JP3736593B2 - Image processing apparatus and image smoothing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus that processes digital image data, and more particularly to an image processing apparatus that performs smoothing processing on multivalued digital image data and an image smoothing method thereof.
[0002]
[Prior art]
In recent years, with the development and popularization of editing software, image input devices such as scanners and electronic still cameras, for example, an image in which a pattern portion such as a photograph or illustration and a line drawing portion such as a character are mixed (hereinafter referred to as a mixed image). Opportunities to print out or copy are increasing. When printing out such a mixed image, the line drawing portion is printed out by performing a smoothing process for smoothing the step as disclosed in, for example, US Pat. No. 4,437,122. It is generally done. On the other hand, it is preferable not to perform the smoothing process on the pattern portion because the fidelity to the original image may be reduced by the smoothing process.
[0003]
As a conventional technique using such a method, for example, there is a technique disclosed in JP-A-8-139918. This technique separates an input multi-valued image by a threshold value, and for a portion below the threshold value, dither processing is performed using fine pixels obtained by dividing the pixel into n pieces (n is an integer of 2 or more) in the main scanning direction. For the portion exceeding the threshold, smoothing processing is performed using the same fine pixels as in the dither processing, and the two processed images are combined by logical sum. However, for example, a dither pattern (line screen pattern) that is a group of straight lines parallel to the sub-scanning direction and whose line width is proportional to the input density value is used as a dither pattern. When this technique is applied when there is a character on the background, there may be a pixel added by smoothing processing and a pixel with a dither pattern in the same pixel. If pixels of both images exist in the same pixel in this way, unnecessary pixel connection occurs, which not only reduces the effect of smoothing, but also causes unnecessary character and line drawing fatness. is there.
[0004]
On the other hand, as another technique, for example, as disclosed in Japanese Patent Application Laid-Open No. 7-221971, multivalued image data constituting a plurality of images is compared, and an image having the maximum or minimum color component is prioritized. There is a technique for synthesizing a plurality of images. In this document, the user specifies in advance whether to give priority to an image having the largest color component or to give priority to an image having the smallest color component. It is considered that such a synthesis technique is applied to the above-described smoothing process, and for example, a line screen pattern is used as a dither pattern, and an image that has been subjected to the entire dither process and an image that has been subjected to the smoothing process only on a character portion. In this case, only a pixel added by the smoothing process or a pixel having a dither pattern by the dither process can be selected. Therefore, for example, if the pixel added by the smoothing process has a smaller color component, the effect of smoothing will not appear if the maximum value is given priority, and if the minimum value is given priority, it will be added by the smoothing process. There was a problem that the pixel and the dither pattern became white at the joint.
[0005]
For example, in Japanese Patent Laid-Open No. 8-23446, a character / line image is extracted from a multi-valued image and smoothed, and then synthesized with the pattern part data. However, the result of the smoothing process is other than 0,255. In some cases, the result of the smoothing process is preferentially output, and for example, priority is given to the pixels added by the smoothing process. Therefore, the character / line image portion is smoothed to obtain a good image quality. However, as described above, there is a possibility that the edge portion causes white spots and the image quality is deteriorated.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described circumstances. When smoothing an image, the present invention prevents the occurrence of white spots or the like at the joint between the image by the smoothing process and other images, and smoothes the image. It is an object of the present invention to provide an image processing apparatus and an image smoothing method for forming an image that can be printed out with higher image quality by maximizing the above effect.
[0007]
[Means for Solving the Problems]
The present invention performs smoothing processing on the input multi-valued original image data, determines whether each pixel of the input original image data is an edge, and determines the original image data based on the determination result. When the pixel is determined to be an edge, the pixel that has been smoothed by the smoothing process and the pixel with the larger value among the pixels of the original image data are selected and output, and the pixel is not determined to be an edge Outputs the original image data. For example, when there is a possibility that white spots are noticeable in pixels added by the smoothing process, the pixels of the original image data are selected to avoid white spots and the white spots are not noticeable. In some cases, the smoothed pixels can be selected to exert the effect of the smoothing process. For this reason, it is possible to maximize the effect of the smoothing process without causing problems such as white spots, and to output an image capable of obtaining an output image with higher image quality.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an embodiment of an image processing apparatus of the present invention. In the figure, 1 is a buffer, 2 is a binarization unit, 3 is a smoothing processing unit, 4 is an edge detection unit, and 5 is a selector.
[0009]
The buffer 1 temporarily stores the original image data input to the input terminal a, adjusts the delay amount, and performs a block of m pixels in the main scanning direction × n pixels in the sub scanning direction (hereinafter, m) in the subsequent processing. When the data of x blocks is required, the block data is formed. The binarization unit 2 creates binary image data based on the original image data. The smoothing processing unit 3 performs smoothing processing on the binary image data created in the binarizing unit 2 and outputs smoothed image data. The edge detection unit 4 detects an edge from the original image data and outputs edge information related to the edge. The selector 5 selects either the original image data in the buffer 1 or the smoothed image data output from the smoothing processing unit 3 for each pixel based on the edge information output from the edge detection unit 4 and outputs The image data is output to the output terminal b.
[0010]
FIG. 2 is a flowchart showing an outline of the operation in the embodiment of the image processing apparatus of the present invention. In FIG. 2, i and j are indices indicating pixel positions in the sub-scanning and main-scanning directions when the first pixel of the first line is the origin, and K and L are pixels in the main-scanning and sub-scanning directions of the input image data. Is a number. P is original image data, P ′ is smoothed image data, and subscripts i and j indicate the j-th pixel in the main scanning direction and the i-th pixel in the sub-scanning direction of each image. Here, P and P ′ are multi-value data. The function smooth represents that the image is smoothed, and the function max represents the maximum value.
[0011]
First, in S101, subscripts i and j indicating pixel positions are both reset to 0, and the pixel to be processed is set as the first pixel of the first line of the image. In S102, the original image data P stored in the buffer 1 is binarized by the binarizing unit 2, and then smoothed by the smoothing processing unit 3 to obtain smoothed image data P ′. .
[0012]
On the other hand, in the edge detection unit 4, the original image data P stored in the buffer 1. _{i, j} Checks if is an edge. This is determined in S103, and if it is not an edge, in S104, the selector 5 selects the original image data P. _{i, j} Select to output. Original image data P _{i, j} Is determined to be an edge, in S105, the selector 5 determines that the original image data P is in accordance with the edge information output by the edge detection unit 4. _{i, j} Alternatively, smoothed image data P ′ smoothed by the smoothing processing unit 3 _{i, j} Select one of these to output. Here, the selector 5 is the image data P _{i, j} Is the edge, the original image data P _{i, j} And smoothed image data P ′ _{i, j} Whichever larger one is selected. For example, when the pixel value added by the smoothing process is small and the pixel value of the original image data is large at the edge portion, if the smoothed image data is selected as it is, white spots may be conspicuous. However, when the pixel value of the original image data is larger by this process, the original image data can be selected and white spots can be avoided. Further, when the pixel value of the smoothed image data is larger, smoothing processing can be performed to improve the image quality of the line drawing portion.
[0013]
In S106, it is determined whether or not the position of the pixel to be processed has reached the end of the line. If it is in the middle of the line, the value of the subscript j is increased by 1 in S107, and the position of the pixel to be processed is determined. Move to the next. Then, the process returns to S102 and a process for a new pixel is performed. If the position of the pixel to be processed in S106 has reached the end of the line, it is determined in S108 whether or not the last line has been processed. If an unprocessed line remains, S109 is determined. The value of the subscript i is incremented by 1 to set the next line to be processed, and the value of the subscript j is set to 0 to set the pixel at the beginning of the line to be processed. Then, the process returns to S102 and a process for a new pixel is performed. In this way, the process is repeated by repeatedly performing the process from the pixel serving as the origin to the pixel at the end of the last line.
[0014]
This flowchart shows a processing algorithm for one color component. When the input image data has a plurality of color components, this algorithm may be applied for each color component. For example, when each color component of the input image data is field sequential, for example, when the input image data is composed of yellow (Y), magenta (M), cyan (C), and black (K) components, Y → M → C → When the original image data is input in the order of K, the image of each color component may be processed in the input order. Of course, the order of the input colors is arbitrary, and it is not necessary to input them in the frame order. In this case, the colors are temporarily stored in a buffer or the like, or this image processing apparatus is provided for each color, and the multiplexer You may make it switch by. Also, the color of the input image data is not limited to YMCK, but for example RGB or L ^* a ^* b ^* Other color component configurations may be used.
[0015]
The image processing apparatus according to an embodiment of the present invention will be further described while partially using specific examples. In the following description, as a specific example of the input original image data, it is assumed that the image data has 8-bit gradation information per pixel, that is, image data in which the pixel value takes an integer value in the range of 0 to 255. Here, when the pixel value is 0, the minimum density, when the pixel value is 255, the maximum density, and when the pixel value is 1 to 254, the intermediate density corresponding to the value is represented. In addition, one pixel at a time is input to the input terminal a in order from the first pixel of the first line of the original image data, and when the image data has a plurality of color components, the color components are input in a frame sequential manner. . Of course, the input original image data is not limited to these conditions, and the meaning of the present invention can be achieved by changing the number of gradations per pixel of each image data or the meaning of the pixel value in each image data. It does not deviate.
[0016]
The image data input to the input terminal a is subjected to delay adjustment in the buffer 1 and then output to the binarization unit 2 and the selector 5, and is also formed in, for example, an m × n block and output to the edge detection unit 4. The Here, as an example, it is assumed that 3 × 3 blocks are passed to the edge detection unit 4.
[0017]
The binarization unit 2 compares the image data input from the buffer 1 with a predetermined threshold value for each pixel. If the input image data is greater than or equal to the threshold value, the value is “1”, and the input image data is less than the threshold value. If it is smaller, '0' is output. FIG. 3 is a block diagram showing an example of the binarization unit in the embodiment of the image processing apparatus of the present invention. In the figure, 11 is a register and 12 is a comparator. The register 11 stores a threshold value for binarization. The comparator 12 compares the original image data output from the buffer 1 and the threshold value for binarization output from the register 11 for each pixel, and if the pixel value is equal to or greater than the threshold value, sets “1” to the pixel If the value is smaller than the threshold value, “0” is output as binary image data. Here, an example using a binarization method using a fixed threshold is shown, but the present invention is not limited to this, and another binarization method may be used.
[0018]
The smoothing processing unit 3 performs smoothing processing on the binary image data input from the binarizing unit 2 and outputs the result. 4 is a block diagram showing an example of a smoothing processing unit in an embodiment of the image processing apparatus of the present invention, FIG. 5 is an explanatory diagram of 5 × 5 block data, and FIG. FIG. 7 is a diagram illustrating an example of a pattern detection unit, and FIG. 8 is a diagram illustrating an example of the contents of a memory. In the figure, 21 is a buffer, 22a to 22x are pattern detection units, 23 is a memory, 24a to 24d are logical negation elements, and 25 is a logical product element. The smoothing processing unit 3 smoothes the binary image data output from the binarizing unit 4. Here, as an example, a case where a smoothing pattern is output based on data of 5 × 5 blocks and matches with a predetermined pattern is shown. Of course, the size of the block is arbitrary, and the method for determining the pixel value is also arbitrary. Furthermore, the method of smoothing processing is also arbitrary.
[0019]
The buffer 21 uses, for example, 5 × 5 block block data (P) shown in FIG. 5 from the binary image data output from the binarization unit 2. _{0, 0} , ..., P _4,0 , P _0,1 , ..., P _4,4 ) And P _2,2 Is output as the target pixel value.
[0020]
The pattern detection units 22a to 22x compare 5 × 5 block data output from the buffer 21 with predetermined patterns (a) to (x) as shown in FIG. In the pattern shown in FIG. 6, a white part is a pixel having a pixel value “0”, a black part is a pixel having a pixel value “1”, and a hatched part may have a pixel value “0” or “1”. Is shown. These patterns are arbitrary as long as the pixel to be smoothed can be determined. The number of patterns is also arbitrary. Here, the pattern detection unit is arranged for each pattern, but a single pattern detection unit may be configured to compare with several or all patterns. As a result of the comparison, for example, the pattern detection units 22a to 22x output “1” when the pattern to be compared and the 5 × 5 block pattern match, and output “0” when they do not match.
[0021]
For example, the pattern detection unit 22a can be configured by a logic element as shown in FIG. From the pattern shown in FIG. 6A to be compared by the pattern detection unit 22a, P of 5 × 5 block data _1,0 , P _1,1 , P _2,1 , P _2,2 Is '0', P _2,0 , P _3,1 , P _3,2 If “1” is “1”, the output is “1”. For this logic, P _1,0 , P _1,1 , P _2,1 , P _2,2 Is inverted by the logic negating elements 24a to 24d and inputted to the AND element 25, and P _2,0 , P _3,1 , P _3,2 Is input to the AND element 25 as it is. The logical product element 25 calculates these logical products and sets them as output values. Of course, the configuration of the pattern detection units 22a to 22x is not limited to this.
[0022]
The memory 23 holds image data and control data corresponding to outputs from the pattern detection units 22a to 22x. For example, the memory 23 can store data having contents as shown in FIG. When '1' is output from any one of the pattern detection units 22a to 22x, an image corresponding to the pattern compared by the pattern detection unit that outputs '1' based on the data shown in FIG. Data and control data are output as smoothed image data. For example, as a result of comparing the pattern shown in FIG. 6 (a) with the 5 × 5 block pattern of the original image data by the pattern detection unit 22a, a match “1” is output, and the other pattern detection units 22b to 22x When “0” is output, “63” is output as image data and “0111b” is output as control data from the data shown in FIG. In addition, the thing with 'b' at the end of the numerical value represents a binary number, and so on. The control data will be described later.
[0023]
Further, when “1” is output from two or more pattern detectors, and when “0” is output from all pattern detectors, the pixel value corresponding to the target pixel value input from the buffer 21 is determined. Image data and control data are output as smoothed image data. For example, when the target pixel value input from the buffer 21 is “1”, “255” as image data, “1111b” as control data, “0” as image data when “0”, and control data '1111b' is output. When two or more patterns are detected, for example, a priority order is determined in advance between the patterns, and image data and control are performed from the memory 23 according to the pattern having the highest priority among the detected patterns. Data may be output.
[0024]
The edge detection unit 4 detects from the m × n block output from the buffer 1 whether or not the central pixel of the block is an edge, and outputs information about the detection result to the selector 5 as edge information. Here, as an example, it is assumed that 3 × 3 blocks of data are passed from the buffer 1. In addition, an example in which information indicating the edge direction as well as the presence or absence of the edge is output as the edge information. FIG. 9 is a block diagram showing an example of an edge detection unit in an embodiment of the image processing apparatus of the present invention, FIG. 10 is an explanatory diagram of an example of a filter for detecting an edge in a specific direction, and FIG. It is explanatory drawing of the edge information produced | generated in an information creation part. In the figure, 31a to 31d are filters, and 32 is an edge information creation unit.
[0025]
In the example illustrated in FIG. 9, the edge detection unit 4 includes filters 31 a to 31 d and an edge information creation unit 32. The filters 31a to 31d are filters that detect edges in a specific direction. For example, the calculation is performed on 3 × 3 block data using the edge detection operator shown in FIGS. 10A to 10D, and the result is output. The number of filters to be used, the filter shape, and the filter coefficient are not limited to these, and any filter may be used as long as the edge of the original image data can be detected. Of course, the block size is not limited to 3 × 3.
[0026]
The edge information creation unit 32 compares the maximum absolute value of the outputs of the filters 31a to 31d with a threshold value to obtain a comparison result. Further, it is determined which filter has the maximum absolute value of the output, and the determination result and the positive / negative of the output whose absolute value is the maximum are obtained. Edge information is created and output based on the obtained comparison result, determination result, and output positive / negative. At this time, for example, edge information can be created according to data as shown in FIG. For example, when the maximum absolute value of the output is equal to or less than the threshold value, “000b” is output as the edge information. For example, when the maximum absolute value of the output is larger than the threshold value and the output is output from the filter 34b, and the output is positive, '101b' is output. The threshold value may be set arbitrarily. This edge information indicates whether or not the first bit is an edge, and the second and third bits indicate the direction of the edge.
[0027]
When the absolute values of the outputs from two or more filters are the same and maximum, it is assumed here that the priority order shown in FIG. 11 is followed. Alternatively, edge information may be obtained from a combination of filters having the same output absolute value. Note that the data shown in FIG. 11 may be set arbitrarily.
[0028]
In the selector 5, the pixel value of either one of the original image data input from the buffer 1 or the smoothed image data input from the smoothing processing unit 3 is compared with the pixel value comparison result and edge detection. A selection is made based on the edge information output from the unit 4, and the selection is output to the output terminal b. FIG. 12 is an explanatory diagram of an example of the selector selection operation. In FIG. 12, the original image data is expressed as “IMAGE”, and the smoothed image data is expressed as “SMOOTH”. As shown in FIG. 12, the selector 5 includes the 3-bit edge information output from the edge detector 4, the comparison result of the pixel values of the original image data and the smoothed image data, and the pixel value of the original image data. And output image data. In this example, the selector 5 also outputs control data for controlling the output device described later together with the image data.
[0029]
For example, when the edge detection unit 4 does not detect an edge, the edge information is “000b”. Therefore, the original image data is selected and output as output image data, and “1111b” is output as control data. For example, when the edge is detected by the edge detection unit 4 and the edge information is '101b', the pixel value of the original image data and the pixel value of the smoothed image data are further compared, and the pixel of the smoothed image data If the value is larger, the pixel value and control data of the smoothed image data are selected and output, and if the pixel value of the original image data is larger, the pixel value of the original image data is selected and output, and as control data '1011b' is output.
[0030]
In this way, at the edge portion, the larger pixel value is selected depending on which pixel value is larger between the original image data and the smoothed image data obtained by smoothing the original image data. As a result, for example, in the portion where the background portion of the line drawing is a conspicuous color and pixels are added by the smoothing processing and thus white spots are generated conventionally, the result of the smoothing processing is not adopted and the original image data is not used. If pixels are selected to avoid white spots, or if the background is not conspicuous, the result of smoothing processing can be used to output image data that can smoothly reproduce a line drawing. Therefore, the image quality of the image reproduced using the output image data can be improved.
[0031]
Note that the edge information includes information related to the edge direction, and the image data and control data to be output are distinguished by the edge direction in FIG. 12 as well, and this is in accordance with the characteristics of an example of an output device described later. It is a thing. Depending on the output device, the edge detection unit 4 may not consider the directionality of the edge, and the operation of the selector 5 as shown in FIG. 12 may be set accordingly. Of course, information on the directionality of the edge may be used in accordance with the subsequent image processing and the output device. Further, the data shown in FIG. 12 may be set as appropriate according to the subsequent image processing and output device. The conditions for selection can also be set arbitrarily.
[0032]
Next, an example is shown in which output processing is performed in accordance with the image data and control data output from the image processing apparatus of the present invention. Here, as an example, the case of outputting to a laser beam printer having a pulse width modulation function and an intensity modulation function will be described. First, pulse width modulation and intensity modulation will be described. FIG. 13 is a block diagram illustrating a configuration example for realizing a pulse width modulation function in a laser beam printer. In the figure, 41 is a D / A converter, 42 is a reference wave generator, and 43 is a comparator. The pulse width modulation is a function for controlling the light emission timing of the laser light emitting element to control the print width and print position of the pixel in the main scanning direction. For example, the laser beam printer has a configuration as shown in FIG. Realize. The D / A converter 41 converts the input pixel into a signal having a voltage level corresponding to the value. The reference wave generator 42 generates a reference wave having a period that is a natural number multiple of the period in which the pixels are input. The comparator 43 compares the output signal of the D / A converter 41 with the reference wave generated by the reference wave generator 42. When the voltage level of the output signal of the D / A converter 41 is high, laser light emission is performed. A signal of a voltage level at which the element emits light is generated at a voltage level at which the laser light emitting element does not emit light when the voltage level of the reference wave is large.
[0033]
14 to 17 are explanatory diagrams of an example of the pulse width modulation operation in the laser beam printer. The waveforms at each point a, b, c, and d shown in FIG. 13, the reference clock, and the printing result are shown. In these examples, “FFh”, “BFh”, “7Fh”, “3Fh”, and “0h” are sequentially input as the pixel values input to the terminal a. Here, the value with “h” added at the end indicates a hexadecimal number, and so on. 14 to 17, the shapes of the reference waves generated by the reference wave generator 42 are different. In the example shown in FIG. 14, the reference wave has a triangular wave shape that falls during one clock and rises again. Therefore, when the voltage converted by the D / A converter 41 is compared with this reference wave by the comparator 43, a signal of a voltage level at which the laser light emitting element emits light at the center of one clock is output. The width is wider when the voltage converted by the D / A converter 41 is higher, and the width becomes narrower as the voltage decreases. Therefore, as a result of printing according to this example, an area having a width corresponding to the pixel value input to the terminal a is printed at the center of each pixel.
[0034]
The example shown in FIG. 15 shows a case where a sawtooth waveform that gradually decreases in one clock is generated as a reference wave. In this case, the area to be printed in one pixel is printed closer to the right end of each pixel. Also, the example shown in FIG. 16 shows a case where a sawtooth reference wave that gradually increases in one clock is generated. In this case, the area to be printed in one pixel is printed closer to the left end of each pixel. In these cases as well, the width corresponds to the pixel value.
[0035]
In the example shown in FIG. 17, a reference wave in which the gradually decreasing waveform shown in FIG. 15 and the gradually increasing waveform shown in FIG. 16 are alternately generated is used. In this case, the area to be printed is printed on the left or right side every other pixel. Also in this case, printing is performed with a width corresponding to the pixel value.
[0036]
FIG. 18 is a block diagram showing a configuration example for realizing the intensity modulation function in the laser beam printer. In the figure, 44 is a laser light emitting element, and 45 is a current controller. The intensity modulation is a function for controlling the light emission intensity of the laser light emitting element 44 to change the size of the exposure spot and to control the printing width of the pixel in the sub-scanning direction. For example, it is realized by providing a laser beam printer with a configuration as shown in FIG. The current controller 45 controls the drive current supplied to the laser light emitting element 44 according to the input value.
[0037]
FIG. 19 is an explanatory diagram of an example of the intensity modulation operation in the laser beam printer. The waveforms at the points a and b shown in FIG. 18, the reference clock, and the printing result are shown. In this example, “FFh”, “BFh”, “7Fh”, “3Fh”, and “0h” are sequentially input as the pixel values input to the terminal a. The current output from the current controller 45 is controlled according to the pixel value input to the terminal a, and the print width of the pixel in the sub-scanning direction changes as shown in the print result. In this way, printing can be performed with a printing width corresponding to the pixel value.
[0038]
By using the pulse width modulation function and the intensity modulation function provided in such a laser beam printer, it is possible to print a small area of one pixel or less by a smoothing process. For example, when printing the smoothing result of the vertical line, a small area of one pixel or less may be added to the vertical line using the pulse width modulation function shown in FIGS. In the case of a horizontal line, a smoothing result can be obtained by adding a small area of one pixel or less using the intensity modulation function.
[0039]
In order to select such a function, control data output from the above-described image processing apparatus is used. For example, among the 4-bit control data output from the selector 5 as shown in FIG. 12, the upper 2 bits are used as the reference wave selection instruction signal. For example, it is possible to control to select the reference wave shown in FIG. 15 when the upper 2 bits of the control data are “01b”, FIG. 16 when it is “10b”, and FIG. 14 when it is “11b”. . Further, the lower 2 bits of the control data can be used as a signal for selecting the modulation intensity. For example, when the lower 2 bits of the control data are “11b”, the print width in the sub-scanning direction is the full width. When the lower 2 bits are “00b”, the print width is 1/4, and when the lower 2 bits is “01b”, 1 / The current controller 45 can be configured to control the drive current supplied to the laser light-emitting element 44 so that the print width is 2 and the print width is 3/4 when it is “10b”.
[0040]
In this way, by performing printing and recording in accordance with the image data and control data output from the above-described image processing apparatus, it is possible to print an image that has been subjected to smoothing processing. Due to the smoothing process, for example, a case where only a narrow area is printed in one pixel occurs as in the case where the pixel value is “3Fh” in FIGS. For this reason, when the value of the pixel of the original image data is larger than the value of the pixel added by the smoothing process, conventionally white spots are conspicuous at the edge portion. However, in the image processing apparatus of the present invention, when such white spots are considered to be conspicuous, the pixels are printed as pixels of the original image data. If white spots are not noticeable, printing is performed according to the smoothing result, so that the edge portion is printed well by the output control as described above. In this way, a high-quality image can be obtained.
[0041]
Hereinafter, the operation will be described using specific examples of image data. FIG. 20 is an explanatory diagram of a specific example of image data input in the embodiment of the image processing apparatus of the present invention, and FIGS. 21 to 29 are explanatory diagrams of a specific example of image data in the same process. In each figure, a rectangle represents a pixel, and each pixel value or each value is as shown on the right side of each figure and is distinguished by hatching. In addition, the pixel value takes a value in the range of 0 to 255. In the following description, each figure shows how the entire image is processed, and in order to show a specific process, as an example, pixels at intersections of rows and columns indicated by arrows in each figure, that is, 8 in the main scanning direction. Pixel P in the fourth row in the column and sub-scanning direction _7,3 Pay attention to.
[0042]
Assume that the original image data shown in FIG. 20 is input to the input terminal a. In this original image data, an oblique straight line is drawn with a pixel value “255”, the right side thereof is white, and the left side is filled with a pixel value “80”.
[0043]
The original image data input to the input terminal a is subjected to delay adjustment in the buffer 1 and then input to the binarization unit 2 and binarized. For example, if binarization is performed with a fixed threshold value and the threshold value for binarization is set to “255”, only the portion having a pixel value of “255” or more is extracted from the image shown in FIG. As shown in FIG. 21, binary image data is obtained. Pixel P _7,3 Becomes '0'.
[0044]
The binarized image data binarized by the binarizing unit 2 as shown in FIG. 21 is input to the smoothing processing unit 3 and subjected to smoothing processing. For example, when pattern detection is performed using the patterns (a) to (x) shown in FIG. 6 and the binarized image data shown in FIG. 21 is smoothed according to the contents of the memory 23 shown in FIG. Smoothed image data shown in FIG. 22 and control data shown in FIG. 23 are obtained. For example, pixel P _7,3 Corresponds to the pattern (a) shown in FIG. 6, and the pixel value “63” and the control data “0111b” are obtained from the memory contents shown in FIG.
[0045]
The original image data input to the input terminal a is input to the edge detection unit 4 in a 3 × 3 block formed by the buffer 1. The edge detection unit 4 creates edge information based on the conditions shown in FIG. 11 after the filter processing using the filter as shown in FIG. Pixel P _7,3 Then, “−175” is calculated in the filter 31b having the pattern shown in FIG. 10B, and “0” is output for the other filters. If, for example, the threshold value is set to “85” in accordance with the conditions shown in FIG. 11, the absolute value of the output from the filter 34b is larger than the threshold value, and the output of the filter 34b is negative, so “100b” is output as edge information.
[0046]
The selector 5 selects either the original image data pixel shown in FIG. 20 input from the buffer 1 or the smoothed image data pixel shown in FIG. 22 input from the smoothing processing unit 3. At this time, based on the edge information shown in FIG. 24 output from the edge detection unit 4, the comparison result of the pixel value of the original image data and the pixel value of the smoothed image data, the pixel value of the original image data, etc. Select according to the data as shown. The control data is also selected according to the pixel selection result.
[0047]
For example, pixel P _7,3 Then, the edge information output from the edge detector 6 is “100b”. Further, the pixel value of the original image data shown in FIG. 20 is “80”, and the pixel value of this pixel obtained from the smoothed image data shown in FIG. 22 is “63”. The value is large. This condition corresponds to the second line in FIG. 12, and the pixel value “80” of the original image data is selected and output as the image data. Further, “0111b” is output as control data. That is, the pixel P _7,3 Then, as shown in FIG. 22, it is added to a straight line by the smoothing process and output as a pixel constituting a part of the straight line, but the pixel value of the original image data is more than the pixel value added by the smoothing process. Since it is large, the original image data was selected as described above. In this way, the pixel P _7,3 In, printing is performed according to the original image data having a large pixel value without causing the pixel value to be reduced due to the addition of the pixel by the smoothing process and causing white spots.
[0048]
Based on the output image data and control data shown in FIGS. 25 and 26, an image is formed by a laser beam printer using an electrophotographic system having a pulse width modulation function and an intensity modulation function as described above. Then, as shown in FIG. 27, each pixel is irradiated with a laser beam, and a printed image as shown in FIG. 28 is obtained.
[0049]
The embodiment of the image processing apparatus according to the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and any mode may be used as long as it does not depart from the gist of the present invention. For example, in the above-described example, since the input image data is input for each color component in the case of a grayscale image or a color image, the smoothing process is performed by adjusting the density. Smoothing processing may be performed in which color conversion is performed based on color information of neighboring pixels.
[0050]
In the above description, a laser beam printer using an electrophotographic method having a pulse width modulation function and an intensity modulation function is used as a specific example of the output device. However, the output device is arbitrary, and the present invention is applied according to the output destination. Modifications can be made without departing from the spirit of the present invention. For example, even when outputting to a laser beam printer using an electrophotographic method, if the printer has only a pulse width modulation function, a portion that performs smoothing processing using intensity modulation May be smoothed using pulse width modulation. In addition, when outputting to a laser beam printer using an electrophotographic system, the printer operates the counter based on a clock having a frequency that is a natural number multiple of the frequency of the input reference clock of the image data instead of the pulse width modulation function. In the case of having a so-called DSG (Digital Screen Generate) function for printing a pixel in accordance with the result of comparing the count value of the counter and the pixel value, control data for controlling the selection of the reference wave described above is provided. The control data may be replaced with control data for controlling the operation of the counter.
[0051]
Further, the present invention can be applied not only to a laser beam printer using an electrophotographic method but also to a printer using another printing method such as an ink jet printer or a thermal transfer printer. Further, the present invention can be applied to the case of outputting to an image display device such as a CRT or a liquid crystal display instead of a printer.
[0052]
【The invention's effect】
As is apparent from the above description, according to the present invention, smoothing processing is performed on the input original image data, and whether or not each pixel of the original image data is an edge is determined. Then, either the pixel of the original image data or the pixel of the image data subjected to the smoothing process is selected and output. In the selection, for example, when it is determined that the pixel of the original image data is an edge, the pixel having the larger pixel value is selected from the pixels of the smoothed image data and the pixels of the original image data. It can be configured to output. In this way, in a portion where white spots are likely to occur by adding pixels in the smoothing process, original image data can be selected to avoid white spots. Further, in a portion where white spots are not conspicuous, it is possible to improve the image quality such as a line segment by selecting a smoothing process result. For this reason, there is an effect that problems due to the smoothing process can be eliminated, the effect of the smoothing process can be maximized, and image data that can be printed out with higher image quality can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an embodiment of an image processing apparatus according to the present invention.
FIG. 2 is a flowchart showing an outline of an operation in the embodiment of the image processing apparatus of the present invention.
FIG. 3 is a block configuration diagram showing an example of a binarization unit in the embodiment of the image processing apparatus of the present invention.
FIG. 4 is a block configuration diagram showing an example of a smoothing processing unit in an embodiment of the image processing apparatus of the present invention.
FIG. 5 is an explanatory diagram of 5 × 5 block data.
FIG. 6 is an explanatory diagram of an example of a pattern to be compared with 5 × 5 block data by a pattern detection unit.
FIG. 7 is a configuration diagram illustrating an example of a pattern detection unit.
FIG. 8 is an explanatory diagram of an example of the contents of a memory.
FIG. 9 is a block configuration diagram showing an example of an edge detection unit in the embodiment of the image processing apparatus of the present invention.
FIG. 10 is an explanatory diagram of an example of a filter for detecting an edge in a specific direction.
FIG. 11 is an explanatory diagram of edge information generated in an edge information creation unit.
FIG. 12 is an explanatory diagram of an example of a selector selection operation.
FIG. 13 is a block diagram showing an example of a configuration for realizing a pulse width modulation function in a laser beam printer.
FIG. 14 is an explanatory diagram of an example of pulse width modulation operation in a laser beam printer.
FIG. 15 is an explanatory diagram of another example of the operation of pulse width modulation in the laser beam printer.
FIG. 16 is an explanatory diagram of still another example of the operation of pulse width modulation in the laser beam printer.
FIG. 17 is an explanatory diagram of still another example of the operation of pulse width modulation in the laser beam printer.
FIG. 18 is a block diagram showing an example of a configuration for realizing an intensity modulation function in a laser beam printer.
FIG. 19 is an explanatory diagram of an example of an intensity modulation operation in the laser beam printer.
FIG. 20 is an explanatory diagram of a specific example of original image data input in the embodiment of the image processing apparatus of the present invention.
FIG. 21 is an explanatory diagram of a specific example of binarized image data according to an embodiment of the image processing apparatus of the present invention.
FIG. 22 is an explanatory diagram of a specific example of smoothed image data according to an embodiment of the image processing apparatus of the present invention.
FIG. 23 is an explanatory diagram of a specific example of control data output from the smoothing processing unit in the embodiment of the image processing apparatus of the invention.
FIG. 24 is an explanatory diagram of a specific example of edge information in the embodiment of the image processing apparatus of the invention.
FIG. 25 is an explanatory diagram of a specific example of output image data in the embodiment of the image processing apparatus of the invention.
FIG. 26 is an explanatory diagram of a specific example of control data output in the embodiment of the image processing apparatus of the present invention.
FIG. 27 is an explanatory diagram of a specific example of a laser irradiation image when an image is formed by a laser beam printer based on output image data and control data output in an embodiment of the image processing apparatus of the present invention.
FIG. 28 is an explanatory diagram of a specific example of an image formed by a laser beam printer based on output image data and control data output in an embodiment of the image processing apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Buffer, 2 ... Binarization part, 3 ... Smoothing process part, 4 ... Edge detection part, 5 ... Selector, 11 ... Register, 12 ... Comparator, 21 ... Buffer, 22a-22x ... Pattern detection part, 23 ... Memory, 24a to 24d ... Logical negation element, 25 ... Logical product element, 31a to 31d ... Filter, 32 ... Edge information creation unit, 41 ... D / A converter, 42 ... Reference wave generator, 43 ... Comparator, 44: Laser light emitting element, 45: Current controller.

Claims (4)

  Smoothing processing means for performing smoothing processing on the input multi-valued original image data, edge determination means for determining whether each pixel of the input original image data is an edge, and the edge determination means When the pixel of the original image data is determined to be an edge, the pixel smoothed by the smoothing processing unit and the pixel having the larger value among the pixels of the original image data are selected and output, An image processing apparatus comprising pixel selection means for outputting the original image data when it is not determined to be an edge.   The image processing apparatus according to claim 1, wherein the edge determination unit determines whether or not a central pixel of the block is an edge from the block of the input original image data.   The input multi-valued original image data is subjected to smoothing processing, and it is determined whether each pixel of the input original image data is an edge. If it is determined that there is a pixel that has been smoothed by the smoothing process and the pixel of the original image data, the pixel having the larger value is selected and output. An image smoothing method characterized by outputting original image data.   4. The image smoothing method according to claim 3, wherein the determination of whether or not the edge is performed is performed for a central pixel of the input original image data block.

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