JPH11136517A - Picture processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a picture processor which can prevent a compression rate from deteriorating even if a ground removal processing is executed. SOLUTION: The picture processor executing a prescribed picture processing on output picture data of a picture read means reading the picture of an original is provided with a ground detection means 41 detecting the ground level of picture data, a conversion means setting a level obtained by adding a first offset value to the ground level detected by the ground detection means 41 and converting picture data lower than the first level into the first level, an encoding means 45 encoding picture data converted by the conversion means, a decoding means 47 decoding encoding data encoded by the encoding means 45 and a ground removal means 48 which ground-removes decoding data decoded by the decoding means 47 by a value obtained by adding a second offset value larger than the first offset value and the ground level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for use in a copying machine, a printer, and the like. The present invention relates to an image processing device for outputting.

[0002]

2. Description of the Related Art Conventionally, an image processing apparatus used in a copier or a printer of this type performs, for example, predetermined image processing on image data of a document read by an image reading apparatus, The image data is encoded and compressed, temporarily stored in a storage unit, and then the image data is decoded and output. Examples of such an image processing apparatus include those disclosed in Japanese Patent Application Laid-Open Nos. Hei 4-223774 and Hei 4-223774.

The image processing apparatus disclosed in Japanese Patent Application Laid-Open No. 4-223774 has a means for detecting a background (background) portion in an image, a means for separating a base image composed of the base portion and a remaining component image, It is configured to have means for separately encoding the types of images.

The image processing apparatus disclosed in Japanese Patent Application Laid-Open No. 7-307869 is based on the proposal of the present applicant. This image processing apparatus is based on image data output from an image reading apparatus. The background density of the input image is detected by the background density detection circuit, and the background removal processing is performed by the background removal circuit in accordance with the background density of the input image detected by the background density detection circuit. It is intended to include a configuration adapted to be used.

[0005]

However, the prior art described above has the following problems. That is, Japanese Patent Application Laid-Open No.
In the case of the image processing apparatus disclosed in JP-A-307869 or the like, the compression ratio is increased by removing the background (background) and removing unnecessary information before compressing the image data. However, depending on the document, there is a problem that the compression ratio is reduced if the background removal processing is simply performed.

More specifically, originals read by the image reading apparatus include various types of images such as images composed of characters, images composed of halftone dots, and images composed of photographs. Of the images included in these originals, the image consisting of halftone dots is an image displayed by halftone dots having different areas and densities, as shown in FIG. A large number of halftone dots having different areas and densities are distributed on the portion and contain many high-frequency components as grayscale image information.
As shown in FIG. 0, the background portion is uniformly at the zero level,
On the contrary, there has been a problem that the amplitude and the frequency of the high frequency component increase and the compression ratio decreases.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to reduce the compression ratio even when the background is removed. An object of the present invention is to provide an image processing apparatus capable of preventing the image processing.

[0008]

According to a first aspect of the present invention, there is provided an image processing apparatus for performing predetermined image processing on output image data of image reading means for reading an image of a document. A background detecting means for detecting a background level of the data; and a level obtained by adding a first offset value to the background level detected by the background detecting means is a first level, and image data lower than the first level is defined as a first level. A converting unit for converting the image data converted by the converting unit into one level, an encoding unit for encoding the image data converted by the converting unit, a decoding unit for decoding the encoded data encoded by the encoding unit, The decoded data decoded by the decoding means
And a background removing means for removing the background with a value obtained by adding the second offset value larger than the offset value and the background level.

As described above, according to the first aspect of the present invention, the level obtained by adding the first offset value to the background level detected by the background detection unit is set as the first level by the conversion unit,
The image data that is lower than the first level is converted to a first level, and the image data that has been converted by the conversion unit is encoded by an encoding unit, and then the encoded data is encoded by the encoding unit. The data is decoded by the decoding means, and the decoded data decoded by the decoding means is added to a second offset value larger than a first offset value and the background level by a background removing means by a background removing means. By the removal, the converting means performs a mask process on the background density based on the first offset value, so that the roughness of the background of the document can be suppressed. The data is the background density + the first offset value. Since the background is not removed here, it does not become zero unlike the conventional case, and the mask processing is performed as described above. When the data is encoded by the encoding unit, the amplitude of the image data subjected to the mask processing is smaller than the amplitude of the data after the background removal is performed before the encoding as in the related art. As a result, the difference between the DC components of the adjacent image data becomes smaller, so that the data compression ratio can be increased accordingly.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

Embodiment 1 FIG. 1 shows an embodiment of a multi-transfer type digital color copying machine to which an image processing apparatus according to the present invention can be applied.

In FIG. 2, reference numeral 1 denotes a main body of a digital color copying apparatus. An image reading apparatus 3 (Image Input Terminator) for reading an image of a document 2 is provided at an upper end of the main body 1 of the digital color copying apparatus.
l) is arranged. The image reading device 3 illuminates the image of the document 2 placed on the platen glass 4 with the light source 6 while the document 2 placed on the platen glass 4 is pressed by the platen cover 5. First and second scanning mirrors 7 and 8 reflect the reflected light image of document 2.
The CCD sensor 10 scans and exposes the color material reflected light image of the original 2 to a predetermined dot density (for example, 16 dots / m) by the CCD sensor 10 via the imaging lens 9.
m).

The color material reflected light image of the original 2 read by the image reading device 3 is, for example, original reflectance data of three colors of red (R), green (G), and blue (B) (8 bits each). As the image processing device 12 (Image Process)
The image processing device 12 sends the reflectance data of the document 2 to predetermined data such as shading correction, positional deviation correction, lightness / color space conversion, gamma correction, frame erasure, color / movement editing, and the like. Image processing is performed.

The image data subjected to the predetermined image processing by the image processing device 12 as described above includes black (K), yellow (Y), magenta (M), and cyan (C) (8 bi each).
t) is converted into the original color material gradation data of the three colors ROS1
5 (Raster Output Scanner), and the ROS 15 performs image exposure with laser light in accordance with the original color material gradation data.

As shown in FIG. 2, the ROS 15 modulates the semiconductor laser 16 in accordance with the document color material gradation data, and emits a laser beam LB from the semiconductor laser 16 in accordance with the gradation data. The laser beam LB emitted from the semiconductor laser 16 is deflected and scanned by the rotary polygon mirror 17 and is reflected by the photosensitive drum 2 via the reflection mirror 18.
Scanning exposure is performed on 0.

The photosensitive drum 20 on which the laser beam LB is scanned and exposed by the ROS 15 is driven to rotate at a predetermined speed in a direction indicated by an arrow by driving means (not shown). The surface of the photosensitive drum 20 is
After being charged to a predetermined potential by the charging corotron 21 in advance, an electrostatic latent image is formed by scanning and exposing a laser beam LB in accordance with document color material gradation data. The electrostatic latent images formed on the photoreceptor drum 20 include four color developing units 22K, 22Y, 22M, 22C of black (K), yellow (Y), magenta (M), and cyan (C).
Are sequentially developed by a rotary type developing device 22 provided with a toner image having a predetermined color.

The toner image formed on the photosensitive drum 20 is transferred onto a transfer material 24 such as a transfer sheet held on a transfer drum 23 disposed adjacent to the photosensitive drum 20 by a transfer corotron. The images are sequentially transferred by the charging of 25. As shown in FIG. 2, the transfer material 24 includes a plurality of paper feed cassettes 2 stored in a lower portion of the copying apparatus main body 1.
8, 29, 30, or a manual feed tray 38 disposed on a side surface outside the copying apparatus main body 1. The material 24 is conveyed to the surface of the transfer drum 23 by the conveying roller 32 and the registration roller 33 at a predetermined timing. The transfer material 24 is held on the surface of the transfer drum 23 in a state where the transfer material 24 is electrostatically attracted to the surface of the transfer drum 23 by charging of the transfer corotron 25 which also serves as a charger for electrostatic attraction. In addition, from the manual feed tray 38, a transparent OH for an overhead projector other than a non-standard-size transfer paper such as a postcard is provided.
A P sheet or the like can be fed, and an image can be formed on an OHP sheet or the like. From the manual feed tray 38, the transfer material 24 on which an image is formed on one side is fed upside down, so that double-sided copying is possible.

The transfer material 24 onto which the toner image of a predetermined number of colors has been transferred from the photosensitive drum 20 is separated from the surface of the transfer drum 23 by discharging the corotron 34 for separation, and then the fixing device 35 The toner image is transferred to the transfer material 24 by heat and pressure by the fixing device 35.
The color image is fixed on the sheet and discharged onto the sheet discharge tray 36, thereby completing the color image forming process.

In FIG. 2, reference numeral 37 denotes a charge removing corotron pair for removing charge from the transfer drum 23.

The image processing apparatus according to this embodiment includes a background detection unit for detecting a background level of image data, and a first background level detected by the background detection unit.
A level to which the offset value is added as a first level, a conversion unit for converting image data lower than the first level to the first level, and a code for coding the image data converted by the conversion unit. Decoding means, decoding means for decoding the encoded data encoded by the encoding means, and a second offset value larger than the first offset value by decoding the decoded data decoded by the decoding means. And a background removal means for removing the background with a value obtained by adding the background level and the background level.

FIG. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention.

In FIG. 1, reference numeral 40 denotes an input correction section, to which image information of the document 2 read by the IIT 3 as the above-mentioned image reading means is input. As the image information input from the IIT 3, for example, the color material reflected light image from the original 3 is converted into original reflectance data of three colors of red (R), green (G), and blue (B) (each of 8 bits). Is used after photoelectric conversion. In the input correction unit 40, the reflectance data of the original 2 is subjected to shading correction, gradation correction such as lightness / color space conversion, and the like, and a lightness signal L ^* , a chromaticity signal a ^* ,
is converted to b ^* . If the document has only black and white images, only the brightness signal L ^* is obtained.

The corrected image data subjected to gradation correction and the like by the input correction unit 40 is input to a background detection unit 41 and an image processing unit 42. The background detection unit 41 detects the density of the background portion of the document from the corrected image data. In the background detection unit 41, for example, a prescan of the image of the original is performed by the IIT 3, and at the time of the prescan, a histogram of the density distribution of the image of the original 2 is obtained. The peak value is detected as the density of the background portion of the document. Further, the background detection unit 41 calculates the average density of the pixels of the n × n blocks while reading the image data of the document in real time, and detects the minimum value of the average density as the density of the background of the document. You may comprise. further,
The image processing unit 42 performs image processing such as MTF processing on the corrected image data that has been subjected to gradation correction and the like by the input correction unit 40.

The CPU 43 for controlling the image processing operation of the image processing apparatus, based on the background density of the image data of the original document detected by the background detection unit 41, sets a first offset value (offset1) and a second offset value (offset1). Offset value (off
set2), and the first offset value and the second offset value are output to the mask circuit 44 and a background removal unit described later, respectively.

Further, in the mask circuit 44, the CPU
Mask processing is performed based on the first offset value output from 43. In the mask circuit 44, the background density + first offset value (offset1) is applied to the image data subjected to the predetermined image processing by the image processing unit 42.
Is applied, and if the image data is equal to or smaller than the background density + first offset value (offset1), the background density + first offset value (offset1)
The image data is converted into a value of t1), and only image data exceeding the background density + first offset value (offset1) is output as image data.

The image data output from the mask circuit 44 is compressed by an encoding unit 45 using orthogonal coordinate transformation and the like, and is further encoded using entropy encoding such as Huffman encoding. The encoded data encoded by the encoding unit 44 is temporarily stored in a memory 46 such as a hard disk. Then, the memory 4
The coded data once stored in 6 is sequentially read out and decoded by the decoding unit 47, and the decoded image data is sent to the background removal unit 48.

The background removing unit 48 performs a background removing process on the image data decoded by the decoding unit 47. In the background removing unit 48, for example, the image data is obtained by calculating the background density + the second offset value (offset).
If 2) or less, the image data is set to 0, and the image data is the background density + the second offset value (offset2)
The contrast adjustment is performed for a value exceeding. As this contrast adjustment, for example, as shown in FIG. 3, the image data is the background density + the second offset value (of
fset2), rise at a predetermined slope,
After that, a device that adjusts the dynamic range of image data in accordance with a straight line having a gradient 1 where input data = output data is used. However, the present invention is not limited to this. For example, as shown in FIG. 4, the image data is obtained by dividing the image data by the background density + the second offset value (offset2).
Is set to 0 and the dynamic range of the image data is adjusted so that it rises linearly. As shown in FIG. 5, the image data suddenly rises when the image data exceeds the background density + the second offset value. For example, data that corrects image data according to a straight line having a gradient 1 where input data = output data may be used.

The image data whose background has been removed by the background removing unit 48 is subjected to gradation correction in accordance with output characteristics by the output correcting unit 49 and output. The gradation correction in the output correction unit 49 is performed to adjust the image data output from the image processing apparatus to the characteristics of a color copying machine, a printer, or the like that outputs the image data. The output correction unit 49 converts, for example, image data consisting only of the brightness signal L ^* , chromaticity signals a ^* , b ^* , or the brightness signal L ^* subjected to image processing as described above into a color copier or the like. It outputs data obtained by performing tone correction on image data such as yellow (Y), magenta (M), cyan (C), and black (K) that match the characteristics.

With the above configuration, the image processing apparatus according to this embodiment can prevent the compression ratio from being lowered even when the background removal processing is performed as follows.

That is, in the image processing apparatus according to this embodiment, as shown in FIG. 1, the image data read by the IIT 2 as the image reading apparatus of the digital color copying machine is input to the input correction unit 40. Is done. The image data input from the IIT 2 to the input correction unit 40 includes, for example, a color material reflected light image from a document in three colors of red (R), green (G), and blue (B) (8 bits each). Data obtained by photoelectrically converting document reflectance data is used. The input correction unit 40 performs shading correction and tone correction such as brightness / color space conversion on the reflectance data of the original, and converts the image data into a brightness signal L ^* and a chromaticity signal a. ^* , B ^* . If the original has only black and white images, only the brightness signal L ^* is output.

The corrected image data subjected to gradation correction and the like by the input correction unit 40 is input to a background detection unit 41 and an image processing unit 42, and the background detection unit 41 converts the corrected image data from the image data. The density of the background portion of the document is detected. Also,
The image processing unit 42 performs image processing such as MTF processing on the corrected image data that has been subjected to gradation correction and the like by the input correction unit 40.

On the other hand, as shown in FIG. 6, the CPU 43 determines a first offset value and a second offset value based on the background density of the image data of the document detected by the background detection unit 41. These first offset value and second
Are output to the mask circuit 44 and the background removal unit 48 described later. Here, the first offset value is set to a value which is equal to or higher than the background density of the image data of the document and which can sufficiently remove the roughness of the background of the document. However, if the first offset value is set too high, information in the low-density portion of the image data may be lost. Therefore, it is desirable to set the first offset value to a value low enough to remove the influence of noise and the like. . on the other hand,
The second offset value is set to a value equal to or greater than the first offset value. However, if the second offset value is set to be much larger than the first offset value, information of a low density portion of the image data may also be lost. Therefore, it is desirable to set a value slightly larger than the first offset value.

Further, in the mask circuit 44, as shown in FIG. 6, based on the first offset value output from the CPU 43, the background density + the first offset value (of
fset1), mask processing is performed, and image data having a background density + the first offset value or less is removed. Image data having the background density + the first offset value or less is shown in FIG. As described above, the value of the background density + the first offset value is used, and only image data exceeding the background density + the first offset value is output as image data.

The image data output from the mask circuit 44 is compressed by an encoding unit 45 using orthogonal coordinate transformation or the like, and further encoded using entropy encoding such as Huffman encoding. The encoded data encoded by the encoding unit 44 is temporarily stored in a memory 46 such as a hard disk. Then, the memory 4
The coded data once stored in 6 is sequentially read out and decoded by the decoding unit 47, and the decoded image data is sent to the background removal unit 48.

In the background removing unit 48, as shown in FIG. 8, if the image data is equal to or less than the background density + the second offset value, the image data decoded by the decoding unit 47 is processed. The data is set to 0, and for a value of the image data exceeding the background density + the second offset value, the image data is output as it is or the contrast is adjusted as needed.

The image data from which the background has been removed by the background removing unit 48 is subjected to tone correction in accordance with the output characteristics by the output correcting unit 49 and output. The gradation correction in the output correction unit 49 is performed to adjust the image data output from the image processing apparatus to the characteristics of a color copying machine, a printer, or the like that outputs the image data.

As described above, in the image processing apparatus according to the above-described embodiment, the background density of the image data of the original is detected by the background detection unit 41, and the background density is determined based on the first offset value (offset1). Since the mask processing is performed, even when the background processing is performed, the image data of the portion having the background density or less becomes the background density + the first offset value (offset1) and does not become zero as in the related art. As a result, when the data subjected to the mask processing as described above is encoded by the encoding unit 45, as shown in FIG. 7, the amplitude of the data subjected to the mask processing becomes the amplitude after the background removal is performed. Since the amplitude becomes smaller than the data amplitude, and as a result, the difference between the DC components of the adjacent image data becomes smaller, the data compression ratio can be increased accordingly.

Therefore, among the images included in the original, many halftone dots having different areas and densities are distributed on a background portion such as a white background of the paper of the original such as an image composed of halftone dots, and Even if the image information contains a lot of high frequency components, the data of the portion below the background density is converted to the background density +
Since the data is converted to the first offset value (offset1) and encoded (compressed), the amplitude (data amount) of the data to be encoded can be reduced. Rate can be increased. As a result, the capacity of the memory in which the capacity is set for the document having the lowest compression ratio can be set small, and the cost of the image processing apparatus can be reduced accordingly.

[0038]

As described above in detail, according to the present invention, the conversion means converts the level obtained by adding the first offset value to the background level detected by the background detection means to the first level.
, The image data lower than the first level is converted to the first level, and the image data converted by the conversion unit is encoded by the encoding unit.
Thereafter, the encoded data encoded by the encoding unit is decoded by the decoding unit, and the decoded data decoded by the decoding unit is set to a second offset value larger than the first offset value. The background removal is performed by the background removal unit using the value obtained by adding the background level, so that the conversion unit performs a mask process on the background density based on the first offset value, thereby suppressing the background roughness of the document. The image data of the portion below the background density is the background density + the first offset value, and since the background is not removed here, it does not become zero unlike the conventional case, and the mask processing is performed as described above. When the encoded data is encoded by the encoding means, the amplitude of the image data subjected to the mask processing is the same as the amplitude of the data after performing background removal before encoding as in the related art. Compare to decrease, the difference in DC component of the image data with each other to result neighboring decreases,
The data compression ratio can be increased accordingly.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention.

FIG. 2 is a configuration diagram showing an embodiment of a digital color image forming apparatus to which the image processing apparatus according to the present invention can be applied.

FIG. 3 is a graph showing characteristics of contrast adjustment in a background removal unit.

FIG. 4 is a graph illustrating another characteristic of contrast adjustment in the background removal unit.

FIG. 5 is a graph showing another characteristic of the contrast adjustment in the background removal unit.

FIG. 6 is a graph showing image data before the background removal processing.

FIG. 7 is a graph showing image data that has been subjected to mask processing based on the result of background detection.

FIG. 8 is a graph showing image data on which background removal processing has been performed.

FIG. 9 is a graph showing image data.

FIG. 10 is a graph showing image data subjected to a conventional background removal process.

[Explanation of symbols]

40: input correction unit, 41: background detection unit, 42: image processing unit, 43: CPU, 44: mask circuit, 45: encoding unit, 46: memory, 47: decoding unit, 48: background removal unit, 49 : Output correction unit.

Claims (1)

[Claims] An image processing apparatus for performing predetermined image processing on output image data of image reading means for reading an image of a document, a background detecting means for detecting a background level of the image data, and a background detecting means. Converting means for adding a first offset value to the background level detected by the means as a first level, and converting image data lower than the first level into the first level; Coding means for coding the processed image data; decoding means for decoding the coded data coded by the coding means; and decoding data decoded by the decoding means to the first An image processing apparatus comprising: a background removing unit configured to remove a background with a value obtained by adding a second offset value larger than the offset value of the above and the background level.