JP2001008036A - Image processor and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image high in quality and high in reliability by improving phenomena such as irregularity of density and void of image. SOLUTION: Image data entered in a memory 201 that stores data by a plurality of lines is subjected to image area separation in real time, character area data in line data are extracted, an addition/subtraction reference level is calculated for every line on the basis of the data, a correction coefficient K is obtained so that the addition/subtraction reference level is a white reference level of an original, the correction coefficient K is multiplied with the character are data of the data line to correct a background density level of the character area data for every line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing apparatus and an image processing method applicable to an image forming apparatus and the like capable of correcting a background density level of an original image in real time.

[0002]

2. Description of the Related Art A method of correcting the background density level of a document image in real time in a conventional image forming apparatus will be described.

When real-time background density correction of a document image that is relatively scanned with respect to a document reading unit such as a CCD is performed, an analog pixel corresponding to an addition / subtraction reference level is obtained for each effective pixel data of the document image. The background level is corrected in real time by calculating the signal level and feed-hacking it to the reference voltage of the image forming unit and the A / D converter.

FIG. 11 is a flowchart showing an example of a real-time background correction process. This example shows a control level real time feed hack.

In step S801, copying is started.

In step S802, the start of document reading is detected.

In step S803, the background density at the leading edge of the document is calculated.

In step S804, the magnitude relationship between the image data and the control level is compared. If the image data is greater, the process proceeds to step S805, and the UP counter is incremented by one.

In step S806, it is checked whether the comparator has reached a predetermined count. If the count has reached the predetermined count, the flow advances to step S807.

In step S807, the control level is added, the UP counter is reset, and the process proceeds to step S811.

On the other hand, if the image data is smaller in step S804, the flow advances to step S808 to increment the DOWN counter by one.

In step S809, it is checked whether the comparator has reached a predetermined count.

Then, in step S810, the control level is subtracted, the DOWN counter is reset, and the process proceeds to step S811.

In step S811, the latest control level adjusted in real time when counting is performed for each pixel is obtained.

The calculated level value is obtained at step S80.
4 is fed back as a comparator of the comparator.

In step S812, a correction coefficient K for the character area at that time is calculated.

In step S813, the background correction of the character area is performed using the correction coefficient K.

In step S814, an image forming process including a character area subjected to background correction is performed.

[0019]

In the conventional background correction processing as described above, when most of the image of the target read line is an image such as a black band, the adjustment reference level becomes extremely small. In other words, a blank image may be caused in other portions on the same line, a blank may be caused in image data of an adjacent line, and furthermore, an adjustment reference level may be determined at the beginning of reading of the main scanning line and at the end of reading. There is a case where an image is formed with a density difference due to density unevenness.

Accordingly, an object of the present invention is to provide an image processing apparatus and an image processing method capable of forming a high quality and highly reliable image by improving phenomena such as density unevenness and image white spots. It is in.

[0021]

SUMMARY OF THE INVENTION The present invention relates to an apparatus for correcting the background density of image data, comprising: storage means for storing one-dimensional image data for a plurality of lines; From the image data, a character area,
An area separating unit that separates the image data into regions other than the character region; an extracting unit that extracts data of a desired character region in the image data according to the separated result; Correction means for calculating a correction coefficient converging to the background density level of the data for each line, and correcting the background density level of the data in the character area for each line using the calculated correction coefficient. Thus, an image processing apparatus is configured.

The correction means calculates the adjustment reference level for each line using the data of the extracted character area, and the correction adjustment level is calculated based on the white reference value of the document. It may include means for calculating a correction coefficient to be a level, and means for multiplying the data of the character area of the data line used for the calculation by the calculated correction coefficient.

The correction means approximates the calculated adjustment reference level to a background density level, and compares the value of the adjustment reference level of the target line with the adjustment reference level of a plurality of adjacent front lines. Means for judging the validity of the calculated adjustment reference level based on the comparison result, and means for calculating the value of the adjustment reference level of the previous line as the adjustment reference level of the target line if the judgment is not appropriate. And may be included.

The image processing apparatus further includes means for dividing image data constituting one line, and obtains a background density level by substituting one of the adjustment reference levels calculated based on each of the divided data. You may do so.

The division of one line can be performed by thinning division at a constant interval including even and odd columns.

Data of the color having the maximum value of the adjustment reference level among the adjustment reference levels calculated based on the image data of the same line can be used as a value common to all colors.

An add / subtract reference level is calculated based on one data obtained by dividing the main scanning signal among a plurality of data of the designated color, and data of the other divided area and the same line are calculated. , A common correction coefficient is calculated for the data of the other colors corrected to the image data, and the calculated correction coefficient is multiplied to the data of each character area.

A line image sensor for converting an original image into an electric signal as one-dimensional image data; and a one-dimensional image data by moving the original image relative to the line image sensor in a two-dimensional direction. And a document reading means for connecting the two-dimensional image data, and the read one-dimensional image data may be stored in the storage means for a plurality of lines.

According to the present invention, there is provided an image processing method for correcting background density of image data, comprising: a storage step of storing one-dimensional image data for a plurality of lines; A character area and an area separation step of separating the character area into areas other than the character area; an extraction step of extracting data of a desired character area inside the image data according to the separation result; A correction coefficient that converges to the background density level of the data in the character area for each line, and corrects the background density level of the data in the character area for each line using the calculated correction coefficient. And an image processing method is provided.

The present invention is a medium in which a program for correcting and controlling the background density of image data by a computer is recorded. The control program causes the computer to store one-dimensional image data for a plurality of lines. A character region and a region other than the character region are separated from the stored plurality of lines of image data, and data of a desired character region inside the image data is extracted according to the result of the separation. Then, a correction coefficient converging to the background density level of the extracted character area data is calculated line by line, and the background density level of the character area data is calculated line by line using the calculated correction coefficient. Is provided, thereby providing a medium in which an image processing control program is recorded.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[Outline] First, an outline of the present invention will be described.

According to the present invention, a character area and a photograph / halftone data area are separated in real time based on image data input to a line memory for a plurality of lines, and data of the character area is extracted and extracted. A correction coefficient K that converges on the background density level of the data of the character area thus calculated is calculated for each line, and the background density level of the data of the character area is corrected for each line using the calculated correction coefficient. It is characterized by the following.

In this case, an addition / subtraction reference level is calculated for each line using the extracted character area data, and a correction coefficient K such that the calculated value of the addition / subtraction reference level becomes the white reference level of the document. Is calculated, and the correction coefficient K is multiplied by the data of the character area of the data line used for the calculation to correct the background density level of the data of the character area for each line.

In the photographic area, in order to give priority to image quality, an image is formed without multiplying the correction coefficient K obtained by the adjustment reference level.

[Specific Example] Next, a specific example will be described with reference to FIGS. In this example, an image forming apparatus will be described as an example of an apparatus capable of correcting the background density of a document image in real time.

(System Configuration) First, an outline of the overall configuration of the present system will be described.

In FIG. 1, the image forming apparatus of this embodiment is roughly divided into an image reading section 1 for reading a document or the like, an image processing section 2 including a signal processing section 106 according to the present invention, and an image forming section 3. You.

Here, a schematic configuration of the image reading section 1 and the signal processing section 106 which constitutes a part of the image processing section 2 will be described.

The image reading section 1 will be described.

Reference numeral 101 denotes a photoelectric conversion element that reads an original and converts the original into an electric signal. The photoelectric conversion element 10 here
As 1, a one-line CCD line sensor or a three-line color CCD line sensor can be used.

Reference numeral 102 denotes an analog IC 102 for performing adjustments such as sample hold, offset adjustment, and gain adjustment.

Reference numeral 103 denotes an A / D converter for converting an analog signal into a digital signal.

A drive / control clock generator 104 generates various drive clocks and control clocks required in the apparatus. Various clocks (φ1, φ2, S / H1, CL) generated by the clock generator 104
K, HSYNC, etc.) are CCD101, Anapro IC1
02, the A / D converter 103, and the signal processing unit 106, respectively, and thereby each unit is drive-controlled.

In this case, the clock HSYNC is output from the CCD
It is generated as a synchronization signal along the driving cycle of 101. This clock HSYNC is synchronized with the clock CLK, and further, the output v of the A / D converter 103 is v
Synchronized with the video signal.

Reference numeral 105 denotes a crystal oscillator as an oscillating means for generating an operation reference inside the document reading apparatus, and serves as a source of the clock.

The image processing section 2 will be described.

Reference numeral 106 denotes a signal processing unit 106 according to the main configuration of the present invention, which is a part for correcting the background density level of the original image to the white level.

Reference numeral 107 denotes C from the main scanning image area data.
A shading correction unit that corrects variations in the pixels of the CD 101 and corrects the inclination of the light distribution of the light source. The image subjected to the shading correction is corrected so as to minimize the factors that the elements and the light source give to the image.

Reference numeral 108 denotes an image area separation unit which cuts out a character area using the image data after shading correction.

A frame memory 201 capable of storing image data for a plurality of lines is built in the image area separating unit 108. This frame memory 20
1 can be used to form a matrix of n × n pixels, and a discrimination process is performed for each divided area. The internal configuration of the image area separation unit 108 and its processing will be described in detail with reference to FIG. 10
Reference numeral 9 denotes an area signal generator, which generates a character area signal S1 as shown in FIG.

Reference numeral 110 denotes a line correction memory 110a,
And a video selector 110b.

The line correction memory 110a adjusts the phase between the character area signal S1 and the original image data. The video selector 110 b separates actual image data using the character area signal S 1, and uses the separated image data as an input signal of the comparator 112.

A reference 111 outputs the reference variable S2 to the comparator 112 to obtain a final reference variable S4.
4 is a reference variable generation unit that outputs 4 to the image correction coefficient generation unit 113. In this case, the reference variable S2 has been reset by the image signal S3 so as to be synchronized with the line data.

Reference numeral 112 denotes a comparator for sequentially comparing the reference variable S2 with the image level of the character area using the character area signal S1. Based on the comparison result, addition and subtraction control of the reference variable S2 is performed so that the value of the reference variable S2 converges to the background level of the character document section.

Reference numeral 113 denotes an image correction coefficient generator which receives the final reference variable S4 from the reference variable generator 111, calculates a correction coefficient K by calculation, and outputs it. The image correction coefficient generation unit 113 stores the previous line variable memory 114
And a variable comparison unit 115 to which the reference variable K is input, and a correction coefficient calculation unit 116 for obtaining the correction coefficient K.

An integrator 117 corrects the background density level of the character area on a line-by-line basis by multiplying the image data of the character area as the character area signal S1 by the correction coefficient K.

Reference numeral 118 denotes a line memory for storing the correction value obtained by the integrator 117.
After being sent to the remaining part of the image processing unit and subjected to predetermined image processing, the image is output to the image forming unit 3 and processing such as printing is performed.

The configuration of the image forming section 3 is not particularly limited. For example, printing may be performed by an ink jet system, an electrophotographic system, or the like, or may be displayed on a display device.

(System Operation) Next, the operation of the present system will be described.

In the image reading section 1, a document is read by the CCD 1. The read data is
Sample hold, offset adjustment,
Adjustment processing such as gain adjustment is performed. The analog data on which the adjustment processing has been performed is supplied to the A / D converter 103.
Is converted into digital data by the signal processing unit 10
6 is input to the shading correction unit 107.

In the signal processing unit 106, the shading correction unit 107 converts the main scanning image data
01 and the inclination of the light distribution of the light source are corrected. The image data that has been subjected to the shading correction is corrected so as to minimize the factors that the elements and the light source give to the image, and is input to the image area separation unit 108. Image area separation unit 108
In, the character area is cut out using the image data after the shading correction.

FIG. 2 shows the processing in the image area separation unit 108.

The line data after shading is stored in the frame memory 201 for each of a plurality of lines.

The image data composed of a plurality of lines stored in the frame memory 201 is supplied to the block separation circuit 2
02 divides the image into blocks of 8 × 8 pixels as shown by 208.

The image data of each block is subjected to a two-dimensional discrete cosine transform (DCT) by the DCT circuit 203.
Is performed to obtain DCT transform coefficients.

This DCT transform coefficient is represented by 64 frequency components, and is represented by a matrix of 8 rows × 8 columns as shown at 209. In this case, the DCT transform coefficients (matrix components) are arranged so that the lower left part of the matrix represents lower frequency components and the lower right part represents high frequency components. Also, in 209, the coefficient of the filled portion at the upper left of the matrix represents a direct current (DC) component,
Other coefficients represent alternating current (AC) components.

Then, the DCT transform coefficient is input to the representative value calculation circuit 204 to calculate the representative value of the block.

The calculated representative value of the block is input to the block determination circuit 205 to determine whether the block is a character area or a photograph area.

Here, the area for discriminating between the character area and the photograph area is the same as the block of 8 × 8 pixels divided for DCT.

FIG. 3 shows a block representative value calculating process and a block determining process performed by the representative value calculating circuit 204 and the block determining circuit 205 of the image area separating unit 108.

The arithmetic circuit 302 included in the representative value calculating circuit 204 obtains the absolute value sum (AS) of five low frequency alternating current (AC) components of the DCT transform coefficient 301 and sets the sum as the representative value of the block. This sum of absolute values (AS) is calculated by the two comparison circuits 303 and 30 included in the block determination circuit 205.
4 is output.

On the other hand, threshold values 1 (= 400) and 2 (= 20) are input to the comparison circuits 303 and 304, respectively, and the representative value (AS) is compared with the respective threshold values. The comparison result is output to the OR circuit 30 included in the block determination circuit 205.
5 is output.

As a result, if the representative value (AS) is larger than the threshold value 1 or smaller than the threshold value 2, the block is determined to be a character area, and otherwise, it is determined to be a photographic area. This determination is based on the image characteristic that a block having a large representative value (AS) has a character edge, and a block having a small representative value is almost flat (corresponding to a character background portion).

As described above, by using the two thresholds 1 and 2, the character area including the character background can be extracted. The area determination result obtained by the above block determination is stored in the area determination memory 206 shown in FIG. The area determination result is sent to the character area signal generation circuit 207 (corresponding to the area signal generation unit 109 in FIG. 1).

FIG. 4A shows a state where the area determination result is stored in the area determination memory 206. Area A indicates a character area, and area B indicates a photograph / halftone dot area. FIG.
(B) shows a character area signal S1 corresponding to the areas A and B.
Is shown.

The character area is at the “H” level, and the photograph / dot area is at the “L” level.

The character area signal S thus created
1 is updated in units of 8 lines, and is sequentially updated while reading the original.

By the time the character area signal S1 as described above is generated, the phase of the image signal is advanced by several lines. Therefore, in order to compensate for this, as shown in FIG.
Using a, the phase of the character area signal S1 and the original image data from which the character area signal S1 is obtained are adjusted.

Further, using the character area signal S 1, actual image data is separated by the video selector 110 b inside the memory selector 110, and is used as an input signal of the comparator 112.

In the comparator 112, the reference variable generator 111
Is successively compared with the image level of the character area signal S1, and addition and subtraction control of the reference variable S2 is executed based on the comparison result. The value of the reference variable S2 is determined based on the background of the character document section. Control is performed so as to converge to the density level.

Since the reference variable S2 is reset by the image signal S3 at the time of reading the original, it is generated for each line. The reference variable S2 always holds the final convergence data while reading one document, except for performing convergence control to the background density level in the character area.

The reference variable thus determined is used as a reference signal S4 in synchronization with the HSYNC signal.
The data is transferred line by line to the variable comparison unit 115 of the image correction coefficient generation unit 113.

The variable comparing section 115 compares the newly inputted reference signal S4 with the reference variables for a plurality of lines of the reference signal stored in the previous line variable memory 114.
As a result of this comparison, if the reference variable fluctuates extremely, it is determined that the character area is erroneously determined, and the reference coefficient of the previous line is substituted and substituted (for example, the value of the reference variable falls to half the value). If you do).

Thus, the determined reference variable is converted in the correction coefficient calculating section 116 into a correction coefficient K obtained by the following equation: K = 256 ÷ reference signal (1). The calculated correction coefficient K is input to the integrator 117.

The integrator 117 multiplies the correction coefficient K by the character area signal S1 corresponding to only the image data of the character area. By this multiplication, the intermediate density level (the background density level of the character document) can be corrected to a white level near 256. Then, the multiplied value is sent to the line memory 118 and stored as a correction value of the background density level for each line.

FIG. 5 shows the circuit 111 shown in FIG.
To the circuit 10 showing the configuration including the circuit 118 in more detail.
00.

Reference numeral 501 denotes an image signal (that is, S3) which also serves as a reset signal. Reference numeral 502 denotes a character area signal 502 obtained by the area signal generation unit 109 (ie,
S1). 504 and 505 are video data (image signals).

The comparators 507 and 508, the D flip-flops 509 to 512, and the determination circuit 513 are included in the comparator 112 described above.

The control level calculation circuit 514 is included in the above-described reference variable generator 111. The control level calculation circuit 514 calculates the image destination signal 501 (S3).
Reset by

The character area correction coefficient calculation circuit 516 corresponds to the correction coefficient calculation section 116 described above. Integrator 521
Corresponds to the integrator 117 described above.

In such a circuit 1000, the character area signal 502 (S1) and the picture destination signal 501 (S
3) are D flip-flops 509 to 51 by NOR gate 503 via buffers 503a and 503b.
2 is an enable (EN) signal, which is set to a state where it does not function outside the character area.

The character area signal 502 (S1) is input to the video data phase control unit 517, like the video signals (image signals) 504 and 505.

Video signals (image signals) 504, 505
Is input to the comparators 507 and 508 and also to the video data phase control unit 517.

The comparators 507 and 508 compare the input video data (image signal) 504 and 505 with the control level (reference variable). As a result of the comparison, if the image signal is larger than the reference variable, the contro1 of the D flip-flops 509 and 511 When UP is equal to or smaller than the image signal, contro1 of D flip-flops 510 and 512 is used. DOWN
Are output to the determination circuit 513, respectively.

Then, based on the input signal, the judgment circuit 513 sends an adjustment control signal corresponding to the information from the judgment condition setting section 515 to the control level calculation circuit 51.
Send to 4.

Here, the addition / subtraction control signal is supplied to the judgment circuit 513.
A> B and A ≦ B are defined by the number of signals, and when each of them is counted a predetermined number of times, control signals [+1] and [−1] are sent to the control level calculation circuit 514 (one pixel unit). It is difficult to converge if controlled by). When these [+1] and [-1] control signals are output, the counter is reset. When the count numbers of the [+1] and [-1] control signals are different, the operation tends to be as follows.

Counter setting value of [+1]> Counter setting value of [-1]: The followability to the change of the background density in the darkening direction is improved.

Counter setting value of [+1] <Counter setting value of [−1]: Followability to a change in the direction in which the background density becomes brighter is improved.

The control mode signal 523 is a signal for selecting an operation mode of the control level calculation circuit 514, and is input via the AND circuit 525. When the control mode signal 523 is input to the control level calculation circuit 514, the control level signal 506 for selecting whether to switch for each pixel or for each line is output to the comparators 507 and 508.
Is input to

Reference numeral 522 denotes a selection signal for selecting whether or not to execute the background correction processing.
24, and is input to the character area correction coefficient calculation circuit 516.

In this case, if the selection signal 522 is H,
The control level signal 506 calculated by the control level calculation circuit 514 becomes H (FF), whereby the correction coefficient of the character area correction coefficient calculation circuit 516 becomes 1
Becomes If the selection signal 522 is L, the control level signal 506 is sent to the character area correction coefficient calculation circuit 516 as it is. As described above, the ON / OFF control of the background correction is performed using the selection signal 522.

The reason why the operation mode is intentionally switched is that the reference variable must be changed to the background density level of the original document while reading the margin at the top of the printer output. In other words, the reference variable is considered so as to slightly change from the initial value.
Once you reach the background density level of the original,
By updating the reference variables on a line-by-line basis, it is possible to judge whether or not the operation is normal from a change in the reference variables for each line, and it is possible to prevent a density unevenness of image data in the main scanning direction.

X1 of the input of the AND circuit 519 indicates the coefficient of the image data other than the character area. The photograph / halftone area becomes the image data faithful to the original, and the image data of the character area is the background density level. Is calculated by the character area correction coefficient calculation circuit 516 and multiplied by the character area correction coefficient calculation circuit 516, whereby the background can be made white.

NOT circuit 517, AND circuits 518-5
20, using the integrator 521, the image data is corrected by multiplying the character area by the calculated correction coefficient K and multiplying the photograph / halftone area by the correction coefficient 1.

Note that, in FIG.
4, 505 correspond to the odd and even signals of the CCD 101, and only the odd or
It can be seen that the determination can be made using only even, and in practice it hardly changes. From this,
Even if the output of the CCD 101 is divided into multiples with the increase in speed, a similar result can be obtained by processing one input. The same applies to a color CCD. However, in the case of a color CCD,
Since the color balance of R, G, and B changes, similar results can be obtained by focusing on the color with the largest output, such as the G signal.

FIG. 6 shows the signal level of each part in the circuit 1000 of FIG.

Reference numeral 601 denotes an image destination signal (S3), which is generated at the leading edge of the original when reading an image.

Reference numeral 602 denotes a character area signal (S1).
It is generated by the area signal generator 109 corresponding to the document.

An image signal 603 is input to the OR circuit 503 after passing through the inverter 503a.

A character area signal 604 is input to the OR circuit 503 after passing through the inverter 503b.

An output signal 605 of the OR circuit 503 is input as an enable (EN) signal of the D flip-flops 509 to 512.

606 is an ABC_Enable signal 52
2, which corresponds to a control signal for the background correction operation.

Reference numeral 607 denotes a control mode signal 523.
This is a signal for selecting whether to return the control level signal 506 (reference variable) fed back to the comparators 507 and 508 on a line basis or on a pixel basis.

Reference numeral 608 denotes an output signal of the AND circuit 525. If the output signal 608 is H, the control level adjustment value for each pixel is fed back to the comparators 507 and 508 (that is, the control level is fed back by UP / DOWN for each designated count number). If the output signal 608 is L, the control level adjustment value is output to the comparator 50 for each main scanning line.
7, 508.

FIGS. 7 to 9 schematically illustrate the background correction processing described above.

Reference numeral 701 in FIG. 7 shows a document in which a character area 701 and a photograph area 702 are mixed. ρ1, ρ
In the case of cutting by the main scanning line of No. 2, the waveform of the cut is as shown in FIG.

Here, it should be noted that there is no misunderstanding.
The text area 701 and the photo area 702 are not missing, but are merely separated for the sake of clarity in the description, and are actually adjacent to each other.

FIG. 9 corresponds to the circuit of FIG. 5, in which the character area 701 is multiplied by the calculated correction coefficient for each line, and the photograph area 702 is multiplied by a coefficient 1.

Next, the background correction process for a character area according to the present invention will be described with reference to FIG.

The processing of steps S901 to S911 is the same as that of the conventional example shown in FIG.
Since the processing is the same as the processing in step 811, the description is omitted here.

Here, there are two methods of feedback of the control level.

First, when the feedback of the control level is returned because it is the output of step S911, the feedback is sequentially applied as in FIG.
At the same time, the process proceeds to step S912.

In step S912, the presence or absence of the input of the HSYNC signal is checked. If there is no input, the scanning for one line is not completed, and the process returns to step S911. Then, when the HSYNC signal is input, step S913 is performed.
Proceed to.

In step S913, a correction coefficient K is calculated by multiplying the final value of one line by the entire character area of one line.

In step S 914, it is checked whether the above is the character area 701 or the photograph area 702. Character area 7
In the case of 01, the process proceeds to step S915, and the photograph area 70
In the case of 2, the process proceeds to step S916.

In step S915, since the area is the character area 701, the correction coefficient K calculated by the line processing is multiplied.

In step S 916, since the area is the photograph area 702, the coefficient is multiplied by one.

By performing such processing for each line, an image having the background density level corrected in step S917 is formed.

On the other hand, when the feedback of the control level is returned from the beginning, that is, when the feedback is performed after detecting the HSYNC signal, the control level is updated every line.

By updating each line in this manner, in a document having many low-density areas on the document, the adjustment can be performed by the control level averaged over one line, so that good image formation can be performed. Becomes

In this example, the following processing can be performed in the background correction processing.

Of the reference variables obtained based on the image data of the same data line on the document, the data of the color with the maximum value of the reference variable can be used as a value common to all colors. This makes it possible to prevent the color balance of the image data constituting one data line from being lost.

[0134] Incidentally, when the ak = FF _H傾数and k, a: b: c = ak: bk: ratios ck is the same, but not collapse balance, a, b,
The color of c differs from the colors of ka, kb, and kc in color.

(R, G, B) = (128, 128, 12)
8) and (256, 256, 256) have different colors.

In this case, among the designated color information, a reference variable is calculated based on one divided data among the data obtained by dividing the main scanning signal into a plurality of pieces, and data of another divided area is calculated. Further, a correction coefficient common to the other color data corrected to the image data of the same line on the document by the sub-scanning line correction means of the color data of the color sensor is calculated, and the calculated correction coefficient is calculated. The correction process may be executed by multiplying each character area.

However, if the character is black, the data is ideally R, G, B, = (0, 0, 0) (actually, a slightly larger value) and a small level. The effect can be neglected by passing through the table (1, γ).

Further, even if the character density is multiplied by the inclination number, the level becomes substantially negligible, so that the correction processing can be performed without any problem. ).

The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer).
The present invention may be applied to an apparatus including two devices (for example, a copying machine and a facsimile machine).

Further, it is needless to say that the present invention can be applied to a case where the present invention is achieved by supplying a program to a system or an apparatus. Then, a storage medium storing a program represented by software for achieving the present invention is supplied to a system or an apparatus, and the computer (or CPU or M) of the system or the apparatus is supplied.
(PU) reads out and executes the program code stored in the storage medium, so that the effects of the present invention can be enjoyed.

In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, magnetic tape, nonvolatile memory card, ROM
(A mask ROM, a flash EEPROM, or the like) can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a function expansion port inserted into the computer or a memory provided in a function expansion unit connected to the computer, the program code is read based on the instruction of the program code. It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0145]

As described above, according to the present invention,
Image area separation is performed in real time based on image data input to the line memory for a plurality of lines, character area data is extracted from the line data, and the adjustment reference level is set for each line based on the data. By calculating a correction coefficient K such that the calculated value of the adjustment reference level becomes the white reference level of the document, and multiplying the correction coefficient K by the data of the character area of the data line used in the calculation, ,
Since the background density level of the data in the character area is corrected for each line, a large change in the background level caused by data other than the character area on image formation is prevented, and the correction coefficient is set for each line. By calculating K, it is possible to improve the density unevenness in the main scanning direction, suppress the drawing in of image data between adjacent lines, correct the original, and correct the background density at a high level. Accordingly, a phenomenon that has conventionally occurred due to the correction performed for each pixel, that is, a level pull-in phenomenon caused by the influence of the black band on the document, causes an image near the black band to be abnormally whitened out, or a band and band to be removed. The problem that the density during the period cannot follow the appropriate density can be improved.

Further, according to the present invention, in order to give priority to the image quality, the image is formed without multiplying the correction coefficient obtained by the adjustment reference level. , So that a very good output image can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating an internal configuration of an image area separation unit.

FIG. 3 is a block diagram illustrating area determination for image area separation.

FIG. 4 is an explanatory diagram showing a character area signal corresponding to a character area of a document.

FIG. 5 is a block diagram illustrating a circuit configuration of a background density correction unit for a document.

6 is a waveform chart showing an example of a signal waveform used in the circuit of FIG.

FIG. 7 is an explanatory diagram showing an image area on a document.

8 is a waveform diagram showing a signal waveform corresponding to the image area of FIG.

FIG. 9 is a circuit diagram showing a multiplication process of a correction coefficient related to FIGS. 7 and 8;

FIG. 10 is a flowchart illustrating a background correction process according to the present invention.

FIG. 11 is a flowchart showing a conventional background correction process.

[Explanation of symbols]

 Reference Signs List 1 image reading unit 2 image processing unit 3 image forming unit 101 CCD 106 signal processing unit 107 shading correction unit 108 image area separation unit 109 area signal generation unit 110 memory selector unit 111 reference variable generation unit 112 comparator 113 image correction coefficient generation Unit 114 previous line variable memory 115 variable comparison unit 116 correction coefficient operation unit 117 multiplier 118 line memory

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (24)

[Claims] 1. An apparatus for correcting background density of image data, comprising: storage means for storing one-dimensional image data for a plurality of lines; a character area from the stored plurality of lines of image data; An area separating unit that separates the image data into an area other than the character area; an extracting unit that extracts data of a desired character area in the image data according to the separated result; Correction means for calculating, for each line, a correction coefficient that converges on the background density level of the data, and correcting the background density level of the data in the character area for each line using the calculated correction coefficient. An image processing apparatus characterized by the above-mentioned. 2. The apparatus according to claim 1, wherein the correction unit calculates an adjustment reference level for each line using the extracted character area data, and calculates the adjustment reference level as a white reference level of a document. 2. The image according to claim 1, further comprising: means for calculating a correction coefficient that satisfies: and means for multiplying the data of the character area of the data line used for the calculation by the calculated correction coefficient. Processing equipment. 3. The correction means approximates the calculated adjustment reference level to a background density level, and compares a value of the adjustment reference level of the target line with an adjustment reference level of a plurality of adjacent front lines. Comparing means; means for determining the validity of the calculated adjustment reference level based on the comparison result; and when determining that the calculated adjustment reference level is not appropriate, calculating the value of the adjustment reference level of the previous line as the adjustment reference level of the target line. 3. The image processing apparatus according to claim 2, further comprising: 4. The apparatus further comprises means for dividing image data constituting one line, wherein a background density level is substituted for one of the adjustment reference levels calculated based on each of the divided data. 4. The image processing apparatus according to claim 2, wherein 5. The image processing apparatus according to claim 4, wherein the division of one line is performed by thinning-out division at a constant interval including an even number column and an odd number column. 6. The data of a color having the maximum value of the adjustment reference level among the adjustment reference levels calculated based on the image data of the same line is used as a value common to all colors. 6. The image processing device according to any one of 2 to 5. 7. An addition / subtraction reference level is calculated based on one data obtained by dividing a main scanning signal into a plurality of pieces of data of a designated color, and the data of the other divided area; 7. The method according to claim 6, wherein a common correction coefficient is calculated for data of another color corrected to the image data of the same line, and the calculated correction coefficient is multiplied to the data of each character area. Image processing device. 8. A line image sensor for converting a document image into an electric signal as one-dimensional image data; and moving the document image relative to the line image sensor in a two-dimensional direction, thereby obtaining the one-dimensional image data. 8. The apparatus according to claim 1, further comprising a document reading means for connecting the image data, wherein the read one-dimensional image data is stored in the storage means for a plurality of lines. Image processing device. 9. An image processing method for correcting background density of image data, comprising: a storage step of storing one-dimensional image data for a plurality of lines; and a character area from the stored plurality of lines of image data. An area separation step of separating the character data into an area other than the character area; an extraction step of extracting data of a desired character area in the image data according to the result of the separation; Calculating a correction coefficient that converges on the background density level of the data of the area for each line, and correcting the background density level of the data of the character area for each line using the calculated correction coefficient. An image processing method characterized by comprising: 10. The correction step includes: calculating an adjustment reference level for each line using the extracted character area data; and determining the calculated adjustment reference level as a white reference level of a document. 10. The image according to claim 9, further comprising: calculating a correction coefficient that satisfies the following condition: and multiplying the calculated correction coefficient by the data of the character area of the data line used for the calculation. Processing method. 11. The correcting step approximates the calculated adjustment reference level to a background density level, and compares a value of the adjustment reference level of the target line with an adjustment reference level of a plurality of adjacent front lines. A comparing step, a step of determining the validity of the calculated adjustment reference level based on the comparison result, and calculating the value of the previous line's adjustment reference level as the adjustment reference level of the target line if the determination is not appropriate. 11. The image processing method according to claim 10, further comprising: 12. The method according to claim 1, further comprising the step of dividing the image data constituting one data line, wherein one of the adjustment reference levels calculated based on each of the divided data is substituted for the background density. 12. The image processing method according to claim 10, wherein a level is obtained. 13. The image processing method according to claim 12, wherein the division of one line is performed by thinning division at a constant interval including an even number column and an odd number column. 14. The data of a color having the maximum value of the adjustment reference level among the adjustment reference levels calculated based on the image data of the same line is used as a value common to all colors. 14. The image processing method according to any one of 10 to 13. 15. An add / drop reference level is calculated based on one data obtained by dividing a main scanning signal among a plurality of data of a designated color, and the data of the other divided area; The method according to claim 14, wherein a common correction coefficient is calculated for data of another color corrected to the image data of the same line, and the calculated correction coefficient is multiplied to each character area data. Image processing method. 16. A one-dimensional image processing method comprising: using a line image sensor that converts a document image into an electric signal as one-dimensional image data; and moving the document image relative to the line image sensor in a two-dimensional direction. The image processing method according to any one of claims 9 to 15, further comprising a document reading step of connecting the plurality of image data, wherein the read one-dimensional image data is stored for a plurality of lines. . 17. A medium recording a program for correcting and controlling the background density of image data by a computer, the control program causing the computer to store one-dimensional image data for a plurality of lines. From the image data for the plurality of lines, a character region and a region other than the character region are separated, and according to the result of the separation, data of a desired character region inside the image data is extracted, A correction coefficient converging to the background density level of the extracted character area data is calculated for each line, and the background density level of the character area data is corrected for each line using the calculated correction coefficient. A medium having recorded thereon an image processing control program. 18. An adjustment reference level is calculated for each line using the extracted character area data, and a correction coefficient is calculated so that the calculated adjustment reference level becomes a white reference level of the document. 18. The medium according to claim 17, wherein the calculated correction coefficient is multiplied by the data of the character area of the data line used for the calculation. 19. The calculated adjustment reference level is approximated to a background density level, and a value of the adjustment reference level of the target line is compared with an adjustment reference level of a plurality of adjacent front lines. 19. The method according to claim 18, further comprising: determining whether the calculated reference level is appropriate, and if not, calculating the value of the reference level of the previous line as the reference level of the target line. A medium on which the image processing control program described above is recorded. 20. Dividing image data constituting one data line, and obtaining a background density level by substituting one of the adjustment reference levels calculated based on each of the divided data. 19. The method according to claim 18, wherein
Or a medium recording the image processing control program according to 19. 21. The medium according to claim 20, wherein one line is divided by thinning-out division at a constant interval including an even number column and an odd number column. 22. Data of a color having the maximum value of the adjustment reference level among the adjustment reference levels calculated based on the image data of the same line is used as a value common to all colors. Item 22. A medium recording the image processing control program according to any one of Items 18 to 21. 23. An adjustable reference level is calculated based on one piece of data obtained by dividing a main scanning signal among a plurality of pieces of data of a designated color, and the data of the other divided areas; 23. The method according to claim 22, wherein a common correction coefficient is calculated for data of another color corrected to the image data of the same line, and the calculated correction coefficient is multiplied by the data of each character area. A medium in which the image processing control program is recorded. 24. A one-dimensional image processing method comprising: using a line image sensor that converts an original image into electric signals as one-dimensional image data; and moving the original image relative to the line image sensor in a two-dimensional direction. 3. The image data of claim 1, wherein the read one-dimensional image data is stored for a plurality of lines.
3. A medium recording the image processing control program according to any one of 3.