Image processing device and image forming device

Abstract

To suppress deterioration in image quality of an output image when outputting an original image after reducing a file size by reading the original at different resolutions depending on the scanning direction and performing high resolution conversion to make the resolutions in both scanning directions the same. [Solution] The system includes an intermediate image generation unit 101 that performs resolution conversion on the read image data obtained by reading a document using a document reading unit 5, thereby generating intermediate image data with the same resolution in both scanning directions; a character area detection unit 102 that detects character areas within the image represented by the intermediate image data; an image correction unit 104 that corrects the intermediate image data so as to increase the density of low-density character areas in the character areas that are lower in density than a predetermined reference density and decrease the density of high-density character areas that are higher in density than the reference density; and an output image generation unit 105 that converts the resolution of the corrected intermediate image data to a predetermined output resolution and generates output image data.

Description

[Technical Field]

[0001] The present invention relates to an image processing apparatus and an image forming apparatus that are provided with a document reading unit that reads an image of a document. [Background technology]

[0002] In copiers and multifunction devices with copy functions, scanning an original at high resolution (for example, 600 x 600 dpi or higher) generally improves the reproducibility of the print, but scanning an original at low resolution (for example, 300 x 300 dpi) generally results in a decrease in the reproducibility of the print. Therefore, to improve the quality of the output image, it is better to scan the original at a high resolution rather than a low resolution. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-165325 Summary of the Invention [Problem to be solved by the invention]

[0004] However, scanning a document at high resolution results in a large file size for the scanned image data, which is not desirable for internal image processing such as image transfer and storage. For this reason, documents are sometimes scanned at different resolutions depending on the scanning direction (e.g., 300 x 600 dpi) to reduce the file size of the scanned image data.

[0005] In addition, for scanned image data obtained by scanning a document at different resolutions depending on the scanning direction, resolution conversion may be performed to make the resolution in both scanning directions the same (e.g., 300 x 300 dpi) before printing or other output.

[0006] However, when the image is output after the resolution conversion to make the resolution the same as described above, differences in the reproducibility of details occur between the main scanning direction and the sub-scanning direction, which can cause the vertical and horizontal balance of characters to be lost, resulting in visually blurred characters and partial thickening of characters, which can cause degradation of image quality. This is because there are character regions where the pixels that make up the image are thinned out a lot, and character regions where the pixels that make up the image are not thinned out or are thinned out little.

[0007] The above-mentioned Patent Document 1 describes an invention for preventing deterioration in the quality of an output image, but does not mention deterioration in image quality caused by reading an original at different resolutions depending on the scanning direction.

[0008] The present invention has been made in consideration of the above circumstances, and aims to suppress degradation in image quality of the output image when the file size is reduced by reading the original document at different resolutions depending on the scanning direction, and then high-resolution conversion is performed to make the resolution in both scanning directions the same before outputting the original document image. [Means for solving the problem]

[0009] An image processing device according to one aspect of the present invention comprises an original reading unit that reads an image of an original at different resolutions in the main scanning direction and the sub-scanning direction, an intermediate image generation unit that generates intermediate image data with the same resolution in both scanning directions by performing resolution conversion on the read image data obtained by reading the original by the original reading unit, a character area detection unit that detects a character area within an image represented by the intermediate image data generated by the intermediate image generation unit, an image correction unit that corrects the intermediate image data by increasing the density of low-density character areas that are lower in density than a predetermined reference density by a predetermined first density and decreasing the density of high-density character areas that are higher in density than the reference density by a predetermined second density in the character area detected by the character area detection unit, and an output image generation unit that generates output image data by converting the resolution of the intermediate image data corrected by the image correction unit to a predetermined output resolution.

[0010] Furthermore, an image forming apparatus according to one aspect of the present invention includes an image processing apparatus according to one aspect of the present invention described above, and an image forming unit that forms an image on a recording medium based on the output image data generated by the output image generation unit. [Effects of the Invention]

[0011] In this invention, by increasing the density of low-density character regions, pixel thinning in these character regions is reduced, and by decreasing the density of high-density character regions, pixel thinning in these character regions is increased. This allows the thinning in both character regions to be closer, making it possible to reduce differences in the reproducibility of details between the main scanning direction and the sub-scanning direction. Therefore, when the file size is reduced by scanning an original at different resolutions depending on the scanning direction, and then high-resolution conversion is performed to make the resolutions in both scanning directions the same before outputting the original image, degradation in the image quality of the output image can be suppressed. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a functional block diagram illustrating a schematic main internal configuration of an image forming apparatus to which an image processing apparatus according to an embodiment of the present invention is applied; [Figure 2] 1A and 1B are diagrams showing images of read image data obtained by reading a document by a document reading unit. [Figure 3] 10A and 10B are diagrams showing an example of the correspondence between input density values ​​and output density values. [Figure 4] 10A to 10D are diagrams showing the transition of data from read image data obtained by reading an original by an original reading unit until output image data is generated. [Figure 5] 10A to 10C are diagrams showing, as a comparative example, the transition of data from read image data obtained by reading an original document by an original document reading unit until output image data is generated. [Figure 6] 10 is a flowchart illustrating an example of processing performed by a control unit of the image forming apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0013] An image processing device and an image forming device according to an embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a functional block diagram showing the main internal configuration of an image forming device to which an image processing device according to an embodiment of the present invention is applied. Image forming device 1 is a multifunction device that combines multiple functions, such as a copy function, a printer function, a scanner function, and a facsimile function.

[0014] The image forming apparatus 1 includes a control unit 10, a document feeding unit 6, a document reading unit 5, an image forming unit 12, a fixing unit 13, a paper feeding unit 14, an operation unit 47, a network interface unit 9, and a memory unit 8.

[0015] The document feeder 6 is configured to be openable and closable by a hinge or the like (not shown) on the top surface of the document reading unit 5, and functions as a document pressing cover when reading a document placed on a platen glass (not shown). The document feeder 6 is also called an ADF (Auto Document Feeder), and is equipped with a document placement tray (not shown), and supplies documents placed on the document placement tray to the document reading unit 5.

[0016] The document reading unit 5 has a plurality of image capturing elements arranged in the main scanning direction, and is equipped with a scanner or the like that reads the image of the document by moving these plurality of image capturing elements in a sub-scanning direction perpendicular to the main scanning direction, and is capable of reading the image of the document at different resolutions depending on the scanning direction, and reads the document fed from the document feeding unit 6 or the document placed on the platen glass. The document reading unit 5 is also capable of sequentially reading the images of the plurality of documents sent from the document feeding unit 6.

[0017] The following describes the case where a document reading operation is performed in the image forming apparatus 1. The document reading unit 5 optically reads an image of a document supplied to the document reading unit 5 by the document feeding unit 6 or a document placed on the platen glass, and generates read image data. The read image data generated by the document reading unit 5 is stored in an image memory or the like (not shown).

[0018] 2(A) and (B) are diagrams showing images of scanned image data obtained by scanning a document using the document scanning unit 5. FIG. 2(A) is a diagram showing an image of scanned image data DA obtained when a document is scanned at the same resolution (600 x 600 dpi) in both the main scanning direction and the sub-scanning direction. FIG. 2(B) is a diagram showing an image of scanned image data DB obtained when a document is scanned at a different resolution (300 x 600 dpi) depending on the scanning direction. In the diagram shown in FIG. 2(B), the length of a pixel in the main scanning direction (horizontal direction in the diagram) is twice the length of a pixel in the sub-scanning direction (vertical direction in the diagram). Hereinafter, when indicating numerical values ​​of resolution, the main scanning direction is indicated first, followed by the sub-scanning direction.

[0019] The following describes an image forming operation performed by the image forming apparatus 1. The image forming unit 12 is equipped with a photosensitive drum, charging device, exposure device, developing device, and primary transfer device for each color, and is a mechanism for forming an image on recording paper as a recording medium by secondary transfer via an intermediate transfer belt. The image forming unit 12 forms a toner image on recording paper fed from the paper feed unit 14 based on image data generated by a document reading operation, image data stored in an image memory, etc., and image data received from a computer connected via a network, to create a printed matter.

[0020] The fixing unit 13 is a fixing device equipped with a heat roller, a pressure roller, and a drive mechanism for rotating these rollers. The fixing unit 13 heats and presses the recording paper on which the toner image has been formed by the image forming unit 12 at the nip between the two rollers, fixing the toner image to the recording paper. The recording paper that has been fixed is then discharged to an output tray (not shown).

[0021] The paper feed unit 14 includes a paper feed cassette (not shown), a pickup roller that picks up recording paper from the paper feed cassette and feeds it to the image forming unit 12, a transport roller, a transport path, and a rotation drive mechanism for each roller.

[0022] The operation unit 47 includes various hard keys that are operated by the user, and receives instructions from the user, such as an instruction to execute an image forming operation, regarding various operations and processes that the image forming apparatus 1 can execute in response to the operation of the hard keys.

[0023] The operation unit 47 includes a display unit 473 that displays operation guides and the like to the operator. The operation unit 47 also receives input of instructions from the user based on the user's operation (touch operation) on the screen displayed on the display unit 473 via a touch panel that the display unit 473 has.

[0024] The display unit 473 is composed of an LCD (Liquid Crystal Display) or the like. When the operator touches a button or key displayed on the screen, the touch panel receives an instruction associated with the touched position. In this case, the touch panel functions as an operation unit.

[0025] The network interface unit 9 is a communication interface for transmitting and receiving various data to and from an external device (for example, a personal computer) within a local area or on the Internet.

[0026] The storage unit 8 is a large-capacity storage device such as a hard disk drive (HDD) or a solid state drive (SSD), and stores various control programs and the like.

[0027] The control unit 10 includes a processor, a RAM (Random Access Memory), a ROM (Read Only Memory), and a dedicated hardware circuit. The processor may be, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), or an MPU (Micro Processing Unit). The control unit 10 includes a control unit 100, an intermediate image generation unit 101, a character region detection unit 102, an image processing unit 103, an image correction unit 104, and an output image generation unit 105.

[0028] The control unit 10 functions as a control unit 100, an intermediate image generating unit 101, a character area detecting unit 102, an image processing unit 103, an image correcting unit 104, and an output image generating unit 105 through operation by the processor in accordance with a control program stored in the storage unit 8. However, the control unit 100 and the like can also be configured by hardware circuits, without relying on operation in accordance with a control program by the control unit 10. Unless otherwise stated below, the same applies to each embodiment.

[0029] The control unit 100 is responsible for overall operational control of the image forming apparatus 1. The control unit 100 is connected to the document feeding unit 6, the document reading unit 5, the image forming unit 12, the fixing unit 13, the paper feeding unit 14, the operation unit 47, the network interface unit 9, and the storage unit 8, and controls the driving of these units and executes various processes required for image formation by the image forming apparatus 1.

[0030] The intermediate image generation unit 101 performs resolution conversion on the read image data DB (FIG. 2B) obtained by reading the document by the document reading unit 5, thereby generating intermediate image data with the same resolution in both scanning directions. The intermediate image generation unit 101 converts the resolution of the read image data in the main scanning direction or the sub-scanning direction to match the smaller resolution of the other scanning direction. In this embodiment, the document reading unit 5 reads the document at different predetermined resolutions in the main scanning direction and the sub-scanning direction (here, 300×600 dpi is used as an example), and the intermediate image generation unit 101 converts the read image data having the resolution at the time of reading to, for example, 300×300 dpi, to generate intermediate image data.

[0031] The text area detection unit 102 detects text areas within the image represented by the intermediate image data generated by the intermediate image generation unit 101. For example, the text area detection unit 102 uses a known area determination technique to determine, from pixel information in the intermediate image data, text areas where text is drawn and graphic areas (areas other than text areas) where photographs, diagrams, or tables are drawn. For example, using the known area determination technique, the text area detection unit 102 recognizes, as a text area, a portion where the circumscribing rectangle of connected pixels is smaller than a predetermined size, and recognizes, as a graphic area, a portion where the circumscribing rectangle is not smaller.

[0032] The image processing unit 103 performs various image processing on the intermediate image data generated by the intermediate image generation unit 101. For example, the image processing unit 103 performs known edge enhancement processing on the intermediate image data of the character region detected by the character region detection unit 102, and performs known smoothing processing on the intermediate image data other than the character region.

[0033] The image correction unit 104 corrects the intermediate image data by increasing the density of low-density character areas LA, which have a density lower than a predetermined reference density RC, by a predetermined first density, and decreasing the density of high-density character areas HA, which have a density higher than the reference density RC, by a predetermined second density. For example, the image correction unit 104 corrects the intermediate image data based on predetermined input / output characteristics that indicate the relationship between input density values ​​VI and output density values ​​VO. Furthermore, for example, the predetermined reference density RC is a pixel value of 190 or a value around 190 in the case of a 256-level image representation (pixel values ​​0-255).

[0034] The predetermined input / output characteristics are set so that the output density value VO increases or remains constant without decreasing as the input density value VI increases, and so that (i) when the input density value VI is lower than the reference density RC, the output density value VO is higher than the input density value VI and lower than the reference density RC, and (ii) when the input density value VI is higher than the reference density RC, the output density value VO is lower than the input density value VI and higher than the reference density RC. That is, the image correction unit 104 determines the predetermined first density amount according to (i) above, and determines the predetermined second density amount according to (ii) above.

[0035] 3A and 3B show examples of input / output characteristics, illustrating an example of the correspondence between input density values ​​VI and output density values ​​VO. The horizontal axis represents the input density values ​​VI, the vertical axis represents the output density values ​​VO, and the dashed line L11 indicates the case where the input density values ​​VI and the output density values ​​VO are equal.

[0036] The input-output characteristics indicated by the solid lines L1 and L2 are the predetermined input-output characteristics. That is, in this embodiment, either the input-output characteristics indicated by the solid lines L1 or L2 can be adopted. The input-output characteristics indicated by the solid line L1 are set so that the output density value VO increases linearly with the input density value VI, the slope becomes smaller at the density value C1, and the slope becomes zero at the density value C2. That is, the input-output characteristics indicated by the solid line L2 are set so that the output density value VO increases linearly with the input density value VI, and the slope becomes smaller at the density value C3.

[0037] The output image generation unit 105 converts the resolution of the intermediate image data corrected by the image correction unit 104 (here, 300×300 dpi is taken as an example) into a predetermined output resolution (here, 600×600 dpi is taken as an example) to generate output image data. For example, the output image generation unit 105 generates output image data from the corrected intermediate image data using a known gradation processing technique (such as an error diffusion method).

[0038] 4A to 4D are diagrams showing the progression of data from the scanned image data obtained by scanning an original document using the original document scanning unit 5 to the generation of output image data through image processing according to this embodiment. Note that in FIGS. 4A to 4C, the image diagrams are expressed as multi-value images, while in FIG. 4D, the image diagrams are expressed as binary images.

[0039] 4(A) is a diagram showing an image of a character area included in the scanned image data D1 (DB) obtained by scanning an original document at a resolution (300 × 600 dpi) that varies depending on the scanning direction by the document scanning unit 5. In the image shown in FIG. 4(A), the length of a pixel in the main scanning direction (horizontal direction in the diagram) is twice that in the sub-scanning direction (vertical direction in the diagram).

[0040] 4(B) is a diagram showing an image of intermediate image data D2 (resolution: 300 × 300 dpi) that has the same resolution in both scanning directions and is generated by performing resolution conversion on the read image data D1 by the intermediate image generation unit 101. The intermediate image data D2 has twice the length of pixels in the sub-scanning direction (vertical direction in the figure) as the read image data D1, so the image density of horizontal lines is lower.

[0041] Since the horizontal pixel length in the figure does not change, the vertical line character area (solid black area) remains solid black (high density character area HA), but since the vertical pixel length in the figure doubles, the horizontal line character area (solid black area) is converted to a gray area (low density character area LA). In Figure 4(B), the areas with low image density are represented in gray.

[0042] Fig. 4(C) is a diagram showing an image of intermediate image data D21 obtained by correction by image correction unit 104. Based on the above-mentioned input / output characteristics (here, Fig. 3(A)), image correction unit 104 corrects intermediate image data D2 so as to increase the density of low-density character areas LA, which have a density lower than the reference density RC, and decrease the density of high-density character areas HA, which have a density higher than the reference density RC, thereby generating intermediate image data D21. The intermediate image data D21 has higher image density for horizontal lines and lower image density for vertical lines than the intermediate image data D2.

[0043] In other words, in the high-density character area HA (solid black area) of vertical lines, the pixels that make up the image are slightly thinned out, changing from solid black to gray, and in the low-density character area LA (gray area) of horizontal lines, the pixels that make up the image are slightly interpolated, making the gray area darker, resulting in a good balance of vertical and horizontal density.

[0044] FIG. 4D is a diagram showing an image of output image data D3 generated by the output image generating unit 105 after converting the resolution of the intermediate image data D21 into a predetermined output resolution (600×600 dpi).

[0045] 5A to 5C are diagrams showing the progression of data from scanned image data obtained by scanning an original document using the original document scanning unit 5 to the generation of output image data by image processing as a comparative example not according to this embodiment. Note that in Figs. 5A and 5B, the image is expressed as a multi-value image, while in Fig. 5C, the image is expressed as a binary image.

[0046] Fig. 5(A) is a diagram showing an image of a character region included in scanned image data D1 (DB) obtained by scanning a document with a resolution (300 x 600 dpi) that varies depending on the scanning direction by the document scanning unit 5. Fig. 5(B) is a diagram showing an image of intermediate image data D2 (resolution: 300 x 300 dpi) that has the same resolution in both scanning directions and is generated by performing resolution conversion on the scanned image data D1. Up to this point, the image processing according to this embodiment is the same as Figs. 4(A) and 4(B).

[0047] 5C is a diagram showing an example of output image data D4 generated by converting the resolution of intermediate image data D2 to a predetermined output resolution (600 x 600 dpi). In the comparative example, unlike the image processing according to this embodiment, the image correction unit 104 does not generate the intermediate image data D21, and the intermediate image data D21 is not subject to resolution conversion to the output resolution. The intermediate image data D2 is subject to resolution conversion to the output resolution to generate output image data D4.

[0048] In the output image data D4 of the comparative example shown in Fig. 5(C), thinning is present in the horizontal direction but not in the vertical direction, resulting in poor density balance between the vertical and horizontal directions. On the other hand, in the output image data D3 produced by the image processing of this embodiment shown in Fig. 4(D), thinning can be made to occur to the same extent in both the horizontal and vertical directions, resulting in good density balance between the vertical and horizontal directions.

[0049] Next, image processing and image formation according to this embodiment will be described with reference to the flowchart shown in Fig. 6. This processing is performed when an original is placed on the platen glass, for example, and the operation unit 47 receives a copy instruction from the user.

[0050] When the operation unit 47 receives a copy instruction from the user, the control unit 100 controls the operation of the document reading unit 5 and causes the document reading unit 5 to read the document image placed on the platen glass at a predetermined resolution (for example, 300 x 600 dpi as mentioned above) that varies depending on the scanning direction (S1).

[0051] Next, the intermediate image generation unit 101 performs resolution conversion on the read image data D1 obtained by reading the document by the document reading unit 5 at a resolution (using the above-mentioned 300 x 300 dpi as an example) to generate intermediate image data D2 with the same resolution in both scanning directions (S2).

[0052] The character area detection unit 102 detects character areas in the image represented by the intermediate image data D2 generated by the intermediate image generation unit 101 (S3). The image processing unit 103 performs edge enhancement processing on the intermediate image data of the character areas of the intermediate image data D2 generated by the intermediate image generation unit 101, and performs smoothing processing on the intermediate image data other than the character areas (S4).

[0053] Based on the above-mentioned input / output characteristics, the image correction unit 104 corrects the intermediate image data D21 so as to increase the density of low-density character areas LA, which have a density lower than a predetermined reference density RC, and decrease the density of high-density character areas HA, which have a density higher than the reference density RC, in the character areas within the image represented by the intermediate image data D2, which has been image processed by the image processing unit 103 (S5).

[0054] The output image generation unit 105 converts the resolution of the intermediate image data D21 corrected by the image correction unit 104 into a predetermined output resolution (600 x 600 dpi) and generates output image data D3 (S6). The control unit 100 controls the image forming unit 12, the paper feed unit 14, and the fixing unit 13 to form an image on recording paper based on the output image data D3 generated by the output image generation unit 105 (S7). After this, the processing ends.

[0055] In the above embodiment, increasing the density of the low-density character area LA (a character area with a lot of pixel thinning) reduces pixel thinning in this character area, and decreasing the density of the high-density character area HA (a character area with little or no pixel thinning) increases pixel thinning in this character area. This makes it possible to achieve the same degree of thinning in both character areas, and prevents differences in the reproduction of details between the main scanning direction and the sub-scanning direction.

[0056] Therefore, by reading the document at different resolutions depending on the scanning direction to reduce the file size, and then performing high-resolution conversion to make the resolution the same in both scanning directions before outputting the document image, it is possible to suppress degradation in the image quality of the output image.

[0057] The present invention is not limited to the configuration of the above embodiment, and various modifications are possible. In addition, in the above embodiment, the configuration and processing shown in the above embodiment using Figures 1 to 6 are merely one embodiment of the present invention, and it is not intended that the present invention be limited to these configurations and processing. [Explanation of symbols]

[0058] 1. Image forming device 5 Document reading section 12 Image forming unit 100 control section 101 Intermediate image generation unit 102 Character area detection unit 104 Image correction unit 105 Output image generation unit

Claims

1. an original reading unit that reads an image of an original at different resolutions in a main scanning direction and a sub-scanning direction; an intermediate image generating unit that generates intermediate image data having the same resolution in both scanning directions by performing resolution conversion on read image data obtained by reading the document by the document reading unit; a character area detection unit that detects a character area within an image represented by the intermediate image data generated by the intermediate image generation unit; an image correction unit that corrects the intermediate image data by increasing the density of low-density character regions, which have a density lower than a predetermined reference density, by a predetermined first density and decreasing the density of high-density character regions, which have a density higher than the reference density, by a predetermined second density in the character regions detected by the character region detection unit; an output image generation unit that generates output image data by converting the resolution of the intermediate image data corrected by the image correction unit into a predetermined output resolution.

2. the image correction unit performs the correction of the intermediate image data based on a predetermined input / output characteristic that indicates a relationship between an input density value and an output density value; The input / output characteristics are: The output density value is set to increase or remain the same as the input density value increases, without decreasing; When the input density value is lower than the reference density, the output density value is higher than the input density value and lower than the reference density; 2. The image processing apparatus according to claim 1, wherein when the input density value is higher than the reference density, the output density value is set to be lower than the input density value and higher than the reference density.

3. an image processing unit that performs edge enhancement processing on the character region in the intermediate image data and smoothing processing on regions other than the character region detected by the character region detection unit, The image processing device according to claim 2 , wherein the image correction unit performs the correction on the intermediate image data after image processing by the image processing unit.

4. the intermediate image generation unit generates the intermediate image data by performing resolution conversion to convert the resolution of the read image data in the main scanning direction to match the resolution of the read image data in the other scanning direction, whichever is smaller, of the resolution of the read image data in the main scanning direction and the resolution of the read image data in the sub-scanning direction; 4. The image processing device according to claim 1, wherein the output image generation unit converts the resolution of the intermediate image data by setting the larger of the resolution of the read image data in the main scanning direction and the resolution of the read image data in the sub-scanning direction as the predetermined output resolution.

5. The image processing device according to claim 1 ; an image forming unit that forms an image on a recording medium based on the output image data generated by the output image generating unit;

Images