JP7510611B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

One image processing device detects edges in a target image for each of the colors cyan, magenta, yellow, and black (CMYK), and treats pixels in which an edge is detected in any of the colors as contours, performing emphasis processing on those contours (edge portions) (see, for example, Patent Document 1).

JP 2015-109573 A

However, with the above-mentioned image processing device, if there is text on a background image, the text will be overly emphasized by the emphasis process, even if this is not the user's intention.

Furthermore, if emphasis processing is not performed, different screen processing is performed on the text and background images, which can result in visible noise such as hollow dots at the boundary between the text and background due to discontinuity in the screen.

The present invention has been made in consideration of the above problems, and aims to obtain an image forming device that prevents characters on a background image from being unintentionally emphasized.

The image forming apparatus according to the present invention comprises a pixel attribute determination unit which determines whether the pixel attribute of a pixel of interest in an input image is character or not; a local color characteristic derivation unit which, if the pixel attribute of the pixel of interest is character, derives a predetermined color characteristic value for pixels within a window of a predetermined size including the pixel of interest, whose pixel attribute is character, as a first color characteristic value, and also derives a predetermined color characteristic value for pixels whose pixel attribute is not character, as a second color characteristic value; a pixel attribute change unit which changes the pixel attribute of the pixel of interest from character to non-character, if the difference between the first color characteristic value and the second color characteristic value is less than a predetermined threshold; and an output image processing unit which performs different predetermined image processing for pixels whose pixel attribute is character and pixels whose pixel attribute is non-character, and generates an output image from the input image.

The present invention provides an image forming device that prevents unintentional emphasis on characters on a background image.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a window corresponding to a pixel of interest. FIG. 3 is a flowchart illustrating the operation of the image forming apparatus shown in FIG.

Below, an embodiment of the present invention is explained based on the figures.

Figure 1 is a block diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in Figure 1 is a device having a printing function, such as a printer, a copier, or a multifunction device.

The image forming device shown in Figure 1 comprises an image input unit 1, an image processing unit 2, and an image output unit 3.

The image input unit 1 specifies an input image to the image processing unit 2.

For example, the image input unit 1 is equipped with an image reading device, which optically reads the original image one page at a time, generates image data of the original image, and outputs it to the image processing unit 2 as image data of the input image.

For example, the image input unit 1 is equipped with a communication device such as a network interface, receives a print request specifying an input image from a host device such as a personal computer, and outputs it to the image processing unit 2.

The image processing unit 2 performs various image processing on the input image specified by the image input unit 1, and outputs the image data after image processing to the image output unit 3.

The image output unit 3 has, for example, an electrophotographic color print engine, and prints an image based on the image data from the image processing unit 2 onto printing paper.

The image processing unit 2 is equipped with a computer that executes a program or an ASIC (Application Specific Integrated Circuit), and operates as an input image processing unit 11, a pixel attribute determination unit 12, and an output image processing unit 13 by executing software processing and/or hardware processing on the computer or ASIC.

The input image processing unit 11 generates color image data and attribute data for the input image specified by the image input unit 1. The color image data is data that indicates a combination of color component values for each pixel, and the attribute data is data that indicates pixel attributes (character, non-character (image), etc.) for each pixel.

For example, when image data of an input image obtained by an image reading device is input from the image input unit 1, the input image processing unit 11 performs, for example, an existing region separation process to identify the pixel attributes of each pixel of the input image and generate attribute data indicating the attributes of each pixel of the input image.

For example, when a print request received by a communication device is input from the image input unit 1, the input image processing unit 11 performs raster image processing, etc. on the print request to generate color image data and attribute data for the input image.

The pixel attribute determination unit 12 analyzes the color image data and attribute data, and changes the pixel attributes of pixels in the attribute data that satisfy specified conditions from character to non-character.

The pixel attribute determination unit 12 includes a pixel attribute judgment unit 21, a local color characteristic derivation unit 22, and a pixel attribute modification unit 23.

The pixel attribute determination unit 21 sequentially selects a pixel of interest in the input image and determines whether the pixel attribute of the pixel of interest is a character or not based on the attribute data input by the input image processing unit 11.

Based on the color image data input by the input image processing unit 11, when the pixel attribute of the pixel of interest is character, the local color characteristic derivation unit 22 derives a predetermined color characteristic value for pixels whose pixel attribute is character among pixels in a window of a predetermined size including the pixel of interest as a first color characteristic value, and also derives a predetermined color characteristic value for pixels whose pixel attribute is not character as a second color characteristic value. Note that when the pixel attribute of the pixel of interest is not character, the local color characteristic derivation unit 22 does not derive the above-mentioned color characteristic value.

Specifically, the local color characteristic derivation unit 22 derives the average value of each color component of pixels whose pixel attribute is character as the first color characteristic value, and derives the average value of each color component of pixels whose pixel attribute is not character as the second color characteristic value.

Here, the above-mentioned color components are hue H, saturation S, and lightness V in the HSV color space, and the average value Ht of hue H, the average value St of saturation S, and the average value Vt of lightness V for pixels in the window whose pixel attribute is character, as well as the average value Hi of hue H, the average value Si of saturation S, and the average value Vi of lightness V for pixels in the window whose pixel attribute is non-character, are derived.

Here, the color space used to calculate the above-mentioned color characteristic values is HSV, but other color spaces may also be used.

Figure 2 shows an example of a window corresponding to a pixel of interest. For example, in the case shown in Figure 2, the window has a size of 9 pixels by 9 pixels, the pixel of interest is located at the center of the window, and the pixel attribute of the pixel of interest is character. Note that the size of the window in the main scanning direction and the size in the sub-scanning direction may be the same or different.

The size of this window is set to a fixed value according to the maximum character size of the characters in the input image. In other words, the larger the maximum character size, the larger the size of this window is set.

The pixel attribute change unit 23 changes the pixel attribute of the pixel of interest from character to non-character if the difference between the above-mentioned first color characteristic value and the above-mentioned second color characteristic value is less than a predetermined threshold value, and if not, keeps the pixel attribute of the pixel of interest as character.

Specifically, the pixel attribute change unit 23 (a) derives the difference in the average values for each of the above-mentioned color components as the difference between the first color characteristic value and the second color characteristic value, and (b) if the difference in the average values for each color component for all color components is less than the threshold value for each color component, changes the pixel attribute of the pixel of interest from character to non-character.

Here, the above-mentioned color components are hue H, saturation S, and lightness V in the HSV color space, and for the differences |Ht-Hi|, |St-Si|, |Vt-Vi| and thresholds TH_H, TH_S, TH_V, if |Ht-Hi|<TH_H and |St-Si|<TH_S and |Vt-Vi|<TH_V, the pixel attribute of the pixel of interest is changed from character to non-character.

For example, for a pixel of interest, if (Ht, St, Vt) = (0, 0, 182), (Hi, Si, Vi) = (0, 0, 191), and TH_H, TH_S, TH_V = 10, then |Ht-Hi| = 0, |St-Si| = 0, |Vt-Vi| = 9, and since |Ht-Hi| < TH_H and |St-Si| < TH_S and |Vt-Vi| < TH_V, the pixel attribute of the pixel of interest is changed from character to non-character.

The output image processing unit 13 performs predetermined image processing that differs between pixels whose pixel attribute is character and pixels whose pixel attribute is non-character, and generates an output image from the input image.

For example, the output image processing unit 13 performs color conversion processing, color correction processing, black generation/UCR (Under Color Removal) processing, screen processing, etc., corresponding to the pixel attribute. Specifically, the output image processing unit 13 performs screen processing with different line numbers for pixels whose pixel attribute is character and pixels whose pixel attribute is non-character, and color conversion processing with different UCR (Under Color Removal) rates for pixels whose pixel attribute is character and pixels whose pixel attribute is non-character. Furthermore, the color conversion characteristics are adjusted according to the line number of the screen processing. Also, for achromatic pixels, the color of pixels whose pixel attribute is character is color converted to a single color (such as K) if possible, and the color of pixels whose pixel attribute is not character is color converted to a mixed color (CMYK).

Next, the operation of the image forming apparatus will be described. Figure 3 is a flowchart illustrating the operation of the image forming apparatus shown in Figure 1.

First, the input image processing unit 11 acquires image data and attribute data of the input image based on a print request from the image input unit 1 and image data of the original image (step S1).

The pixel attribute determination unit 21 selects a pixel of interest in the input image in a predetermined scanning order (step S2), and determines whether the pixel attribute of the pixel of interest is a character or not based on the attribute data (step S3).

If it is determined that the pixel attribute of the pixel of interest is character, the local color characteristic derivation unit 22 identifies a pixel in the window corresponding to the pixel of interest, and further identifies character attribute pixels (pixels whose pixel attribute is character) and non-character attribute pixels (pixels whose pixel attribute is not character) in the window based on the attribute data, and calculates the average values Ht, St, Vt of each color component of the character attribute pixels and the average values Hi, Si, Vi of each color component of the non-character attribute pixels (step S4).

Then, the pixel attribute modification unit 23 calculates the average value differences |Ht-Hi|, |St-Si|, and |Vt-Vi| for each color component, and determines whether |Ht-Hi|<TH_H and |St-Si|<TH_S and |Vt-Vi|<TH_V (step S5).

If |Ht-Hi|<TH_H and |St-Si|<TH_S and |Vt-Vi|<TH_V, the pixel attribute change unit 23 changes the pixel attribute of the pixel of interest in the attribute data from character to non-character (step S6).

On the other hand, if |Ht-Hi|<TH_H and |St-Si|<TH_S and |Vt-Vi|<TH_V are not satisfied, the pixel attribute change unit 23 does not change the pixel attribute of the pixel of interest from character to non-character, but leaves it as character. Also, if it is determined in step S3 that the pixel attribute of the pixel of interest is not character, the processes of steps S4, S5, and S6 are skipped.

Then, the pixel attribute determination unit 21 determines whether the current pixel of interest is the last pixel of the input image (step S7), and if the current pixel of interest is not the last pixel of the input image, the process returns to step S2 and the next pixel of interest is selected. Then, the same process from step S3 onwards is performed on the next pixel of interest.

On the other hand, if the current pixel of interest is the last pixel of the input image, the pixel attribute determination unit 12 outputs the image data and attribute data of the processed input image to the output image processing unit 13, and the output image processing unit 13 performs the above-mentioned image processing on the input image based on the image data and attribute data, and generates an output image (step S8).

Then, the image output unit 3 prints the output image (step S9).

As described above, according to the above embodiment, the pixel attribute determination unit 21 determines whether the pixel attribute of the pixel of interest in the input image is character. When the pixel attribute of the pixel of interest is character, the local color characteristic derivation unit 22 derives a predetermined color characteristic value for pixels whose pixel attribute is character among pixels in a window of a predetermined size including the pixel of interest as a first color characteristic value, and also derives a predetermined color characteristic value for pixels whose pixel attribute is not character as a second color characteristic value. When the difference between the derived first color characteristic value and the second color characteristic value is less than a predetermined threshold, the pixel attribute change unit 23 changes the pixel attribute of the pixel of interest from character to non-character. The output image processing unit 13 performs predetermined image processing that differs between pixels whose pixel attribute is character and pixels whose pixel attribute is non-character, and generates an output image from the input image.

As a result, when the density and color of the characters and their background are similar, the same image processing is applied to the characters and their background, reducing the discontinuity at the boundary between the characters and their background in the output image after image processing (i.e. the image to be printed), and preventing the characters on the background image from being unintentionally emphasized.

In other words, if a user wants to make the colors of the text and its background in the image to be printed similar to make the text less visible on the printed product, the image to be printed will be printed without the text on the background image being unintentionally emphasized, making the text less visible on the printed product.

It should be noted that various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. In other words, such changes and modifications are intended to be included within the scope of the claims.

For example, in the above embodiment, the first color characteristic value and the second color characteristic value are average values of the color components within the window, but they may also be other characteristic values (median, maximum, minimum, etc.).

The present invention is applicable, for example, to an image forming apparatus.

Claims (4)

a pixel attribute determination unit that determines whether a pixel attribute of a pixel of interest in an input image is a character;
a local color characteristic derivation unit that, when a pixel attribute of the pixel of interest is character, derives a predetermined color characteristic value for pixels whose pixel attribute is character as a first color characteristic value among pixels within a window of a predetermined size including the pixel of interest, and derives a predetermined color characteristic value for pixels whose pixel attribute is not character as a second color characteristic value;
a pixel attribute change unit that changes a pixel attribute of the pixel of interest from character to non-character when a difference between the first color characteristic value and the second color characteristic value is less than a predetermined threshold value;
an output image processing unit that performs different predetermined image processing on pixels whose pixel attribute is character and pixels whose pixel attribute is non-character, and generates an output image from the input image;
An image forming apparatus comprising: the local color characteristic deriving unit derives, as the first color characteristic value, an average value of each color component of pixels whose pixel attribute is character, and derives, as the second color characteristic value, an average value of each color component of pixels whose pixel attribute is not character;
the pixel attribute change unit derives a difference in the average values for each color component as a difference between the first color characteristic value and the second color characteristic value, and changes a pixel attribute of the pixel of interest from character to non-character when the difference in the average values for all color components is less than a threshold value for each color component;
2. The image forming apparatus according to claim 1, The image forming device of claim 1, characterized in that the size of the window is set according to the maximum character size of the characters in the input image. The image forming device according to claim 1, characterized in that the output image processing unit performs at least one of a screen processing in which the number of lines is different for pixels whose pixel attribute is character and pixels whose pixel attribute is non-character, and a color conversion processing in which the UCR rate is different for pixels whose pixel attribute is character and pixels whose pixel attribute is non-character.

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