JP2006191294A - Image processor, program and image-processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of establishing the compatibility suitable for respective processing results between regions whose sharpness is desirably emphasized and regions whose granularity and gradation are desirably emphasized, providing processing results respectively suitable for character regions and photo regions without image quality deterioration applied to an input image where characters and photos are intermingled, and also providing processing results with excellent sharpness for the character regions even applied to small letters and low contrast characters or the like. <P>SOLUTION: A halftone processing means 24 for carrying out a halftone process selects a quantization threshold value depending on whether object type information of a target pixel stored in an object type information memory 23 emphasizes the sharpness or the granularity and the gradation and carries out quantization processing by taking a quantization error from pixels around the target pixel into account. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus, a program, and an image processing method that perform image quality improvement processing of an output image of rasterized digital image data.

  When a page-description language (PDL) created using an application such as a word processor installed in a personal computer is output to a printer, characters and graphics expressed by PDL commands The image is expanded into a two-dimensional bitmap image for output to a printer and temporarily stored in the memory.

  In recent years, when characters and figures represented by PDL commands are expanded and stored in a two-dimensional bitmap image, object type information is stored corresponding to each pixel at the same time. Based on the image data, halftone images such as natural images and binary images such as characters are mixed by switching halftone processing and color correction suitable for each character / photo area of the image data. In contrast, a technique for obtaining a high-quality image is disclosed.

  In Japanese Patent Laid-Open No. 2004-228867, the developed bitmap image is subjected to an image area separation process mainly mounted in a color copying machine, thereby separating a character area from an image in which characters and photographs are mixed. A technique for obtaining a high-quality image by switching and executing processing suitable for each region is disclosed. At this time, the image area separation process does not necessarily detect all the character areas, and the natural image area is erroneously detected as a character area. Therefore, the image area is referred to by referring to the object type information data. Reliability is improved by performing separation processing.

  In Patent Document 2, there is a drawback that it takes a lot of time to perform the image area separation used in Patent Document 1 on the entire image, and a pixel whose original image data is a character is not a character due to a misjudgment. In order to compensate for the problem that the image area may be determined, a technique for executing image area separation after determining a range for performing image area separation processing based on object type information data in advance is disclosed.

  However, according to the techniques disclosed in Patent Document 1 and Patent Document 2, halftone processing is switched based on the object type information and the image area separation result, and sharpness emphasis appropriate for each of the character area / photograph area / It is possible to apply processing that emphasizes graininess and gradation, but on the other hand, when switching between halftone processing with such different properties, the response to image quality degradation that occurs at the boundary is considered. Not. More specifically, for example, when applying a high line number dither process for an area determined to be a character area and applying a low line number dither process for an area determined to be a photographic area, both processes are applied. At the switching contact, the portion where the dot pitch is denser or connected is displayed with a high density and appears as a bordered image, and the portion where the dot pitch is coarser than any dither has a lower density. There is a problem that it appears as an image that looks like white spots.

  Therefore, in order to solve this problem, processing results with excellent sharpness in the character area for the input image in which characters and photographs are mixed in an MFP (Multi Function Peripheral) machine. Patent Document 3 discloses a technique related to a halftone processing method capable of obtaining a processing result with excellent performance. More specifically, the edge degree of the input image is calculated, and based on the edge amount calculation result, error diffusion processing with a fixed threshold is performed when the edge amount is large, and dither threshold error diffusion processing is performed when the edge amount is small. By doing so, it is possible to obtain a high-quality processing result even for an image in which characters and photographs are mixed without switching halftone processing. According to the halftone processing method of Patent Document 3 described above, processing results that are excellent in sharpness in the character area only by switching the threshold value without switching the halftone process for each area, and the graininess and gradation in the photographic area. Therefore, it is possible to obtain a high-quality image even for an image in which characters and photographs are mixed without deterioration in image quality in the above-described process switching portion.

JP 2000-134468 A JP 2000-259819 A JP 2001-128004 A

  However, in the halftone processing method of Patent Document 3 as described above, the edge amount is calculated for the input image, and the threshold value is switched based on the edge amount calculation result. For low-contrast characters and the like, since the processing for a photograph is performed without being detected as a character region, there is a problem that the quality of the processed image is deteriorated. In addition, since the threshold value is switched based on the edge amount calculation result, only the character edge may be detected as a character region for a thick character, and the inside of the character may not be detected as a character region.

  The present invention has been made in view of the above, and can achieve a processing result suitable for each of an area in which sharpness is to be emphasized and an area in which granularity / gradation is to be emphasized. A processing result suitable for each of the character area and the photographic area can be obtained without deterioration in image quality, and processing with excellent sharpness for the character area even for lowercase letters, low-contrast characters, etc. An object is to realize an image processing apparatus, a program, and an image processing method capable of obtaining a result.

  In addition, the present invention places importance on resolution (sharpness) even for regions where sharpness is preferable, such as lines and characters included in an image when the object type information is an image object. An object is to realize an image processing apparatus, a program, and an image processing method capable of performing processing.

  In order to solve the above-described problems and achieve the object, an image processing apparatus according to a first aspect of the present invention develops an image expressed by a drawing command into two-dimensional bitmap data and stores it in a bitmap memory. Data storage means, and object type information storage means for storing the object type information of the image expressed by the rendering command in the object type information memory in association with each pixel of the image developed into the bitmap data, The quantization threshold is switched according to whether the object type information of the pixel of interest stored in the object type information memory emphasizes sharpness, or emphasizes graininess / gradation, and Halftone processing for performing quantization processing on bitmap data stored in the bitmap memory in consideration of quantization error It includes a stage, a.

  According to a second aspect of the present invention, there is provided an image processing apparatus comprising: data storage means for expanding an image represented by a drawing command into two-dimensional bitmap data and storing the data in a bitmap memory; Object type information storage means for storing object type information of an image stored in the object type information memory in association with each pixel of the image developed into the bitmap data, and bitmap data stored in the bitmap memory A feature amount calculation means for calculating the feature amount of the bitmap data, a feature amount of the bitmap data stored in the bitmap memory calculated by the feature amount calculation means, and a pixel of interest stored in the object type information memory. From the object type information, the pixel of interest emphasizes sharpness, or the pixel emphasizes graininess and gradation A determination signal generation unit that generates a threshold determination signal of some, and a quantization threshold is switched according to the threshold determination signal generated by the determination signal generation unit, the quantization error from the surrounding pixel of the pixel of interest Halftone processing means for performing quantization processing on the bitmap data stored in the bitmap memory.

  According to a third aspect of the present invention, in the image processing apparatus according to the second aspect, the feature amount of the bitmap data calculated by the feature amount calculating means is an edge amount that is a value indicating an edge degree for each pixel. is there.

  According to a fourth aspect of the present invention, in the image processing apparatus according to the third aspect, the feature quantity calculating means determines whether the object type information of the target pixel stored in the object type information memory emphasizes sharpness. Alternatively, the edge amount calculation method is switched according to whether the graininess / gradation is important.

  According to a fifth aspect of the present invention, in the image processing device according to any one of the first to fourth aspects, the halftone processing means stores the object type information of the pixel of interest stored in the object type information memory. Switching between at least the first quantization threshold and the second quantization threshold depending on whether sharpness is important or granularity / gradation is important, the first quantization threshold is: The threshold value has a constant value regardless of the pixel position and corresponds to the object type information that emphasizes sharpness, and the second quantization threshold value is a threshold value that vibrates periodically in the image space, and has granularity and gradation. It corresponds to the object type information that emphasizes the nature.

  According to a sixth aspect of the present invention, in the image processing apparatus according to any one of the first to fourth aspects, the halftone processing means stores the object type information of the target pixel stored in the object type information memory. Switching between at least the first quantization threshold and the second quantization threshold depending on whether sharpness is important or granularity / gradation is important, the first quantization threshold is: Corresponding to object type information that is a threshold that periodically vibrates on the image space and emphasizes sharpness, the second quantization threshold is periodically larger in amplitude width on the image space than the first threshold. It corresponds to object type information that is a threshold value for vibration and emphasizes granularity and gradation.

  According to a seventh aspect of the present invention, in the image processing apparatus according to any one of the first to fourth aspects, the halftone processing means stores the object type information of the pixel of interest stored in the object type information memory. Switching between at least the first quantization threshold and the second quantization threshold depending on whether sharpness is important or granularity / gradation is important, the first quantization threshold is: A threshold that periodically oscillates in the image space, corresponds to object type information that emphasizes sharpness, and the second quantization threshold is a threshold that oscillates periodically in the image space larger than the first threshold. It corresponds to object type information that places importance on graininess and gradation.

  According to an eighth aspect of the present invention, in the image processing apparatus according to any one of the first to seventh aspects, an image based on the bitmap data quantized by the halftone processing unit is formed on a recording medium. Image forming means is included.

  According to a ninth aspect of the present invention, there is provided a data storage function for expanding an image expressed by a drawing command into two-dimensional bitmap data and storing the data in a bitmap memory, and an image expressed by a drawing command. Object type information storage function for storing the object type information in the object type information memory in association with each pixel of the image developed into the bitmap data, and the object of the target pixel stored in the object type information memory The quantization threshold is switched depending on whether the type information emphasizes sharpness or whether graininess / gradation is emphasized, and is stored in the bitmap memory in consideration of quantization errors from pixels around the pixel of interest. And a halftone processing function for performing a quantization process on the current bitmap data.

  According to a tenth aspect of the present invention, there is provided a data storage function for developing an image expressed by a drawing command into two-dimensional bitmap data and storing the data in a bitmap memory, and an image expressed by the drawing command. Object type information storage function for storing object type information in the object type information memory in association with each pixel of the image developed into the bitmap data, and feature quantity of the bitmap data stored in the bitmap memory The feature amount calculation function for calculating the feature amount, the feature amount of the bitmap data stored in the bitmap memory calculated by the feature amount calculation function, and the object type information of the target pixel stored in the object type information memory Therefore, the pixel of interest emphasizes sharpness or is a pixel that emphasizes graininess and gradation. A determination signal generation function for generating a threshold determination signal, and a quantization threshold is switched according to the threshold determination signal generated by the determination signal generation function, and the quantization error from the surrounding pixels of the target pixel is taken into account A computer is caused to execute a halftone processing function for performing quantization processing on bitmap data stored in the bitmap memory.

  An image processing method according to an eleventh aspect of the present invention is a data storage step of expanding an image expressed by a drawing command into two-dimensional bitmap data and storing the data in a bitmap memory, and the image processing method expressed by the drawing command. Object type information storage step for storing object type information of an image in the object type information memory in association with each pixel of the image developed into the bitmap data, and a target pixel stored in the object type information memory The quantization threshold is switched according to whether the object type information emphasizes sharpness, or emphasizes graininess / gradation, and the bitmap memory is added to the bitmap memory in consideration of the quantization error from the surrounding pixels of the target pixel. A halftone processing step of performing a quantization process on the stored bitmap data.

  According to a twelfth aspect of the present invention, there is provided an image processing method comprising: a data storage step of developing an image represented by a drawing command into two-dimensional bitmap data and storing the data in a bitmap memory; Object type information storing step of storing object type information of an image stored in the object type information memory in association with each pixel of the image developed into the bitmap data, and bitmap data stored in the bitmap memory A feature amount calculation step of calculating the feature amount of the image, a feature amount of the bitmap data stored in the bitmap memory calculated by the feature amount calculation step, and a target pixel stored in the object type information memory Based on the object type information, whether the pixel of interest emphasizes sharpness or an image that emphasizes graininess and gradation A threshold value determination signal for generating a threshold value determination signal and a threshold value determination signal generated by the determination signal generation step, and a quantization threshold value is switched. A halftone processing step of performing a quantization process on the bitmap data stored in the bitmap memory.

  According to a thirteenth aspect of the present invention, in the image processing method according to the twelfth aspect, the feature amount of the bitmap data calculated in the feature amount calculation step is an edge amount that is a value indicating an edge degree for each pixel. is there.

  The invention according to claim 14 is the image processing method according to claim 13, wherein in the feature amount calculation step, the object type information of the pixel of interest stored in the object type information memory emphasizes sharpness. Alternatively, the edge amount calculation method is switched according to whether the graininess / gradation is important.

  The invention according to claim 15 is the image processing method according to any one of claims 11 to 14, wherein in the halftone processing step, the object type information of the target pixel stored in the object type information memory is stored. Switching between at least the first quantization threshold and the second quantization threshold depending on whether sharpness is important or granularity / gradation is important, the first quantization threshold is: The threshold value has a constant value regardless of the pixel position and corresponds to the object type information that emphasizes sharpness, and the second quantization threshold value is a threshold value that vibrates periodically in the image space, and has granularity and gradation. It corresponds to the object type information that emphasizes the nature.

  According to a sixteenth aspect of the present invention, in the image processing method according to any one of the eleventh to fourteenth aspects, in the halftone processing step, the object type information of the pixel of interest stored in the object type information memory is stored. Switching between at least the first quantization threshold and the second quantization threshold depending on whether sharpness is important or granularity / gradation is important, the first quantization threshold is: Corresponding to object type information that is a threshold that periodically vibrates on the image space and emphasizes sharpness, the second quantization threshold is periodically larger in amplitude width on the image space than the first threshold. It corresponds to object type information that is a threshold value for vibration and emphasizes granularity and gradation.

  According to a seventeenth aspect of the present invention, in the image processing method according to any one of the eleventh to fourteenth aspects, in the halftone processing step, the object type information of the pixel of interest stored in the object type information memory is stored. Switching between at least the first quantization threshold and the second quantization threshold depending on whether sharpness is important or granularity / gradation is important, the first quantization threshold is: A threshold that periodically oscillates in the image space, corresponds to object type information that emphasizes sharpness, and the second quantization threshold is a threshold that oscillates periodically in the image space larger than the first threshold. It corresponds to object type information that places importance on graininess and gradation.

  According to the first aspect of the invention, in the halftone processing in the halftone processing means, the object type information of the pixel of interest stored in the object type information memory places importance on sharpness, or graininess / gradation The quantization threshold is switched according to whether or not importance is placed on the image, and quantization processing is performed in consideration of the quantization error from the surrounding pixels of the target pixel. As a result, even when the quantization threshold is switched based on the object type information, image quality deterioration does not occur at the switching portion between the area where the sharpness is to be emphasized and the area where the granularity / gradation is emphasized, and the sharpness is improved. Since it is possible to achieve both processing results suitable for the area that you want to emphasize and the area that you want to emphasize graininess and gradation, the character area, without image quality degradation, for input images that contain both characters and photos A processing result suitable for each photographic area can be obtained, and a processing result excellent in sharpness for a character area can be obtained even for small letters and low contrast characters.

  According to the invention of claim 2, in the halftone processing in the halftone processing means, the feature value of the bitmap data stored in the bitmap memory and the object of the target pixel stored in the object type information memory From the type information, a threshold determination signal is generated as to whether the pixel of interest is a pixel that emphasizes sharpness or a pixel that emphasizes graininess / gradation, and the quantization threshold is switched according to the generated threshold determination signal. At the same time, a quantization process is performed in consideration of quantization errors from pixels around the target pixel. Thereby, even when the quantization threshold is switched based on the object type information and the feature amount, image quality deterioration does not occur in a switching portion between an area where sharpness is important and an area where granularity / gradation is important, Since it is possible to achieve both processing results suitable for areas that want to emphasize sharpness and areas that want to emphasize graininess and gradation, there is no deterioration in image quality for input images that contain both text and photos. The processing result suitable for each of the character region and the photographic region can be obtained, and the processing result excellent in sharpness for the character region can be obtained even for small letters and low contrast characters.

  According to the invention of claim 3, the feature amount of the bitmap data calculated by the feature amount calculating means is an edge amount that is a value indicating the edge degree for each pixel, so that the object type information is imaged. Even in a region where it is preferable that the sharpness is preferable, such as a line or a character included in an image in the case of an object, there is an effect that processing that emphasizes sharpness can be performed.

  According to the invention of claim 4, the feature quantity calculating means emphasizes sharpness in the object type information of the target pixel stored in the object type information memory, or emphasizes graininess and gradation. By switching the edge amount calculation method according to whether or not the edge portion of a line, graph, or the like composed of a plurality of color plates can solve the problem of different thicknesses or colors depending on the plates. There is an effect.

  Further, according to the invention according to claim 5, there is an effect that it is possible to surely achieve both the processing results suitable for the area where the sharpness is important and the area where the graininess / gradation is important.

  Further, according to the invention of claim 6, there is an effect that it is possible to surely achieve both the processing results suitable for the area where the sharpness is important and the area where the graininess and gradation are important.

  Further, according to the invention of claim 7, there is an effect that it is possible to surely achieve both processing results suitable for the region where sharpness is important and the region where granularity / gradation is important.

  According to the eighth aspect of the present invention, an image is formed on a recording medium without causing image quality deterioration at a switching portion between a region where sharpness is important and a region where granularity / gradation is important. There is an effect that can be.

  According to the ninth aspect of the present invention, in the halftone processing in the halftone processing function, the object type information of the target pixel stored in the object type information memory places importance on sharpness, or the graininess / gradation level. The quantization threshold is switched according to whether tonality is important, and a quantization process is performed in consideration of quantization errors from pixels around the target pixel. As a result, even when the quantization threshold is switched based on the object type information, image quality deterioration does not occur at the switching portion between the area where the sharpness is to be emphasized and the area where the granularity / gradation is emphasized, and the sharpness is improved. Since it is possible to achieve both processing results suitable for the area that you want to emphasize and the area that you want to emphasize graininess and gradation, the character area, without image quality degradation, for input images that contain both characters and photos A processing result suitable for each photographic area can be obtained, and a processing result excellent in sharpness for a character area can be obtained even for small letters and low contrast characters.

  According to the invention of claim 10, in the halftone processing in the halftone processing function, the feature value of the bitmap data stored in the bitmap memory and the object of the pixel of interest stored in the object type information memory From the type information, a threshold determination signal is generated as to whether the pixel of interest is a pixel that emphasizes sharpness or a pixel that emphasizes graininess / gradation, and the quantization threshold is switched according to the generated threshold determination signal. At the same time, a quantization process is performed in consideration of quantization errors from pixels around the target pixel. Thereby, even when the quantization threshold is switched based on the object type information and the feature amount, image quality deterioration does not occur in a switching portion between an area where sharpness is important and an area where granularity / gradation is important, Since it is possible to achieve both processing results suitable for areas that want to emphasize sharpness and areas that want to emphasize graininess and gradation, there is no deterioration in image quality for input images that contain both text and photos. The processing result suitable for each of the character region and the photographic region can be obtained, and the processing result excellent in sharpness for the character region can be obtained even for small letters and low contrast characters.

  According to the invention of claim 11, in the halftone processing in the halftone processing step, the object type information of the target pixel stored in the object type information memory places importance on sharpness, or the graininess / gradation level. The quantization threshold is switched according to whether tonality is important, and a quantization process is performed in consideration of quantization errors from pixels around the target pixel. As a result, even when the quantization threshold is switched based on the object type information, image quality deterioration does not occur at the switching portion between the area where the sharpness is to be emphasized and the area where the granularity / gradation is emphasized, and the sharpness is improved. Since it is possible to achieve both processing results suitable for the area that you want to emphasize and the area that you want to emphasize graininess and gradation, the character area, without image quality degradation, for input images that contain both characters and photos A processing result suitable for each photographic area can be obtained, and a processing result excellent in sharpness for a character area can be obtained even for small letters and low contrast characters.

  According to the invention of claim 12, in the halftone processing in the halftone processing step, the feature amount of the bitmap data stored in the bitmap memory and the object of the pixel of interest stored in the object type information memory From the type information, a threshold determination signal is generated as to whether the pixel of interest is a pixel that emphasizes sharpness or a pixel that emphasizes graininess / gradation, and the quantization threshold is switched according to the generated threshold determination signal. At the same time, a quantization process is performed in consideration of quantization errors from pixels around the target pixel. Thereby, even when the quantization threshold is switched based on the object type information and the feature amount, image quality deterioration does not occur in a switching portion between an area where sharpness is important and an area where granularity / gradation is important, Since it is possible to achieve both processing results suitable for areas that want to emphasize sharpness and areas that want to emphasize graininess and gradation, there is no deterioration in image quality for input images that contain both text and photos. The processing result suitable for each of the character region and the photographic region can be obtained, and the processing result excellent in sharpness for the character region can be obtained even for small letters and low contrast characters.

  According to the thirteenth aspect of the present invention, the feature amount of the bitmap data calculated in the feature amount calculation step is an edge amount that is a value indicating the edge degree for each pixel, so that the object type information is an image. Even in a region where it is preferable that the sharpness is preferable, such as a line or a character included in an image in the case of an object, there is an effect that processing that emphasizes sharpness can be performed.

  According to the fourteenth aspect of the present invention, in the feature amount calculation step, the object type information of the target pixel stored in the object type information memory emphasizes sharpness, or emphasizes graininess and gradation. By switching the edge amount calculation method according to whether or not the edge portion of a line, graph, or the like composed of a plurality of color plates can solve the problem of different thicknesses or colors depending on the plates. There is an effect.

  Further, according to the fifteenth aspect of the present invention, there is an effect that it is possible to surely achieve both the processing results suitable for the region where sharpness is important and the region where granularity / gradation is important.

  Further, according to the sixteenth aspect of the present invention, there is an effect that it is possible to surely achieve both processing results suitable for the region where sharpness is important and the region where granularity / gradation is important.

  According to the seventeenth aspect of the invention, there is an effect that it is possible to surely achieve both the processing results suitable for the region where sharpness is important and the region where granularity / gradation is important.

  Exemplary embodiments of an image processing apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. This embodiment shows an example in which the present invention is applied to a monochrome laser printer as an image processing apparatus.

  FIG. 1 is a schematic diagram showing a construction example of a printing system according to the first embodiment of the present invention. The printing system according to the present embodiment assumes a system in which a plurality of computers 1 are connected to a monochrome laser printer P1 that is an image processing apparatus via a network N such as a LAN (Local Area Network). The digital document data created in (1) is transmitted to the monochrome laser printer P1 via the network N, and the transmitted digital document data is output as a hard copy from the monochrome laser printer P1.

  First, the computer 1 will be briefly described. The computer 1 is a general or standard personal computer, and as an application program operating on an operating system (OS), word processor software such as Microsoft Word (registered trademark) or Adobe page maker (registered trademark). The printer driver for controlling the monochrome laser printer P1 is stored in the HDD (not shown) in order to perform printing in accordance with the print instructions of the page layout software, word processor software and page layout software.

  Digital document data created by word processor software or page layout software is transferred to a printer driver via an operating system (OS). Digital document data delivered to the printer driver is generally a PDL command (rendering command) corresponding to document contents described in a page description language (PDL). This PDL command is usually composed of the following three types of objects. There are three types: a character object indicating a character, a graphic object indicating an electronic image that can be described by vector information such as a line, a graph, a figure, and a gradation, and an image object indicating a natural image such as a photograph read by a scanner or the like. The page description language (PDL) is a language processing system or printer control code designed for the purpose of describing data for printer output in a format independent of only a specific printer. Typical page description languages (PDL) include GDI (registered trademark) and Postscript (registered trademark).

  The printer driver that has received the PDL command transmits the PDL command to the monochrome laser printer P1 via the network N.

  Next, a schematic configuration example of the control system of the monochrome laser printer P1 will be described with reference to the block diagram shown in FIG. As this control system, a CPU (Central Processing Unit) 13 constituting a microcomputer is provided together with a ROM (Read Only Memory) 11 and a RAM (Random Access Memory) 12. In accordance with a control program stored in the ROM 11, the CPU 13 starts driving control of a paper transport motor 14 and a printer engine 15 which is an image forming means for forming an image on a recording medium by a known electrophotographic method. Responsible for overall control of the monochrome laser printer P1. The RAM 12 is used as a work area (for example, a bitmap memory 22 or an object type information memory 23 (see FIG. 3)) for temporarily storing data necessary for performing various processes. The ROM 11 stores an image processing program and other various programs. Further, via the I / O interface 16, the motor 14 and the printer engine 15 and other input / output devices necessary for controlling the monochrome laser printer P1 are connected. The CPU 13, ROM 11, RAM 12, and I / O interface 16 are connected by an address bus 17 and a data bus 18, and perform address designation and data input / output.

  FIG. 3 is a block diagram showing a functional configuration of the monochrome laser printer P1. As shown in FIG. 3, in the monochrome laser printer P1, the CPU 13 follows the image processing program stored in the ROM 11, so that the PDL interpretation means 21, the bitmap memory 22, the object type information memory 23, and the halftone process Means 24 are implemented.

  The PDL interpretation means 21 interprets the contents of characters, lines, figures, photographs, etc. expressed by the PDL commands transmitted from the printer driver of the computer 1, converts them into two-dimensional bitmap data, and converts the characters, figures, etc. Each module of the page components is rasterized in accordance with the output size in page units and temporarily stored in the bitmap memory 22 (data storage means). At the same time, the PDL interpretation unit 21 obtains object type information indicating whether the image represented by the PDL command is a character object, a graphic object, or an image object for each pixel of the image expanded into bitmap data. And is temporarily stored in the object type information memory 23 (object type information storage means). An image expressed by a PDL command can be easily distinguished by a command whether it is a character object, a graphic object, or an image object.

  The halftone processing means 24 receives the bitmap data stored in the bitmap memory 22 as input image data, selects a quantization threshold based on the object type information received from the object type information memory 23, and reduces the small value. Process.

  Here, the configuration and operation of the halftone processing means 24 will be described in detail with reference to FIG. As shown in FIG. 4, the halftone processing unit 24 includes a threshold selection unit 31, a corrected input value calculation unit 32, an output gradation value determination unit 33, an error calculation unit 34, an error buffer 35, and an error sum. It is comprised with the calculation part 36. FIG.

  In the threshold selection unit 31, based on the object type information received from the object type information memory 23, when the target pixel is a character object, that is, when it is desirable to perform processing that emphasizes resolution (sharpness), When it is desirable to use a fixed threshold value that does not change the threshold value depending on the pixel position of the pixel and the target pixel is a graphic object or an image object, that is, it is desirable to perform processing that emphasizes graininess and gradation, as shown in FIG. Quantization is determined using the threshold matrix M1 and the determined threshold information is sent to the output tone value determination unit 33.

  In the corrected input value calculation unit 32, a corrected input that is the sum of the pixel data of the pixel of interest in the input image data received from the bitmap memory 22 and the error sum of the surrounding pixels obtained from the error sum calculation unit 36 described later. The value is calculated and sent to the output tone value determination unit 33 in the subsequent stage.

  In the output tone value determination unit 33, the magnitude relationship between the threshold value corresponding to the target pixel from the threshold value information (fixed threshold value or threshold value matrix M1) received from the threshold value selection unit 31 and the corrected input value received from the corrected input value calculation unit 32. Are compared to determine the output gradation value.

  Here, a processing example when the threshold selection unit 31 determines to use a fixed threshold will be described. In this embodiment, both the input gradation value and the output gradation value take integer values from “0” to “255”, with “0” having the lowest density and “255” having the highest density. To do. When the threshold selection unit 31 determines to use a fixed threshold, for example, the threshold for determining whether to output a dot corresponding to the output gradation value “255” is set to “128”, and the correction input of the target pixel is performed. If the value is “128” or less, the output gradation value is “0”, and if the corrected input value of the target pixel is greater than “128”, the output gradation value is “255”.

  Next, a processing example when the threshold selection unit 31 determines to use the threshold matrix M1 shown in FIG. 5 will be described. A threshold value matrix M1 shown in FIG. 5 is a threshold value for determining whether or not to output a dot corresponding to the output gradation value “255”, and represents a halftone dot screen of about 212 lines and 45 degrees at an output resolution of 600 dpi. It is a threshold value matrix for binary output. The position corresponding to the target pixel on the threshold matrix is determined depending on which position in the threshold matrix the target pixel corresponds to when the output image size is repeatedly tiled. That is, when the threshold matrix size is horizontal w pixels and vertical h pixels, the target pixel at the horizontal X and vertical Y positions in the output image coordinates is horizontal (X-mw) and vertical ( Y−nh) position threshold is used. Here, n and m are numbers with the smallest coordinates. In the threshold value matrix M1 shown in FIG. 5, w = h = 4. For example, for an attention pixel in which (X, Y) = (9, 6) in the output image coordinates, (x, y) = Output pixel value is obtained using the threshold value at the position of (1, 2). That is, if the corrected input value of the target pixel is equal to or less than the threshold value “176” for determining whether or not to output a dot corresponding to the output gradation value “255”, the output gradation value is “0”, “176”. If it is larger, the output gradation value is “255”.

  The error calculation unit 34 calculates a value obtained by subtracting the output tone value determined by the output tone value determination unit 33 from the corrected input value calculated by the correction input value calculation unit 32 as a quantization error value, and calculates the calculated quantum value. The error value is stored in the error buffer 35.

  On the other hand, the error sum calculation unit 36 calculates the sum of errors related to the target pixel using an error matrix M2 as shown in FIG. In FIG. 6, the position indicated by “x” means the target pixel. For example, if the quantization error value of the pixel immediately above the target pixel is “32”, the value corresponding to that pixel in the error matrix M2 shown in FIG. 6 is “4/32”. The error value related to the pixel of interest from that pixel is 4 which is the product of both. In this way, the quantization error values of a total of 17 pixels, that is, 7 pixels on 2 lines, 7 pixels on 1 line, and 3 pixels on the same line, are read from the error buffer 35 for one pixel of interest, and FIG. An error sum related to the pixel of interest is calculated by performing a product-sum operation with the error matrix M2 shown, and the error sum is sent to the corrected input value calculation unit 32. The error matrix M2 shown in FIG. 6 is designed to be “1” when all elements are added. This is because the generated error value is used in surrounding pixels without excess or deficiency.

  In order to calculate the error value, an error matrix M3 as shown in FIG. 7 may be used. The error matrix M3 shown in FIG. 7 is obtained by multiplying each value in the error matrix M2 shown in FIG. 6 by 32 times. For example, when the quantization error value of a pixel immediately above the target pixel is “32”, the value corresponding to that pixel in the error matrix M3 shown in FIG. 7 is “4”. Therefore, the error value related to the pixel of interest is “128” which is the product of both. In this manner, the quantization error values of a total of 17 pixels, that is, 7 pixels on 2 lines, 7 pixels on 1 line, and 3 pixels on the same line, are read from the error buffer 35 for one pixel of interest. An error sum related to the pixel of interest is calculated by performing an operation with the error matrix M3 shown. By adopting such a method, it is possible to calculate a sum of errors related to the pixel of interest by high-speed shift calculation or integer calculation. Thereafter, since each value in the error matrix is multiplied by 32, the error sum is divided by 32.

  The above is the description of the configuration and operation of the halftone processing means 24. In the halftone processing in the halftone processing means 24 as described above, the quantization processing is performed in consideration of the quantization error from the surrounding pixel of the target pixel. Therefore, even when the threshold value is switched based on the object type information, the sharpness is emphasized. The image quality deterioration does not occur at the switching portion between the desired area and the area where the graininess and gradation are important.

  The data that has been reduced in value by the halftone processing unit 24 in this manner is then sent to the printer engine 15 where image formation on the storage medium in the printer engine 15 is executed.

  As described above, according to the present embodiment, in the halftone processing in the halftone processing means 24, the object type information of the target pixel stored in the object type information memory 23 places importance on sharpness, or the graininess / The quantization threshold is switched depending on whether the gradation is important, and a quantization process is performed in consideration of quantization errors from pixels around the target pixel. As a result, even when the quantization threshold is switched based on the object type information, image quality deterioration does not occur at the switching portion between the area where the sharpness is to be emphasized and the area where the granularity / gradation is important, and the sharpness Since it is possible to achieve both processing results suitable for the area that you want to emphasize and the area that you want to emphasize graininess and gradation, the character area, without image quality degradation, for input images that contain both characters and photos A processing result suitable for each photographic area can be obtained, and a processing result excellent in sharpness for a character area can be obtained even for small letters and low contrast characters.

  In this case, the halftone processing means 24 at least in accordance with whether the object type information of the target pixel stored in the object type information memory 23 emphasizes sharpness, or emphasizes graininess / gradation. The first quantization threshold (fixed threshold) and the second quantization threshold (threshold matrix M1) are switched and applied, and the first quantization threshold (fixed threshold) has a constant value regardless of the pixel position. And the second quantization threshold (threshold matrix M1) is a threshold that periodically vibrates in the image space, and object type information that places importance on graininess and gradation. Corresponding to

In the present embodiment, the output gradation value of the fixed threshold value in the output gradation value determining unit 33 of the halftone processing unit 24 has an example in which one of the binary values “0” and “255” is taken. However, the configuration based on the present invention is not limited to this. For example, a configuration having multi-value output gradation values such as three-value, four-value, eight-value, and sixteen-value may be used. For example, in the case of four-value output, the adjustment value may be any one of unequal values such as “0”, “128”, “192”, and “255”. Further, in the case of performing quantization using a threshold matrix, the present embodiment shows an example in which the output gradation value takes one of two values “0” and “255”. For example, a threshold matrix for determining whether or not to output dots corresponding to output gradation values “85”, “170”, and “255” in the case of quaternary output. The
(1) For output gradation value “255” (2) For output gradation value “170” (3) Prepare a total of three sheets for output gradation value “85”, respectively (1) → (2 ) → (3) in order from the threshold matrix corresponding to the larger output gradation value, the corresponding output gradation value may be output when the corrected input value of the pixel of interest is greater than or equal to the threshold value.

  In the present embodiment, the threshold value selection unit 31 of the halftone processing unit 24 uses the object type information received from the object type information memory 23, and emphasizes sharpness when the pixel of interest is a character object. An example is shown in which a fixed threshold that does not change the threshold depending on the position is used, and quantization is performed using a threshold matrix that emphasizes gradation when the pixel of interest is a graphic object or an image object. There is no need. For example, in the case of graphic objects such as lines and graphs, it may be preferable to emphasize sharpness. Therefore, a fixed threshold is used for character objects and graphic objects, and a threshold matrix is used only for image objects. It is good also as a combination. Which combination is adopted can be output to the user by providing the user with a place of choice on the printer driver of the computer 1 or a panel (not shown) provided in the monochrome laser printer P1. It becomes.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. The same parts as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is also omitted.

  In the threshold selection unit 31 of the halftone processing unit 24 in the first embodiment, the pixel of interest performs processing that places importance on resolution (sharpness) based on the object type information received from the object type information memory 23. When is desirable, a fixed threshold value that does not change the threshold value depending on the pixel position of the target pixel is used. On the other hand, in the present embodiment, when it is desirable that the pixel of interest performs processing focusing on resolution (sharpness) based on the object type information received from the object type information memory 23, FIG. The point that the threshold value matrix M4 as shown in FIG. 6 is used is different from the first embodiment described above.

  The threshold value matrix M4 shown in FIG. 8 is a threshold value matrix having a smaller dither amplitude width than the threshold value matrix M1 shown in FIG. By reducing the dither amplitude width in this way, when quantization is performed, the threshold matrix M4 can improve resolution (sharpness) compared to the threshold matrix M1.

  That is, in the threshold selection unit 31, based on the object type information received from the object type information memory 23, when the target pixel is a character object, that is, when it is desirable to perform processing that emphasizes resolution (sharpness). , It is desirable to perform quantization using a threshold value matrix M4 as shown in FIG. 8, and when the pixel of interest is a graphic object or an image object, that is, it is desirable to perform processing that places importance on graininess and gradation. In this case, it is determined that the quantization is performed using the threshold value matrix M1 as shown in FIG. 5, and the determined threshold value information (threshold value matrix M4 or threshold value matrix M1) is sent to the output gradation value determining unit 33.

  As described above, in the case of switching between the threshold matrixes M4 and M1 having different dither amplitudes based on the object type information received from the object type information memory 23, the pixel of interest is the same as in the first embodiment. Since quantization processing is performed taking into account quantization errors from surrounding pixels, image quality deterioration does not occur at the switching section between areas where resolution (sharpness) is important and areas where granularity and gradation are important. .

  As described above, according to the present embodiment, in the halftone processing in the halftone processing means 24, the object type information of the target pixel stored in the object type information memory 23 places importance on sharpness, or the graininess / The quantization threshold is switched depending on whether the gradation is important, and a quantization process is performed in consideration of quantization errors from pixels around the target pixel. As a result, even when the quantization threshold is switched based on the object type information, image quality deterioration does not occur at the switching portion between the area where the sharpness is to be emphasized and the area where the granularity / gradation is important, and the sharpness Since it is possible to achieve both processing results suitable for the area that you want to emphasize and the area that you want to emphasize graininess and gradation, the character area, without image quality degradation, for input images that contain both characters and photos A processing result suitable for each photographic area can be obtained, and a processing result excellent in sharpness for a character area can be obtained even for small letters and low contrast characters.

  Here, the halftone processing means 24 at least in accordance with whether the object type information of the target pixel stored in the object type information memory 23 emphasizes sharpness, or emphasizes graininess / gradation. The first quantization threshold (threshold matrix M4) and the second quantization threshold (threshold matrix M1) are switched and applied, and the first quantization threshold (threshold matrix M4) periodically oscillates in the image space. The second quantization threshold (threshold matrix M1) is a threshold that is a threshold and vibrates periodically with a larger amplitude width in the image space than the first threshold. This corresponds to the object type information that emphasizes the characteristics and gradation.

  In the present embodiment, the threshold matrixes M4 and M1 having different dither amplitude widths are switched and used so that processing that emphasizes resolution (sharpness) and processing that emphasizes graininess and gradation are compatible. However, it is not necessary to limit the switching to the dither amplitude. For example, a threshold value matrix M5 as shown in FIG. 9 may be used instead of the threshold value matrix M4 as shown in FIG. The threshold value matrix M5 shown in FIG. 9 has the same dither amplitude as the threshold value matrix M1 shown in FIG. 5, but has a smaller matrix size. By reducing the matrix size in this way, when quantization is performed, the threshold value matrix M5 can improve resolution (sharpness) as compared with the threshold value matrix M1, so that threshold values having different matrix sizes can be obtained. The same purpose can be achieved by switching between the matrices M5 and M1.

  Here, the halftone processing means 24 at least in accordance with whether the object type information of the target pixel stored in the object type information memory 23 emphasizes sharpness, or emphasizes graininess / gradation. The first quantization threshold (threshold matrix M5) and the second quantization threshold (threshold matrix M1) are switched and applied, and the first quantization threshold (threshold matrix M5) periodically oscillates in the image space. The second quantization threshold value (threshold value matrix M1) is a threshold value that periodically vibrates in an image space larger than the first threshold value, and corresponds to object type information that emphasizes sharpness. Corresponds to object type information that emphasizes tonality.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIGS. The same parts as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is also omitted.

  In the halftone processing unit 24 of the first embodiment, the bitmap data stored in the bitmap memory 22 is received as input image data, and a threshold value is determined based on the object type information received from the object type information memory 23. The selection was made and the value reduction process was performed. On the other hand, the present embodiment is different from the first embodiment described above in that the threshold value is selected in consideration of the edge amount calculated from the input image data received from the bitmap memory 22. Is.

  FIG. 10 is a block diagram illustrating a functional configuration of a monochrome laser printer P1 according to the third embodiment. As shown in FIG. 10, in the monochrome laser printer P1, the CPU 13 follows the image processing program stored in the ROM 11, so that the PDL interpretation means 21, the bitmap memory 22, the object type information memory 23, and the halftone process Means 24, edge amount calculation means 25, and determination signal generation means 26 are realized.

  First, the edge amount calculation means 25 will be described. The edge amount calculation unit 25 functions as a feature amount calculation unit. In general, the edge amount calculation unit 25 receives bitmap data stored in the bitmap memory 22 as input image data, and receives edge data from the received input image data. Calculate the amount.

  Here, the configuration and operation of the edge amount calculation means 25 will be described in detail with reference to FIG. As shown in FIG. 11, the edge amount calculation means 25 includes a primary differential filter unit 41, an absolute value calculation unit 42, and a maximum value selection unit 43.

  The primary differential filter unit 41 performs a primary differential filter operation on the input image data received from the bitmap memory 22. More specifically, the first-order differential filter unit 41 uses the first-order differential filters 1001 to 1004 shown in FIG. To obtain four types of primary differential values and send them to the absolute value calculator 42.

  The absolute value calculator 42 calculates the absolute value of the primary differential value received from the primary differential filter unit 41 and sends it to the maximum value selector 43.

  The maximum value selection unit 43 sends the maximum value among the absolute values of the four types of primary differential values received from the absolute value calculation unit 42 to the next determination signal generation unit 26 as the edge amount of the target pixel.

  Next, the determination signal generation unit 26 will be described. The determination signal generation unit 26 inputs the object type information received from the object type information memory 23 and the edge amount calculated by the edge amount calculation unit 25 from the input image data received from the bitmap memory 22. A threshold value determination signal indicating whether resolution (sharpness) is important or a pixel that emphasizes graininess / gradation is generated, and the generated threshold determination signal is sent to the halftone processing unit 24. FIG. 13 is an explanatory diagram illustrating an example of a method for generating a threshold determination signal. As shown in FIG. 13, when the edge amount is equal to or greater than a predetermined value (th1) or the object type information is a character object, emphasis is placed on resolution (sharpness). Generate a threshold determination signal for emphasizing gradation.

  Then, the threshold selection unit 31 of the halftone processing unit 24 determines a threshold used for quantization based on the threshold determination signal received from the determination signal generation unit 26. For example, when a threshold determination signal emphasizing resolution (sharpness) is received, a threshold emphasizing resolution (sharpness) such as a fixed threshold is used to receive a signal emphasizing graininess and gradation. In such a case, it is determined to use a threshold value that emphasizes graininess and gradation, such as a threshold matrix. Subsequent processing is the same as in the first embodiment.

  As described above, according to the present embodiment, the threshold value is switched based not only on the object type information but also on the edge amount calculated from the input image data, so that the resolution based on the object type information is achieved. While realizing both processing that emphasizes (sharpness) and processing that emphasizes graininess and gradation, image quality deterioration does not occur at the switching part between them, and at the same time, for example, the object type information is an image object Even in a region where better sharpness is preferable, such as a line or a character included in an image in the case, processing that emphasizes resolution (sharpness) can be performed.

  In this embodiment, the determination signal generation unit 26 performs a binary determination as to whether or not the edge amount sent from the edge amount calculation unit 25 is equal to or greater than a certain value (th1). In particular, it is not necessary to make a binary determination, and a plurality of threshold values such as th1, th2, th3,... Are prepared, and as a multilevel determination, the threshold determination signal is not binary but multilevel data. May be output to the threshold selection unit 31 of the halftone processing means 24. In this case, when the edge amount is determined to be greater than or equal to the largest threshold value, or when the object type information is determined to be a character object, the threshold determination signal is emphasized with the highest resolution (sharpness). It is natural to generate a signal to that effect.

  In the present embodiment, the edge amount is calculated based on the first-order differential value. However, the present invention is not limited to this. For example, for the purpose of detecting the inside of the thin line, the filters 1001 to 1004 shown in FIG. Instead, a secondary differential filter is used, a feature amount is calculated based on the magnitude of the input gradation value to determine whether it is foreground or background, or a feature amount is calculated using a combination of these. There may be.

  In the present embodiment as well, as in the first embodiment, the output gradation value when a fixed threshold is used and the output gradation value when a threshold matrix is used are not necessarily binary. Multi-valued. In addition, it is not always necessary to limit only the character object to processing that emphasizes resolution (sharpness), and the character object and graphic object may be processed to emphasize resolution (sharpness).

(Fourth embodiment)
A fourth embodiment of the present invention will be described with reference to FIGS. The same parts as those in the first to third embodiments described above are denoted by the same reference numerals, and description thereof is also omitted.

  In the first to third embodiments, the monochrome laser printer P1 is assumed as the image processing apparatus. However, in the present embodiment, the color laser printer P2 is assumed as the image processing apparatus. However, assuming that both the image data and the image forming apparatus have a plurality of colors, the halftone processing in the halftone processing unit 24 described in the third embodiment is performed only for the data color plate of the output image. Will be implemented. For example, when the color laser printer P2 is a CMYK printer, any one of C, M, Y, and K4 color data is used as input image data, and the edge amount calculation unit 25 calculates the edge amount for the corresponding color. The color is output up to monochromatic image data, and finally all colors are superimposed in the color laser printer P2. When such a configuration is adopted, for example, when a red line is processed, the M plate has a large edge amount and processing that emphasizes resolution (sharpness) is performed, and the Y plate has a large edge amount. In some cases, different processing methods are performed, such as processing that places importance on graininess and gradation. As a result, the thickness of the line between the M plate and the Y plate is different, and the color may be reproduced with a color different from the desired color. Therefore, in the present embodiment, a color laser printer P2 is assumed as an image processing apparatus, and such a problem is solved.

  FIG. 14 is a block diagram illustrating a functional configuration of a color laser printer P2 according to the fourth embodiment. As shown in FIG. 14, in the color laser printer P2, the CPU 13 follows the image processing program stored in the ROM 11, so that the PDL interpretation means 21, the bitmap memory 22, the object type information memory 23, the halftone process Means 24 and edge amount calculation means 40 are realized.

  In the third embodiment, the threshold determination signal is generated based on the object type information received from the object type information memory 23 and the edge amount calculated by the edge amount calculating means 25 from the input image data received from the bitmap memory 22. The threshold value used for quantization is determined based on the threshold value determination signal generated by the determination signal generation unit 26 and generated by the determination signal generation unit 26. On the other hand, in the present embodiment, as shown in FIG. 14, while referring to the object type information received from the object type information memory 23, from the input image data received from the bitmap memory 22 by the edge amount calculation means 40. The edge amount is calculated, and the halftone processing unit 24 determines a threshold value used for quantization based on the calculated edge amount. Here, the edge amount calculation means 40 of the present embodiment is different from the edge amount calculation means 25 of the third embodiment in that the edge amount calculation method is switched depending on the object type information. Hereinafter, a method of switching the edge amount calculation method in the edge amount calculation means 40 will be described.

  When the object type information received from the object type information memory 23 is a character object or a graphic object, the edge amount calculating means 40 of this embodiment, as shown in FIG. 15, C, M, Y, K After calculating the edge amount for each color, the maximum value of the edge amount calculated for each color is extracted. The maximum edge amount extracted in this way is used as the edge amount of each color, and is sent to the determination signal generation means 26. In the determination signal generation unit 26, a threshold determination signal is generated based on the maximum edge amount extracted by the edge amount calculation unit 40 and sent to the threshold selection unit 31 for each color of the halftone processing unit 24.

  On the other hand, when the object type information received from the object type information memory 23 is an image object, the edge amount calculation means 40 has an edge amount for each color of C, M, Y, and K as shown in FIG. The calculated edge amount for each color is directly used as the edge amount for each color as it is, and is sent to the determination signal generating means 26. In the determination signal generation unit 26, a threshold determination signal is generated based on the edge amount for each color of C, M, Y, and K calculated by the edge amount calculation unit 40, and for each color of the halftone processing unit 24. Each is sent to the threshold selection unit 31.

  As described above, the edge amount calculation means 40 switches the edge amount calculation method according to the object type information received from the object type information memory 23, so that the edge portion such as a line or graph composed of a plurality of color plates can be used. , You can solve the problem of different thickness and color.

  The programs executed by the monochrome laser printer P1 and the color laser printer P2 that are the image processing apparatuses according to the embodiments are provided in the ROM 11 in advance. However, the present invention is not limited to this. The file may be recorded in a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD as a file in an executable format or an executable format.

  Furthermore, the programs executed by the monochrome laser printer P1 and the color laser printer P2 that are the image processing apparatuses according to the embodiments are stored on a computer connected to a network such as the Internet, and are provided by being downloaded via the network. You may comprise so that it may do. The program executed by the monochrome laser printer P1 or the color laser printer P2 that is the image processing apparatus of each embodiment may be provided or distributed via a network such as the Internet.

It is a schematic diagram which shows the construction example of the printing system concerning the 1st Embodiment of this invention. FIG. 2 is a block diagram illustrating a schematic configuration example of a printer control system. It is a block diagram which shows the function structure of a monochrome laser printer. It is a block diagram which shows a structure and operation | movement of a halftone processing means. It is a schematic diagram which shows the threshold value matrix M1. It is a schematic diagram which shows the error matrix M2. It is a schematic diagram which shows the error matrix M3. It is a schematic diagram which shows the threshold value matrix M4 concerning the 2nd Embodiment of this invention. It is a schematic diagram which shows the threshold value matrix M5. It is a block diagram which shows the function structure of the monochrome laser printer concerning the 3rd Embodiment of this invention. It is a block diagram which shows a structure and operation | movement of an edge amount calculation means. It is a schematic diagram which shows a primary differential filter. It is explanatory drawing which shows an example of the production | generation method of a threshold determination signal. It is a block diagram which shows the function structure of the color laser printer concerning the 4th Embodiment of this invention. It is explanatory drawing which shows the edge amount calculation method in the edge amount calculation means in case object type information is a character object or a graphic object. It is explanatory drawing which shows the edge amount calculation method in the edge amount calculation means in case object type information is an image object.

Explanation of symbols

22 Bit map memory 23 Object type information memory 24 Halftone processing means 25 Feature quantity calculating means 26 Determination signal generating means P1, P2 Image processing device

Claims (17)

Data storage means for expanding an image represented by a drawing command into two-dimensional bitmap data and storing it in a bitmap memory;
Object type information storage means for storing object type information of an image expressed by a drawing command in an object type information memory in association with each pixel of the image developed into the bitmap data;
The quantization threshold is switched according to whether the object type information of the pixel of interest stored in the object type information memory emphasizes sharpness, or emphasizes graininess / gradation, and Halftone processing means for performing quantization processing on the bitmap data stored in the bitmap memory in consideration of quantization error;
An image processing apparatus comprising: Data storage means for expanding an image represented by a drawing command into two-dimensional bitmap data and storing it in a bitmap memory;
Object type information storage means for storing object type information of an image expressed by a drawing command in an object type information memory in association with each pixel of the image developed into the bitmap data;
A feature amount calculating means for calculating a feature amount of bitmap data stored in the bitmap memory;
The attention pixel emphasizes sharpness from the feature amount of the bitmap data stored in the bitmap memory calculated by the feature amount calculation means and the object type information of the attention pixel stored in the object type information memory. Determination signal generating means for generating a threshold determination signal as to whether the pixel is a pixel with emphasis on graininess and gradation,
Quantization processing for the bitmap data stored in the bitmap memory taking into account the quantization error from the surrounding pixels of the pixel of interest by switching the quantization threshold according to the threshold determination signal generated by the determination signal generation means Halftone processing means for performing
An image processing apparatus comprising: The feature amount of the bitmap data calculated by the feature amount calculating means is an edge amount that is a value indicating the edge degree for each pixel.
The image processing apparatus according to claim 2. The feature amount calculation means uses an edge amount calculation method according to whether the object type information of the target pixel stored in the object type information memory emphasizes sharpness, or emphasizes graininess and gradation. Switch,
The image processing apparatus according to claim 3. The halftone processing means includes at least the first quantum depending on whether the object type information of the target pixel stored in the object type information memory emphasizes sharpness, or emphasizes graininess / gradation. The first quantization threshold is a threshold having a constant value regardless of the pixel position and corresponds to object type information that emphasizes sharpness, The second quantization threshold is a threshold that periodically oscillates in the image space, and corresponds to object type information that emphasizes granularity and gradation.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. The halftone processing means includes at least the first quantum depending on whether the object type information of the target pixel stored in the object type information memory emphasizes sharpness, or emphasizes graininess / gradation. The first quantization threshold is a threshold that periodically oscillates in the image space, corresponds to object type information that places importance on sharpness, and is applied to the first quantization threshold and the second quantization threshold. The quantization threshold of 2 is a threshold that periodically vibrates with a larger amplitude width in the image space than the first threshold, and corresponds to object type information that places importance on graininess and gradation.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. The halftone processing means includes at least the first quantum depending on whether the object type information of the target pixel stored in the object type information memory emphasizes sharpness, or emphasizes graininess / gradation. The first quantization threshold is a threshold that periodically oscillates in the image space, corresponds to object type information that places importance on sharpness, and is applied to the first quantization threshold and the second quantization threshold. The quantization threshold of 2 is a threshold that periodically oscillates in an image space larger than the first threshold, and corresponds to object type information that places importance on granularity and gradation.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. Image forming means for forming an image based on the bitmap data quantized by the halftone processing means on a recording medium;
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. A data storage function for expanding an image represented by a drawing command into two-dimensional bitmap data and storing the data in a bitmap memory;
An object type information storage function for storing object type information of an image expressed by a rendering command in an object type information memory in association with each pixel of the image developed into the bitmap data;
The quantization threshold is switched according to whether the object type information of the pixel of interest stored in the object type information memory emphasizes sharpness, or emphasizes graininess / gradation, and A halftone processing function for performing quantization processing on bitmap data stored in the bitmap memory in consideration of quantization error;
A program that causes a computer to execute. A data storage function for expanding an image represented by a drawing command into two-dimensional bitmap data and storing the data in a bitmap memory;
An object type information storage function for storing object type information of an image expressed by a rendering command in an object type information memory in association with each pixel of the image developed into the bitmap data;
A feature amount calculation function for calculating a feature amount of bitmap data stored in the bitmap memory;
The attention pixel emphasizes sharpness from the feature amount of the bitmap data stored in the bitmap memory calculated by the feature amount calculation function and the object type information of the attention pixel stored in the object type information memory. A determination signal generation function for generating a threshold determination signal as to whether the pixel is a pixel with emphasis on graininess or gradation, and
Quantization processing for bitmap data stored in the bitmap memory by switching the quantization threshold according to the threshold determination signal generated by the determination signal generation function and taking into account the quantization error from the surrounding pixels of the target pixel Halftone processing function
A program that causes a computer to execute. A data storage step of expanding an image represented by a drawing command into two-dimensional bitmap data and storing the data in a bitmap memory;
An object type information storage step of storing object type information of an image expressed by a drawing command in an object type information memory in association with each pixel of the image developed into the bitmap data;
The quantization threshold is switched according to whether the object type information of the pixel of interest stored in the object type information memory emphasizes sharpness, or emphasizes graininess / gradation, and A halftone processing step for performing quantization processing on the bitmap data stored in the bitmap memory in consideration of quantization error;
An image processing method comprising: A data storage step of expanding an image represented by a drawing command into two-dimensional bitmap data and storing the data in a bitmap memory;
An object type information storage step of storing object type information of an image expressed by a drawing command in an object type information memory in association with each pixel of the image developed into the bitmap data;
A feature amount calculating step of calculating a feature amount of bitmap data stored in the bitmap memory;
The pixel of interest emphasizes sharpness from the feature amount of the bitmap data stored in the bitmap memory calculated in the feature amount calculation step and the object type information of the pixel of interest stored in the object type information memory. A determination signal generation step for generating a threshold determination signal as to whether the pixel is a pixel with emphasis on graininess or gradation,
Quantization processing for the bitmap data stored in the bitmap memory taking into account the quantization error from the surrounding pixels of the pixel of interest by switching the quantization threshold according to the threshold determination signal generated by this determination signal generation step A halftone processing step,
An image processing method comprising: The feature amount of the bitmap data calculated in the feature amount calculation step is an edge amount that is a value indicating an edge degree for each pixel.
The image processing method according to claim 12. The feature amount calculating step uses an edge amount calculation method depending on whether the object type information of the target pixel stored in the object type information memory emphasizes sharpness, or emphasizes graininess and gradation. Switch,
The image processing method according to claim 13. The halftone processing step includes at least the first quantum depending on whether the object type information of the target pixel stored in the object type information memory emphasizes sharpness, or emphasizes graininess and gradation. The first quantization threshold is a threshold having a constant value regardless of the pixel position and corresponds to object type information that emphasizes sharpness, The second quantization threshold is a threshold that periodically oscillates in the image space, and corresponds to object type information that emphasizes granularity and gradation.
The image processing method according to claim 11, wherein the image processing method is an image processing method. The halftone processing step includes at least the first quantum depending on whether the object type information of the target pixel stored in the object type information memory emphasizes sharpness, or emphasizes graininess and gradation. The first quantization threshold is a threshold that periodically oscillates in the image space, corresponds to object type information that places importance on sharpness, and is applied to the first quantization threshold and the second quantization threshold. The quantization threshold of 2 is a threshold that periodically vibrates with a larger amplitude width in the image space than the first threshold, and corresponds to object type information that places importance on graininess and gradation.
The image processing method according to claim 11, wherein the image processing method is an image processing method. The halftone processing step includes at least the first quantum depending on whether the object type information of the target pixel stored in the object type information memory emphasizes sharpness, or emphasizes graininess and gradation. The first quantization threshold is a threshold that periodically oscillates in the image space, corresponds to object type information that places importance on sharpness, and is applied to the first quantization threshold and the second quantization threshold. The quantization threshold of 2 is a threshold that periodically oscillates in an image space larger than the first threshold, and corresponds to object type information that places importance on granularity and gradation.
The image processing method according to claim 11, wherein the image processing method is an image processing method.

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