JP2007300580A - Image processing apparatus and toner save method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of reducing toner consumption without incurring image quality deterioration. <P>SOLUTION: The image processing apparatus includes a filter processing unit 3 which sets a DC component of filter characteristics to <1 and uses an image processing filter with a predetermined filter strength to perform filter processing on image data. Therefore, the density can be reduced in a solid portion wherein the density of an image is uniform, and the density is not reduced in an edge portion. Therefore, toner consumption can be reduced without incurring image quality deterioration. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus having a toner saving function.

  In recent years, a function for reducing toner consumption has been installed in image forming apparatuses such as a copy, a printer, and a facsimile.

  For example, Patent Document 1 proposes a method for saving toner without degrading the quality of a portion to be focused on by separating an image into a character portion, a line drawing portion, and a photograph portion and applying different toner saving methods. Yes.

  In Patent Document 2, the edge portion of the image and the other portion are discriminated and extracted, and the density is set in the extracted edge portion and the other portion according to the recording mode of the image. Discloses a technique for reducing toner consumption by performing data conversion.

JP 2001-219626 A JP-A-10-276333

  However, since the disclosed techniques of Patent Document 1 and Patent Document 2 perform processing such as region separation and edge determination, if an erroneous determination occurs in boundary separation or region determination, image quality deteriorates at the portion where the erroneous determination has occurred. Becomes remarkable. Depending on the result of the determination, a thin line or character information may be lost.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image processing apparatus and a toner saving method capable of reducing toner consumption without causing image quality degradation.

In order to achieve such an object, the image processing apparatus of the present invention sets a DC component of a filter characteristic to be less than 1 and performs a filtering process on image data using an image processing filter having a predetermined filter strength. It has composition which has.
As described above, the present invention uses the filter having a DC characteristic of the filter characteristic of less than 1 and having a predetermined filter strength for the filter processing, thereby reducing the density at the solid portion where the density of the image is uniform, and the edge. Do not decrease the density in the part. For this reason, it is possible to reduce toner consumption without causing image quality degradation.

  In the image processing apparatus, the image processing filter may have a filter characteristic that lowers the density of the image signal at a solid portion having a uniform density and does not lower the density of the image signal at an edge portion.

The image processing apparatus of the present invention includes a density conversion table, and the first image processing means for reducing the density of the entire image using the density conversion table, and the density at the edge portion of the image are And a second image processing unit that performs a filtering process so as to be in a state before the processing by the first image processing unit.
As described above, the present invention reduces the density of the entire image by the first image processing unit and increases the density of only the lowered edge portion by the second image processing unit. Toner consumption can be reduced.

  In the image processing apparatus, the first image processing means includes a plurality of density conversion tables corresponding to toner save amounts, and the second image processing means is used in the first image processing means. The filter used for the filter process may be changed according to the density conversion table.

  In the toner saving method of the present invention, the first step of reducing the density of the entire image using the density conversion table, and the density at the edge portion of the image are in a state before the processing by the first step. A second step of filtering. In the first step, a plurality of density conversion tables are switched and used in accordance with the save amount of toner, and in the second step, the density conversion table used in the first step is used. Accordingly, the filter used for the filtering process may be changed.

  According to the present invention, it is possible to reduce toner consumption without causing image quality degradation.

  Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  First, the configuration of the image processing apparatus 1 of the present embodiment will be described with reference to FIG. As shown in FIG. 1, the image processing apparatus 1 according to the present embodiment includes an image input unit 2, a filter processing unit 3, a first gradation correction unit 4, a first color space conversion unit 5, and a second gradation. A correction unit 6 and an image output unit 7 are provided.

  The image processing apparatus 1 shown in FIG. 1 performs various image processing on the RGB signal of the image read by the image input unit 2, and then converts the image signal into a YMCK signal by the first color space conversion unit 5. 7 is output. In addition, as shown in FIG. 2, the RGB signal of the image read by the image input unit 2 is converted into a Lab signal that does not depend on the device by the second color space conversion unit 10, and various types of images are converted to the Lab signal. After the processing, the third color space conversion unit 11 may convert the signal into a YMCK signal and output it to the image output unit 7.

  The filter processing unit 3 performs edge enhancement filter processing for enhancing high frequency components on the image signal. FIG. 3B shows filter characteristics used in this example. Normally, the image processing filter is designed with the DC component as 1, as shown in FIG. 3A, but in this embodiment, the DC component is set to be less than 1. By using such an image processing filter, the density of the “solid” portion of the uniformly filled image can be reduced. Further, as apparent from a comparison between FIGS. 3A and 3B, the filter strength maintains the same strength as a normal filter that does not reduce the density. Thus, the edge information can be maintained in a state before the toner amount is reduced. Therefore, the fine line and character information can maintain the sharpness of the image quality. The characters include thick characters and thin characters, but all information is maintained for thin characters, and outline information is maintained for thick characters. FIG. 4A shows a normal image processing filter, and FIG. 4B shows an example of an image processing filter in which the DC component is less than 1. The normal image processing filter shown in FIG. 4A becomes “1” when all the coefficients are added. However, the image processing filter of this embodiment shown in FIG. Less than 1 ”(0.7 in this embodiment).

  The first gradation correction unit 4 performs gradation conversion depending on the device characteristics of the image input unit 2 for the R, G, and B color image signals captured from the image input unit 2.

  The first color space converter 5 converts the RGB image signal into a YMCK image signal.

  The second gradation correction unit 6 performs gradation correction according to the characteristics of the image output unit 7. In other words, the gradation correction is performed so as to cancel the adverse effects (such as poor gray balance and gradation nonlinearity) caused by the device characteristics of the image output unit 7.

  As described above, in this embodiment, the density of the solid image portion can be reduced by using a filter having a DC component of less than 1 as the image processing filter used in the filter processing unit 3. Further, by setting the filter strength to the same strength as that of a normal filter, edge information such as characters and line drawings does not disappear.

A second embodiment of the present invention will be described with reference to the accompanying drawings.
In this embodiment, as shown in FIG. 5, a density conversion LUT (Look Up Table) unit 12 and a LUT / filter selection unit 13 are newly provided. In the embodiment shown in FIG. 5, image processing is performed on the RGB signal output from the image input unit 2 and then converted into a YMCK signal. Similarly, the RGB signal is converted into a Lab signal to perform image processing. Both are shown and then converted to YMCK signals.

  The image processing apparatus 1 of the present embodiment is provided with a plurality of modes for reducing the toner consumption. The first reduction mode for reducing the toner consumption amount and the second reduction mode for further reducing the toner consumption amount than the first reduction mode. When the toner reduction mode is selected from the user by an operation unit (not shown), toner consumption is reduced in the selected mode.

  The density conversion LUT unit 12 includes three types of density conversion LUTs shown in FIGS. 6 (A), 6 (B), and 6 (C). The density conversion LUT shown in FIG. 6A is an LUT that is used in a normal time without reducing toner consumption, and the density conversion LUT shown in FIG. 6B is an LUT that is used in the first reduction mode described above. The density conversion LUT shown in FIG. 6C is the LUT used in the second reduction mode described above. The density conversion LUT shown in FIG. 6A is a table for outputting an input image as it is. Further, as can be seen by comparing FIGS. 6B and 6C, the density LUT shown in FIG. 6C is a table set such that the output density is lower than the input density.

  When a mode for reducing toner consumption is input from the operation unit (not shown), the control unit (not shown) notifies the LUT / filter selection unit 13 of the setting input from the operation unit. The LUT / filter selection unit 13 notifies the density conversion LUT unit 12 of the density conversion LUT to be used in accordance with an instruction from the control unit.

  The filter processing unit 3 stores three types of image processing filters shown in FIGS. 7A, 7B, and 7C. The image processing filter shown in FIG. 7A is a normal image processing filter that does not reduce toner consumption, and the image processing filter shown in FIG. 7B uses the image processing used in the first reduction mode described above. The image processing filter shown in FIG. 7C is an image processing filter used in the above-described second reduction mode.

  In the normal mode in which the toner consumption is not reduced, the LUT / filter selection unit 13 instructs the filter processing unit 3 to select a normal image processing filter shown in FIG. When the first reduction mode is selected, the LUT / filter selection unit 13 instructs the filter processing unit 3 to use the image processing filter shown in FIG. When the second reduction mode is selected, the LUT / filter selection unit 13 instructs the filter processing unit 3 to use the image processing filter shown in FIG.

  If the density conversion LUT shown in FIGS. 6B and 6C is used in the density conversion LUT unit 12, the density of the entire image is reduced, and the density of the edge portions of characters and line drawings is also reduced. Therefore, in this embodiment, as shown in FIGS. 7B and 7C, filter processing is performed using a filter in which the filter strength is set larger than that of a normal filter. By setting the filter strength high, it is possible to prevent the edge portion from being emphasized and the characters and line drawings from becoming thin. Note that the image processing filter shown in FIG. 7C has a higher filter strength than the image filter shown in FIG.

  As described above, also in this embodiment, it is possible to prevent the deterioration of the edge portion while reducing the toner consumption.

The processing procedure of the present embodiment will be described with reference to the flowchart shown in FIG.
When toner save mode selection is input from an operation unit (not shown) (step S1), the control unit 20 changes the selected save mode (first reduction mode or second reduction mode) to the LUT / filter selection unit 13. Notify The LUT / filter selection unit 13 selects the density conversion LUT and the filter according to the mode notified from the control unit, and notifies the density conversion LUT unit 12 and the filter processing unit 3 respectively (step S2). When the toner save mode is not selected (step S1 / NO), the control unit 20 notifies the LUT / filter selection unit 13 of the normal mode, and the LUT / filter selection unit 13 receives the control from the control unit 20. According to the notification, the density conversion LUT in the normal mode and the filter are selected and notified to the density conversion LUT unit 12 and the filter processing unit 3 (step S3).

  Thereafter, the image signal input by the image input unit 2 is subjected to density conversion by the density conversion LUT unit 12 and filter processing by the filter processing unit 3. The density conversion LUT unit 12 and the filter processing unit 3 perform image signal conversion using the density conversion LUT selected by the LUT / filter selection unit 13 and the filter, respectively (step S4). The image signal after the filter processing is sequentially output to the first gradation correction unit 4, the first color space conversion unit 5, and the second gradation correction unit 6 shown in FIG. After the tone correction according to the output characteristics of the unit 7 is performed, it is output to the image output unit 7.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

1 is a block diagram illustrating a configuration of an image processing apparatus according to a first exemplary embodiment. FIG. 10 is a block diagram illustrating a modification of the image processing apparatus according to the first embodiment. It is a figure which shows the filter characteristic of the image processing filter used by a filter process part. (A) is a normal edge enhancement filter that does not perform toner save, and (B) is a filter for toner save. FIG. 6 is a block diagram illustrating a configuration of an image processing apparatus according to a second embodiment. It is a figure which shows LUT used by a density | concentration conversion LUT part. It is a figure which shows the filter used by a filter process part. 10 is a flowchart illustrating a processing procedure of the image processing apparatus according to the second exemplary embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image processing apparatus 2 Image input part 3 Filter processing part 4 1st gradation correction part 5 1st color space conversion part 6 2nd gradation correction part 7 Image output part 10 2nd color space conversion part 11 3rd color space conversion Unit 12 density conversion LUT unit 13 LUT / filter selection unit

Claims (6)

  An image processing apparatus comprising: a filter processing unit that sets a DC component of a filter characteristic to be less than 1 and performs filter processing on image data using an image processing filter having a predetermined filter strength.   2. The image processing according to claim 1, wherein the image processing filter has a filter characteristic in which the density of the image signal is lowered at a solid portion having a uniform density and the density of the image signal is not lowered at an edge portion. apparatus. A first image processing unit that includes a density conversion table, and reduces the density of the entire image using the density conversion table;
An image processing apparatus comprising: a second image processing unit that performs a filtering process so that a density at an edge portion of an image is in a state before the processing by the first image processing unit. The first image processing means includes a plurality of density conversion tables corresponding to the amount of saved toner,
4. The image processing apparatus according to claim 3, wherein the second image processing unit changes a filter used for the filter processing in accordance with the density conversion table used in the first image processing unit. . A first step of reducing the density of the entire image using the density conversion table;
And a second step of performing a filtering process so that the density at the edge portion of the image is in a state before the processing by the first step. In the first step, a plurality of density conversion tables are switched and used in accordance with the amount of toner saved,
6. The toner saving method according to claim 5, wherein in the second step, a filter used for the filter processing is changed in accordance with the density conversion table used in the first step.

Images