Method for improving the resolution of an optical printer

Abstract

A method for improving the resolution of a radiation-sensitive microcapsule-based printer includes generating a plurality of sub-pixels in a sub-scanning direction. The method further includes mapping a plurality of grids onto a photosensitive medium, the plurality of grids corresponding to the plurality of sub-pixels. The method further includes determining the exposure energy required for each grid of the plurality of grids. The method further includes assigning the exposure energy required for each grid to a first exposure level and a second exposure level. The method further includes sequentially exposing each grid of the photosensitive medium to the corresponding first exposure level and the corresponding second exposure level as the photosensitive medium passes through a radiation-sensitive microcapsule-based printer in the sub-scanning direction.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority to U.S. Application No. 17 / 827,501, filed on May 27, 2022, the entire content of which is incorporated herein by reference.

[0002] This technology generally relates to a method for improving the resolution of an optical printer. More specifically, this technology relates to a method for improving the resolution of an optical printer in the sub - scanning direction by applying a set of printing algorithms.

Background Art

[0003] A portable small optical printer may be equipped with, for example, a self - contained photosensitive image sheet or medium. In an optical printer, a photographic print head including an array of exposure elements is typically used to expose a photosensitive medium to light of varying brightness and color to form a latent image, which is then developed in place to form a color image on the medium.

Summary of the Invention

[0004] As semiconductor technology improves, it has become commonplace to capture, store, and wirelessly upload / download ultra - high - resolution images (e.g., over 10 megapixels) using various portable devices (e.g., smartphones, stand - alone digital cameras). In comparison, the progress of the resolution and image quality of printed images generated by portable printing devices has been relatively slower.

[0005] The present disclosure describes exemplary non-limiting implementations that address the aforementioned deficiencies. One embodiment relates to a method for improving the resolution of a radiation-sensitive microcapsule-based printer. The method includes generating, by a controller, a plurality of sub-pixels in a sub-scanning direction based on an image data set of an image to be printed on a photosensitive medium. The method further includes mapping, by the controller, a plurality of grids onto the photosensitive medium, the plurality of grids corresponding to the plurality of sub-pixels. The method further includes determining, by the controller, the exposure energy required for each grid of the plurality of grids based on corresponding sub-pixels of the plurality of sub-pixels. The method further includes assigning, by the controller, the exposure energy required for each grid to a first exposure level and a second exposure level. The method further includes sequentially exposing, by the controller, each grid of the photosensitive medium to the corresponding first exposure level and the corresponding second exposure level as the photosensitive medium passes in a sub-scanning direction through a radiation-sensitive microcapsule-based printer.

[0006] Another embodiment relates to a method for improving the resolution of a radiation-sensitive microcapsule-based printer. The method includes generating, by a controller, a plurality of sub-pixels in a sub-scanning direction based on an image data set of an image to be printed on a photosensitive medium. The method further includes mapping, by the controller, a plurality of grids onto the photosensitive medium, wherein the plurality of grids corresponds to the plurality of sub-pixels. The method further includes determining, by the controller, the exposure energy required for each grid of the plurality of grids based on the corresponding image sub-pixels of the plurality of sub-pixels. The method further includes assigning, by the controller, the exposure energy required for each grid to a set of sub-energy exposure levels, wherein the number of sub-energy exposure levels in the set of sub-energy exposure levels is N. The method further includes sequentially exposing, by the controller, each grid of the photosensitive medium to the set of corresponding sub-energy exposure levels as the photosensitive medium passes in a sub-scanning direction through a radiation-sensitive microcapsule-based printer.

[0007] Another embodiment relates to a radiation-sensitive microcapsule-based printer comprising an exposure element array, a media transport system, and a controller. The exposure element array includes a set of exposure elements. The media transport system is configured to transport a photosensitive medium along a sub-scanning direction. The controller includes a processor and a memory storing instructions. The instructions, when executed by the processor, cause the processor to generate a plurality of sub-pixels in the sub-scanning direction based on an image data set of an image to be printed on the photosensitive medium. The instructions, when executed by the processor, further cause the processor to map a plurality of grids onto the photosensitive medium, the plurality of grids corresponding to the plurality of sub-pixels. The instructions, when executed by the processor, further cause the processor to determine the exposure energy required for each grid of the plurality of grids based on corresponding sub-pixels of the plurality of sub-pixels. The instructions, when executed by the processor, further cause the processor to assign the exposure energy required for each grid to a first exposure level and a second exposure level. The instructions, when executed by the processor, further cause the processor to sequentially expose each grid of the photosensitive medium to a corresponding first exposure level and a corresponding second exposure level as the photosensitive medium passes through the radiation-sensitive microcapsule-based printer in the sub-scanning direction.

[0008] Further features, characteristics, and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description of embodiments of the present disclosure with reference to the accompanying drawings. In the accompanying drawings, the same reference numerals refer to the same element characteristics.

Brief Description of the Drawings

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[0010] Various embodiments are described below. It should be noted that specific embodiments are not intended as an exhaustive description or as a limitation to a broader aspect considered herein. One aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced with any other embodiment(s).

[0011] The following terms are used throughout and are defined as follows.

[0012] As used in this specification and the appended claims, singular articles such as "a", "an", and "the" and similar reference terms in the context of describing an element (particularly in the context of the following claims) are to be construed to cover both the singular and the plural unless otherwise indicated herein or clearly contradicted by the context. The recitation of a range of values herein is intended, unless otherwise indicated herein, merely as a shorthand way of referring individually to each separate value within the range, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or clearly contradicted by the context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein is merely intended to make the embodiments more clear and is not intended to limit the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential.

[0013] The embodiments illustratively described in this specification can be suitably implemented without any element or elements, limitation or limitations not particularly disclosed herein. Thus, for example, terms such as "comprising", "including", "containing", etc. shall be understood in a broad sense without limitation. Further, the terms and expressions used in this specification are used as terms of explanation rather than limitation, and the use of such terms and expressions is not intended to exclude any equivalents of the features shown and described or parts thereof, and it is recognized that various modifications are possible within the scope of the claimed technology. The expression "comprising" means "including but not limited to".

[0014] Unless otherwise indicated, all numbers representing amounts, parameters, conditions, etc. of properties used in this specification and the claims should be understood to be modified by the term "about" in all instances. Thus, unless the contrary meaning is otherwise indicated, the numerical parameters set forth in the following specification and the appended claims are approximations. Any numerical parameter should be construed in light of the reported number of significant digits, applying normal rounding procedures. The term "about", when used in front of numerical notations, such as ranges including temperature, time, amount, and concentration, indicates an approximation that can vary by (+) or (-) 10%, 5% or 1%.

[0015] As will be understood by those skilled in the art, for any and all purposes, particularly from the perspective of providing a written description, all ranges disclosed herein also include any and all possible sub-ranges and combinations of those sub-ranges. Any recited range can be readily recognized as enabling and fully describing the same range being broken down into at least one-half, one-third, one-fourth, one-fifth, one-tenth, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower one-third, middle one-third, and upper one-third, etc. Also, as will be understood by those skilled in the art, all language such as "maximum", "at least", "greater than", "less than", etc. includes the recited numbers and refers to ranges that can then be broken down into sub-ranges as discussed above. Finally, as will be understood by those skilled in the art, ranges include each individual member.

[0016] Furthermore, certain terms are used throughout this specification and the following claims to refer to particular components. As will be understood by those skilled in the art, hardware manufacturers may refer to components by different names.

[0017] The present disclosure provides a method for improving the resolution of an optical printer. Generally, achieving a higher printing resolution has various benefits. For example, a higher printing resolution provides a printed image that shows finer details with an excellent modulation transfer function (MTF). Further, a higher printing resolution enables the gradient area image to have a smoother performance with a smaller quantization error.

[0018] Conventionally, the maximum printing resolution of an optical printer has been limited by the physical dimensions of individual exposure elements (e.g., LED chips on a print head) on the print head. For example, if each exposure element is 100 μm × 100 μm, the maximum resolution has traditionally been limited to 254 × 254 DPI, which is an excellent resolution achievable under the condition that the dot gain is equal to 1. The dot gain is generally defined as the ratio of the minimum dot size achievable on a photosensitive medium to the actual size of the exposure element. However, the dot gain is typically greater than 1. Therefore, the printing resolution usually further deteriorates because the minimum dot size is larger than the size of the exposure element.

[0019] Most commercially available optical printers are page-width type optical printers that include a print head having an array of exposure elements extending in the main scanning direction and covering the entire width of the photosensitive medium to be printed. Depending on the different mechanical architectures, the exposure process is performed either by transporting the medium to pass through the array of exposure elements or by moving the array of exposure elements across the entire medium. In the case of a page-width type optical printer, since the array of exposure elements does not move in the main scanning direction (i.e., perpendicular to the sub-scanning direction), there is no prospect of increasing the resolution in the main scanning direction.

[0020] However, the method of the present disclosure enables an improvement in resolution in the sub-scanning direction, which is defined as the direction in which the array of exposure elements is scanned across the medium (either by transporting the medium to pass through the array of exposure elements or by moving the array of exposure elements across the entire medium). Specifically, the method described herein utilizes various multi-pass printing algorithms to create an improved sub-pixel grid having individual sub-pixels that can be smaller than the physical dimensions of the individual exposure elements within the array of exposure elements. Therefore, the method provided herein makes it possible to increase the resolution in the sub-scanning direction of the printed image by effectively breaking the conventional limitations of the physical dimensions of the exposure elements.

[0021] Furthermore, after improvement, the method described in this specification effectively preserves the sharp edge image information while performing resolution improvement so that the sharpness and fine features of the image are retained. Furthermore, the method described in this specification can be implemented without structural changes to various existing optical printers, and thus does not result in increased costs.

[0022] It should be understood that the method described in this specification relates to the improvement of resolution in the sub-scanning direction, and in a non-page-width type optical printer (for example, an optical printer having a cross-scanning head), a similar method can be implemented to increase the resolution in the main scanning direction.

[0023] FIG. 1 is a perspective view of an optical printer 100 according to an exemplary embodiment of the present disclosure. In some examples, the optical printer 100 is a radiation-sensitive microcapsule-based printer (for example, a printer configured to be utilized using a radiation-sensitive microcapsule system). The optical printer 100 includes an exposure element array 102 (also referred to as an "optical print head"), a media cassette 104, a media conveyance system (for example, conveyance devices such as a motor 106, a gear train 108, a media roller 110, a developing roller 112, etc.), a media sensor 114, and a control unit (controller) 116. The developing roller 112 is disposed behind the exposure element array 102.

[0024] It should be noted that the optical printer 100 illustrated in FIG. 1 includes only a subset of the components that can be used within an optical printer. However, the basic structure and possible components of an optical printer are generally within the understanding of those skilled in the art, and it should be understood that the optical printer 100 can be adapted to include various additional or alternative components and / or to implement the optical printer 100 using appropriate devices or equipment, where applicable.

[0025] In some embodiments, control unit 116 includes a processor and a memory storing instructions that, when executed by the processor, cause the processor (and thus control unit 116) to perform any of the various processes described herein. For example, in some embodiments, control unit 116 is configured to control various components of the optical printer 100 to perform a printing process for printing an image on a photosensitive medium dispensed from within the media cassette 104 (e.g., via the media transport system). The media cassette 104 is configured to store the photosensitive medium until it is utilized in the printing process. The media cassette 104 is further configured to prevent the photosensitive medium from being exposed to stray light while the photosensitive medium is held within the media cassette 104.

[0026] According to the present disclosure, the control unit 116 can be programmable to execute printing according to various printing processes. For example, in some examples, the control unit 116 can be programmable to execute a first printing process or a second printing process. During the first printing process, the control unit 116 executes so-called one-pass printing. The control unit 116 controls the media conveyance system to use the media roller 110 to take in a media (such as a film like an instant film) and convey the media along the sub-scanning direction 118 (which can be the direction in which the media is conveyed) toward a media outlet proximate to the media sensor 114. The media sensor 114 (such as a photo-interrupter sensor) is configured to detect the media. When the leading edge of the media reaches the media sensor 114, the media sensor 114 detects the media, and the control unit 116 starts an exposure timer counter. When the exposure timer counter value reaches a predetermined value (for example, based on the forward speed of the media and the dimensions of the exposure elements in the exposure element array 102), the leading edge of the media is directly below the exposure element array 102, and the control unit 116 immediately starts line exposure. The exposure element array 102 extends across the entire width of the media (for example, along the main scanning direction 120), and as a result, the exposure element array 102 is configured to simultaneously expose a full-width line of dots on the photosensitive media. Thus, as the media exits the media outlet and continues to move forward at a constant speed, the control unit 116 continues to trigger line exposure at regular time intervals until the entire image is formed on the photosensitive media.

[0027] In the above-described first printing process, the resolution of the print output (i.e., the image on the photosensitive medium) is determined by the physical dimensions of the exposure elements of the exposure element array 102. That is, the dot size marked on the photosensitive medium by each exposure element is greater than or equal to the size of the exposure element itself. Therefore, the print output resolution is limited by this constrained dot size. As follows, instead of the first printing process, the control unit 116 may be configured to execute a second printing process different from the first printing process. As used herein, the terms "first" and "second" are intended to mean different printing processes, not in order.

[0028] For example, FIG. 2 is a schematic diagram of an exposure element array 102 comprising a set of exposure elements 122 according to an exemplary embodiment of the present disclosure. In some examples, the exposure element 122 can be, for example, a light-emitting diode configured to emit light. In some other examples, various other types of exposure elements can be utilized as desired for a given application. As shown, the dimensions of the exposure element are D x ×D y and can be defined as, where D x is the length along the main scanning direction 120, and D y is the length along the sub-scanning direction (e.g., sub-scanning direction 118). In this scenario, if the exposure time interval (t) is equal to the time required for the photosensitive medium to advance a distance equal to D y , the exposure element array 102 does not repeatedly expose each of the set of pixels of the photosensitive medium. In other words, each pixel of the photosensitive medium can be exposed only once. Thus, the aforementioned first process corresponds to one-pass printing.

[0029] However, instead of setting an exposure time interval equal to the time required for the photosensitive medium to advance a distance equal to D y , the control unit 116 may be configured to execute a second printing process different from the first printing process described above. For example, the control unit 116 can set the exposure time interval to D ySet it to be equal to the time required for the photosensitive medium to advance a distance equal to / N. Similarly, the exposure element array 102 can be triggered to expose the photosensitive medium at each exposure interval as follows. Therefore, each of the plurality of grids on the photosensitive medium is exposed N times. This second printing process can be referred to as multi-pass printing.

[0030] For example, FIG. 3 shows a method 300 of a multi-pass printing operation that is a two-pass printing procedure (N = 2). The method 300 effectively improves the resolution of an optical printer (e.g., optical printer 100) in the sub-scanning direction 118 according to an exemplary embodiment. Similarly, FIG. 4 provides an exemplary schematic diagram 400 of a two-pass printing procedure for an overly simplified set of six consecutive image sub-pixels 402 in a single column (i.e., a stack extending along the sub-scanning direction 118 created by the same exposure element 122) according to an exemplary embodiment. Only the exposure sequence 404 of a single exposure element 122 of the exposure element array 102 is shown in FIG. 4, but it should be understood that a similar exposure sequence is simultaneously applied by the remaining exposure elements 122 of the exposure element array 102, such that the photosensitive medium is exposed to light line by line to effectively create a printed image. Further, D x and D y are not drawn to scale in FIG. 4. Instead, D x extends over the width of one sub-pixel and D y extends over two consecutive sub-pixels for illustrative purposes.

[0031] Also, in practice, the number of image sub-pixels can be the same size as DPI×L×F in each column extending along the sub-scanning direction 118 (i.e., corresponding to each individual exposure element 122), where DPI, L, and F are, respectively, the number of dots per inch achievable by the print head (e.g., by the exposure element array 102), the length (in inches) of the image medium printed in the sub-scanning direction 118, and the upscaling factor. For example, using a print head corresponding to 300 DPI, an image medium with a length of 3 inches in the sub-scanning direction 118, and an upscaling factor of 2, the number of image sub-pixels generated for each column is 1800 (i.e., 300×3×2 = 1800).

[0032] As illustrated in FIG. 2, the physical dimensions of the exposure element are D x ×D y However, in the two-pass printing procedure of FIGS. 3 and 4, since the sub-scanning resolution is improved by a factor of 2, the improved sub-pixel size is D x ×D y / 2. The value of each sub-pixel 402 shown in FIG. 4 indicates the required exposure energy (represented as an 8-bit value within the range of 0 to 255).

[0033] Referring again to FIG. 3, method 300 begins at step 302, where control unit 116 is configured to generate a set of image sub-pixels in the sub-scanning direction 118 based on high-resolution image data at step 304. For example, to print a high-resolution image captured by a high-resolution device (e.g., a digital camera or smartphone with over 10 megapixels), control unit 116 first downsamples the original image data to a set of appropriately scaled image data according to the downscaling ratio of optical printer 100, and then upsamples the set of downscaled image data to generate a set of image sub-pixels in the sub-scanning direction 118. The downscaling ratio is based on the print resolution of optical printer 100. In some examples, the print resolution of optical printer 100 can be determined based on the spot size of exposure elements 122 in exposure element array 102 (e.g., based on the dimensions of exposure elements 122).

[0034] Once the set of image sub-pixels is generated, control unit 116 then divides the photosensitive medium into a grid corresponding to the sub-pixels generated in the sub-scanning direction 118 to be printed at step 306. That is, control unit 116 maps each image sub-pixel to be printed during the printing process to a corresponding grid on the photosensitive medium to determine the division. For example, in the illustrated example provided in FIG. 4, the number of grids and the dimensions of each of the grids are also 6 and D x ×D y / 2, respectively.

[0035] Next, at step 308, the control unit 116 calculates the exposure energy level (E) required for each grid on the medium according to the corresponding image sub-pixel. For example, the control unit 116 calculates the exposure energy level (E) to be exposed in each of the grids of the medium based on the spectral sensitivity of the medium to be printed and according to a set of upsampled image sub-pixels of the downscaled image data. For example, the corresponding exposure element may expose the first grid at the exposure energy level illustrated as E(1) in FIG. 4, and in the particular example illustrated, E(1) is 10. Similarly, the exposure element may expose the second to sixth grids at the exposure energy levels respectively shown as E(2) to E(6). In the particular example provided in FIG. 4, E(2) to E(6) are 20, 30, 40, 50, and 60 respectively.

[0036] Next, when the exposure energy (E) required for each grid is calculated, the control unit 116 divides, in step 310, the exposure energy of each grid into a first exposure level and a second exposure level. For example, as shown in FIG. 4, the exposure energy level E(1) of the first grid (corresponding to the first sub-pixel 402) is divided into exposure energy levels E1(1) and E2(1). Similarly, the exposure energy level E(2) of the second grid (corresponding to the second sub-pixel 402) is divided into exposure energy levels E1(2) and E2(2), and so on. Specifically, in the first exposure interval T1, the exposure element 122 simultaneously exposes the first grid and the second grid to light at exposure energy levels E2(1) and E1(2). Therefore, the exposure energy level E2(1) is equal to the exposure energy level E1(2). Similarly, in the second exposure interval T2, the exposure element 122 simultaneously exposes the second grid and the third grid to light at exposure energy levels E2(2) and E1(3). Therefore, the exposure energy level E2(2) is equal to the exposure energy level E1(3). As can be understood, such a simultaneous exposure pattern continues for each pair of overlapping grids, as shown in FIG. 4. Further, a dummy exposure energy level can be set to zero with respect to the first exposure energy level of the first grid (i.e., E1(1) is equal to zero).

[0037] Next, when the exposure energy of each grid is divided, the control unit 116 controls, in step 312, the optical printer 100 to advance the medium and sequentially expose each grid of the medium to light in the sub-scanning direction 118 at the corresponding first and second exposure levels as the medium passes through the exposure element array 102. For example, as discussed above, the dimension of each exposure element 122 is D x ×D y Thus, in a two-pass printing procedure, the control unit 116 is D ySet an exposure time interval equal to the time required for the photosensitive medium to advance a distance equal to / 2, trigger the exposure element array 102, and expose the photosensitive medium to light with appropriate exposure energy light at each exposure interval.

[0038] For example, as shown in FIG. 4, the first grid (corresponding to the first sub-pixel 402) is sequentially exposed with E1(1) and E2(1), and the second grid (corresponding to the second sub-pixel 402) is sequentially exposed with E1(2) and E2(2), and so on. In summary, the relationship between the exposure energy level, the first exposure energy level, and the second exposure energy level can be constrained by the following equations (1) and (2): E(i)=E1(i)+E2(i) (1) E2(i)=E1(i+1) (2) Where E(i) is the exposure energy level of the i-th grid, E1(i) is the first exposure energy level of the i-th grid, and E2(i) is the second exposure energy level of the i-th grid. In the exemplary schematic diagram 400 provided in FIG. 4, the exposure value of the image increases monotonically, and as a result, the constraint equations (1) and (2) discussed above can be satisfied. However, as will be discussed below, in some examples, various exception handling may be implemented to avoid unrealistic or infeasible exposure requirements.

[0039] Referring back to FIG. 3, when the entire medium has passed through the exposure element array 102 and the image is completely formed, the method 300 ends at step 314. In a two-pass printing process, each grid of the photosensitive medium is exposed to light twice, which enables each grid to have a dimension smaller than the corresponding exposure element 122 in the sub-scanning direction 118, thereby effectively improving the image resolution, particularly the image gray level in the sub-scanning direction 118.

[0040] Referring now to FIGS. 5A - 5C, instead of the monotonically increasing exposure values shown in FIG. 4, image data includes a single color (FIG. 5A), the exposure value decreases monotonically (FIG. 5B), and image data includes sharp edges (FIG. 5C), various additional exemplary schematic diagrams 500 (shown in FIG. 5A), 500' (shown in FIG. 5B), and 500'' (shown in FIG. 5C) of the two - pass printing procedure considered above. Each of FIGS. 5A - 5C similarly includes a plurality of sub - pixels 502 and corresponding exposure sequences 504. In some examples, when the two - pass printing procedure is applied to a single - color region as shown in FIG. 5A, at least one dummy pixel can be used to satisfy the constraint equations (1) and (2) considered above. However, since at least one dummy pixel is outside the media boundary, no printing - related problems are caused. Similarly, in both FIGS. 5B and 5C, where the two - pass printing procedure requires the exposure value to decrease monotonically or is applied to an image including sharp edges, the constraint equations (1) and (2) considered above can be satisfied as well.

[0041] Accordingly, the above examples (i.e., FIGS. 4 - 5C) show cases where the constraint equations (1) and (2) can be satisfied. However, in some examples, the image data may be more complex and non - uniform than the previous examples. For example, the image data may instead be random. Random images generally include various high - frequency components, making it difficult or even impossible to satisfy the constraint equations (1) and (2). To solve this problem, the exemplary method described herein performs pre - processing (e.g., down - scaling and up - sampling performed in step 304) on the image to smooth these high - frequency components.

[0042] For example, in some instances, a user may use the optical printer 100 to print high - resolution photos taken by an image capture device (e.g., a stand - alone digital camera, a smartphone, or a camera incorporated into an image sensor array, etc.). Since the resolution of the optical printer 100 is generally much lower than that of the camera, the image data of the high - resolution photo must be scaled down to scaled - down image data in order to match the photosensitive medium and the printer's resolution. That is, the image data is scaled down from a first resolution (high resolution) to a second resolution lower than the first resolution. The image data of a 16 - megapixel photo is 4920×3264 pixels. If the printer's resolution (without image processing) is 300×300 DPI and the size of the photosensitive medium is 2 inches×3 inches, the image data is scaled down to 600×900 pixels. When a two - pass printing procedure is applied, the printer's resolution is improved to 300×600 DPI, and the image data can be upsampled to 600×1800 pixels.

[0043] In this case, if a 16 - megapixel image is directly scaled down to the final resolution of 600×1800 pixels for printing, the direct scaling - down operation often leads to a "random" image with various high - frequency components that cannot satisfy the constraints of two - pass printing, as discussed above. However, instead of directly scaling down the image to the final resolution, the method described herein first scales down the image using the unimproved printer performance (i.e., 300×300 DPI) to create a scaled - down image at 600×900 pixels, and then performs upsampling in the sub - scanning direction to reach the final resolution of 600×1800 pixels. As described below, the upsampling can be performed using pixel interpolation such that each upsampled or added pixel is the average of two corresponding adjacent pixels. By utilizing such pixel interpolation, the high - frequency components can be effectively smoothed.

[0044] FIG. 6 shows a table illustrating a two-pass printing procedure for interpolated random image data according to an exemplary embodiment of the present disclosure. As shown, the image sub-pixels are shown as P1 to P21. The second column from the left is the exposure energy level applied to the corresponding grid on the photosensitive medium by each image sub-pixel. Each of the odd image sub-pixels (P1, P3, P5, etc.) has a corresponding exposure energy level that is the same as the set of original image pixels. Each of the even image sub-pixels (P2, P4, P6, etc.) has a corresponding exposure energy level that is upsampled through a linear interpolation procedure using two adjacent image pixels. In other words, the exposure energy level of the even sub-pixels is the average of the adjacent odd sub-pixels. For example, E(P4) = (E(P3) + E(P5)) / 2.

[0045] As discussed above, each exposure energy level is divided into a first exposure energy level and a second exposure energy level. For example, the exposure energy level E(P1) of the first sub-pixel P1 is divided into exposure energy levels E1(P1) and E2(P1), the exposure energy level E(P2) of the second sub-pixel P2 is divided into the first exposure energy level E1(P2) and the second exposure energy E2(P2), and so on. As illustrated, E1(P1) is equal to 0 (not shown in FIG. 6), while E2(P1) is equal to 20, E1(P2) is equal to 20, E2(P2) is equal to 0, and so on. It should be understood that the first and second exposure energy levels of each sub-pixel are calculated such that the constraint equations (1) and (2) discussed above are satisfied. However, as shown in FIG. 6, the second exposure energy level of P18 and the first exposure energy level of P19 are each negative. Therefore, as discussed below, it may be desirable to use this procedure in combination with various other algorithms and strategies to avoid these negative exposure energy levels.

[0046] FIG. 7 shows a table illustrating a two-pass printing procedure for interpolated random image data, similar to that shown in FIG. 6, according to another exemplary embodiment of the present disclosure. For example, even image sub-pixels are similarly upsampled through a linear interpolation procedure using two adjacent image pixels. However, in the embodiment shown in FIG. 7, the exposure energy level E(P1) of the first sub-pixel P1 is set to zero, and all of the first exposure energy level and the second exposure energy level are non-negative. Specifically, when a set of image pixels is upsampled through a linear interpolation procedure to obtain a set of image sub-pixels and the first exposure energy level of the first image sub-pixel is set to zero, the first and second exposure energy levels of the set of image sub-pixels become non-negative. That is, by performing both interpolating the image data and setting the first sub-pixel exposure energy level to zero, both constraint equations (1) and (2) for any image data are satisfied.

[0047] However, a side effect of interpolation is that it may lose important high-frequency components (e.g., sharp edges) of the original image. For example, in some examples, if the difference value between the exposure energy levels of two adjacent image pixels is greater than a threshold value, this can be considered to be a sharp edge or otherwise indicative of a sharp edge. In some examples, this threshold value can be defined as one-third of the difference value between the maximum value of the exposure energy level of the image pixels and the minimum value of the exposure energy level of the image pixels. However, in other examples, the threshold value can be defined in various other manners.

[0048] Referring back to FIG. 7 and using the aforementioned threshold definition, there is a sharp edge between the image data associated with pixels P9 and P11 from the original image. Specifically, the difference value between the exposure energy level E(P11) of P11 and the exposure energy level E(P9) of P9 is 100 (i.e., 220 - 120). This value is greater than the threshold value (which is 73.33). That is, the threshold value (i.e., 73.33) for the image date shown in FIG. 7 is one-third of the difference between the maximum value (i.e., 220 at P11) and the minimum value (i.e., 0 at P1) of the exposure energy level. Therefore, in the original image, there was a sharp edge between the image data associated with P9 and P11.

[0049] However, after performing linear interpolation, the difference values between E(P9) and E(P10), or between E(P10) and E(P11), each become 50 (i.e., 170 - 120 or 220 - 170), which is lower than the threshold value. Therefore, the sharp edge no longer exists in the interpolated image data. In fact, in order to preserve the sharp edge, the basic premise of interpolation has to be broken, so it is generally not possible to use the two-pass printing method to preserve the sharp edge using only interpolation. One possible way to address the sharp edge problem is to apply a sharpening filter to the image data before interpolation to help improve the sharp edges within the image data. However, even in this case, the interpolation step will still smooth the sharp edge and the MTF will be inferior compared to the original non-interpolated image.

[0050] Therefore, in some examples, in order to preserve the sharp edges in the image data, linear interpolation for any two adjacent image pixels having sharp edges can be replaced by the nearest neighbor algorithm.

[0051] For example, FIG. 8 shows a table illustrating a two-pass printing procedure for interpolated random image data that retains sharp edges using a nearest neighbor algorithm, according to another exemplary embodiment of the present disclosure. As illustrated, the odd sub-pixels in FIG. 8 are the same as the odd sub-pixels in FIG. 7. However, in FIG. 8, the nearest neighbor algorithm is executed using E(P9) and E(P11) to determine E(P10). That is, E(P10) is set equal to E(P9) instead of being (E(P9)+E(P11)) / 2. Accordingly, the difference value between E(P10) and E(P11) is 100 (e.g., 220 - 120) which is higher than the threshold value. In other words, the sharp edge between the original P9 and P11 is retained between P10 and P11. However, as shown in FIG. 8, the second exposure energy level of P18 and the first exposure energy level of P19 are negative. Thus, in order to avoid these negative exposure energy levels, as discussed below, it may also be desirable to utilize such a composite procedure (i.e., combining linear interpolation with nearest neighbor exception handling) in conjunction with various other algorithms and strategies.

[0052] Referring now to FIG. 9, shown is an ideal media characteristic of the optical density value (OD) with respect to exposure energy, according to an exemplary embodiment of the present disclosure. In some examples, a self - contained media utilized by the optical printer 100 (e.g., contained within the media cassette 104) is based on a photosensitive microcapsule system produced by coating a substrate film with non - carbon type microcapsules having a diameter of several microns. These microcapsules include distinct walls surrounding an internal phase composition of monomers having a photosensitive initiator and a dye precursor. Exposure of the media sheet cures the internal phase of the microcapsules, providing resistance to rupture. Thus, a latent image is formed as a pattern of the image width of hard (exposed) and soft (unexposed) microcapsules. The visible image is physically developed by bringing the sheet exposed under uniform pressure into contact with a receiving sheet, whereby only the soft microcapsules rupture and deliver the leuco dye to the receiving sheet. The leuco dye then reacts with a coating on the receiving sheet to produce a visible image.

[0053] The chemical process leading to the latent image in a microencapsulated acrylate system (e.g., the photosensitive microcapsule system discussed above) includes three distinct and consecutive mechanisms: (a) photoinitiation, where free radicals are generated by the action of light, (b) auto - oxidation, which overcomes the inhibitory effect of oxygen, as is well known in acrylate chemistry, and (c) polymerization of acrylate monomers to cure the internal phase of the microcapsules.

[0054] As shown in FIG. 9, in Zone I, as the exposure energy increases, the optical density (OD) value remains constant at D max and the exposure energy remains less than E shoulder . During the induction exposure, no detectable polymerization occurs until the oxygen concentration in the acrylate monomer drops to a few percent of the equilibrium value, so the OD value remains constant. Thus, there is no change in the OD value until the induction period has elapsed. Thus, for a given grid on the photosensitive media, Eshoulder If any exposure energy smaller than is applied, the OD value of the grid remains at D max On the other hand, in Zone III, since almost all microcapsules in the grid are polymerized, while the exposure energy remains above E toe the OD value can remain constant at D as the exposure energy decreases. However, in Zone II, the OD value decreases as the exposure energy increases. Therefore, for a given grid with a target OD value of D min the required exposure energy can be expressed by the following equation. j For a given grid with a target OD value of D E(j)=E shoulder +△E(j) (3) where E shoulder is the energy level required to overcome the inhibitory effect of oxygen and to pass through the induction period, and △E(j) is the energy level required for a given grid to reach the target OD value (D j ).

[0055] In Equation (3), E shoulder can be regarded as a barrier and thus can be used as an offset. Specifically, when the photosensitive medium is exposed with an exposure energy within an offset range less than E shoulder the optical density on the grid of the photosensitive medium can be invariant regardless of where the exposure energy is within the offset range. Therefore, the characteristics of this offset range can be utilized to solve the edge retention problem shown in FIG. 8.

[0056] For example, FIG. 10 shows a table illustrating a two-pass printing procedure for interpolated random image data that uses the nearest neighbor algorithm to maintain sharp edges and includes an offset of the exposure energy level, according to another exemplary embodiment of the present disclosure. In FIG. 10, the second column from the left includes the original exposure energy level for each of the image sub-pixels. The third column from the left includes the offset exposure energy levels, which are the offsets of the exposure energy levels (e.g., E shoulder) is calculated by adding to each of the original exposure energy levels. In some examples, as shown in FIG. 10, the offset of the exposure energy level can be set to the value 255. However, in other examples, the exposure energy level can be set to different values based on the media characteristics of the photosensitive medium used in the printing process.

[0057] As shown in FIG. 10, there are four sharp edges in the original image data between P5 and P7, between P15 and P17, between P19 and P21, and between P25 and P27. However, when the nearest neighbor algorithm is executed to calculate the intermediate image sub-pixels, some of the first exposure energy levels and the second exposure energy levels are negative. Therefore, as discussed below, in order to avoid these negative exposure energy levels, it may also be desirable to utilize such a composite procedure (i.e., combining linear interpolation, nearest neighbor exception handling, and an offset of the exposure energy level) in conjunction with various other algorithms and strategies.

[0058] For example, in some examples, the control unit 116 can further adjust the exposure energy of the first image sub-pixel by a predetermined amount configured to prevent either the first and / or second exposure energy levels from becoming negative. In some examples, the predetermined amount can be selected or determined to offset the most negative exposure energy level from the set of image sub-pixels.

[0059] For example, FIG. 11 shows a table illustrating a two-pass printing procedure for interpolated random image data similar to FIG. 10, in which the exposure energy of the first image sub-pixel is further adjusted to prevent negative exposure energy levels, according to another exemplary embodiment of the present disclosure. As shown in FIG. 10, the most negative exposure energy level calculated was -95. Therefore, in FIG. 11, the predetermined amount by which the first sub-pixel exposure energy level is adjusted is set to 95 to offset the most negative exposure energy level that would otherwise have resulted. 95 is E shoulderSince it is less than, adjusting the exposure energy in the first sub-pixel from 0 to 95 does not change the OD value.

[0060] In other words, by adjusting the exposure energy of the first image sub-pixel (e.g., setting it to 95) so as to offset the negative exposure energy level, the two-pass printing procedure can be applied to any image while retaining the sharp edges from the original image data. Specifically, when the exposure energy of the first image pixel is adjusted (e.g., set to 95) so as to offset the negative exposure energy level, all first and second exposure energy levels are positive or zero. In this way, the exposure element 122 is configured to apply an appropriate set of first and second exposure energy levels to a corresponding set of grids on the photosensitive medium.

[0061] Therefore, the two-pass printing method described herein can effectively improve the resolution in the sub-scanning direction 118, while effectively retaining the edge information from the original image data.

[0062] The above discussion refers to a two-pass printing procedure, but it should be understood that method 300 can be adapted to further improve the resolution in the sub-scanning direction by utilizing any number of additional "passes" in the printing procedure. For example, FIG. 12 provides an exemplary schematic diagram 1200 of an N-pass printing procedure for (i) image sub-pixels 1202, each having a corresponding exposure energy level (shown as E(1) to E(i)) and receiving an exposure sequence 1204, according to an exemplary embodiment of the present disclosure. As shown in the N-pass printing procedure, the control unit 116 sets an exposure interval equal to the time required for the photosensitive medium to advance a distance equal to D y / N, and similarly triggers the exposure element array 102 to (e.g., T1 to T NFor each exposure interval (successively shown thereby), the photosensitive medium is exposed. Thus, the sub-pixels 1202 and the corresponding grid sections generated in method 300 (e.g., steps 304 and 306) are each the length of the exposure element (in the sub-scanning direction 118) divided by N. Thus, the resolution in the sub-scanning direction is increased by a factor of N (i.e., the upsampled image has N times as many sub-pixels in the sub-scanning direction 118 as the number of image pixels in the scaled image), and each grid on the photosensitive medium is exposed N times.

[0063] Referring to the 2-pass printing procedure, it should be understood that the upsampling (e.g., interpolation procedure and nearest neighbor algorithm) discussed above can similarly be applied to the N-pass printing procedure. For example, to generate a set of image sub-pixels in the sub-scanning direction, the step of upsampling a set of image pixels of the scaled image data set can similarly be performed using linear interpolation to add (N - 1) sub-pixels between each pair of adjacent image pixels.

[0064] As illustrated, during the exposure sequence 1204, the i-th grid is successively exposed at E1(i), E2(i), ···, and E N (i). Further, although only E N (1) is shown in FIG. 12, it should be understood that the first grid can similarly be successively exposed at E1(1), E2(1), and E N (1). In summary, the relationship between the exposure energy levels, the first exposure energy level to the N-th exposure energy level, can be expressed as equations (4) and (5), E(i) total = E1(i) + E2(i) + ··· + E N (i) (4) E N (i) = E N-1 (i + 1) = ··· = E2(i + (N - 2)) = E1(i + (N - 1)) (5) where E(i) is the exposure energy level of the i-th grid, and E N(i) is the Nth exposure energy level of the ith grid.

[0065] The foregoing summarizes exemplary embodiments of the general algorithms and procedures of the present disclosure. In the following sections, exemplary experimental results of the present disclosure will be described in somewhat more detail. These exemplary experimental results are intended to demonstrate the feasibility of the present disclosure in accordance with the exemplary embodiments of the general algorithms and procedures discussed above. Therefore, a detailed description of these experiments is provided solely for illustrative purposes and is not intended to limit the scope of the present disclosure.

[0066] Figures 13A and 13B show experimental equipment associated with performing exemplary experiments in accordance with the above algorithms and techniques, according to an exemplary embodiment of the present disclosure. For example, Figure 13A illustrates experimental equipment having an OLED panel 1301 for exposing a media sheet 1302, and Figure 13B illustrates experimental equipment having a developing holder 1303 for developing an image on the media sheet 1302.

[0067] As shown in Figure 13A, during an exemplary experiment, the OLED panel 1301 is used as an exposure device and the media sheet 1302 is placed on top of the OLED panel 1301. The OLED panel 1301 is then configured to apply exposure to the media sheet 1302. After the exposure process is completed, the media sheet 1302 is transported to a developing holder 1303 (shown in Figure 13B) to develop the image. For example, the media sheet 1302 is transported in the media outlet direction 1305 by a media feed motor 1304. The media sheet 1302 then passes through a pressure roller 1306 that provides a uniform pressure to the media sheet 1302. The uniform pressure applied to the media sheet 1302 by the pressure roller 1306 ruptures only the soft microcapsules, thereby delivering the leuco dye and developing a visible image on the media sheet 1302.

[0068] Referring now to FIGS. 14A-14H, there are shown various schematic diagrams depicting an experimental process and corresponding result grids for a two-pass printing method (shown in FIGS. 14A-14E) and a one-pass printing method (shown in FIGS. 14F-14H) according to an exemplary embodiment of the present disclosure. Using the above-described equipment and general exemplary experimental process, the experimental results (e.g., shown in FIG. 14E) achieved by applying the above two-pass printing method indicate that the resolution and color smoothness in the sub-scanning direction are effectively improved by applying the two-pass printing method described herein as compared to the experimental results (e.g., shown in FIG. 14H) achieved by applying the conventional one-pass printing method.

[0069] To avoid light leakage from the surrounding environment, each experiment of the two-pass and one-pass printing methods was performed in a darkroom. The media sheet used in the experiment was monochrome and contained only magenta microcapsules. In each experiment, the exposure procedure was controlled to trigger the OLED panel 1301 at a specific timing to display a specific display image. FIGS. 14A-14D and FIGS. 14F-14G show the display images displayed on the OLED panel 1301 for the two-pass printing method (shown in FIGS. 14A-14D) and the one-pass printing method (shown in FIGS. 14F-14G), respectively.

[0070] For the two-pass printing experiment, the display images shown in FIGS. 14A-14D were sequentially displayed on the OLED panel 1301 to simulate the media exposure process of the two-pass printing method described herein. For example, a single exposure element of the exposure element array was simulated using the white square in each display image. According to the foregoing description of the two-pass printing method, since the dimensions of the square (e.g., the simulated exposure element) were 2 cm × 2 cm, the corresponding grid dimensions of each grid of the result on the media sheet were 2 cm × 1 cm.

[0071] The exposure process of the two - pass printing experiment starts by triggering the OLED panel 1301 to display the display image in FIG. 14A, and the first two grids (e.g., grids 1401 and 1402 in FIG. 14E) are exposed on the media sheet 1302. After the first exposure is completed, instead of advancing the media sheet to the position where the second grid 1402 and the third grid 1403 are exposed by the simulated exposure elements (white squares), the OLED panel 1301 moves the exposure elements (white squares) by a distance equal to half of the side length of the square (e.g., 1 cm) to expose the second grid 1402 and the third grid 1403, and displays the display image shown in FIG. 14B. Thus, by sequentially displaying the display images from FIGS. 14A - 14D, the experiment effectively resulted in five exposed grids (e.g., grids 1401, 1402, 1403, 1404, 1405 shown in FIG. 14E) on the media sheet 1302. After the exposure process of the two - pass printing experiment shown in FIGS. 14A - 14D is completed, it should be understood that the second grid 1402, the third grid 1403, and the fourth grid 1404 are each exposed twice, and the first grid 1401 and the fifth grid 1405 are each exposed only once.

[0072] FIGS. 14F and 14G show the exposure process of the one - pass printing experiment. For example, in the one - pass printing experiment, the display images shown in FIGS. 14F and 14G are sequentially displayed on the OLED panel 1301. As illustrated, the white squares in these display images are similarly used to simulate a single exposure element of the exposure element array. However, each grid is exposed only once in the one - pass printing method, in contrast to being exposed twice in the two - pass printing method, so the grid dimensions in the one - pass printing experiment were equal to the simulated exposure element dimensions (e.g., 2 cm×2 cm).

[0073] For example, the exposure process of the one-pass printing experiment starts by triggering the OLED panel 1301 to display the display image shown in FIG. 14F and exposing the media sheet 1302, and exposes the first grid 1406 shown in FIG. 14H. After the first exposure is completed, the OLED panel 1301 moves the exposure element (white square) by a distance of one square side length (e.g., 2 cm) and displays the display image in FIG. 14G to expose the second grid 1407. Therefore, by displaying the display images shown in FIGS. 14F and 14G, the experiment effectively resulted in two exposed grids (e.g., grids 1406 and 1407 shown in FIG. 14H) on the media sheet 1302. It should be understood that after the exposure process of the one-pass printing experiment shown in FIGS. 14F and 14G, the first grid 1406 and the second grid 1407 are each exposed only once.

[0074] FIGS. 15A-15C show exemplary experimental images and corresponding experimental result data from the two-pass printing experiment and the one-pass printing experiment, similar to those discussed above with respect to FIGS. 14A-14H. For example, FIG. 15A is an image of the media sheet after applying the two-pass printing experiment. Specifically, the display images shown in FIGS. 14A-14D were sequentially used to expose the media sheet shown in FIG. 15A. Since the brightness of the white squares in FIGS. 14A-14D is all equal, the exposure energy level is proportional to the display duration of these display images. The display durations of these display images were set as follows. Image shown in FIG. 14A: 1 second, Image shown in FIG. 14B: 1 second, Image shown in FIG. 14C: 2 seconds, Image shown in FIG. 14D: 2 seconds.

[0075] In FIG. 15A, the grid boundaries between adjacent grids are marked with dotted lines. According to the foregoing description, five grids on the media sheet are exposed through the foregoing exposure process, but only four grids (marked as a1, a2, a3, and a4) are shown in FIG. 15A. It will be understood that these four grids generally correspond to grids 1401-1404 shown in FIG. 14E. As described herein, in the case of two-pass printing, the total exposure time proportional to the total exposure energy level of each grid is the sum of the first exposure time and the second exposure time. Therefore, the exposure times of grids a1-a4 were as follows. Grid a1: 1 second (1 second + 0 second), Grid a2: 2 seconds (1 second + 1 second), Grid a3: 3 seconds (1 second + 2 seconds), Grid a4: 4 seconds (2 seconds + 2 seconds).

[0076] FIG. 15B shows an image of the media sheet after applying the one-pass printing method. Specifically, the media sheet shown in FIG. 15B was exposed using the display images shown in FIGS. 14F and 14G sequentially. The display durations of these two images were set as follows. Image shown in FIG. 14F: 1 second, Image shown in FIG. 14G: 4 seconds.

[0077] In FIG. 15B, the grid boundaries between adjacent grids are similarly marked with dotted lines. As illustrated, only two grids (marked as b1 and b2) are shown on the media sheet of FIG. 15B. It will be understood that these two grids generally correspond to grids 1406, 1407 shown in FIG. 14H. As described herein, in the case of one-pass printing, the total exposure time of each grid is equal to the duration of the OLED panel 1301 that displays the corresponding display image. Therefore, the exposure times of grid b1 and grid b2 were 1 second and 4 seconds, respectively.

[0078] Figure 15C is a graph showing the measured OD values of each grid on both of the media sheets shown in Figures 15A and 15B. As illustrated, the OD value transition of the two-pass printing was smoother than that of the one-pass printing. Specifically, since the grid size of the two-pass printing experiment was only half of that of the one-pass printing experiment, the resolution of the media sheet from the two-pass printing experiment was twice that of the media sheet from the one-pass printing experiment.

[0079] Figures 16A - 18C provide additional exemplary experimental images and corresponding data. These images and data were derived by applying the same procedures disclosed in the description of Figures 15A - 15C. For example, Figures 16A, 17A, and 18A each show an image of the media sheet after applying the corresponding two-pass printing experiment, Figures 16B, 17B, and 18B each show an image of the media sheet after applying the corresponding one-pass printing experiment, and Figures 16C, 17C, and 18C are graphs showing the measured OD values of the corresponding grids on both of the media sheets from the corresponding two-pass and one-pass experiments respectively (e.g., Figure 16C shows the measured OD values of Figures 16A and 16B, Figure 17C shows the measured OD values of the media sheets of Figures 17A and 17B, and Figure 18C shows the measured OD values of the media sheets of Figures 18A and 18B). The exposure times of each grid in these figures are listed in the following table (in seconds).

Table 1

[0080] Accordingly, the present disclosure provides a method for improving the resolution of an optical printer in the sub-scanning direction by applying a set of printing algorithms. In a broad sense, the set of printing algorithms described herein can be applied to any printing system that utilizes radiation energy-sensitive (e.g., light) microcapsules. Compared to conventional optical printing procedures, the present disclosure provides a higher resolution in the sub-scanning direction while still retaining any sharp edges within the image data (e.g., not limited by the dimensions of each individual exposure element).

[0081] The present disclosure contemplates a method, system, and program product on any machine-readable medium for achieving various operations of, for example, the control unit 116. Embodiments of the present disclosure can be implemented using an existing computer processor or by a dedicated computer processor for a suitable system incorporated for this or another purpose or by a wired-connected system. For example, the above description, steps, procedures, and / or processes including the suggested steps can be implemented using hardware, software, firmware (known as a combination of computer instructions and data that exist as a read-only software on a hardware device and the hardware device), an optical printer, or a combination thereof. Examples of hardware can include analog, digital, and mixed-signal circuits known as microcircuits, microchips, or silicon chips. Examples of optical printers can include system-on-chip (SoC), system-in-package (SiP), computer-on-module (CoM), and electrical systems.

[0082] Embodiments within the scope of the present disclosure include a program product that includes a machine-readable medium for carrying or having stored machine-executable instructions or data structures. Such a machine-readable medium can be any available medium that can be accessed by a general-purpose or special-purpose computer or other machine equipped with a processor (e.g., control unit 116). By way of example, such a machine-readable medium can be read-only memory (ROM), flash memory, random access memory (RAM), EPROM, EEPROM, a hard disk, other optical disk storage devices, magnetic disk storage devices or magnetic storage devices, or any other medium that can be used to carry or store the desired program code in the form of machine-executable instructions or data structures and that can be accessed by a general-purpose or special-purpose computer or other machine equipped with a processor and executed to perform the various operations described herein.

[0083] The figures may show a particular order of method steps, but the order of the steps may differ from that depicted. For example, in some embodiments, two or more steps may be performed simultaneously or partially simultaneously. Further, in some embodiments, the steps described above may be performed in the order as described or even in reverse. All such variations are within the scope of the present disclosure. Although various aspects and embodiments are disclosed herein, other aspects and embodiments will be apparent to those of ordinary skill in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and not intended to be limiting, and the scope and spirit of the invention are indicated by the following claims.

Claims

**Claim 1** A method for improving the resolution of a radiation-sensitive microcapsule-based printer, the method comprising: generating, by a controller, a plurality of sub-pixels in a sub-scanning direction based on an image data set of an image to be printed on a photosensitive medium; mapping, by the controller, a plurality of grids onto the photosensitive medium, the plurality of grids corresponding to the plurality of sub-pixels; determining, by the controller, the exposure energy required for each grid of the plurality of grids based on corresponding sub-pixels of the plurality of sub-pixels; assigning, by the controller, the exposure energy required for each grid to a first exposure level and a second exposure level; sequentially exposing, by the controller, each grid of the photosensitive medium to the corresponding first exposure level and the corresponding second exposure level as the photosensitive medium passes through the radiation-sensitive microcapsule-based printer in the sub-scanning direction. **Claim 2** The generating of the plurality of sub-pixels in the sub-scanning direction comprises: generating, by the controller, a scaled image data set by scaling the image data set; upsampling, by the controller, a set of image pixels of the scaled image data set to generate a set of image sub-pixels in the sub-scanning direction, wherein the number of image sub-pixels in the set of image sub-pixels is twice the number of image pixels in the set of image pixels. The method according to claim 1. **Claim 3** The upsampling of the set of image pixels of the scaled image data set comprises performing linear interpolation by the controller to add sub-pixels between at least one pair of adjacent image pixels in the sub-scanning direction within the scaled image data set. The method according to claim 2. **Claim 4** The upsampling of the set of image pixels of the scaled image data set comprises: The controller determines that a difference between at least one other pair of exposure energy levels of the image pixels adjacent in the sub-scanning direction within the scaled image data set is greater than a threshold value; When it is determined that the difference between the at least one other pair of exposure energy levels of the adjacent image pixels is greater than the threshold value, the controller further executes a nearest neighbor algorithm to add the sub-pixels between at least one other pair of the adjacent image pixels. The method according to claim 3.

5. The method according to claim 4, wherein the threshold value is defined as one third of a difference between a maximum value and a minimum value of the exposure energy levels of the set of image pixels from the scaled image data set.

6. The method according to claim 4, wherein the fact that the difference between the at least one other pair of the exposure energy levels of the adjacent image pixels is greater than the threshold value indicates a sharp edge in the image.

7. The method according to claim 4, wherein determining the exposure energy required for each grid includes the controller applying an offset of the exposure energy level to at least one grid of the plurality of grids.

8. The size of each grid of the photosensitive medium is D ｘ × D ｙ / 2, where D ｘ is the length of the exposure element along the main scanning direction, and D ｙ is the length of the exposure element along the sub-scanning direction, and the main scanning direction is perpendicular to the sub-scanning direction. The method according to claim 1

9. The method according to claim 1, wherein the total exposure energy level for each grid of the plurality of grids is equal to the corresponding first exposure level for the grid + the corresponding second exposure level for the grid.

10. The method according to claim 1, wherein the second exposure level for the first grid of the plurality of grids is equal to the first exposure level for a second grid that is directly adjacent to the first grid and immediately after the first grid when the photosensitive medium is moved in the sub-scanning direction.

11. The method according to claim 2, further including the controller determining a printing resolution of the radiation-sensitive microcapsule-based printer based on a spot size of an exposure element.

12. Generating the scaled image data set by scaling the image data set is performed based on the determined printing resolution of the radiation-sensitive microcapsule-based printer, the method according to claim 11.

13. A method for improving the resolution of a radiation-sensitive microcapsule-based printer, the method comprising: Generating, by a controller, a plurality of sub-pixels in a sub-scanning direction based on an image data set of an image to be printed on a photosensitive medium; Mapping, by the controller, a plurality of grids onto the photosensitive medium, wherein the plurality of grids correspond to the plurality of sub-pixels; Determining, by the controller, the exposure energy required for each grid of the plurality of grids based on the corresponding image sub-pixels of the plurality of sub-pixels; Assigning, by the controller, the exposure energy required for each grid to a set of sub-energy exposure levels, wherein the number of sub-energy exposure levels in the set of sub-energy exposure levels is N; Sequentially exposing, by the controller, each grid of the photosensitive medium to the corresponding set of sub-energy exposure levels as the photosensitive medium passes through the radiation-sensitive microcapsule-based printer in the sub-scanning direction.

14. Generating the plurality of sub-pixels comprises: Generating, by the controller, a scaled image data set by scaling the image data set; Upsampling, by the controller, a set of image pixels of the scaled image data set to generate a set of image sub-pixels in the sub-scanning direction, wherein the number of image sub-pixels in the set of image sub-pixels is N times the number of image pixels in the set of image pixels, the method according to claim 13.

15. To generate the set of the image sub-pixels in the sub-scanning direction, the controller upsamples the set of the image pixels of the scaled image data set, including performing linear interpolation to add N - 1 sub-pixels between at least one pair of the image pixels adjacent in the sub-scanning direction within the scaled image data set. The method according to claim 14.

16. A radiation-sensitive microcapsule-based printer, comprising an exposure element array including a set of exposure elements, a medium conveyance system configured to convey a photosensitive medium along a sub-scanning direction, a controller including a processor and a memory storing instructions, wherein when the instructions are executed by the processor, the processor is caused to generate a plurality of sub-pixels in the sub-scanning direction based on an image data set of an image to be printed on the photosensitive medium; map a plurality of grids onto the photosensitive medium, wherein the plurality of grids correspond to the plurality of sub-pixels; determine exposure energy required for each grid of the plurality of grids based on corresponding sub-pixels among the plurality of sub-pixels; allocate the exposure energy required for each grid to a first exposure level and a second exposure level; sequentially expose each grid of the photosensitive medium to the corresponding first exposure level and the corresponding second exposure level as the photosensitive medium passes through the radiation-sensitive microcapsule-based printer in the sub-scanning direction. A radiation-sensitive microcapsule-based printer.

17. Generating the plurality of sub-pixels in the sub-scanning direction includes generating a scaled image data set by scaling the image data set. To generate a set of image sub-pixels in the sub-scanning direction, upsampling a set of image pixels of the scaled image data set, wherein the number of image sub-pixels in the set of image sub-pixels is twice the number of image pixels in the set of image pixels, and upsampling, the radiation-sensitive microcapsule-based printer according to claim 16.

18. Upsampling the set of image pixels of the scaled image data set includes performing linear interpolation to add sub-pixels between at least one pair of adjacent image pixels in the sub-scanning direction within the scaled image data set, the radiation-sensitive microcapsule-based printer according to claim 17.

19. Upsampling the set of image pixels of the scaled image data set is the controller determines that the difference between the exposure energy levels of at least one other pair of adjacent image pixels in the sub-scanning direction within the scaled image data set is greater than a threshold value; when it is determined that the difference between the exposure energy levels of at least one other pair of adjacent image pixels is greater than the threshold value, further including the controller performing a nearest neighbor algorithm to add the sub-pixels between at least one other pair of adjacent image pixels, the radiation-sensitive microcapsule-based printer according to claim 18.

20. The threshold value is defined as one-third of the difference between the maximum value and the minimum value of the exposure energy levels of the set of image pixels from the scaled image data set, the radiation-sensitive microcapsule-based printer according to claim 19.

Images