk that the pixels immediately following line n+1 will erroneously color due to heat propagation, so the process proceeds to step S905.

[0059] In step S905, when the pixel on line n of the image data, indicated by a circle in Fig. 8, is set as the pixel of interest, it is determined whether pixels on lines n-3 to n+1 shown in Fig. 8 exist as a data area. Line n is the pixel of interest, n-3 to n-1 are the three pixels immediately before, and line n+1 is the one pixel immediately after. If the determination result is Yes, the process proceeds to step S906, and if the determination result is No, the process proceeds to step S908.

[0060] In step S906, the 8-bit (0 to 255) R, G, and B values ​​of pixel data on lines n-3 to n+1 are passed to the processing in steps S907 and onwards.

[0061] In step S907, thermal history determination 1 is performed. In thermal history determination 1, it is determined which of the black color patterns in FIG. 8(a) to (h) the pixels on line n-3 to line n-1, which are the three pixels immediately preceding the pixel of interest marked with a circle in FIG. 8 in the transport direction, belong to. Whether or not a pixel is black can be determined from the R, G, and B of the input pixel data. This can be determined by defining a value range, such as determining that pixels with RGB values ​​of R=0 to r0, G=0 to g0, and B=0 to b0 are black. r0, g0, and b0 can be set according to the value range in which you want the pixel to be black. If r0=0, g0=0, and b0=0, pixel data with R=0, G=0, and B=0 is determined to be black (diagonal lines in FIG. 8), and data with any other value is determined to be not black (white pixels in FIG. 8). As a result, the three immediately preceding pixels are determined to belong to one of the patterns in FIG. 8(a) to (h).

[0062] In step S908, next pixel determination 1 is performed. In next pixel determination 1, a condition determination is made to determine whether the pixel marked with a double circle, which is the pixel immediately upstream in the transport direction from the pixel of interest marked with a circle in FIG. 8, satisfies the condition that the image-forming layer 18, which is the bottom layer of the recording medium 10, is a target for color development. Since the image-forming layer 18 of the recording medium 10 in this embodiment is C, the image-forming layer 18 is a target for color development when at least C monochromatic color development, G color development, B color development, and K color development are performed. Whether the image-forming layer 18 is a target for color development can be determined by whether all of R = r1 to r2, G = g1 to g2, and B = b1 to b2 are satisfied. r1, g1, b1, r2, g2, and b2 may be appropriately set to values ​​that at least cause the image-forming layer 18 to be a target for color development. For example, if r1 = 0, g1 = 0, b1 = 0, r2 = 0, g2 = 0, and b2 = 0, and the pixel immediately following the circle in Figure 8 has R = 0, G = 0, and B = 0, the pixel immediately following the circle in Figure 8 will be a pixel that will produce black, and the image-forming layer 18 will be determined to be the target for color production. Here, we explain why we focus on the image-forming layer 18. Image-forming layers 14 and 16 correspond to Y and M, respectively, in Figure 5. Both have higher heating temperatures than the heating temperature required to produce C, but the heating time is shorter. This is because the temperature can be raised in a short time at a depth shallow from the surface of the recording medium 10, and the temperature of the recording medium 10 also decreases quickly. Therefore, if the heating pulses that produce color in the image-forming layers 14 and 16 are set to zero within the pixel of interest, or if no pulses are applied to produce color in either layer, the temperatures of each layer will drop below their color production temperature in a short time. As a result, the heat propagation of the heating pulse applied to the pixel of interest (O) makes it unlikely that the image-forming layers 14 and 16 of the immediately succeeding pixel (◎) will exceed their respective color-developing temperatures, resulting in erroneous color development. On the other hand, because the image-forming layer 18 is located deep beneath the surface of the recording medium 10, it takes time for the temperature of the image-forming layer 18 to rise and fall. Even if the heating pulse that caused the image-forming layer 18 to develop color is further reduced to zero within the pixel of interest, i.e., no pulses for color development are applied to any of the layers, it still takes time for the temperature of the image-forming layer 18 to fall below its color-developing temperature. As a result, the heat propagation of the heating pulse from the pixel of interest may cause the image-forming layer 18 of the immediately succeeding pixel to exceed its color-developing temperature, resulting in color development, even though no pulse for color development C is applied to the immediately succeeding pixel.For the above reasons, in this embodiment, heating pulse control focuses on whether the bottom layer of the recording medium 10 is the target for color development. Since the control target of this embodiment is input data in which the heat propagation of a heating pulse to the trailing pixel of a solid image with an image density of 100% causes the pixel immediately following it, which is originally a white image, to erroneously develop color, it is advisable to set the values ​​of r0, g0, and b0 described above so as to include this input data.

[0063] In step S909, 8-bit (0 to 255) R, G, B values, which are pixel data of existing lines among pixels from line n-3 to line n+1 shown in FIG. 8, are passed to the processing from S910 onwards.

[0064] In step S910, thermal history determination 2 is performed. In thermal history determination 2, it is determined which of the black coloring patterns in FIG. 8(a) to (h) corresponds to the pixels on line n-3 to line n-1, which are the three pixels immediately preceding the pixel of interest marked with a circle in FIG. 8 in the transport direction. Whether or not the pixels are black can be determined from the R, G, and B of the input pixel data, as in step S907. If all of line n-3 to line n-1 have been input, the three pixels immediately preceding the pixel are determined to correspond to one of lines (a) to (h) in FIG. 8, as in step S907. If only line n-2 to line n-1 have been input, line n-2 and line n-1 in lines b, d, f, and h in FIG. 8 are referenced to determine which pattern corresponds. If only line n-1 has been input, line n-1 in lines d and h in FIG. 8 is referenced to determine which pattern corresponds. If line n-1 has not been input, it is determined to correspond to pattern h in FIG.

[0065] In step S911, next pixel determination 2 is executed. In next pixel determination 2, if n+1 pixels have been input, similarly to step S908, it is determined whether the pixel marked with a double circle, which is one pixel immediately following the pixel of interest marked with a circle in Fig. 8 in the transport direction, satisfies the condition that the image forming layer 18, which is the lowest layer of the recording medium 10, is a target for color development. If n+1 pixels have not been input, it is determined that the image forming layer 18 of the next pixel is not a target for color development.

[0066] In step S912, it is determined whether the pixel of interest marked with a circle in Fig. 8 is likely to be a black internal pixel. Here, if in step S907 it is determined that the thermal history is equal to or greater than a predetermined value, as in any of (a) to (d) in Fig. 8, and if in step S908 it is determined that the lowermost image forming layer 18 is the target for color development, the process proceeds to step S913. Otherwise, if it is determined that the thermal history is not equal to or greater than a predetermined value, the process proceeds to step S914. Note that an example of finely controlling the heating pulse for each of the patterns (a) to (h) in Fig. 8 will be described later.

[0067] In step S913, a high density pulse is set for the pixel of interest marked with a circle in Fig. 8. This can be set as follows using a three-dimensional lookup table (3D_LUT). High density pulse = 3D_LUT[R][G][B][0] The 3D_LUT is composed of a 256 x 256 x 256 x 3 data table. As shown in Figure 7, each data set is configured by combining the R, G, and B values ​​for the timing, width, and number of heating pulses to be applied at each timing. The high-density pulse is set with an emphasis on the color development of each solid image. Figure 10 shows the high-density pulse, low-density pulse, and high-density pulse for black. In step S910, the high-density pulse shown in Figure 10(0) is set. The low-density pulse will be described later in step S915, and the high-density pulse will be described later in step S916. When a high-density pulse for black is applied to a pixel of interest, it is set to a level that causes the image-forming layer 18, the lowest layer of the pixel immediately following it, to develop color, thereby increasing the density of the solid black. As mentioned above, since it takes time for the image-forming layer 18, the lowest layer, to heat up, the color development of the pixel immediately following it due to heat propagation from the pixel of interest effectively contributes to the density development of the pixel immediately following it when the pixel immediately following it is colored black. The high-density pulse for black has a higher duty ratio (wider pulse width or narrower pulse interval) or a larger number of pulses than the low-density pulse described in step S614. In other words, it has greater thermal energy. Note that the high-density pulse does not need to have greater thermal energy than the low-density pulse for all RGB values. The color development of the immediately succeeding pixel due to the heat applied to the pixel of interest varies depending on the combination of the printhead, print medium, and print speed. Depending on the combination, the high-density pulse can be set to have greater thermal energy than the low-density pulse for R, G, and B values ​​that can produce a higher density by coloring the immediately succeeding pixel. Depending on the color to be developed, increasing the thermal energy of the pixel of interest may not cause the immediately succeeding pixel to develop color. For the R, G, and B values ​​corresponding to such colors, the high-density pulse does not need to have greater thermal energy than the low-density pulse.

[0068] In step S914, it is determined whether the pixel of interest is a black trailing edge pixel. Here, if in step S907 it is determined as any of (a) to (d) in Figure 8 and in step S908 it is determined that the bottom layer of the immediately following pixel is not a target for coloring, the process proceeds to step S915. If not, that is, if it corresponds to (e) to (h) in Figure 8 and the bottom layer of the immediately following pixel is not a target for coloring, the process proceeds to step S916.

[0069] In step S915, a low density pulse is set for the pixel of interest marked with a circle in Fig. 8. This can be set as follows using a three-dimensional lookup table (3D_LUT). Low density pulse = 3D_LUT[R][G][B][1] The low-density pulse is set to color the trailing pixel of each solid image, but to prevent the heat applied to the trailing pixel from accidentally coloring the pixel immediately following it. In step S915, the low-density pulse shown in FIG. 10(1) is set for the black pixel. Compared to the high-density pulse, the low-density pulse has a narrower pulse width, such as the pulse at timing py in FIG. 10. Alternatively, the pulse interval is wider, such as the pulse after pm. Alternatively, the number of pulses is reduced, such as the pulse after pc. FIG. 10(1) shows a pulse that incorporates all of the following: narrow pulse width, wide pulse interval, and reduced pulse number. However, any pulse incorporating at least one of these techniques can be effective. In this way, the thermal energy applied to the recording medium 10 is reduced compared to the high-density pulse. The black low-density pulse, when applied to the pixel of interest, is set to a level that does not cause color development in the image-forming layer 18 at the bottom of the pixel immediately following it, thereby preventing color development in the bottom layer of the pixel immediately following it, which is not the target of color development.

[0070] In step S916, a leading edge pulse is set for the pixel of interest marked with a circle in Fig. 8. The setting can be made as follows using a three-dimensional lookup table (3D_LUT). Tip pulse = 3D_LUT[R][G][B][2] In step S916, the leading edge pulse shown in FIG. 10(2) is set for the black pixel. The leading edge pulse is made wider than the high density pulse, like the pulse at timing py, pm, or pc in FIG. 10. The number of pulses is increased, like the pulses at pm or pc and after. In this way, it is preferable to apply a larger amount of heat energy to the recording medium 10 than the high density pulse. The pixel of interest in step S916 is likely to be the leading edge of the image, and heat propagation from the immediately preceding pixel is small. For this reason, applying a larger amount of heat energy to the recording medium 10 than the high density pulse can improve the color development of the leading edge of the image.

[0071] In step S917, head control is executed, and the pulses set in step S913, step S915, or step S916 are applied to the head to cause the recording medium 10 to develop color.

[0072] In step S918, it is checked whether printing of the page is complete, and if the result is No, the process returns to step S903, and the next pixel is set as the pixel of interest (pixel on line n+1) to print the rest of the page. If step S918 is Yes, the printing process ends in step S919.

[0073] Using the method described above, when the thermal history is greater than a predetermined value and the bottom layer of the immediately succeeding pixel is a target for color development, a pulse with greater thermal energy is applied to the black pixel of interest compared to when the thermal history is the same but the bottom layer of the immediately succeeding pixel is not a target for color development. As shown in Figure 10, increasing the pulse width or shortening the pulse interval—that is, increasing the pulse duty—can increase the thermal energy. Increasing the number of pulses also increases the thermal energy. Figure 11 plots the temperature of the image-forming layer 18 versus time when pulses (0) and (1) in Figure 10 are applied to one pixel. The thick line represents the result of the high-density pulse in Figure 10(0). The thin line represents the result of the low-density pulse in Figure 10(1). The dashed line represents the color temperature of the image-forming layer 18; the image-forming layer 18 develops color when the temperature exceeds the color temperature. The high-density pulse extends the range above the color temperature more than the low-density pulse. This is because the high-density pulse increases at least one of the temperature and the time spent above the color temperature compared to the low-density pulse. As a result, the rear end of a high-density image is recorded using a low-density pulse to suppress the color development of the white pixels immediately after the rear end of the solid image, while the high-density pulse suppresses the density decrease in the internal area of ​​the solid image, allowing the image to be recorded.

[0074] 9, RGB values ​​are used to determine the color development of pixels, but this is not limiting. For example, the color development level of each pixel may be determined based on CMY values ​​obtained by converting RGB values ​​into CMY values.

[0075] Next, a method for finely controlling the heating pulse according to the thermal history will be described. When the temperature of the recording head 30 or the recording medium 10 is high, the recording head 30 or the recording medium 10 may be damaged depending on the recording head, the recording medium, and the heating pulse. Therefore, in order to prevent damage to the recording head 30 or the recording medium 10, the heating pulse can be controlled according to the thermal history.

[0076] FIG. 12 shows an example of finely controlling the high-density pulse in accordance with the thermal history. This control is executed in step S913. The following describes the case where step S907 or step S910 determines that the result is one of (a) to (g) in FIG. 8, and step S908 or step S911 determines that the bottom layer is the target for color development. In step S912, it is determined whether the above case exists, and the pixel of interest marked with a circle in FIG. 8 is determined to be a black internal pixel. Then, in step S913, heating pulses (a) to (g) in FIG. 12 corresponding to (a) to (g) in FIG. 8, respectively, are set. This can be set using a 3D_LUT. High-density pulse (a) = 3DLUT [R] [G] [B] [0] [0] High-density pulse (b) = 3DLUT [R] [G] [B] [0] [1] High-density pulse (c) = 3DLUT [R] [G] [B] [0] [2] High-density pulse (d) = 3DLUT [R] [G] [B] [0] [3] High-density pulse (e) = 3DLUT [R] [G] [B] [0] [4] High-density pulse (f) = 3DLUT [R] [G] [B] [0] [5] High-density pulse (g) = 3DLUT [R] [G] [B] [0] [6] The above 3D_LUT is composed of a 256 x 256 x 256 x 3 x 7 data table. The heating pulse in Figure 12(g) is the same as the high-density pulse in Figure 10(0). As the temperature estimated from the thermal history increases, heating pulses with lower thermal energy than those in Figure 12(g) are set, as shown in Figures 12(a) to 12(f). The high-density pulses in Figure 12(a) to 12(g) have higher thermal energy than the low-density pulses in Figure 13(a) to 13(g).

[0077] FIG. 13 shows an example of finely controlling the low-density pulse in accordance with the thermal history. This control is executed in step S915. The following describes a case where step S907 or step S910 determines that the result is one of (a) to (g) in FIG. 8, and step S908 or step S911 determines that the bottom layer is not a target for color development. In step S913, it is determined whether the above case exists, and the pixel of interest marked with a circle in FIG. 8 is determined to be a black trailing edge pixel. Then, in step S915, heating pulses (a) to (g) in FIG. 13 corresponding to (a) to (g) in FIG. 8, respectively, are set. Low-density pulse (a) = 3DLUT[R][G][B][1][0] Low density pulse (b) = 3DLUT[R][G][B][1][1] Low density pulse (c) = 3DLUT[R][G][B][1][2] Low density pulse (d) = 3DLUT[R][G][B][1][3] Low density pulse (e) = 3DLUT[R][G][B][1][4] Low density pulse (f) = 3DLUT[R][G][B][1][5] Low density pulse (g) = 3DLUT[R][G][B][1][6] The higher the temperature estimated from the thermal history, the lower the heat energy of the heating pulses set, as shown in Figures 13(a) to (f) compared to Figure 13(g). Also, the low-concentration pulses shown in Figures 13(a) to (g) have higher heat energy than the high-concentration pulses shown in Figure 12(a) to (g).

[0078] Even when the pulse is finely controlled based on the thermal history, the leading edge pulse can be set by storing the pulse data in FIG. 10(2) in 3DLUT[R][G][B][2][0] in step S916. Tip pulse = 3DLUT[R][G][B][2][0] 3DLUT[R][G][B][2][1]~[6] are not referenced here, so any data can be stored.

[0079] The method described using FIGS. 12 and 13 can suppress damage to the recording head 30 or the recording medium 10, suppress color development of white pixels immediately after the trailing edge of a solid image, and realize recording that suppresses density reduction of the solid image.

[0080] (Second embodiment) In the first embodiment, an example was described in which a high-density pulse was obtained by increasing at least one of the duty ratio or the number of times of application of the heating pulse. In the present embodiment, an example is described in which a high-density pulse is obtained by shortening the blank time before the pixel immediately following the target pixel during the recording time (pulse value range) of the target pixel.

[0081] FIG. 14 shows pulses with varying blank times (described later) in the pulse range. FIG. 14(a) is the same as the high-density pulse in FIG. 10(0). The high-density pulse in this embodiment is shown in FIG. 14(0). The low-density pulse in this embodiment is shown in FIG. 14(1). The pulse width, pulse interval, and number of pulses can be set arbitrarily within the pulse range shown in FIG. 14. A pulse set within the pulse range is applied to one pixel. The high-density pulse in FIG. 14(0) has a shorter blank time during which no pulse is applied within the pulse range compared to FIG. 14(a). During the blank time, the temperature of the recording head 30 and recording medium 10 drops. Therefore, the pulse in FIG. 14(0), which has a short blank time, results in a smaller temperature drop per pixel, allowing the temperature of the image-forming layer to exceed the color-developing temperature and the time it remains above the color-developing temperature to be longer. On the other hand, the low-density pulse in FIG. 14(1) has a longer blank time compared to the high-density pulse in FIG. 14(0). Therefore, the low-density pulse in Figure 14(1) reaches a lower temperature than the high-density pulse in Figure 14(0) at which the image-forming layer reaches or exceeds the color-developing temperature, and the time it remains above the color-developing temperature is shorter. The flow for controlling the heat pulse to print can be the same as that explained using Figure 9 in the first embodiment. The differences are as follows:

[0082] In step S913, High density pulse = 3DLUT[R][G][B][0] 14(0) is set in the 3DLUT instead of the pulse data in FIG. 10(0) (FIG. 14(a)). By doing so, in step S912, the high density pulse in FIG. 14(0) can be set for the black of the pixel of interest that is determined to be a black internal pixel.

[0083] Also, in step S915, Low density pulse = 3DLUT[R][G][B][1] 14(1) is set in the 3DLUT instead of the pulse data in Fig. 10(1). By doing so, in step S914, the low density pulse in Fig. 14(1) can be set for the black of the pixel of interest determined to be the black trailing edge pixel.

[0084] With the method described above, when the thermal history is equal to or greater than a predetermined value and the bottom layer of the immediately succeeding pixel is subject to color development, a pulse with greater thermal energy is applied to the black pixel of interest compared to when the thermal history is the same but the bottom layer is not subject to color development. As a result, printing can be achieved in which the low-density pulse suppresses color development of the white pixel immediately following the trailing edge of the solid image, while the high-density pulse suppresses density reduction in the interior area of ​​the solid image.

[0085] (Third embodiment) In the first and second embodiments, a low-density pulse is described in which a pulse for coloring Y, a pulse for coloring M, and a pulse for coloring C are applied in this order in the pulse value range. In this embodiment, an example is described in which a pulse for coloring C is applied first to form a low-density pulse.

[0086] FIG. 15 shows an example in which the pulse order in the pulse value range is changed. The high-density pulse in this embodiment is shown in FIG. 15(0), which is the same as FIG. 10(0). The low-density pulse in this embodiment is shown in FIG. 15(1). The pulse width, pulse interval, and number of pulses can be set arbitrarily within the pulse value range shown in FIG. 15. Pulses set in the pulse value range are applied to one pixel. The reason why the pulses in FIG. 15(0) are high density is as explained using FIG. 10 in the first embodiment. Here, we will explain why the pulses in FIG. 15(1) are low density. The high-density pulse in FIG. 15(0) is in the order of a Y color-emitting pulse, an M color-emitting pulse, and a C color-emitting pulse. On the other hand, the low-density pulse in FIG. 15(1) is in the order of a C color-emitting pulse, a Y color-emitting pulse, and an M color-emitting pulse. As already explained, when pulses are applied to a pixel of interest in the order shown in FIG. 15(0), the image-forming layer 18, which is the bottom layer of the immediately succeeding pixel, will emit color (here, C). In Figure 15(1), the order of the C color-forming pulses is changed to the first one at timing pc, so that the heat applied to the pixel of interest causes C to color preferentially. Next, a long blank time is provided between the last C color-forming pulse and the Y color-forming pulse at timing py, as indicated by the arrow in Figure 15(1). This blank time is set to be longer than the time required for the temperature of the image-forming layer 18, where C is colored, to drop below its color-forming temperature. After the image-forming layer 18 has dropped to a temperature at which C does not color, Y color-forming pulses and M color-forming pulses are applied at timings py and pm, respectively, to color the pixel of interest black. The Y color-forming pulse and M color-forming pulse raise the temperature of the image-forming layer 14 for Y color and the image-forming layer 16 for M color above their color-forming temperatures, but are set so that the image-forming layer 18 for C color is below its color-forming temperature. Applying the Y color-forming and M color-forming pulses in a relatively short time, as with the R color-forming pulse in Figure 7, can prevent C from coloring. Furthermore, when the application of the pulse is stopped, the temperatures of the image forming layers 14 and 16 can be lowered faster than the image forming layer 18. In this way, the pixel of interest can be colored black, but the image forming layer 18 of the pixel immediately following it can be prevented from coloring.

[0087] The flow for controlling heat pulses to print can be the same as that explained using Figure 9 in the first embodiment. The differences are as follows.

[0088] In step S915, Low density pulse = 3DLUT[R][G][B][1] 15(1) is set in the 3DLUT instead of the pulse data in Fig. 10(1). By doing so, in step S914, the low density pulse in Fig. 15(1) can be set for the black of the pixel of interest determined to be the black trailing edge pixel.

[0089] With the method described above, when the thermal history is equal to or greater than a predetermined value and the bottom layer of the immediately succeeding pixel is subject to color development, a pulse with greater thermal energy is applied to the black pixel of interest compared to when the thermal history is the same but the bottom layer is not subject to color development. As a result, printing can be achieved in which the low-density pulse suppresses color development of the white pixel immediately following the trailing edge of the solid image, while the high-density pulse suppresses density reduction in the interior area of ​​the solid image.

[0090] (Fourth embodiment) In the first to fourth embodiments, an example was described in which the thermal energy in the inner region of a black image is made greater than that in the rear end of the image. In the present embodiment, an example will be described in which the thermal energy in the inner region of an image is made greater than that in the left and right ends of the image.

[0091] In the first embodiment, it was explained that the heat propagation of the heating pulse from the pixel of interest can cause the image-forming layer 18 of the pixel immediately following the pixel to exceed its color-developing temperature, resulting in color development. The heat propagation direction of the heating pulse from the pixel immediately following the pixel of interest is not limited to the pixel immediately following the pixel of interest; if the temperature of the pixel to the left or right of the pixel of interest is lower than that of the pixel of interest, the heat propagates to the pixels to the left and right. Therefore, a high-density pulse from the left and right edge pixels of a solid black image can cause the image-forming layer 18 of the adjacent white pixel to develop color C.

[0092] FIG. 16 is a diagram illustrating the pixels referenced for controlling the heating pulse in this embodiment. FIGS. 16(a) to 16(d) each show a pixel of interest marked with a circle, three adjacent pixels to the right, and one adjacent pixel marked with a double circle, in the direction of the printhead. The diagonally shaded pixels indicate three adjacent pixels to the right that are colored black, illustrating a three-pixel black coloring pattern. The pixel of interest is targeted for black coloring, and the adjacent right pixel marked with a double circle is a color that does not cause coloring in the image forming layer 18. Furthermore, the same pulse is applied to all black-colored pixels. In FIG. 16(a), all three adjacent pixels are colored, so the temperatures of the printhead 30 and print medium 10 at the pixel of interest are the highest among FIGS. 16(a) to 16(d). In FIG. 16(d), none of the three pixels are colored, so the temperatures of the printhead 30 and print medium 10 at the pixel of interest are the lowest among FIGS. 16(a) to 16(d). Therefore, the temperatures of the printhead 30 and print medium 10 at the pixel of interest are highest in the order of FIGS. 16(a) to 16(d). 16(e) to (h) show patterns obtained by inverting (a) to (d) horizontally, with the temperatures of the recording head 30 and recording medium 10 at the pixel of interest increasing in the order of (e) to (h) in Figure 16. The higher the temperature is, as in Figure 16(a) or (e), the more likely it is that the image forming layer 18 at the pixel in the adjacent n-1 column or n+1 column will develop color C.

[0093] 16 has explained the temperatures of the recording head 30 and the recording medium 10 of the pixel of interest when the same pulse is applied to a pixel that produces black color, regardless of the patterns (a) to (h). Pulse control in consideration of the above will be explained using FIG.

[0094] Figures 17(ae) to (dh) show the heating pulses corresponding to Figures 16(a) to (d) and Figures 16(e) to (h), respectively. In Figure 17, (dh) is a high-density pulse with the highest thermal energy, and (ae) is a low-density pulse with the lowest thermal energy. The order of thermal energy is (dh) > (cg) > (bf) > (ae). For a pixel of interest, if three consecutive columns of pixels adjacent to the pixel of interest are black, as in Figure 16(a) or (e), the heating pulse of Figure 17(ae) is applied to the black of the pixel of interest. For a pixel of interest, if two consecutive columns of pixels adjacent to the pixel of interest are black, as in Figure 16(b) or (f), the heating pulse of Figure 17(bf) is applied to the black of the pixel of interest. If the pixels in the columns before and after the pixel of interest are black, as shown in FIG. 16(c) or (g), the heating pulse of FIG. 17(cg) is applied to the black pixel of the pixel of interest. Even if the n+3 column or n-3 column is black in FIG. 16(c) or (g), the heating pulse of FIG. 17(cg) is applied. If the pixels in the columns before and after the pixel of interest are black, as shown in FIG. 16(d) or (h), the pixels in the n+1 column or n-1 column adjacent to the pixel of interest are not black, the heating pulse of FIG. 17(dh) is applied to the black pixel of the pixel of interest. Furthermore, if a pattern other than those described above is used, for example, if the pixel of interest marked with a circle in FIG. 16 is black and the pixel marked with a double circle is the color that the image forming layer 18 is colored, the pixel of interest can be determined to be a pixel within a solid black area. Therefore, the heating pulse of FIG. 17(dh), which has the greatest thermal energy, is applied.

[0095] As a result, it is possible to realize recording in which the color development of adjacent white pixels at the left and right edges of a black solid image is suppressed by a low-density pulse, while the density reduction in the inner region of the black solid image is suppressed by a high-density pulse.

[0096] (Other embodiments) In the first to third embodiments, a pulse with greater thermal energy is applied to the inner region of the solid black image than to the rear end of the solid black image. This is equivalent to applying a pulse with less thermal energy to the rear end of the solid black image than to the inner region of the solid black image. Steps S914 and S915 may be performed before steps S912 and S913 in FIG. 9. The immediately succeeding pixel is determined to be a black rear end pixel that does not cause the image forming layer 18 to develop color, and a low-density pulse is applied. If it is not a black rear end pixel, it is determined to be a black inner pixel, and a high-density pulse is applied.

[0097] In the first embodiment, r0-2, g0-2, and b0-2 are all set to 0 to represent black, but a value other than 0 may be entered for each. However, it is preferable to set the values ​​to target a color that can increase the image density by determining that the temperature just before the pixel of interest is high due to thermal history, and determining that the image forming layer 18 of the pixel just after the pixel is to be colored, and applying a high-density pulse.

[0098] In the fourth embodiment, a low-density pulse is set at the left and right edges of a solid black image. The first and fourth embodiments can also be combined. The left and right edge pulses shown in FIG. 17 are adjusted based on the temperature that can be estimated from the thermal history. If it is estimated that the temperature of the print head 30 or the print medium 10 has risen due to continuous black printing in the transport direction, the heat energy may be further reduced from each pulse shown in FIG. 17. In addition, in the case of both the left and right edges and the rear edge, the heat energy may also be further reduced from each pulse shown in FIG. 17. [Explanation of symbols]

[0099] 10 Recording medium (infrared imaging material) 12 Base material 13 Protective film layer, 14, 16, 18 Image forming layer 15, 17 spacer layer, 30 Recording head 31 PCB 32 Glaze 33 Convex Glaze, 34 Resistance 35 Heatsink 36 Thermistor 40 Recording Device 41 Storage area 42 conveying roller, 43 Platen 44 Outlet 50 host PCs

Claims

1. A recording device that forms an image on a sheet-like recording medium having a plurality of color-forming layers that correspond to a plurality of colors and that develop color in response to heat, by heating a sheet-like recording medium and causing a desired color-forming layer among the plurality of color-forming layers to develop color, a print head including a plurality of heat generating elements arranged in a predetermined direction, the heat generating element configured to heat the print medium based on image data; a first condition determination means for determining whether or not a first condition that a pixel immediately after the pixel of interest, which is at the same position as the pixel of interest in the predetermined direction and which is to be recorded next to the pixel of interest, is a pixel that causes the color-producing layer at the bottom of the recording medium to develop color, is satisfied; a pulse control means for controlling a pulse to be applied to the recording head when forming the pixel of interest based on the determination result of the first condition determination means; The recording device is characterized in that, when the value of the target pixel in the image data is a predetermined value and the first condition is not satisfied, the pulse control means controls the pulse so that the thermal energy applied by the recording head to the recording medium when forming the target pixel is smaller than when the value of the target pixel in the image data is the predetermined value and the first condition is satisfied.

2. The recording device according to claim 1, characterized in that the pulse control means controls the pulses so that when the recording head reduces the thermal energy applied to the recording medium, at least one of the heating temperature or heating time of the recording head is reduced compared to when the recording head does not reduce the thermal energy applied to the recording medium.

3. 3. The recording apparatus according to claim 1, wherein the pulse control means, when reducing the thermal energy applied to the recording medium by the recording head, applies to the recording head pulses that have at least one of a narrower pulse width, a longer pulse application interval, and a smaller number of pulse applications, compared to when the thermal energy applied to the recording medium by the recording head is not reduced.

4. A recording device as described in any one of claims 1 to 3, characterized in that when the recording head reduces the thermal energy applied to the recording medium, the pulse control means lengthens the time between the pulse applied to the target pixel and the pulse applied to the immediately succeeding pixel compared to when the recording head does not reduce the thermal energy applied to the recording medium.

5. The recording device described in any one of claims 1 to 4, characterized in that when the first condition is satisfied, the pulse control means applies a pulse to cause a color-producing layer other than the bottom layer of the recording medium to color, and finally applies a pulse to cause the bottom layer of the color-producing layer to color, and when the first condition is not satisfied, the pulse control means controls so that a pulse to cause the bottom layer of the recording medium to color is applied, and then a pulse to cause the color-producing layer other than the bottom layer to color.

6. The recording device described in claim 5, characterized in that, when the first condition is not satisfied, the pulse control means provides a time between the pulse for causing the lowest color-forming layer to color and the pulse for causing the color-forming layer other than the lowest layer to color so that the pulse for causing the color-forming layer other than the lowest layer to color does not cause the lowest layer of the recording medium to reach the color-forming temperature.

7. a second condition determining means for determining whether or not a second condition indicating that a thermal history, which is a temperature of the recording head or each image forming layer of the recording medium, is equal to or greater than a predetermined value is satisfied in forming a previous pixel that is at the same position as the target pixel in the predetermined direction and is recorded before the target pixel, A recording device as described in any one of claims 1 to 6, characterized in that when the value of the target pixel in the image data is a predetermined value, the first condition is satisfied, and the second condition is not satisfied, the pulse control means controls the pulse so that the thermal energy applied by the recording head to the recording medium when forming the target pixel is greater than when the value of the target pixel in the image data is the predetermined value, the first condition is satisfied, and the second condition is satisfied.

8. The recording device according to claim 7, characterized in that the pulse control means controls the pulses so that when the recording head increases the thermal energy applied to the recording medium, at least one of the heating temperature or heating time of the recording head is increased compared to when the recording head does not increase the thermal energy applied to the recording medium.

9. The recording device according to claim 7, characterized in that, when the recording head increases the thermal energy applied to the recording medium, the pulse control means applies to the recording head pulses that have at least one of a wider pulse width, a narrower pulse application interval, and a larger number of pulse applications than when the recording head does not increase the thermal energy applied to the recording medium.

10. The recording device according to claim 7, characterized in that the pulse control means, when the recording head increases the thermal energy applied to the recording medium, shortens the time between the pulse applied to the target pixel and the pulse applied to the immediately succeeding pixel compared to when the recording head does not increase the thermal energy applied to the recording medium.

11. A recording device described in any one of claims 7 to 10, characterized in that when the second condition is satisfied and the temperature indicated by the thermal history is a first temperature, the pulse control means controls the pulse so that the thermal energy applied by the recording head to the recording medium is greater than when the second condition is satisfied and the temperature indicated by the thermal history is a second temperature that is greater than the first temperature.

12. A recording device described in any one of claims 7 to 11, characterized in that the second condition determination means determines whether the second condition is satisfied based on the thermal history in forming multiple previous pixels that are recorded before the target pixel and at the same position as the target pixel in the specified direction.

13. A recording method for forming an image on a sheet-like recording medium having a plurality of color-forming layers superimposed thereon, the color-forming layers corresponding to a plurality of colors and capable of developing colors in response to heating, by heating a desired color-forming layer among the plurality of color-forming layers to develop color, the method comprising: a heating step of heating a print head having a plurality of heating elements arranged in a predetermined direction based on image data; a condition determination step of determining whether or not a pixel immediately following the pixel of interest, which is at the same position as the pixel of interest in the predetermined direction and which is to be recorded immediately after the pixel of interest, satisfies a condition that the pixel causes the color-producing layer at the bottom of the recording medium to develop color; a generating step of generating a pulse to be applied to the printhead when forming the pixel of interest based on the determination result of the condition determining step, the generating step generates the pulses so that, when the value of the pixel of interest in the image data is a predetermined value and does not satisfy the condition, the thermal energy applied by the print head to the print medium when forming the pixel of interest is smaller than when the value of the pixel of interest in the image data is the predetermined value and satisfies the condition; The recording method, wherein the heating step heats the recording head in accordance with the pulses generated in the generating step.

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