JP2001257873A - Device and method for image processing and computer- readable storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce moire and also accelerate the processing for that. SOLUTION: Before performing thinning-out type resolution conversion processing wherein the read resolution R2 of an image reader is set to >=2 times as high as specified resolution Rx and image data read with the read resolution R2 are thinned out to thinning-out resolution R3 which is one-integerth of the read resolution R2, this image processing device 101 filters only data of pixels which are left without thinned out through the resolution conversion processing and then carries out the thinning-out type resolution conversion processing and bilinear resolution conversion processing so that the image data after the filter processing and thinning-out type resolution conversion processing have the specific resolution Rx.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing apparatus, method, and computer-readable storage medium suitable for performing image processing for reducing moiré.

[0002]

2. Description of the Related Art As an image reading apparatus, an image scanner using an image sensor is known. Normally, when reading an image, read the image at the specified resolution and output it as it is, or read the image at a scan resolution higher than the specified resolution and perform resolution conversion processing to the specified resolution and output it Or that has been done.

Here, moiré will be described. Moiré occurs when a halftone-printed document is scanned and is related to the arrangement of the halftone dots. This moiré is conspicuous when the original has 150 or more screen lines and the resolution is 150 dpi. In other words, the image of the halftone-printed document is generally composed of the three-primary mixed color Mg.
The halftone dots of / Cy / Ye are regularly arranged, and the color density is represented by its size. When the number of screen lines is 150, the dot density per color is 150 dots / inch, and a different screen line angle (for example, 15 °) for each color.
/ 45 ° / 75 °). Scan resolution is 1
In the case of 50 dpi, the number of read dots in the main scanning direction is
It is 150 dots / inch. Therefore, for example, the halftone dots arranged at the screen line angle of 45 ° correspond to the main scanning direction (0 °).
Direction) is 106 dots / inch, and interference occurs between two different types of repetition frequencies.
= 44 lines / inch (1.7 mm). The same phenomenon occurs in the sub-scanning direction.

As a general method for reducing the above-mentioned moiré, an image reading device reads an image at a resolution exceeding a specified resolution, performs a filtering process on data of all the pixels, and performs a resolution conversion process to the specified resolution. There is a technique to do.

[0005]

However, if an image is read at a scan resolution higher than the resolution (designated resolution) of the image that is ultimately desired to be obtained, and filter processing or the like is performed on the data of all the pixels, the processing must be performed. There is a problem that it takes time. On the other hand, if an image is read with a reduced scanning resolution, the moiré reduction effect will be diminished accordingly.

The present invention has been made in view of the above-described problems, and has as its object to reduce moiré and speed up processing for reducing moiré.

[0007]

An image processing apparatus according to the present invention is an image processing apparatus for processing image data read at a reading resolution exceeding a designated resolution. A thinning-out resolution conversion means for performing a thinning-out resolution conversion process on the other hand,
Filter means for performing filter processing only on data of pixels remaining without being thinned out by the resolution conversion processing of the thinning method, and the designated resolution for image data which has been subjected to the filter processing and the resolution conversion processing of the thinning method And a resolution conversion means for performing a predetermined type of resolution conversion processing so that

Another feature of the image processing apparatus of the present invention is that a resolution designating means for designating the designated resolution and a reading resolution setting means for setting the reading resolution to a value exceeding the designated resolution. In that it has

Another feature of the image processing apparatus of the present invention is that the reading resolution setting means sets the reading resolution to be at least twice the designated resolution.

Another feature of the image processing apparatus of the present invention is that the thinning-out resolution conversion means performs the thinning-out resolution conversion processing so that the resolution after the thinning-out becomes an integral number of the reading resolution. The point is to do.

According to another feature of the image processing apparatus of the present invention, when the filter processing means performs the filter processing on the data of the pixels remaining without being thinned, the resolution of the thinning method is used. The point is that after the conversion process, the filtering process is performed by including data of pixels adjacent in the main scanning direction and the sub-scanning direction.

Another feature of the image processing apparatus according to the present invention is that the image processing apparatus further comprises a judging means for judging whether or not the specified resolution exceeds a predetermined resolution set in advance. In the case where the number exceeds the resolution, the resolution conversion processing of the thinning method, the filter processing, and the predetermined resolution conversion processing are performed.

According to another feature of the image processing apparatus of the present invention, when the designated resolution is equal to or less than the predetermined resolution, the thinning-out resolution converting means does not perform the thinning-out resolution converting process, and The means performs a filtering process on the data of all pixels of the image data read at the reading resolution, and the resolution conversion means performs a predetermined process so that the filtered image data has the specified resolution. The point is that resolution conversion processing is performed.

According to another feature of the image processing apparatus of the present invention, when the filter processing means performs the filter processing on the data of all the pixels, the filter processing means may perform the processing in the main scanning direction and the sub-scanning direction. The filter processing is performed by including data of adjacent pixels.

Another feature of the image processing apparatus of the present invention is that the predetermined resolution is set to 150 dpi.

Another feature of the image processing apparatus of the present invention resides in that the resolution conversion processing of the predetermined method is a resolution conversion processing of a bilinear method.

An image processing method according to the present invention is an image processing method for processing image data read at a reading resolution exceeding a designated resolution. A procedure of performing a conversion process, a procedure of performing a filter process only on data of pixels remaining without being decimated by the resolution conversion process of the decimating method, and an image data subjected to the filter process and the resolution conversion process of the decimating method. And performing a resolution conversion process of a predetermined method for the specified resolution.

A computer-readable storage medium according to the present invention is characterized in that a program for causing a computer to function as each unit of the image processing apparatus is stored.

The computer-readable storage medium of the present invention is characterized in that a program for causing a computer to execute each procedure of the image processing method is stored.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an image processing apparatus, a method, and a computer-readable storage medium according to the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an image processing apparatus 101 connected to an image reading apparatus 102. Image processing device 10
In 1, reference numeral 11 denotes a control unit. An image processing unit 12 performs image processing such as filtering on image data read by the image reading apparatus 102. Reference numeral 13 denotes an output unit that outputs image data on which image processing has been performed. Note that arrows indicated by dotted lines in the drawing indicate the flow of image data.

FIG. 2 schematically shows a configuration example of a so-called flatbed scanner as an example of the image reading apparatus 102. FIG. 2A is a side view, and FIG.
FIG. 3A is a diagram of the document table 1 viewed from the back side. In the figure, 1 is a platen, 2 is a white reference plate for obtaining shading correction data, 3 is an optical unit having an image sensor,
Reference numeral 4 denotes a document reading area of the document table 1. The scanning resolution (reading resolution) of the image reading apparatus 102 can be set in the image processing apparatus 101.

In such an image reading apparatus 102,
By scanning the optical unit 3 in parallel with the document table 1 by a moving means (not shown), the document on the document reading area 4 is read and an image signal is obtained from the image sensor. In this case, as shown in FIG. 2B, the direction from 0 to X is the main scanning direction, and the direction from 0 to Y is the sub-scanning direction (however, the document table 1 is viewed from the back. Be careful). Hereinafter, “mainly adjacent” means that they are adjacent in the main scanning direction, and “sub-adjacent” means that they are adjacent in the sub-scanning direction.

Next, processing operations in the image processing apparatus 101 and the image reading apparatus 102 will be described with reference to the flowcharts shown in FIGS. A predetermined resolution _R0 is set in the image processing apparatus 101 (step S1).
00). Then, when the designated resolution _Rx is input (step S200), the control unit 11 determines whether or not the designated resolution _Rx exceeds the predetermined resolution _R0 (step S300). Control to perform the following two types of processing.

[0025] In the step S300, the designated resolution R _x is the resolution R _1, if it exceeds the above predetermined resolution R _0, the control unit 11, a scan resolution R ₂ of the image reading apparatus 102, the designated to set to be twice or more the resolution R ₁ (step S400). To this way two or more times the scan resolution R ₂ specified resolution R ₁ is
This is because a higher moiré reduction effect can be obtained by performing a filtering process on image data read at a scan resolution twice or more.

[0026] In the image reading apparatus 102 executes the reading of the image in scanning resolution R _2, which are the set, and sends the obtained image data to the image processing unit 12 of the image processing apparatus 101 (step S500).

The image processing unit 12 includes an image reading device 102
Resolution conversion on the image data read, in the case of performing the resolution conversion processing of thinning method to be described later, i.e., decimating the scan resolution R ₂ to the resolution R ₃ is an integral submultiple of the scan resolution R ₂ in when the processing was performed, it specifies the pixel P _x which remains without thinned (step S
600).

In the image processing section 12, the pixel P
Filter processing A for reducing moiré is performed only on _x (step S700). Here, the filter A, characterized in that it included the data of pixels adjacent to the main and sub after resolution conversion processing to the resolution R _3.

After the filter processing A, the image processing unit 12
Run the resolution conversion processing of thinning scheme described above, converts the resolution of thinning the scan resolution R ₂ to the resolution R ₃ is one of the integer fraction (step S800). Since this resolution conversion processing is a thinning-out method, the processing time is short.

As described above, by performing the filter processing (step S700) before performing the resolution conversion processing of the thinning method (step S800), the filter processing can be performed while using the data of the pixels to be thinned, and the moiré can be performed. The reduction effect is enhanced, and a more natural result can be obtained from the final image after processing.

[0031] After the resolution conversion processing of the filter process A and decimation method, performs resolution conversion processing bilinear from the resolution R ₃ to finally specify the resolution R ₁ required (step S900). The reason for using the bilinear resolution conversion method is to obtain a high-quality image free from jaggies and the like.

The image data of the designated resolution R ₁ obtained in this way is output from the output unit 13 as an output in response to the request.

In the present embodiment, the predetermined resolution R ₀
Is set to 150 dpi (step S100). 1
The reason why 50 dpi is used is that most of the halftone printed matter has a screen number of 150 lines, so that moiré is likely to occur near 150 dpi, and an effective method for avoiding it is as follows.
This is because reading is performed at twice or more the resolution. Then, if _R0 is set to 150 dpi, the above step S4
By the processing of 00, an image is always read at a resolution of 300 dpi or more, and if a filtering process is performed therefrom, the effect of reducing moiré is enhanced.

For example, if the designated resolution R _x is R ₁ = 180 dpi
In this case, the scan resolution R ₂ of the image reading apparatus 102 is set to 600 dpi, which is twice or more the 180 dpi.
Is set (step S400).

600 dp obtained from the image reading device 102
For the image data of i (step S500), FIG.
As shown in FIG.
(Step S60)
0, 700). Here, the filtering of the pixel data for each of the main and sub three pixels is performed in a later step S800 because the resolution conversion processing for thinning out to 200 dpi which is one third of 600 dpi is performed. This is because the filter processing is performed only on the data of the pixels remaining after the processing.

In FIG. 5 (c), the hatched pixel at the center is the pixel to be filtered. Then, by applying a 7 × 7 diamond type filter, after performing resolution conversion processing of the thinning-out method, data of adjacent pixels (pixels indicated by reference numeral 1000 in FIG. 5C) are included in the filter processing A It can be performed. Since moire is generated by interference between adjacent pixels, the interference can be reduced by filtering including data of adjacent pixels. In addition, since moiré appears in different directions in the main scanning and sub-scanning directions, the use of a diamond-type filter capable of coping with both directions improves the effect of alleviating interference and provides an image with a high moiré reducing effect. it can.

After the filtering process, a resolution conversion process is performed to reduce the resolution to 200 dpi which is one third of 600 dpi (step S800). By doing so (step S900), desired image data is obtained.

On the other hand, in the step S300, the in designated resolution R _x resolution R _4, when the were given resolution R ₀ or less, the control unit 11, a scan resolution R ₅ of the image reading apparatus 102, the to set to be twice or more specified resolution R ₄ (step S405). To this way scan resolution R ₅ twice or more designated resolution R _4, by performing filter processing on the image data read by the scan resolution to twice or more, a higher moire reduction effect obtained Because it can be done.

[0039] In the image reading apparatus 102 executes the reading of the image in scanning resolution R ₅ which is the set, and sends the obtained image data to the image processing unit 12 of the image processing apparatus 101 (step S505).

The image processing section 12 performs a filter processing B for reducing moire on the data of all pixels (step S750). Here, the filter processing B is characterized in that data of pixels adjacent at least both in the main and sub directions are included.

After the filtering process B, the image processing unit 12
And from the resolution R ₅ to finally specify the resolution R ₄ required performs resolution conversion processing bilinear (step S950). The reason for using the bilinear conversion method is to obtain a high-quality image free from jaggies and the like.

[0042] outputs the image data of the designated resolution R ₄ obtained in this way, the output unit 13 as an output to the request.

[0043] For example, the specified resolution R _x is R ₄ = 100dpi
If there was a in the scan resolution R ₅ of the image reading apparatus 102, 300dpi which is twice or more the 100dpi
(Step S405).

300 dp obtained from the image reading device 102
A 3 × 3 cross filter is applied to the image data of i (step S505) as shown in FIG. 5A (step S750). 3x
By applying the cross-type filter of No. 3 to the data of the pixel to be subjected to the filtering process (the pixel indicated by the hatched portion in the center of FIG. The filter processing B can be performed by including the data of the pixel denoted by reference numeral 1000), and an image having a high moiré reduction effect can be obtained.

Then, the image data of 300 dpi after the filtering process is converted into 100
By performing a scaling process on the dpi (step S950), desired image data is obtained.

As described above, according to the present embodiment, an image is read at a reading resolution exceeding the specified resolution _Rx , filtered, converted, and output to the specified resolution. In addition, when the designated resolution _Rx exceeds the predetermined resolution _R0 , the filter processing is performed only on the finally required pixel data, so that the processing speed can be increased. or,
As described in step S700 or step S750, by setting the filter size to include the data of the main and sub-pixels adjacent to each other, it is possible to obtain an image with a high moiré reduction effect.

As a specific example of steps S400 to S900, a 7 × 7 diamond-type filter is applied.
Although the example in which the resolution conversion processing is thinned out to one third has been described, the present invention is not limited to this.

For example, if the predetermined resolution R ₀ is similarly 150 d
When set to pi, designated resolution R _x is R ₁ = 25
Suppose that it was 0 dpi. In this case, the image reading device 102
The scan resolution R ₂ in is set to 600dpi which is twice or more of the 250 dpi (step S400).

600 dp obtained from the image reading device 102
For the image data of i (step S500), FIG.
As shown in the figure, 5 × 5
(Step S60)
0, 700). In this example, the resolution conversion processing for thinning out to 300 dpi, which is one half of 600 dpi, is performed instead of one third, so that every other pixel after thinning out becomes every other pixel. Therefore, by applying a filter to the pixel data of each of the main and sub two pixels, it is possible to perform a filter process only on the pixel data remaining after the resolution conversion process.

In FIG. 5B, the pixels shaded in the center are the pixels to be filtered. Then, by applying a 5 × 5 diamond type filter, after performing resolution conversion processing of the thinning-out method, data of pixels adjacent to the main and sub-pixels (pixels indicated by reference numeral 1000 in FIG. And the moiré reduction effect can be enhanced.

That is, when determining the filter size,
According to the resolution conversion processing of the thinning method, by selecting the minimum size that includes the main and sub-adjacent pixels after the resolution conversion processing, wasteful processing is omitted, and the moiré reduction effect is maintained. In addition, the processing speed can be improved.

In the above embodiment, the control section 11 and the image processing section 12 are combined to form a resolution specifying section, a reading resolution setting section, a thinning resolution conversion section, a filter section, a resolution conversion section, and a determination section. Functions are realized. Also, in FIG.
Although the image reading device 102 and the image reading device 102 are shown separately, for example, an image processing device may be built in the image reading device.

(Other Embodiments) In order to operate various devices to realize the functions of the above-described embodiments, an apparatus connected to the various devices or a computer in a system is used in the above-described embodiments. Supply the software program code to realize the functions of
The present invention also includes those implemented by operating the various devices according to programs stored in a computer (CPU or MPU) of the system or apparatus.

In this case, the program code of the software implements the functions of the above-described embodiment, and the program code itself and means for supplying the program code to the computer, such as the program The recording medium storing the code constitutes the present invention. As a recording medium for storing such a program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, C
D-ROM, magnetic tape, nonvolatile memory card, R
OM or the like can be used.

When the computer executes the supplied program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) or other operating system in which the program code runs on the computer. It goes without saying that such program codes are also included in the embodiments of the present invention when the functions of the above-described embodiments are realized in cooperation with the application software or the like.

Further, after the supplied program code is stored in a memory provided in a function expansion board of the computer or a function expansion unit connected to the computer, the function expansion board or the function expansion unit is specified based on the instruction of the program code. It is needless to say that the present invention also includes a case where the CPU or the like provided for performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

It should be noted that the shapes and structures of the respective parts shown in the above-described embodiments are merely examples of the embodiment for carrying out the present invention, and the technical scope of the present invention is thereby reduced. It should not be interpreted restrictively. That is, the present invention can be implemented in various forms without departing from the spirit or main features thereof.

[0058]

As described above, according to the present invention, it is possible to reduce moiré and speed up the processing for reducing moiré.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an image processing apparatus 101 according to an embodiment.

FIG. 2 is a diagram showing a configuration example of a so-called flatbed scanner as an example of the image reading apparatus 102;
2A is a side view, and FIG. 2B is a view of the document table 1 of FIG.

FIG. 3 is a flowchart showing a part of a processing operation in the present embodiment.

FIG. 4 is a flowchart showing a part of a processing operation in the present embodiment.

FIGS. 5A and 5B are diagrams for explaining filter processing, wherein FIG.
FIG. 3B is a diagram for explaining filter processing by a 3 × cross filter, FIG. 3B is a diagram for explaining filter processing by a 5 × 5 diamond filter, and FIG. 3C is filter processing by a 7 × 7 diamond filter. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Image processing apparatus 102 Image reading apparatus 1 Original platen 2 White reference plate 3 Optical unit 4 Image reading area 11 Control part 12 Image processing part 13 Output part

Claims (13)

[Claims] An image processing apparatus for processing image data read at a read resolution exceeding a designated resolution, wherein the thinning resolution performs a thinning-type resolution conversion process on the image data read at the read resolution. Conversion means, filter means for performing filter processing only on the data of pixels remaining without being thinned out by the resolution conversion processing of the thinning method, and image data on which the filtering processing and the resolution conversion processing of the thinning method are performed. And a resolution conversion unit for performing a predetermined type of resolution conversion processing so as to achieve the specified resolution. 2. The apparatus according to claim 1, further comprising: resolution specifying means for specifying the specified resolution; and reading resolution setting means for setting the reading resolution to a value exceeding the specified resolution. Image processing device. 3. The image processing apparatus according to claim 2, wherein the reading resolution setting means sets the reading resolution to be at least twice the designated resolution. 4. The thinning-out resolution converting means performs the thinning-out resolution converting process so that the resolution after the thinning-out becomes an integral fraction of the reading resolution. 2. The image processing device according to claim 1. 5. The filter processing means, when performing the filter processing on the pixel data remaining without being thinned out, is adjacent in the main scanning direction and the sub-scanning direction after the resolution conversion processing of the thinning method. The image processing apparatus according to claim 1, wherein the filter processing is performed by including pixel data. 6. A determination means for determining whether the specified resolution exceeds a predetermined resolution set in advance,
2. The resolution conversion process of the thinning method, the filtering process, and the predetermined resolution conversion process are performed when the designated resolution exceeds the predetermined resolution.
The image processing device according to any one of claims 1 to 5. 7. When the designated resolution is equal to or less than the predetermined resolution, the thinning-out resolution conversion means does not perform the thinning-out resolution conversion processing, and the filter means outputs all pixels of the image data read at the reading resolution. 7. The filter processing device according to claim 6, wherein a filter process is performed on the image data, and the resolution conversion unit performs a resolution conversion process of a predetermined method on the filtered image data so as to have the specified resolution. Image processing device. 8. The filter processing means, when performing the filter processing on the data of all the pixels, performs the filter processing by including data of pixels adjacent in the main scanning direction and the sub-scanning direction. The image processing apparatus according to claim 7, wherein: 9. The image processing apparatus according to claim 6, wherein the predetermined resolution is set to 150 dpi. 10. The image processing apparatus according to claim 1, wherein the resolution conversion processing of the predetermined method is a resolution conversion processing of a bilinear method. 11. An image processing method for processing image data read at a reading resolution exceeding a specified resolution, comprising: a step of performing a resolution conversion process of a thinning method on image data read at the reading resolution. A procedure of performing filter processing only on data of pixels remaining without being thinned out by the resolution conversion processing of the thinning method; and a step of performing the specified resolution on the image data on which the filter processing and the resolution conversion processing of the thinning method are performed. Performing a resolution conversion process of a predetermined method so that 12. A computer-readable storage medium storing a program for causing a computer to function as each means according to claim 1. Description: 13. A computer-readable storage medium storing a program for causing a computer to execute the procedures according to claim 11. Description: