JP6665447B2 - Image processing apparatus, image processing method, and program - Google Patents

Description

  The present invention relates to an image processing device, an image processing method, and a program.

2. Description of the Related Art Conventionally, image data has been compressed in order to efficiently store and transmit large-sized image data. Further, in order to increase the efficiency of the compression, various methods have been proposed in which image data is processed and then compressed.
For example, in Patent Document 1, image data is divided into a line segment image element and other parts, and a representative color determined based on the value of a pixel included in the part is used for each part. It is described that the color is limited and then subjected to a compression process.
Patent Document 2 describes that image data is divided into a character or line region and a picture region, and a process of averaging pixel values is performed on the character or line region and then subjected to a compression process. ing.

However, with the above-described conventional methods, it has been difficult to improve the compression efficiency of a pattern portion other than characters and lines. Further, in order to increase the efficiency, resolution reduction processing is performed uniformly, and for an image including a region with a high spatial frequency, there is a problem that the image quality is greatly deteriorated by compression.
The present invention has been made in view of such circumstances, and has as its object to obtain highly compressible image data while maintaining image quality.

To achieve the above object, an image processing apparatus according to the present invention includes a first image processing means for executing the color reduction processing on the picture image data to be processed, with respect to picture image data of the processing target,該絵pattern image data A second image processing means for performing a pixel number reduction process by switching a degree of reducing the number of pixels in accordance with the resolution of the image data, and a calculating means for calculating a complexity indicating a degree of variation of a pixel value in the picture image data to be processed When, in accordance with the complexity of the above calculation means has calculated, or outputs one of the picture image data after the pixel number reduction process by the picture image data and the second image processing unit after the color reduction processing by the first image processing means Bei determining means, the picture image data of the processing target is divided into predetermined areas, and a blocking means for passing the coordinate information of the divided regions to the calculating means for determining ,
The calculating means calculates the complexity for each area based on the coordinate information of the area obtained from the blocking means, and the deciding means calculates the picture image data after the color reduction processing by the first image processing means. And determining which of the picture image data after the pixel number reduction processing by the second image processing means to output is performed for each of the regions .

  According to the above configuration, it is possible to obtain highly compressible image data while maintaining image quality.

FIG. 1 is a block diagram illustrating a hardware configuration of an image forming apparatus according to a first embodiment of the present invention. Among the functions of the image forming apparatus shown in FIG. 1 is a block diagram showing a schematic configuration of a function for compressing the image data. FIG. 3 is a block diagram illustrating a functional configuration of a picture image data compression unit illustrated in FIG. 2. FIG. 4 is a diagram for describing vector quantization processing performed when the color reduction processing unit illustrated in FIG. 3 reduces the number of colors. FIG. 4 is a diagram for describing a determination process performed by a determination unit illustrated in FIG. 3 using a value of a spatial frequency component calculated by a frequency calculation unit. 4 is a flowchart illustrating a procedure of a determination process performed by a determination unit illustrated in FIG. 3. FIG. 9 is a block diagram illustrating a functional configuration of a picture image data compression unit in the image forming apparatus according to the second embodiment. 8 is a flowchart illustrating a procedure of a determination process performed by a determination unit illustrated in FIG. 7. FIG. 11 is a block diagram illustrating a functional configuration of a picture image data compression unit in an image forming apparatus according to a third embodiment. 10 is a flowchart illustrating a procedure of a frequency replacement process performed by a frequency replacement unit illustrated in FIG. 9. It is a block diagram showing the functional composition of the picture image data compression part in the image forming device of a 4th embodiment. 12 is a flowchart illustrating a procedure of a determination process performed by a determination unit illustrated in FIG. It is a block diagram showing the functional composition of the picture image data compression part in the image forming device of a 5th embodiment. 14 is a flowchart illustrating a procedure of a determination process performed by a determination unit illustrated in FIG. It is a block diagram showing the functional composition of the picture image data compression part in the image forming device of a 6th embodiment. 16 is a flowchart illustrating a procedure of a determination process performed by a determination unit illustrated in FIG. FIG. 9 is a diagram illustrating a functional configuration of a picture image data compression unit in an image forming apparatus according to a first modification. FIG. 11 is a diagram illustrating a functional configuration of a picture image data compression unit in an image forming apparatus according to a second modification.

Hereinafter, embodiments for implementing the present invention will be described with reference to the drawings.
[First Embodiment: FIGS. 1 to 6]
First, an image forming apparatus according to a first embodiment of the image processing apparatus of the present invention will be described. FIG. 1 is a block diagram showing a hardware configuration of the image forming apparatus.
The image forming apparatus 10 illustrated in FIG. 1 includes a controller 101, an engine control unit 110, an image reading unit 111, a plotter unit 112, and an image processing unit 113. The controller 101 includes a CPU 102, a RAM 103, a ROM 104, an HDD (hard disk drive) 105, a communication I / F (interface) 106, and an operation unit I / F 107. The operation unit I / F 107 is connected to the operation unit 108. These are connected by a system bus 109.

In the above configuration, the CPU 102 controls the entire image forming apparatus 10 by executing a program stored in the ROM 104 or the HDD 105 using the RAM 103 as a work area, and realizes various functions described below.
The ROM 104 and the HDD 105 are non-volatile storage media (storage means), and store various programs executed by the CPU 102 and various data described below.
The communication I / F 106 is an interface for connecting the image forming apparatus 10 to a network.

The operation unit I / F 107 is an interface for connecting the operation unit 108 to the system bus 109 and enabling control from the CPU 102.
The operation unit 108 is a user interface including an operation unit such as a key, a button, and a touch sensor for receiving an operation from the user, and a display unit such as a display for presenting information to the user .

The image reading unit 111 is an image reading unit having a function of reading an image of a document and obtaining the image data. The plotter unit 112 is an image forming unit having a function of forming an image on a sheet by printing based on input image data. The image processing unit 113 performs various types of image processing including image data processing and compression processing, which will be described later, on image data read by the image reading unit 111 and image data used for image formation in the plotter unit 112. It is.
The engine control unit 110 is a control unit that controls the image reading unit 111, the plotter unit 112, and the image processing unit 113 in accordance with a command supplied from the CPU 102 via the system bus 109.

The above-described image forming apparatus 10 can be configured as, for example, a printer, a facsimile communication apparatus, a digital multifunction peripheral (MFP), or the like.
A characteristic feature of the image forming apparatus 10 is a process of processing image data, which is performed when compressing image data. Hereinafter, this point will be described including the procedure of the compression process.

First, FIG. 2 and FIG. 3 show the configuration of functions provided in the image forming apparatus 10 relating to the compression of image data and the processing performed at the time of compression. FIG. 3 shows the function of the picture image data compression unit 24 shown in FIG. 2 in more detail.
As shown in FIG. 2, the image forming apparatus 10 includes an image data acquisition unit 21, an image data separation unit 22, a character image data compression unit 23, a picture image data compression unit 24, a synthesis unit 25, and an output unit 26. The functions of the image data acquisition unit 21 are as follows: the CPU 102 controls the communication I / F 106 or the image reading unit 111, so that the image data separation unit 22, the character image data compression unit 23, the picture image data compression unit 24, the synthesis unit 25, and the output The functions of the unit 26 are realized by the CPU 102 controlling the image processing unit 113, respectively.

  Further, the image data acquisition unit 21 has a function of acquiring image data to be processed and passing it to the image data separation unit 22. This acquisition is performed when image data that is formed inside the image forming apparatus 10 by a scanning function or the like and is stored in advance is acquired. And the case where image data is acquired via the communication path of (1).

  The image data separating unit 22 separates the acquired image data into character image data obtained by extracting a character portion, which is a portion where characters and lines are shown, and pattern image data obtained by extracting a pattern portion, which is the other portion. The function of the separating means is provided. For this separation processing, a known technique may be appropriately applied. For example, by performing an edge determination on image data to be processed to detect an edge element, and separating each pixel into a character pixel and a pattern pixel based on the result, character image data and pattern image data are separated. Can be separated.

  The image data separation unit 22 has a function of replacing pixels other than the character pixels in the character image data with white pixels and replacing pixels other than the design pixels in the design image data with white pixels during the separation processing. Prepare. Further, the image data separating unit 22 has a function of passing the character image data after the separation processing to the character image data compressing unit 23 and passing the picture image data to the picture image data compressing unit 24, respectively.

The character image data compression unit 23 has a function of acquiring character image data from the image data separation unit 22, performing compression processing on the character image data, and outputting the compressed character image data to the synthesis unit 25.
As the compression processing of the character image data, for example, after binarizing the character image data, lossless compression processing such as run-length encoding may be performed. Various known techniques may be applied to the compression processing, and the compression processing is not limited to the above-described example of the compression processing.

The picture image data compression section 24 has a function of acquiring picture image data from the image data separation section 22, performing compression processing on the picture image data, and outputting the compressed picture image compressed data to the synthesis section 25.
The function of the picture image data compression unit 24 will be described in detail with reference to FIG.

The synthesizing unit 25 has a function of acquiring the compressed character image data from the character image data compression unit 23 and the compressed pattern image data from the pattern image data compression unit 24, respectively, and combining the two pieces of compressed data to generate one image file. . For example, the above-described image file generation can be realized by storing the compressed character image data and the compressed pattern image data in a multiplex format using a format synthesis technique in a PDF (Portable Document Format) file format. However, the method of generating an image file is not limited to this.
The output unit 26 has a function of acquiring and outputting the file synthesized by the synthesis unit 25. This output means that the combined file is passed to the internal HDD 105 in the image forming apparatus 10 in order to save the combined file, or to a portable terminal such as a PC (Personal Computer) or a smartphone, or to an external device such as a scanner. And passing the synthesized file through a communication path such as a network.

Next, FIG. 3 shows the functional configuration of the picture image data compression unit 24 shown in FIG. 2 in more detail.
As shown in FIG. 3, the picture image data compression unit 24 includes a color reduction processing unit 201, a pixel number reduction processing unit 202, a frequency calculation unit 203, a determination unit 204, a control unit 205, and a compression unit 206.
Among these, the color reduction processing unit 201 has a function of a first image processing unit that executes a color reduction process for reducing the number of colors as processing of a first image processing procedure on the picture image data supplied from the image data separation unit 22. Prepare. The color reduction process is a process of setting an arbitrary representative color and replacing another color with the representative color.
For example, in the case of pattern image data in which each bit depth is 8 bits in the RGB mode, a color is represented by a total of 24 bits per pixel. It is conceivable to replace the picture image data with image data expressing colors with 8 bits per pixel by color reduction processing.

Next, replacement of colors in the color reduction processing will be described with reference to FIG. This replacement is performed using the concept of vector quantization. FIG. 4 shows an example of the color space S.
When performing the color reduction processing, first, the color of each pixel in the image data to be processed is plotted at coordinates in a color space. Then, a clustering process is performed for each plotted coordinate, and a representative color is determined for each cluster. Then, the color of each pixel in the cluster is replaced with the representative color of the cluster. Here, the representative color is determined after clustering, but may be determined before clustering.

In FIG. 4, white circles V1a to V1c and V2a to V2f indicate plotting destinations of pixel colors, C1 and C2 indicate ranges of clusters detected by clustering, and black circles Vr1 and Vr2 indicate representative colors of each cluster. Therefore, in the color reduction processing, the color of the pixel corresponding to V1a to V1c may be converted to the color indicated by Vr1, and the color of the pixel corresponding to V2a to V2f may be converted to the color indicated by Vr2.

In order to make the converted image data 8 bits, the representative colors can be determined up to 256 colors, so the maximum number of clusters is also 256. A well-known technique may be appropriately used for the clustering and the method of determining the representative color. Further, the pixel value of each representative color is added to the image data after the color reduction processing as 24-bit data before the color reduction, so that the color can be reproduced when the image data is expanded.
When the color reduction processing unit 201 performs such color reduction processing, the number of colors is reduced, so that the compression efficiency can be improved. Further, since only the number of colors is reduced, the image quality can be maintained without lowering the resolution.

Next, the pixel number reduction processing unit 202 functions as a second image processing unit that executes a process of reducing the number of pixels as a process of a second image processing procedure on the picture image data supplied from the image data separation unit 22. Is provided.
For example, when the size of the picture image data is reduced to 1/16, a process of reducing the number of pixels is performed such that the number of pixels in the vertical and horizontal directions is 1/4 of the original number of pixels. Reducing the number of pixels means lowering the resolution unless the size of image display or printing changes.
Note that how much the number of pixels is reduced, that is, how much the reduction ratio is set, may be switched according to the resolution of the picture image data. For example, it is possible to reduce the difference in image quality due to the difference in resolution by increasing the reduction ratio for high resolution and decreasing the reduction ratio for low resolution.

The frequency calculation unit 203 has a function of a calculation unit that calculates the complexity indicating the degree of change of the pixel value in the image data for the picture image data supplied from the image data separation unit 22. The calculation of the complexity is a process of a calculation procedure.
As the complexity, for example, a specific spatial frequency component (hereinafter, “spatial frequency” is simply “frequency”) obtained by performing discrete cosine transform (DCT), Fourier transform, or the like on picture image data Described below) can be used.

FIG. 5 shows an example of a frequency component used as the complexity.
FIG. 5 is an example of a result obtained by quantizing an 8 × 8 frequency component (DCT coefficient) calculated by performing an orthogonal transformation using DCT on a region of 8 × 8 pixels in the picture image data. In the figure, the component on the right side shows a component with a larger horizontal frequency, and the component on the lower side shows a component with a larger frequency in the vertical direction.
Of these DCT coefficients, the value of one DCT coefficient on the relatively high frequency side can be used as the complexity. For example, the value at the position indicated by the symbol P can be used as the complexity. Which DCT coefficient should be used should be determined so that a desired result can be obtained while confirming the actual processing result. For example, when the number of pixels is reduced, the frequency at which the degree of deterioration of the image quality increases becomes high. It is conceivable to use DCT coefficients.

A determining unit configured to determine which of the picture image data after the color reduction processing and the picture image data after the pixel number reduction processing is to be compressed, based on the complexity calculated by the frequency calculation unit; A function of outputting the determined content to the control unit 205 is provided.
Note that the determination process performed by the determination unit 204 is a process of a determination procedure.

  This determination is made by comparing the value of the complexity with a predetermined threshold value T1. If the value is larger than the threshold value, the pattern image data to be processed contains a large amount of high-frequency components. Is smaller, it is determined that the high-frequency component is smaller (the degree of change in the pixel value is smaller as a whole, and the image is a flat image). In the former case, it is determined to compress the picture image data after the color reduction processing, and in the latter case, it is determined to compress the picture image data after the pixel number reduction processing.

  The reason for this determination is that if the number of pixels is reduced when the degree of change in the pixel value is large, the portion where the hue changes finely will be lost, and the image quality may be significantly degraded. . On the other hand, when the degree of change in the pixel value is small, the image quality does not deteriorate so much even if the number of pixels is reduced. Therefore, in this case, by performing the pixel number reduction processing, the data size of the file can be significantly reduced while maintaining the image quality. Even if 24 bits per pixel is reduced to 8 bits per pixel by the color reduction processing, the data amount is only reduced to 1/3. It can be reduced to 1/16.

Next, in accordance with the determination made by the determination unit 204, the control unit 205 of FIG. 3 converts the pattern image data after the color reduction processing by the color reduction processing unit 201 and the pattern image data after the pixel number reduction processing by the pixel number reduction processing unit 202. It has a function of an output unit that outputs one of them to the compression unit 206. The process of outputting data to the compression unit 206 is a process of an output procedure.
The compression unit 206 has a function of a compression unit that compresses the acquired image data.
These are the various functions of the picture image data compression unit 24. Note that the picture image data compression section 24 outputs the image data after compression by the compression section 206 to the synthesis section 25 shown in FIG.

Next, FIG. 6 shows a procedure of a process of determining a compression target performed by the determination unit 204 described above. This processing is actually executed by the processor included in the image processing unit 113.
In the processing of FIG. 6, first, the determination unit 204 acquires the value of the complexity calculated by the frequency calculation unit 203 (S101). Then, the determination unit 204 determines whether the acquired value of the complexity is larger than a predetermined threshold T1 (S102), and if it is larger (Yes in S102), determines that the degree of change in the pixel value is large, It decides to compress the picture image data after the color reduction processing. If it is not large in step S102 (No in S102), it is determined that the degree of change in the pixel value is small, and it is determined to compress the picture image data after the pixel number reduction processing. Finally, the content determined in step S103 or S104 is notified to the control unit 205 (S105), and this processing ends.

  The above is the description of the first embodiment of the present invention. As described above, by determining whether to perform the color reduction processing or the pixel number reduction processing in accordance with the value of the complexity of the image data, the color reduction processing is performed when the image quality does not deteriorate even if the color reduction processing is performed. In this case, if the data size is reduced and the image quality deteriorates when the color reduction processing is performed, the data size can be reduced while maintaining the image quality by performing the pixel number reduction processing.

[Second Embodiment: FIGS. 7 and 8]
Next, an image forming apparatus according to a second embodiment of the image processing apparatus of the present invention will be described.
The basic configuration of the second embodiment is the same as that of the first embodiment, but there are differences in the functions of the picture image data compression unit 24 and the procedure of the processing to be performed. Therefore, the proof about the common part is omitted, and only the matters related to the differences will be described. In addition, the same reference numerals are used for configurations common to or corresponding to the first embodiment.

FIG. 7 illustrates a functional configuration of the picture image data compression unit 24 in the image forming apparatus 10 according to the second embodiment. Here, portions different from the first embodiment will be described.
The picture image data compression unit 24 includes a blocking unit 207, a reduced color data compression unit 209, a pixel number reduction data compression unit 210, and a combining unit 211 in addition to the functions described in FIG. Further, a control unit 208 is provided instead of the control unit 205 in FIG.
Among these, the blocking unit 207 has a function of dividing the pattern image data supplied from the image data separation unit 22 into predetermined regions (blocks), and the frequency calculation unit 203 transmits the coordinate information of the region into which the pattern image data is divided. And a function to pass. The size of the area divided by the blocking unit 207 is set in advance.

The function of the frequency calculation unit 203 is almost the same as the example of FIG. However, in this embodiment, the value of the complexity is calculated for each area based on the coordinate information of the area acquired from the blocking unit 207.
The function of the determination unit 204 is almost the same as the example of FIG. However, in this embodiment, the comparison between the value of the complexity and the threshold value T1 and the determination of which of the picture image data after the color reduction processing and the picture image data after the pixel number reduction processing are to be compressed are performed for each area. . Then, the determination unit 204 outputs, to the control unit 208, the content of the determination regarding the region together with the coordinate information of each region.

Control unit 208, according to the determined acquired from the determination unit 204, and a function of outputting the area to be compressed to a subtractive color data compressing unit 209 of the picture image data after the color reduction process, among the picture image data after the reduction processing pixel number It has a function of an output unit that outputs a compression target area to the pixel number reduction data compression unit 210.
Note that, here, the control unit 208 converts an area other than the compression target area in the pattern image data after the color reduction processing into a white background area composed of white pixels, and then converts the entire converted pattern image data into a color reduction data compression unit. The above-mentioned output is performed by a method of outputting the data to the 209 and compressing it. Further, after converting the area other than the compression target area in the picture image data after the pixel number reduction processing into a white background area composed of white pixels, the entire converted picture image data is output to the pixel number reduction data compression unit 210. The above-mentioned output is performed by a method of performing compression.

The color reduction data compression unit 209 has a function of a first compression unit that compresses the picture image data after the color reduction processing supplied from the control unit 208 by using an algorithm suitable for the data after the color reduction processing.
The pixel number reduction data compression unit 210 has a function of a second compression unit that compresses the picture image data after the pixel number reduction process supplied from the control unit 208 using an algorithm suitable for the data after the pixel number reduction process.

The combining unit 211 basically has the same function as the combining unit 25. However, the synthesizing unit 211 obtains the compressed picture image data from the color-reduction data compression unit 209 and the pixel number reduction data compression unit 210, and combines the two pieces of compressed image data to generate the compressed image data for output. I do.
The combining unit 211 outputs the compressed image data obtained by combining to the combining unit 25 (see FIG. 2).
The above is the function of the picture image data compression unit 24 in the second embodiment. The functions not mentioned here are the same as the functions described with reference to FIG.

Next, FIG. 8 shows a procedure of a compression target determination process performed by the determination unit 204 described above. This processing is actually executed by the processor included in the image processing unit 113.
In the process of FIG. 8, first, the determination unit 204 acquires the value of the complexity of the picture image data calculated for each area by the frequency calculation unit 203 (S121). Next, the determination unit 204 sets one area that has not yet been determined as a determination target (S122). Next, it is determined whether or not the value of the complexity obtained for the area to be determined is greater than a predetermined threshold T1 (S123). If it is greater than T1, it is determined that the degree of change in the pixel value is large, and the determination target is determined. It is determined that the image data after the color reduction processing is to be compressed for the area (S124). If it is not greater than T1, it is determined that the degree of change in the pixel value is small, and for the determination target area, it is determined that the data after the pixel number reduction processing is to be compressed (S125).

When the processing in step S124 or S125 is completed, the determination unit 204 determines whether there is an area that is not yet a determination target. If there is any area (Yes in S126), the processing returns to step S122 and repeats this processing. On the other hand, if not (No in S126), the contents determined in step S124 or S125 are notified to the control unit 208 for all areas (S127) , and this processing ends. The above is the determination process performed by the determination unit 204.

  The above is the description of the second embodiment of the present invention. As described above, by calculating the complexity value for each area and determining whether to apply the color reduction processing or the pixel number reduction processing, the data size can be reduced while maintaining the image quality more appropriately for each area. It is possible to reduce the size.

[Third Embodiment: FIGS. 9 and 10]
Next, an image forming apparatus according to a third embodiment of the image processing apparatus of the present invention will be described.
Although the third embodiment has the same basic configuration as the second embodiment, there are some differences in the functions of the picture image data compression unit 24 and the procedure of the processing to be performed. Therefore, the proof about the common part is omitted, and only the matters related to the differences will be described. In addition, the same reference numerals are used for configurations common to or corresponding to the second embodiment.

First, FIG. 9 illustrates a functional configuration of the picture image data compression unit 24 in the image forming apparatus 10 according to the third embodiment.
The picture image data compression unit 24 includes a frequency replacement unit 212 in addition to the functions described in FIG. The frequency replacement unit 212 counts the number of regions where the value of the complexity calculated for each region of the pattern image data by the frequency calculation unit 203 exceeds a predetermined threshold. Then, the function of replacing the complexity value of each region calculated by the frequency calculation unit 203 based on the counted number and notifying the determination unit 204 of the complexity value of each region after the replacement is provided.

Here, FIG. 10 shows a procedure of the complexity replacement process for each region performed by the frequency replacement unit 212. This processing is executed by a processor included in the image processing unit 113.
In the process of FIG. 10, first, the frequency replacement unit 212 obtains the complexity value of the picture image data calculated for each region by the frequency calculation unit 203 (S141), and sets the threshold value T1 for the complexity value for each region. The number of areas larger than is counted (S142). Next, the frequency replacement unit 212 determines whether or not the number counted in step S142 is larger than the threshold T2 (S143).

  If Yes in step S143, it is determined whether the number counted in step S142 is smaller than a threshold value T3 (S144). In the case of YES here, the value of the complexity for each region calculated by the frequency calculation unit 203 for the entire region is notified to the determination unit 204 as it is. On the other hand, if No in step S144, the value of the complexity of all regions is replaced with a value L1 larger than the threshold value T1, and the value L1 is notified to the determination unit 204 as the value of complexity of all regions (S146).

If No in step S143, the value of the complexity of the entire area is replaced with a value L2 smaller than the threshold T1, and the determination unit 204 is notified of the value L2 as the value of the complexity of the entire area (S147). When the notification of step S145, S146, or S147 is transmitted to the determination unit 204, the processing performed by the frequency replacement unit 212 ends.
Note that the complexity value L1 may be set to any value as long as the determination unit 204 determines that the high frequency component is large in the processing in FIG. 8 (Yes in step S123). Further, any value may be set as the complexity value L2 as long as the value is determined to have a large number of low frequency components (No in step S123).

  In short, when there are many regions where the complexity value exceeds the threshold value T1, the frequency replacement unit 212 determines that the complexity value exceeds the threshold value T1 for all regions, and replaces the complexity value with the determination unit 204. Is output to Conversely, when there are many regions that do not exceed the threshold value T1, the complexity value is determined not to exceed the threshold value T1 for all regions, and the complexity value is replaced and output to the determination unit 204. In addition, in the intermediate case between them, the value of the complexity calculated by the frequency calculation unit 203 is output to the determination unit 204 as it is.

Here, it is considered that the pattern image data of the area where the value of the complexity exceeds the threshold value T1 contains a large amount of high-frequency components as described with reference to FIG. On the other hand, it is considered that the picture image data of the area not exceeding the threshold value T1 contains a lot of low frequency components. If almost the entire area of the picture image data contains many high-frequency components, it is more efficient to compress the image data after the color reduction processing assuming that all the areas are data containing many high-frequency components from the beginning. . Conversely, if almost the entire area of the picture image data does not contain many high-frequency components, it is better to compress the image data after the pixel number reduction process from the beginning assuming that all the areas do not contain many high-frequency components. Efficient.

  For this reason, in the third embodiment, the above-described frequency replacement unit 212 is provided, and when the number of regions where the complexity value exceeds the threshold value T1 is considerably large (greater than T2) or small (less than T3), The value of the complexity for each area is replaced with a uniform value and supplied to the determination unit 204. This allows the determination unit 204 to make a uniform determination for all regions.

Other functions of each unit are basically the same as those described in the picture image data compression unit 24 of the second embodiment. However, if the control unit 213 obtains from the determination unit 204 a decision to compress the pattern image data after the color reduction processing for the entire area as the compression target, the control unit 213 instructs the pixel number reduction data compression unit 210 to output the data after the pixel number reduction processing. Does not perform compression processing. On the other hand, when it is determined that the picture data after the pixel number reduction processing is to be compressed for the entire area, the reduced color data compression unit 209 is configured not to perform the compression processing on the data after the reduced color processing. I do.
By doing so, unnecessary compression processing is not performed, and an effect is obtained in which the effect of the second embodiment is substantially maintained, and furthermore, efficient compression processing can be performed as a whole.

[Fourth Embodiment: FIGS. 11 and 12]
Next, an image forming apparatus according to a fourth embodiment of the present invention will be described.
The fourth embodiment also has the same basic configuration as the second embodiment, but differs in the functions of the picture image data compression unit 24 and the procedure of the processing to be performed. Therefore, description of common parts is omitted, and only matters relating to differences are described. Further, components common or corresponding to the first to third embodiments have the same reference numerals.

First, FIG. 11 shows a functional configuration of the picture image data compression unit 24 in the image forming apparatus 10 according to the fourth embodiment.
The picture image data compression unit 24 includes a color number counting unit 214 and a pixel number reduction processing unit 215 in addition to the functions described in FIG. 7 includes a determination unit 216 and a control unit 217 instead of the determination unit 204 and the control unit 208 in FIG.
Among these, the color number counting unit 214 has a function of counting the number of colors of the pattern image data to be processed and notifying the determination unit 216 of the number of colors.

  The pixel number reduction processing unit 215 has a function of performing the same pixel number reduction processing as the pixel number reduction processing unit 202 on the pattern image data after the color reduction processing by the color reduction processing unit 201. Accordingly, the color reduction processing unit 201 also has a function of outputting the processed pattern image data to the pixel number reduction processing unit 215 as well as the control unit 217, and the color reduction processing unit 201 and the pixel number reduction processing unit 215 This constitutes three image processing means. Note that the third image processing means may perform a color reduction process after performing the pixel number reduction process.

Next, differences between the determination unit 216 and the determination unit 204 of FIG. 7 in the determination function performed by the determination unit 216 will be described.
The determination unit 216 determines whether or not the number of colors acquired from the number-of-colors counting unit 214 is greater than a preset threshold T4, and determines whether the complexity value for each region acquired from the frequency calculation unit 203 is a predetermined threshold T1. It is determined whether it is greater than or equal to. Then, based on the determination results, the picture image data after the color reduction processing output by the color reduction processing unit 201, the picture image data after the pixel number reduction processing output by the pixel number reduction processing unit 202, and the pixel number reduction processing unit 215 Is determined, which of the pattern image data that has been subjected to both the color reduction processing and the pixel number reduction processing is to be compressed. The determination unit 216 performs these determinations and determinations for each area divided by the blocking unit 207, as in the case of FIG.

  Here, the determination made by the determination unit 216 is one of the following four. (1) If the number of colors is larger than the threshold T4 and the value of the complexity of the area to be processed is larger than the threshold T1, the picture image data after the color reduction processing is set as the compression target. (2) If the number of colors is larger than the threshold T4 and the value of the complexity of the area to be processed is equal to or smaller than the threshold T1, the picture image data after the pixel number reduction processing is set as the compression target. (3) When the number of colors is equal to or smaller than the threshold T4 and the value of the complexity of the area to be processed is larger than the threshold T1, the picture image data after the color reduction processing is to be compressed. (4) When the number of colors is equal to or smaller than the threshold T4 and the value of the complexity of the processing target area is smaller than the threshold T1, the image data subjected to both the color reduction processing and the pixel number reduction processing is set as the compression target. .

The control unit 217 has a function of an output unit that outputs image data to be compressed to the reduced color data compression unit 209 and the reduced pixel number data compression unit 210 according to the determination acquired from the determination unit 216.
First, when the number of colors is larger than the threshold value T4, the determination performed by the determination unit is any of the above (1) and (2) for all the regions. In this case, the control unit 217 outputs the compression target area in the pattern image data after the color reduction processing by the color reduction processing unit 201 to the color reduction data compression unit 209, and the pattern after the pixel number reduction processing by the pixel number reduction processing unit 215. The compression target area of the image data is output to the pixel number reduction data compression section 210.

When the number of colors is not larger than the threshold value T4, the determination made by the determination unit is any of the above (3) and (4) for all the regions. In this case, the control unit 217 outputs to the number of pixels reduces the data compression unit 210 the region to be compressed out of the picture image data after the pixel count reduction process by the pixel number reduction processing unit 215, after the color reduction processing by the subtractive color processing unit 201 The compression target area of the picture image data that has been subjected to both the color reduction processing and the pixel number reduction processing is output to the color reduction data compression unit 209.

In this case, the image data processed by the pixel number reduction processing unit 215 is output instead of the image data processed by the color reduction processing unit 201. The image data processed by the pixel number reduction processing unit 215 is compressed by an algorithm suitable for the image data after the color reduction processing.
In any case, after converting the area other than the area to be compressed in the processed pattern image data into a white background area composed of white pixels, the converted pattern image data is output to the corresponding compression unit. This is similar to the case of the control unit 208 in FIG.

Next, FIG. 12 shows a procedure of the compression target data determination process performed by the determination unit 216 described above. This processing is actually executed by the processor included in the image processing unit 113.
The determination unit 216 obtains the number of colors of the pattern image data from the color count unit 214 and obtains the complexity value for each region from the frequency calculation unit 203 (S161). From among them, one area that has not yet been determined is determined as a determination target (S162).
Next, the determination unit 216 determines whether or not the number of colors of the pattern image data to be determined is larger than the threshold value T4 (S163). If “Yes” here, it is next determined whether or not the value of the complexity of the determination target area is larger than the threshold value T1 (S164). Here also, if Yes, the determination unit 216 determines to compress the picture image data after the color reduction processing (S165).
On the other hand, if No in step S164, the determination unit 216 determines to compress the picture image data after the pixel number reduction processing (S166).

Next, when it is determined as No in step S163, the determination unit 216 determines whether the value of the complexity of the determination target area is larger than the threshold value T1 (S167). If “Yes” here, the determination unit 216 determines to compress the picture image data after the color reduction processing (S168). On the other hand, if No in step S167, the determination unit 216 determines to compress the picture image data that has undergone both the color reduction processing and the pixel number reduction processing (S169).
After performing the processing of steps S163 to S169, the determination unit 216 determines whether there is an area that is not yet a determination target (S170). If Yes, the processing returns to step S162 and repeats this processing. . On the other hand, if No, the control unit 217 is notified of the determination in steps S165, S166, S168, and S169 (S171), and the process ends.

As described above, when compressing image data having a small number of colors, for an area having a small complexity value, if both the color reduction processing and the pixel number reduction processing are performed, the data size of the area can be further reduced. Therefore, the data size of the entire picture image data can be reduced.

[Fifth Embodiment: FIGS. 13 and 14]
Next, an image forming apparatus according to a fifth embodiment of the present invention will be described.
Although the fifth embodiment has the same basic configuration as the first embodiment, there are differences in the functions of the picture image data compression unit 24 and the procedure of the processing to be performed. Therefore, description of common parts is omitted, and only matters relating to differences are described. In addition, the same reference numerals are used for configurations common to or corresponding to the first to fourth embodiments.

First, FIG. 13 shows a functional configuration of the picture image data compression unit 24 in the image forming apparatus 10 according to the fifth embodiment. The design image data compression unit 24 differs from the configuration shown in FIG. 3 in that a resolution acquisition unit 218 and a determination unit 219 are provided instead of the frequency calculation unit 203 and the determination unit 204.
Among these, the resolution obtaining unit 218 has a function of obtaining the resolution of the pattern image data to be processed. If the resolution information is added to the picture image data as a property or the like, the information may be extracted, or may be calculated from the number of pixels and the size of printing or display. In addition, the resolution may be obtained by an arbitrary method.

The determining unit 219 has a function of determining whether the picture image data is high-resolution or low-resolution based on whether the resolution acquired by the resolution acquiring unit 218 exceeds a predetermined threshold T5. An arbitrary value is set in advance as the threshold T5. Then, based on the determination result, the determination unit 219 determines that the pattern image data after the color reduction processing is to be compressed when the resolution is low , and the pattern image after the pixel number reduction processing when the resolution is high. It also has a function of a determination unit that determines that data is to be compressed.
Function of the control unit 205, except for performing therefore output to the determination of the determination unit 219 are similar to those of the control unit 205 of FIG.
The above is the function of the fifth embodiment that is different from the first to fourth embodiments.

Next, FIG. 14 shows a procedure of the compression target data determination process performed by the determination unit 219 described above. This processing is actually executed by the processor included in the image processing unit 113.
In the process of FIG. 14, first, the determination unit 219 acquires the resolution of the picture image data from the resolution acquisition unit 218 (S181). Next, it is determined whether the acquired resolution is greater than the threshold T5 (S182), if it is greater, determines that the compression processing target picture image data after the pixel count reduction processing (S183). If not, it is determined that the picture image data after the color reduction processing is compressed (S184). Finally, the determination unit 219 outputs the determination made in step S183 or S184 to the control unit 205 (S185), and ends the processing in FIG.

  When the resolution of the image data is high, it is possible to maintain the image quality even if the number of pixels is reduced. On the other hand, when the resolution is low, the image quality is degraded if the number of pixels is reduced. Therefore, it is determined whether or not the resolution of the picture image data is high, and it is determined whether to perform the color reduction processing or the pixel number reduction processing. This makes it possible to reduce the data size while maintaining the image quality regardless of the level of the resolution.

  When the resolution of the picture image data is different in the main scanning direction and the sub-scanning direction, the resolution is obtained for each of them, and the ratio of the pixel number reduction in the pixel number reduction processing unit 202 is independently determined according to the resolution in each direction. You may. At this time, the higher the resolution, the more the number of pixels should be greatly reduced.

[Sixth embodiment: FIGS. 15 and 16]
Next, an image forming apparatus according to a sixth embodiment of the present invention will be described. The basic configuration of the sixth embodiment is the same as that of the first embodiment, but there are differences in the functions of the picture image data compression unit 24 and the procedure of the processing to be performed. Therefore, description of common parts is omitted, and only matters relating to differences are described. In addition, the same reference numerals are used for configurations common to or corresponding to the first to fourth embodiments.

First, FIG. 15 illustrates a functional configuration of the picture image data compression unit 24 in the image forming apparatus 10 according to the sixth embodiment.
The picture image data compression unit 24 illustrated in FIG. 15 includes a frequency calculation unit 221, a determination unit 222, a control unit 223, a pixel number reduction processing unit 224, and a compression unit 225. However, no color reduction processing unit is provided.

  Among them, the frequency calculation unit 221 has a function of obtaining a complexity value in each of the main scanning direction and the sub-scanning direction. For example, of the 8 × 1 DCT coefficients obtained in the main scanning direction, a specific coefficient on the high frequency side is obtained as the complexity in the main scanning direction, and among the 1 × 8 DCT coefficients obtained in the sub-scanning direction, It is conceivable to determine the specific coefficient on the side as the complexity in the sub-scanning direction.

The determination unit 222 determines whether or not the value of the complexity of the main scanning direction component is larger than a predetermined threshold T6, and whether or not the value of the complexity of the sub-scanning direction component is larger than a predetermined threshold T7. And a function of a determination unit for determining whether or not to perform the pixel number reduction process for each of the main and sub scanning directions based on the determination result.
If the value of the complexity in the main scanning direction is larger than T6, the determination unit 222 determines that the degree of fluctuation of the pixel value in the main scanning direction is large, and determines not to perform the pixel number reduction process in the main scanning direction. . On the other hand, if it is smaller, it is determined to perform the pixel number reduction process in the main scanning direction. Also in the sub-scanning direction, whether to perform the pixel number reduction process in the sub-scanning direction is determined based on whether or not the value of the complexity is larger than T7.

The control unit 223 has a function of outputting an instruction to the pixel number reduction processing unit 224 as to whether or not to perform the pixel number reduction process in each of the main scanning direction and the sub-scanning direction according to the determination made by the determination unit 222. .
The pixel number reduction processing unit 224 has a function of performing a pixel number reduction process on input picture image data in accordance with an instruction from the control unit 223. When the instruction content from the control unit 223 indicates that the pixel number reduction processing is not performed in any of the main and sub scanning directions, the pixel number reduction processing unit 224 does not perform the pixel number reduction processing. The image data is passed to the compression unit 225.
The compression unit 225 has a function of performing a compression process on the picture image data acquired from the pixel number reduction processing unit 224 as a compression target.

Next, FIG. 16 shows a procedure of the compression target data determination process performed by the determination unit 222 described above. This processing is actually executed by the processor included in the image processing unit 113.
In the processing of FIG. 16, first, the determination unit 222 acquires the complexity value in the main scanning direction and the complexity value in the sub-scanning direction of the input picture image data from the frequency calculation unit 221 (S201). Next, the determination unit 222 determines whether or not the acquired value of the complexity in the main scanning direction is larger than the threshold value T6 (S202). If the value is larger, it is determined that the process of reducing the number of pixels in the main scanning direction is not performed. It is determined (S203). If it is not larger , it is determined to perform the pixel number reduction process in the main scanning direction (S204).

Next, the determination unit 222 determines whether the value of the complexity in the sub-scanning direction acquired in step S201 is larger than the threshold value T7 (S205). If the value is larger, the pixel number reduction process in the sub-scanning direction is not performed. Is determined (S206). If it is not larger , it is determined to perform the pixel number reduction process in the sub-scanning direction (S207).
Finally, the determination unit 222 notifies the control unit 223 of the determination result determined in the processing of steps S202 to S207 (S208), and this processing ends.
In this way, by determining the degree of complexity of the picture image data separately in the main scanning direction and the sub-scanning direction, when the degree of complexity in the main and sub-scanning directions is different, the pixel number reduction processing corresponding to each is performed. By doing so, it is possible to appropriately reduce the data size.

In the processing described with reference to FIGS. 15 and 16, the number of thresholds is one in each of the main scanning direction and the sub-scanning direction. However, the number of thresholds does not need to be one. May be set, and the pixel number reduction rate may be changed according to the value of the complexity.
For example, as shown in Table 1, according to the comparison result between the complexity X in the main scanning direction and two different thresholds Tx1 and Tx2, the pixel number reduction rate in the main scanning direction is set in multiple stages. You may. Table 2 shows an example in which the number of reductions in the number of pixels in the sub-scanning direction is set in multiple stages according to the comparison result between the complexity Y in the sub-scanning direction and two different thresholds Ty1 and Ty2.

[First Modification: FIG. 17]
Next, a modified example of each of the above-described embodiments will be described.
First, a first modified example will be described. The first modification is different from the above-described embodiments in that the color reduction processing and the pixel number reduction processing of the image data are performed for each area. Here, only this change will be described.

FIG. 17 shows a functional configuration of the picture image data compression unit 24 when the first modification is applied to the second embodiment.
In the picture image data compression unit 24 shown in FIG. 17, the functions of the blocking unit 207, the frequency calculation unit 203, the determination unit 204, the color reduction data compression unit 209, the pixel number reduction data compression unit 210, and the synthesis unit 211 are as shown in FIG. Is the same as However, the functions of the control unit 231, the color reduction processing unit 232, and the pixel number reduction processing unit 233 are different from those in FIG.

First, the control unit 231 performs the color reduction on the data of the area in which the image data after the color reduction processing is determined to be compressed among the image data of the respective areas included in the input picture image data in accordance with the result of the determination unit 204. The processing unit 232 has a function of outputting data of an area determined to compress the image data after the pixel number reduction processing to the pixel number reduction processing unit 233.
The color reduction processing unit 232 has a function of performing color reduction processing on image data of each area supplied from the control unit 231 and outputting the image data to the color reduction data compression unit 209.
The pixel number reduction processing unit 233 has a function of performing pixel number reduction processing on image data of each area supplied from the control unit 231 and outputting the image data to the pixel number reduction data compression unit 210.

As described above, if the color reduction processing and the pixel number reduction processing are performed only on the area actually used for compression, the processing load and processing time can be reduced.
Note that these modifications can be applied to each embodiment other than the second embodiment.

[Second Modification: FIG. 18]
Next, a second modified example will be described. The second modification is different from the above-described embodiments in that the size of the area formed by the blocking unit 207 is changed according to the resolution of the picture image data to be processed. Here, only this change will be described.

FIG. 18 shows a functional configuration of the picture image data compression unit 24 when the second modification is applied to the second embodiment.
The configuration shown in FIG. 18 is the same as the configuration of the second embodiment shown in FIG. 7 except that a block adjusting unit 241 is added. Then, the block adjusting unit 241 has a function of a size changing unit that obtains the resolution of the pattern image data to be processed and changes the size of the area of the area division performed by the blocking unit 207 according to the resolution. At this time, if the resolution is high, the area size may be made large, and if the resolution is low, the area size may be made small.

By adjusting the area size according to the resolution in this manner, even when the resolution differs for each piece of picture image data, it is possible to reduce the data size while maintaining the same image quality.
Note that this modification is applicable to each embodiment that performs blocking, other than the second embodiment.

[Other modifications]
This concludes the description of the embodiment of the present invention. However, in the present invention, the specific configuration of the apparatus, the specific processing procedure, the calculation formula, the algorithm, and the like used in the processing are limited to those described in the embodiment. Not something.

In each of the embodiments described above, examples in which the present invention is applied to an image forming apparatus have been described. However, it is not essential that the image processing apparatus of the present invention has an image forming function. For example, the present invention is applicable to image data processing (especially involving compression) in any electronic device having an image processing function or an information processing function, such as a PC, a digital camera, and a smartphone.
In the present invention, it is not essential to divide character image data and picture image data. Even when the entire image data for one sheet is subjected to the processing of the picture image data compression unit 24 in each of the above embodiments without performing these divisions, a certain effect can be obtained.
In addition, the function of the image processing unit 113 in each of the above-described embodiments can be separately provided in a plurality of devices, and the functions of the image processing unit 113 can be realized in cooperation with those devices.
In addition, the present invention can be realized in any form, such as a method, a system, a program, and a recording medium, in addition to being realized as an apparatus.

  As an example, the program of the present invention is a program for causing a computer to control necessary hardware to realize the functions of the image forming apparatus 10 described above, particularly, the functions shown in FIG. Such a program may be stored in an external storage medium or the like in addition to being stored in the ROM 104. Further, it can be provided by being recorded on an arbitrary nonvolatile recording medium such as a memory card, a CD, a DVD, and a Blu-ray disc. Each of the above-described procedures can be executed by installing and executing the program recorded on the recording medium in another image forming apparatus.

It is also possible to download the program from an external device that is connected to a network and includes a recording medium on which the program is recorded, or an external device that stores the program in a storage unit, and installs and executes the program on a computer.
In addition, it is needless to say that the configurations of the above-described embodiments and modified examples can be arbitrarily combined as long as they do not conflict with each other.

10: image forming apparatus, 21: image data acquisition unit, 22: image data separation unit, 23: character image data compression unit, 24: picture image data compression unit, 25, 211: combining unit, 26: output unit, 101: Controller: 102: CPU, 103: RAM, 104: ROM, 105: HDD, 106: Communication I / F, 107: Operation unit I / F, 108: Operation unit, 109: System bus, 110: Engine control unit, 111 : Image reading section, 112: plotter section, 113: image processing section, 201, 232: color reduction processing section, 202, 215, 224, 233: pixel number reduction processing section, 203, 221: frequency calculation section, 204, 216 219,222: determination unit, 205,208,213,217,223,231: control unit, 206, 225: compressor unit, 207: blocking unit, 20 : Subtractive color data compression unit, 210: number of pixels reduces the data compression unit, 212: frequency transposition unit, 214: color number counting unit, 218: resolution obtaining unit, 241: Block adjuster

JP 2005-269271 A JP 2009-159598 A

Claims (8)

First image processing means for performing color reduction processing on the pattern image data to be processed;
To picture image data of the processing target, and the second image processing means for performing the number of pixels reduction processing by switching the degree of reducing the number of pixels according to the resolution of the該絵pattern image data,
Calculation means for calculating the complexity indicating the degree of variation of the pixel value in the pattern image data to be processed,
According complexity of the calculation unit is calculated to determine outputs one of the picture image data after the pixel number reduction process by the picture image data and the second image processing unit after the color reduction processing by said first image processing means Determining means ;
Block processing means for dividing the pattern image data to be processed into predetermined areas, and passing coordinate information of the divided areas to the calculation means ,
The calculating means calculates the complexity for each area based on the coordinate information of the area obtained from the blocking means,
The determining means determines, for each of the areas, which of the picture image data after the color reduction processing by the first image processing means and the picture image data after the pixel number reduction processing by the second image processing means is output. An image processing apparatus characterized by the above-mentioned. The image processing device according to claim 1,
The determining means, when the degree of variation indicated by the complexity is larger than a predetermined threshold, the pattern image data after the color reduction processing by the first image processing means, and when the degree of fluctuation is not larger than the predetermined threshold, An image processing apparatus, which determines to output picture image data after the pixel number reduction processing by a second image processing means. The image processing device according to claim 1 or 2 ,
An image processing apparatus comprising: a size changing unit configured to change a size of the predetermined area according to a resolution of an image indicated by the pattern image data to be processed. The image processing apparatus according to claim 1 , wherein:
The image processing apparatus , wherein the calculating means calculates, as the complexity, a value of a specific spatial frequency component obtained by performing a discrete cosine transform or a Fourier transform on the pattern image data to be processed. The image processing apparatus according to claim 1 , wherein:
A separation unit for separating the input image data into a character portion and a picture portion,
An image processing apparatus, wherein a pattern portion of the input image data is set as the pattern image data to be processed. The image processing apparatus according to claim 1 , wherein:
First compression means for compressing the picture image data after the color reduction processing by the first image processing means;
A second compression unit for compressing the picture image data after the pixel number reduction processing by the second image processing unit;
Of picture image data after compression by the first compression means, and the picture image data to be output according to the determination of said determining means, among the picture image data after compression by the second compression unit, in accordance with the determination of said determining means An image processing apparatus comprising: synthesizing means for synthesizing picture image data to be output and generating compressed image data for output. A first image processing procedure for performing color reduction processing on the pattern image data to be processed;
To picture image data of the processing target, and the second image processing procedure for the pixel number reduction processing by switching the degree of reducing the number of pixels according to the resolution of the該絵pattern image data,
A calculation procedure for calculating a complexity indicating a degree of variation of a pixel value in the pattern image data to be processed;
According complexity of the calculation procedure has been calculated, determines whether to output either of the picture image data after the pixel number reduction processing by the first image processing picture image data and the second image processing procedure after color reduction by procedures Decision procedure ;
Dividing the pattern image data to be processed into predetermined areas, and passing coordinate information of the divided areas to the calculation procedure ,
The calculating step calculates the complexity for each area based on the coordinate information of the area obtained from the blocking step,
The determining step determines, for each of the regions, which of the picture image data after the color reduction processing in the first image processing procedure and the picture image data after the pixel number reduction processing in the second image processing procedure is output. An image processing method comprising: On the computer,
A first image processing procedure for performing color reduction processing on the pattern image data to be processed;
To picture image data of the processing target, and the second image processing procedure for the pixel number reduction processing by switching the degree of reducing the number of pixels according to the resolution of the該絵pattern image data,
A calculation procedure for calculating a complexity indicating a degree of variation of a pixel value in the pattern image data to be processed;
According complexity of the calculation procedure has been calculated, determines whether to output either of the picture image data after the pixel number reduction processing by the first image processing picture image data and the second image processing procedure after color reduction by procedures Decision procedure ;
Dividing the pattern image data to be processed into a predetermined area, and passing the coordinate information of the divided area to the calculation procedure .
In the calculation procedure, based on the coordinate information of the area obtained from the blocking procedure, the complexity is calculated for each area,
In the determining step, a determination is made for each of the areas as to which of the picture image data after the color reduction processing in the first image processing procedure and the picture image data after the pixel number reduction processing in the second image processing procedure is output. Program for.

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