JP2007281591A - Image processing apparatus and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus for performing resolution conversion by taking into account a compression efficiency. <P>SOLUTION: The image processing apparatus 2 calculates a magnification factor or a reduction factor to convert the resolution of respective raster objects in PDL data into an output resolution and performs magnification/reduction processing and revision of an effective resolution at the same time when it is required to decrease the effective resolution of an image at the convenience of image compression of a post-stage in the case that the magnification/reduction processing is applied to any raster object. Further, the processing of decreasing the effective resolution is efficiently carried out at the same time of performing the magnification/reduction processing in the case that adaptive magnification/reduction processing is applied to each pixel so as to avoid fonts and graphics from causing jaggy. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus that converts the resolution of image data.

For example, Patent Document 1 discloses an image output apparatus that reduces image data by resolution conversion and compresses the reduced image data.
JP-A-7-87303

  The present invention has been made from the above-described background, and an object thereof is to provide an image processing apparatus that performs resolution conversion in consideration of compression efficiency.

[Image processing device]
In order to achieve the above object, an image processing apparatus according to the present invention includes an effective resolution determining unit that determines an effective resolution according to input image data, and an effective resolution determined by the effective resolution determining unit. Resolution conversion means for converting the input image data into image data of a predetermined target resolution.

  Preferably, the image processing apparatus further includes a compression unit that compresses the image data subjected to resolution conversion by the resolution conversion unit to a data size equal to or less than a reference value, and the effective resolution determination unit is configured to perform the compression according to a compression rate by the compression unit. Determine the effective resolution.

  Preferably, the image processing apparatus further includes compression evaluation means for evaluating a compression characteristic of the image data based on the input image data, and the effective resolution determination means includes the evaluation result by the compression evaluation means and the resolution conversion means. The execution resolution is determined on the basis of the conversion magnification of the resolution conversion by.

  Preferably, the resolution conversion means selects one of a plurality of resolution conversion methods according to a conversion rate of resolution conversion when the effective resolution is lower than the target resolution, and the selected resolution conversion method The resolution conversion process is performed using.

  Preferably, the resolution conversion means converts the input image data into image data of the target resolution, and the effective resolution of the image data converted to the target resolution determined by the effective resolution determination means. The process of converting to resolution is performed simultaneously.

[program]
The program according to the present invention further includes a step of determining an effective resolution in accordance with the input image data, and converts the input image data into image data having a predetermined target resolution at the determined effective resolution. Causing the computer to execute the steps.

  According to the image processing apparatus of the present invention, it is possible to generate image data having a target resolution while taking into account the compression efficiency after resolution conversion.

First, the background of the present invention will be described.
For example, in an image output device such as a printer device, the input image data is compressed, and the compressed image data is transferred or stored, thereby reducing the bandwidth required for data transfer and data storage. Further, when the resolution of the input image data is smaller than the output resolution, for example, resolution conversion processing is performed in the image output apparatus to generate image data of the output resolution. Therefore, in an image output apparatus capable of outputting at a high resolution, the data amount of image data is particularly large. Therefore, it is desirable to reduce the data amount as much as possible until immediately before output.

  In response to such a request, when image data less than the output resolution is input, the input image data is encoded and transferred or stored as it is, and after being decoded, the image is enlarged to the output resolution. When image data having an output resolution or higher is input, a method of encoding the input image data by reducing it to the output resolution can be considered. However, this method has the following problems.

When there are multiple types of resolution raster objects in the PDL file, two-stage enlargement (reduction) processing is required to finally meet one image enlargement ratio, and since the quantization processing is repeated accordingly, the image quality is high. to degrade.
Further, when the encoding parameters of the image encoding method become tight, a defect due to the encoding method occurs, and the defect is amplified by the subsequent enlargement process and becomes noticeable.
In addition, when the defect is a problem as described above, it is common to reduce the effective resolution of the image, but in that case, if the image is reduced, the font and graphics become jaggy due to the enlargement process after compression, and the image quality is greatly increased. It deteriorates to.

Therefore, the image processing apparatus according to the present embodiment performs resolution conversion and encoding processing (compression processing) as follows.
That is, each raster object in the PDL data is subjected to enlargement / reduction processing according to the output resolution.
When performing the enlargement / reduction process, if it is necessary to reduce the effective resolution of the image due to the subsequent image compression, the enlargement / reduction process and the change of the effective resolution are performed simultaneously.
In the process of reducing the effective resolution, when adaptive enlargement / reduction processing is performed for each pixel so that fonts and graphics do not become jaggy, it is efficiently performed simultaneously with the enlargement / reduction process.

Next, a hardware configuration of the image processing apparatus 2 in the present embodiment will be described.
FIG. 1 is a diagram illustrating a hardware configuration of an image processing apparatus 2 according to the present invention, centering on a control apparatus 20.
As illustrated in FIG. 1, the image processing apparatus 2 includes a control device 20 including a CPU 202 and a memory 204, a communication device 22, a recording device 24 such as an HDD / CD device, an LCD display device or a CRT display device, and a keyboard. A user interface device (UI device) 26 including a touch panel and the like is included.
The image processing device 2 is a processing device provided in the printer device 10, for example, acquires image data via the communication device 22 or the recording device 24, converts the resolution of the acquired image data to an output resolution, The resolution-converted image data is encoded. Here, the output resolution is an example of the target resolution, and is the resolution of an image output by the output device (the printer device 10 in this example).

[Image processing program]
FIG. 2 is a diagram illustrating a functional configuration of the image processing program 5 executed by the control device 20 (FIG. 1).
As illustrated in FIG. 2, the image processing program 5 includes a PDL analysis unit 500, an image decoding unit 510, a resolution conversion unit 520, a code information estimation unit 530, a resolution determination unit 540, an image integration unit 550, and an encoding unit 560. Have
The image processing program 5 analyzes the PDL data, once decodes the code of the raster data, performs an enlargement process to the output resolution, generates print data (PrintReady), and generates the print data ( The output resolution image data) is encoded by controlling the code amount.

In the image processing program 5, the PDL analysis unit 500 analyzes the input PDL file, separates raster data and vector data, rasterizes the vector data, and outputs the raster data to the image integration unit 550. The data is output to the decoding unit 510. In this example, a specific example is a case where raster data is encoded by a predictive encoding method.
Also, the PDL analysis unit 500 compares the resolution of the input image data (PDL file) (hereinafter referred to as input resolution) with the output resolution (target resolution) to calculate the magnification to be enlarged or reduced. The obtained magnification (enlargement ratio or reduction ratio) is output to the resolution determination unit 540.

The image decoding unit 510 decodes the code data input from the PDL analysis unit 500 and outputs the decoded image data to the resolution conversion unit 520.
In addition, the image decoding unit 510 outputs information for evaluating the compression efficiency to the code information estimation unit 530. The image decoding unit 510 in this example outputs a part of symbols generated in the decoding process (in this example, the symbol corresponding to predictive) to the code information estimation unit 530.

The resolution conversion unit 520 performs resolution conversion processing on the image data input from the image decoding unit 510 in accordance with control from the resolution determination unit 540, and performs resolution conversion image data (image data of output resolution). Is output to the image integration unit 550.
The resolution conversion unit 520 of this example converts the input image data into the output resolution according to the effective resolution and output resolution input from the resolution determination unit 540, and converts the effective resolution of the image data of the output resolution. The conversion process is performed at the same time.
In addition, when instructed to protect the font or computer graphics (CG), the resolution conversion unit 520 of the present example protects the font or CG (hereinafter referred to as CG, etc.), and the effective resolution of the image data. Convert.

The code information estimation unit 530 evaluates the compression characteristics of the input image data and outputs the evaluation result to the resolution determination unit 540.
The code information estimation unit 530 of this example calculates a predictive middle rate based on the symbol (a symbol corresponding to the predictive medium) input from the image decoding unit 510, and determines the resolution of the calculated predictive middle rate. Output to the unit 540. The predictive predictive ratio is, for example, (number of pixels for which prediction was successful) / (total number of pixels).

The resolution determination unit 540 (control unit) determines the output resolution based on the compression characteristic evaluation result input from the code information estimation unit 530 and the magnification (enlargement rate or reduction rate) input from the PDL analysis unit 500. The effective resolution in the converted image data is determined, and the determined effective resolution is output to the resolution converter 520.
The resolution determination unit 540 of this example uses the predictive median input from the code information estimation unit 530 and the magnification input from the PDL analysis unit 500 to predictively the image data after being converted to the output resolution. Estimate the median rate, and based on the estimated predictive median rate, determine whether a predetermined compression rate can be achieved with one of the encoding parameters (parameters that control the compression rate) prepared in advance. . The encoding process (compression process) corresponding to the encoding parameters prepared in advance has irreversibility such that image quality deterioration falls within an allowable range.
The resolution determination unit 540 determines the effective resolution so that the predetermined compression rate can be achieved with the encoding parameter prepared in advance when the predetermined compression rate is not achieved with any of the encoding parameters prepared in advance. And the determined effective resolution and the magnification (corresponding to the output resolution) input from the PDL analysis unit 500 are output to the resolution conversion unit 520. The effective resolution is not the resolution determined only by the number of pixels, but the resolution of the image element itself. For example, the effective resolution is represented by the number of image blocks when a uniform size image block is filled with a single pixel value.

  The image integration unit 550 integrates the vector data (after rasterization) input from the PDL analysis unit 500 and the image data (resolution-converted data) input from the resolution conversion unit 520, and outputs the integrated image file. The data is output to the encoding unit 560.

The encoding unit 560 encodes the image file input from the image integration unit 550.
The encoding unit 560 of the present example encodes the resolution-converted image data using a predictive encoding method using any of the encoding parameters prepared in advance. Note that when the effective resolution of the image data is reduced, the predictive predictive ratio is improved, so that the compression efficiency by the predictive coding method is improved.

FIG. 3 is a diagram illustrating resolution conversion by the resolution conversion unit 520. In addition, although this figure demonstrates the resolution conversion of a one-dimensional direction, the resolution conversion of a two-dimensional direction is also the same. In addition, A to H in the figure are pixel values of the pixels 1 to 8, respectively.
When the pixel group (pixel 1 to pixel 8) illustrated in FIG. 3A is enlarged 1.5 times by the nearest neighbor method, the pixel group (pixel 1 to pixel 12) illustrated in FIG. It becomes. This enlargement process converts image data with input resolution into image data with output resolution.
Next, when the effective resolution of the output resolution image data (pixel 1 to pixel 12) is reduced to ½, a pixel group illustrated in FIG. 3C is obtained. In this example, in order to reduce the effective resolution to ½, the image is divided into image blocks composed of two pixels, and each image block is filled with the average pixel value of each image block. That is, the number of pixels included in the image does not change, but since two adjacent pixels are filled with the same pixel value, the resolution of the image is apparently halved as illustrated in FIG. 3D. ing. The process of changing the apparent resolution without changing the number of pixels is called effective resolution conversion.

  The resolution conversion process described with reference to FIG. 3 is a process of converting input resolution image data into output resolution image data (process from FIG. 3A to FIG. 3B), and effective output resolution image data. Including the process of changing the resolution (the process from FIG. 3B to FIG. 3C), but the input image (the image of FIG. 3A) and the output image (the image of FIG. 3C). Can be described in a certain pattern. That is, the resolution conversion unit 520 converts the image data of the input resolution into the image data of the output resolution by preparing a conversion formula associated with the magnification (output resolution / input resolution) and the effective resolution in advance. The process of changing the effective resolution of the image data of the output resolution can be performed simultaneously.

FIG. 4 is a diagram for explaining processing for changing the effective resolution while storing CG and the like. In this figure, the case where the effective resolution is reduced in the one-dimensional direction will be described as a specific example, but the same applies to the case where the effective resolution is converted in the two-dimensional direction. In addition, A to H in the figure are pixel values of the pixels 1 to 10, respectively.
In the pixel group illustrated in FIG. 4A, when adjacent pixels have the same pixel value, these pixels are determined to be pixels constituting CG or the like, and are pixels to be stored. In the case of a two-dimensional image, for example, when the pixel value of the target pixel matches any of the eight pixels around the target pixel, the resolution conversion unit 520 sets the target pixel as a storage target.
Next, the resolution conversion unit 520 divides the pixel group illustrated in FIG. 4A into a plurality of image blocks, and fills each of the divided image blocks with an average pixel value. At that time, the resolution conversion unit 520 excludes the storage target pixel in the calculation process of the average pixel value and the painting process with the average pixel value so that the pixel value of the pixel to be stored does not change. As a result, the pixel group illustrated in FIG. 4A is converted into the pixel group illustrated in FIG.
When the effective resolution is changed without storing CG or the like, as illustrated in FIG. 4C, each image block (a block of pixels 1 to 3, a block of pixels 4 to 6, and The blocks of pixels 7 to 9) are filled with uniform pixel values, and the effective resolution changes uniformly. However, when the effective resolution is changed while storing CG or the like, as illustrated in FIG. In addition, the pixel value corresponding to the pixel such as CG is stored as it is.

FIG. 5 is a flowchart of image processing (S10) by the image processing program 5 (FIG. 2). In this figure, only image processing for one raster object included in the PDL file will be described. Therefore, when a plurality of raster objects are included in the PDL file, image processing (S10) is performed for each raster object.
As shown in FIG. 5, in step 100 (S100), when a PDL file is input from the outside, the PDL analysis unit 500 (FIG. 2) extracts and extracts raster objects (code data) included in the PDL file. The encoded data (raster data) is output to the image decoding unit 510.
In addition, the PDL analysis unit 500 compares the resolution (input resolution) of the raster data with the output resolution, calculates the enlargement or reduction magnification, and outputs the calculated magnification to the resolution determination unit 540.

In step 105 (S105), the image decoding unit 510 decodes the code data input from the PDL analysis unit 500, and outputs the decoded image data (raster data) to the resolution conversion unit 520.
Also, the image decoding unit 510 outputs, to the code information estimation unit 530, a symbol indicating a run (that is, a continuous middle number of predictions) among symbols generated in the middle of decoding the code data.

  In step 110 (S110), the code information estimation unit 530 calculates a predictive middle rate of the entire image based on the run symbol input from the image decoding unit 510, and uses the calculated predictive middle rate as a compression characteristic. The evaluation value is output to the resolution determination unit 540.

In step 115 (S115), the resolution determination unit 540 determines whether image enlargement processing (that is, resolution conversion that increases the number of pixels) is necessary based on the magnification input from the PDL analysis unit 500. To do.
The image processing program 5 proceeds to the process of S120 when the enlargement process is necessary, and proceeds to the process of S140 when the enlargement process is not necessary.

In step 120 (S120), the resolution determination unit 540 uses the evaluation value (predictive median) input from the code information estimation unit 530 and the magnification (enlargement rate or reduction rate) input from the PDL analysis unit 500. Based on the calculated predictive predictive ratio in the image data after being converted to the output resolution, the predetermined compression ratio is achieved with any of the encoding parameters prepared in advance based on the calculated predictive predictive ratio. Determine if you can.
When it is determined that the default compression rate cannot be achieved with any encoding parameter, the image processing program 5 proceeds to the process of S125 in order to reduce the effective resolution of the image. When it is determined that the compression ratio can be achieved, the process proceeds to S140.

In step 125 (S125), the resolution determination unit 540 uses the evaluation value (predictive median) input from the code information estimation unit 530 and the magnification (enlargement rate or reduction rate) input from the PDL analysis unit 500. Based on this, the effective resolution is determined. The effective resolution is determined so that the image data of the output resolution can be converted into a predetermined compression rate by using an encoding parameter in which the image quality deterioration due to the compression processing is within an allowable range. For example, the resolution determination unit 540 has a table in which the effective resolution to be applied and the combination of the magnification and the predictive middle rate are associated with each other, and reads the effective resolution corresponding to the magnification and the predictive middle rate from the table.
The resolution determination unit 540 outputs the determined effective resolution and magnification to the resolution conversion unit 520.

In step 130 (S130), the resolution conversion unit 520 determines whether or not the user has instructed to protect the CG or the like.
If the image processing program 5 is instructed to protect CG or the like, the process proceeds to S135. If the instruction is not directed to protect CG or the like, the image processing program 5 proceeds to S145.

In step 135 (S135), the resolution conversion unit 520 determines whether or not the magnification input from the resolution determination unit 540 is 1.5 or more.
The image processing program 5 proceeds to the process of S145 when the enlargement magnification is 1.5 times or more, and proceeds to the process of S150 when the enlargement magnification is less than 1.5 times.
This is because when the effective resolution conversion is performed at an enlargement ratio of 1.5 times or more, the result does not change even if the effective resolution is converted while protecting CG or the like.

In step 140 (S140), the resolution determination unit 530 prohibits the conversion of the effective resolution and outputs the magnification (enlargement rate or reduction rate) to the resolution conversion unit 520.
The resolution conversion unit 520 enlarges or reduces the image data input from the image decoding unit 510 with the magnification input from the resolution determination unit 530 to generate image data of output resolution.

  In step 145 (S145), as illustrated in FIG. 3, the resolution conversion unit 520 applies the image data input from the image decoding unit 510 according to the magnification and effective resolution input from the resolution determination unit 530. A resolution conversion process for changing the number of pixels and a process for changing the effective resolution of the image are performed.

  In step 150 (S150), as illustrated in FIG. 4, the resolution conversion unit 520 performs the processing on the image data input from the image decoding unit 510 according to the magnification and effective resolution input from the resolution determination unit 530. Then, resolution conversion processing for changing the number of pixels and processing for changing the effective resolution of the image while protecting pixel values such as CG are performed.

In step 155 (S155), the resolution conversion unit 520 outputs the resolution-converted image data to the encoding unit 560 via the image integration unit 550.
The encoding unit 560 encodes input image data by a predictive encoding method using encoding parameters prepared in advance.

  As described above, the image processing apparatus 2 according to the present embodiment performs, for example, enlargement / reduction processing and processing for reducing the effective resolution necessary for code amount control even when printing a high-definition image that is difficult to compress. Since it can be performed simultaneously, each process is not performed sequentially, so that high productivity can be realized.

As a modification, the enlargement / reduction process (process for changing the number of pixels) and the process for changing the effective resolution may be performed in series. Also in this case, the compression efficiency of the output resolution image data (that is, the image data when the enlargement / reduction process is performed) is estimated, and the image data subjected to the enlargement / reduction process is subjected to the estimation result. Change the effective resolution and then encode.
In the above embodiment, the predictive predictive value in the image data of the output resolution is used as the evaluation value of the compression characteristic, but the appearance frequency of the prediction error may be used. Further, when the JPEG method is used, the number of non-zero coefficients may be used.

2 is a diagram illustrating a hardware configuration of an image processing apparatus 2 according to the present invention, centering on a control device 20. FIG. It is a figure which illustrates the function structure of the image processing program 5 performed by the control apparatus 20 (FIG. 1). It is a figure which illustrates resolution conversion by the resolution conversion part 520. FIG. It is a figure explaining the process which changes an effective resolution, preserve | saving CG etc. It is a flowchart of the image processing (S10) by the image processing program 5 (FIG. 2).

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Image processing apparatus 5 ... Image processing program 500 ... PDL analysis part 510 ... Image decoding part 520 ... Resolution conversion part 530 ... Code information estimation part 540 ... Resolution determination part 550: Image integration unit 560: Encoding unit

Claims (6)

Effective resolution determining means for determining the effective resolution according to the input image data;
An image processing apparatus comprising: resolution conversion means for converting input image data into image data having a predetermined target resolution at the effective resolution determined by the effective resolution determination means. Compression means for compressing the image data whose resolution has been converted by the resolution conversion means to a data size of a reference value or less;
The image processing apparatus according to claim 1, wherein the effective resolution determination unit determines the effective resolution in accordance with a compression rate by the compression unit. A compression evaluation means for evaluating the compression characteristics of the image data based on the input image data;
The image processing apparatus according to claim 2, wherein the effective resolution determination unit determines an execution resolution based on an evaluation result by the compression evaluation unit and a conversion magnification of resolution conversion by the resolution conversion unit. The resolution conversion unit selects one of a plurality of resolution conversion methods according to a conversion rate of resolution conversion when the effective resolution is lower than the target resolution, and uses the selected resolution conversion method to select a resolution. The image processing apparatus according to claim 1, wherein conversion processing is performed. The resolution conversion means converts the input image data into image data of the target resolution, and converts the effective resolution of the image data converted to the target resolution into the effective resolution determined by the effective resolution determination means. The image processing apparatus according to claim 1, wherein the processing is performed simultaneously. Determining the effective resolution according to the input image data;
Converting the input image data into image data of a predetermined target resolution at the determined effective resolution.

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