JP3495841B2 - Image processing apparatus and method, and computer program product thereof - Google Patents

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, a method thereof, and a computer program product thereof, for example, binarization of a multi-valued image by determining a binarization threshold value for binarizing the multi-valued image. The present invention relates to an image processing apparatus and method, and a computer program product thereof.

[0002]

2. Description of the Related Art In recent years, image processing technology has been remarkably developed, and image processing apparatuses capable of processing multi-valued images such as full-color images in which photographs / characters are mixed, and character recognition processing in multi-valued images have become widespread. ing.

In such an image processing technique, a photograph /
Binarization processing of multi-valued images in which characters are mixed has become an indispensable technology.

As a conventional binarization method, a maximum value and a minimum value are calculated for each one line or several lines of a document, and a binarization threshold value is determined based on the maximum value and the minimum value.
There was a method of digitization. Further, there is a method of determining the binarization threshold value based on the difference between the maximum value and the minimum value for each block unit of the document and performing the simple binarization. Furthermore, when the histogram of the original is divided into two classes with a certain threshold, the threshold when the variance between the classes becomes maximum is the binarization threshold. The Otsu method (Otsu, “Automatic threshold based on discrimination and least squares criterion Value Selection Method ", IEICE Transactions, vol.J63-
D, no. 4, pp. 349-356, 1980).

[0005]

However, the binarizing method in the conventional image processing apparatus as described above has the following problems.

When binarizing a document in which photographs / characters are mixed in an image, the method of binarizing each line of the document is suitable for each photograph / character because photos / characters on the same line are mixed. It is difficult to set the threshold value, and as a result, the character portion is crushed when the photograph portion is prioritized, and the photograph portion is crushed or faint when the character portion is prioritized. Also, with the method of binarizing each block of the document, it is difficult to set a threshold value suitable for each photo / character because it is difficult to determine whether the inside of the block is a photo area or a character area. The result of mashup was crushed or faint. Further, since the binarization process is performed for each block, block distortion may occur in the binarization result. Also,
When there is a background in one block and a character on it, the density is reproduced even in the background by binarization, and a binary image with a lot of noise in the character part is generated.

Further, in the Otsu method, the characteristics of the distributions of the two classes are different between the photograph part and the character part, and when the distributions of the two classes are extremely different, the threshold value is closer to the larger class. Therefore, a noisy binary image has been generated.

The present invention has been made in order to solve the above-mentioned problems, and an appropriate binary value that appropriately separates the object from the background for each of the character portion and the other portion in the image. It is an object of the present invention to provide an image processing device, a method thereof, and a computer program product thereof, which can automatically set a threshold value and obtain a binary image without block distortion.

Further, according to the present invention, by making it possible to adjust parameters such as a region to be interpolated, the interpolation processing time for smoothing can be shortened, and the interpolation processing according to the specification of the input device or the resolution of the input image can be performed. It is an object of the present invention to provide an image processing apparatus and method capable of realizing the above.

[0010]

In order to achieve the above-mentioned object, the image processing method of the present invention has the following configuration.

[0011]

[0012]

[0013]

[0014]

That is, the brightness frequency is calculated for each block in the multi-valued image, and 2 in block units is calculated based on the brightness frequency.
Calculating a binarization threshold, the pixels by setting the region to interpolate binarization threshold of the block interpolates binarization threshold of the relative said set region Bro <br/> click units The unitary binarization threshold is calculated.

The image processing apparatus of the present invention has the following configuration.

That is, first calculation means for calculating the luminance frequency for each block in the multi-valued image, and second calculation means for calculating the binarization threshold value for each block based on the luminance frequency,
2 of the first setting means and the pixel unit by relative set region by said first setting means for interpolating the binarizing threshold of the block unit for setting a region for interpolating the binarizing threshold of the block And an interpolating means for calculating a threshold value.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a system configuration for executing the binarization processing in the present embodiment. Figure 1
In the figure, 1 is an image processing apparatus that performs image binarization processing, character recognition processing, and the like, 2 is an image input apparatus such as a scanner that inputs an image, and 3 is a processed image that is displayed or a processed image Is an image output device for recording.

In the image processing apparatus 1, 4 is an input section that serves as an interface with the image input apparatus 2, 5 is a storage section such as a memory for storing data being processed, and 6 is a cumulative total of luminance frequencies (histograms) of input images. It is a luminance frequency accumulation unit. Reference numeral 7 is an image feature determination unit that determines whether the input image is a character image, 8 is a binarization threshold value calculation unit that calculates a binarization threshold value for each block of the input image, and 9 is a binarization threshold value for each block. An interpolation processing unit 10 which performs an interpolating process based on the above to calculate a binarization threshold value in pixel units, and 10 creates a binarized image using the binarization threshold value in pixel units calculated in the interpolation processing unit 2 It is a valuation unit. Reference numeral 11 denotes a character recognition unit that performs character recognition processing on the area extracted as the character area, and 12
Is an image processing unit that performs various image processing and image layout processing on a region other than the character region, and 13 is an output unit that serves as an interface with the image display device 3.
Each of these components is comprehensively controlled by the control unit 15 including a CPU, ROM, and RAM.

The character recognition processing executed in the image processing apparatus 1 of the present embodiment having the above-mentioned configuration will be described below.

FIG. 2 is a flowchart showing a character recognition process using the binarization threshold value determining method which is a feature of this embodiment.

First, in step S201, image data is input by the image input device 2 such as a scanner. The input here is performed as 8-bit multivalued image data. Then, in step S202, the electrical noise of the image input device 2 generated at the time of image input is removed, and the input image is corrected such as deterioration of the original image and inclination of the original.
Then, in step S203, step S201
With respect to the multi-valued image input in, the character blocks (blurred character block, blurred character block), which is the feature of the present embodiment, are discriminated, and the optimum binarization threshold value is determined for each of them, A binary image is generated according to the binarization threshold. Then, the process proceeds to step S204 and step S20.
It is determined whether the binary image binarized in 3 is a block determined to be a character block, and step S
In 205, the character block is cut out from the binary image,
Character recognition processing is performed on the binary image, and the recognized character code is output. In step S206, it is determined whether or not there is an unprocessed block in the image. If yes, the process goes to step S204; otherwise, the process goes to step S207. In step S207, the character block and the non-character block are combined to have the same layout as the original image.

<< Binarization Process >> Next, step S203 for performing the binarization process by discriminating the character block (blurred character block, faint character block) which is the feature of this embodiment will be described with reference to FIG. This will be described in detail with reference to the flowchart of FIG.

In FIG. 3, first, in step S301, 8
A multi-valued image of bits is transferred from the storage unit 5 in the image processing apparatus 1 to a memory or the like (not shown) in processing block units (64 pixels × 64
Input for each pixel. It is assumed that the multi-valued image is stored in the storage unit 5 in advance by the image input device 2 such as a scanner. Then, in step S302, a character block (blurred character block, blurred character block) is determined, and threshold value determination processing for binarization is performed for each unit (64 pixels × 64 pixels) of the processing block of the input image. Since there are many strokes of one character with a collapsed character,
Characters that have been crushed and faint characters are those that have become thin. In this example, an optimum threshold can be assigned to these characters as well. Step S
At 303, it is determined whether the character flag MF is "1" (determination whether the block being processed is a character block. Details will be described later). If the result is a character block, go to step S305. If not, go to step S305.
Proceed to 304. In step S304, the threshold TH is limited by the lower limit value L and the upper limit value H. That is, step S
When the threshold value TH determined in 302 is smaller than the lower limit value L, the threshold value TH is represented by L, and when it is larger than the upper limit value H, the threshold value TH is represented by H. The lower limit value L and the upper limit value H are values determined by the characteristics of the image input device 2.

In step S305, it is determined whether the collapsed character flag TF is "1" (determination whether the block being processed is a collapsed character block, which will be described in detail later). If the result is a collapsed character block, step S30.
6. If not a block character block, step S307.
Go to. In step S306, the threshold TH is limited. That is, step S302 or step S304
A limiting process is performed such that the threshold value TH determined in step 3 is multiplied by a constant character TP for preventing character collapse. Here, the constant TP is a value determined by the characteristics of the image input device 2. And
In step S307, it is determined whether or not it is the last processing block (64 pixels × 64 pixels) of the input image. If it is the last processing block, the process proceeds to step S308, and if there is an unprocessed block, the process returns to step S301. In step S308, the threshold value T in block units determined in step S302, step S304, or step S306.
Smoothing processing (described in detail later) is performed on the basis of H to calculate the threshold value TH for each pixel. Finally, step S309
Then, the threshold value TH for each pixel calculated in step S308
Is used to perform a simple binarization process, and this binarization process ends.

<< Threshold Value Determining Process >> Next, the binarizing threshold value determining process in the present embodiment will be described in detail with reference to the flowchart of FIG.

In step S401, the parameter S
Set “0” and “255” to TART and END, respectively. START and END respectively correspond to the start point and end point of the statistic of the brightness value obtained in the subsequent step S402 or step S403. Also, "0" is set to the threshold value determination processing loop count i. In step S401, at the same time, using all the pixels in the processing block (64 pixels × 64 pixels), the frequency (histogram) for each digital value of 8 bits, that is, “0” to “255” is calculated.

In step S402, START to E
An average value AV of pixels corresponding to digital values up to ND is calculated. For example, if START = 0 and END = 255, the average value AV of pixels having values of “0” to “255” is calculated, and if START = 0 and END = 109, “0” to “109”. The average value AV of the pixels having the value of is calculated.

In step S403, START to E
The skew value SK of the pixel corresponding to the brightness value up to ND is calculated. The skew value is a statistic indicating the bias of the histogram distribution. Equation (1) shown below is used to calculate the skew value.

SK = (Σ (Xi-AV) ³ ) / D (1) Here, Xi is the luminance value of the pixel. D is a variance value of the entire image and is calculated by the equation (2).

D = Σ (Xi-AV) ² (2)

In the above equation (1), the skew value is calculated by raising the difference between the luminance value of each pixel and its average value to the third power, but if it is an odd power, it is limited to the third power. is not.

In step S404, the threshold value determination processing loop count i in one processing block is determined (i = 0,
That is, it is determined whether it is the first loop). If i is "0", the process proceeds to step S405, and if i is other than "0", the process proceeds to step S406. In step S405, image feature determination is made as to whether or not the block being processed is a “character block” (details will be described later), and the flow advances to step S414.

In step S406, the magnitude of bias in the histogram is determined as shown in equation (3).

−0.1 <SK and SK <0.1 (3) That is, it is determined whether the absolute value of the skew value SK is less than “0.1”. If step S406 is true, step S4
16. If false, the process advances to step S407.

In step S407, the number i of threshold value determination processing loops is determined. If i is "1", step S4 is performed.
08, if other than "1", the process proceeds to step S409. In step S408, it is determined whether or not the block being processed is a "blurred character block" and the process is performed (details will be described later), and the process proceeds to step S409. In step S409, the number i of threshold value determination processing loops is determined. If i is "9", the process proceeds to step S416, and if it is not "9", the process proceeds to step S410. In step S410, it is determined and processed whether or not the block being processed is a "blurred character block" (details will be described later), and the process proceeds to step S411. In step S411, it is determined whether or not the blurred character flag KF is "1". If "1", the process proceeds to step S416. If not "1", the process proceeds to step S412.

In step S412, the following (4) is shown.
The direction of the bias of the histogram is determined by the formula.

SK> 0 (4)

If the expression (4) is true in step S412 (meaning that the bias of the histogram is in the range of the value larger than the average value AV), the process proceeds to step S413, and false (the bias of the histogram is more than the average value AV). Also means that it is within a small value range), step S414
Go to.

In step S413, the average value AV is set in START and END is not changed. Then, the process proceeds to step S415. In step S414, the STA
The average value AV is set in END without changing RT.
Then, the process proceeds to step S415. In step S415, "1" is added to the threshold value determination processing loop count i, and the process returns to step S402 to again END from the START value.
The average value AV up to the value is calculated.

Finally, in step S416, the average value AV
Is set as the binarization threshold value TH, and the threshold value determination process is ended.

Although the binarization processing in this embodiment is performed as described above, the ranges shown by the equations (3) and (4) are not limited to this.

<< Numerical Arithmetic Process >> Next, the two processes of the average value AV calculation process (S402 of FIG. 4) and the skew value calculation process (S403 of FIG. 4) of this embodiment are realized as a series of processes on a computer. This example will be specifically described with reference to the flowchart of FIG.

In step S1301, effective digit number storage variables Seido1 and Seido2 are determined.

Seido1 is a variable for multiplying the calculated value so that the number of digits of the calculated value is moved up in order to keep the precision of the decimal part in integer calculation, and is determined by the integer effective numerical value inside the computer. In the present embodiment, when the computer internal integer is 16 bits, 256 bits or 32 bits corresponding to 8 bits are used.
In the case of, it is set to 65536 for 16 bits. Since this numerical calculation process handles 8-bit data of a multivalued image, the carry width (S) of the number of digits is increased so as to secure the original numerical value portion of 8 bits or more.
eido1) has been decided.

Seido2 is an integer operation, and the operation result is an integer effective numerical value that can be handled by a computer (32 in this embodiment).
bit) is a variable that divides the calculated value so as to cut off the number of digits of the calculated value in order to prevent it from overflowing (overflow), and is determined by the numerical value of the threshold value determination loop count i in which the average value AV calculation and the skew value calculation are one unit. It As the number of loops for the threshold value determination process increases, the interval between START and END becomes narrower, the number of elements in the histogram decreases, and the possibility of overflow decreases. Therefore, the value of i is determined. In the present embodiment, the threshold determination processing loop count i
The value of Seido2 is determined by the following formula so that the number of digits of the calculated value is reduced as the numerical value of becomes larger.

Seido2 = 2 ^ (10-i) (8) This value is determined by the overflow digit number of the theoretical bit number of the maximum operation digit number for each number of threshold value determination processing loops.

The value of the histogram at the luminance value K is HI.
If ST [K], the average AV can be expressed by the following equation.

[0050]   AV = (Σ (HIST [K] × K)) / (Σ (HIST [K])) (9)

In step S1302, the cumulative variable Sum1
= Σ (HIST [K] × K) and cumulative variable num = Σ (H
IST [K]), and in step S1303, Sum
1 is divided by num to obtain the average value AV.

In step S1304, Sum1 is multiplied by Seido1 determined in step S1301, and in step S1305, a precision ensuring average value AV 'for skew value calculation processing is obtained.

The equations (1) and (2) of the present embodiment are changed into a form that facilitates arithmetic processing.
It is S1313.

In step S1306, the initial value START of the brightness value K of the processing loop of the skew value calculation processing is set.

In step S1307, the intermediate variable Tmp is calculated.

Tmp = (K × Seido1-AV ') ×
For the brightness value K of (K × Seido1-AV ′), the value S determined in step S1301 is determined in the same manner as the accuracy ensuring average value AV ′.
Multiply eido1.

In step S1308, Tmp is divided by Seido2 determined in step S1301. For example i =
1, 64 × 64 processing block unit, 8-bit image,
In the case of ensuring the accuracy of 8 bits, the maximum number of arithmetic digits theoretically exceeds 32 bits and becomes 40 bits in the next step.
In this step, processing to prevent overflow is performed. At this time, the value of Seido2 is 10 in order to provide a margin for each processing block.

In step S1309, Tmp is multiplied by the histogram value HIST [K].

In step S1310, the cumulative variable Sum2
To the cumulative variable Sum3, and Tmp × (K ×
Seido1-AV ') is added.

In step S1311, it is checked whether K = END,
The end of the processing loop of the skew value calculation processing is determined.

In step S1312, 1 is added to K and the process returns to step S1307.

In step S1313, Sum3 is set to Sum.
The skew value SK is calculated by dividing by 2 and the numerator and denominator (Sum
3 and Sum2), the imbalance of the significant number conservation variable (numerator 3
To eliminate the denominator squared term for the power term, step S1
Divide by Seido1 determined in 301.

With the above, the numerical calculation process is completed.

As described above, the average value A of this embodiment
Although the V calculation process and the skew value calculation process are performed, the determination conditions of the effective digit number storage variables Seido1 and Seido2 shown here are not limited to this.

As described above, according to the numerical calculation processing of the present embodiment, the precision below the decimal point can be maintained even in the integer calculation by multiplying the calculated value by the effective digit number storage variable determined by the processing environment of the computer. Enable and
Also, by calculating the average value and skew value as one unit and dividing the calculated value by the effective digit number saving variable obtained for each unit, it is possible to perform the operation without exceeding the integer effective value that the computer can handle. . This makes it possible to obtain a high-speed numerical calculation method for image processing while maintaining a constant accuracy.

<< Image Feature Determination Process >> Next, the image feature determination process in step S405 will be described in detail with reference to FIG. In step S501, "0" is set to the character flag MF indicating whether the block being processed is a "character block". SK representing the first skew value in the threshold value determination processing loop
The skew value SK is set to 0 (this is because this image feature determination processing is performed only in the first loop of the threshold value determination processing loop). In step S502, whether or not the block being processed is a "character block" is determined by the equation (5).

SK0 <MH ... (5) Here, MH is a value indicating whether the block being processed is a “character block”, and here, “MH = −20.
0 ”. If the equation (5) is true in step S502, the process proceeds to step S503, and if false, the image feature determination process is ended. In step S503, the character flag MH indicating that the block being processed is a "character block".
Is set to "1", and the image feature discrimination processing is completed.

Although the image feature discrimination processing according to the present embodiment is performed as described above, the condition shown in equation (5) is not limited to this.

<< Crushed Character Processing >> Next, step S40.
The blurred character processing in 8 will be described in detail with reference to FIG. In step S601, a collapsed character flag TF indicating whether or not the block being processed is a "crushed character block" is set to "0". Further, a flag PF indicating that the histogram of the block being processed has a large bias
Set "0" to. Then, in step S602, the skew value S of the first loop in the threshold value determination processing loop
It is determined whether K0 and the skew value SK of the loop being processed are both negative, and if both are negative, "1" is set to the flag PF in step S603. In step S604, it is determined whether the character flag MF is "1" (that is, whether the block being processed is a character block). If "1", the process proceeds to step S605.
If it is other than "1", this crushed character processing ends. In step S605, whether or not the block being processed is a "blank character block" is determined by the equation (6).

SK0 / SK <−SR (6) Here, −SR is a value indicating whether the block being processed is a “blank character block”, and here, “−SR =
-3.0 ". If the expression (6) is true in step S605, the process proceeds to step S606, and if false, the crushed character processing is ended. In step S606, the collapsed character flag TF indicating that the block being processed is the "crushed character block" is set to "1", and the collapsed character processing is finished.

The crushed character processing in this embodiment is performed as described above, but the condition shown in equation (6) is not limited to this.

<< Faint Character Processing >> Further, step S4
The blurred character processing in 10 will be described in detail with reference to FIG. In step S701, "0" is set to the blurred character flag KF indicating whether the block being processed is a "blurred character block". In step S702, it is determined whether the character flag MF is "1" (whether the block being processed is a character block),
If it is "1", the flow proceeds to step S703, and if it is other than "1", this blurred character processing is ended. In step S703, it is determined whether the flag PF is "1". If "1", the process proceeds to step S704. In step S704, whether or not the block being processed is a "blurred character block" is determined by the equation (7).

SK0 / SK> SR (7) Here, SR is a value indicating whether the block being processed is a “blurred character block”, and here, “SR = 3.
0 ”. If the expression (7) is true in step S704, the process proceeds to step S705, and if false, the faint character process ends. In step S705, the faint character flag KF indicating that the block being processed is a "faint character block" is set to "1", and the faint character processing ends.

Although the faint character processing according to the present embodiment is performed as described above, the condition shown in equation (7) is not limited to this.

The threshold value determination process of this embodiment will be described in more detail below with reference to a specific image example.

First, the process of determining the binarization threshold TH of FIG. 4 in the present embodiment will be described using the example of the histogram shown in FIG.

FIG. 8 shows a blurred character image (8-bit input).
It shows a histogram of. In FIG. 8, the horizontal axis is the digital value of the brightness at which the left end represents “0”, that is, black, and the right end is “255”, that is, white, and the vertical axis represents the frequency of each digital value. FIG. 9 is a diagram showing a change in the value of each parameter during the processing shown in steps S402 and S403 in the binarization processing shown in FIG. 4 described above with respect to the image having the histogram shown in FIG. Is.
Each parameter value shown in FIG. 9 is indicated by the number of times it passes through steps S402 and S403.

First, the first processing that passes through steps S402 and S403 (threshold determination processing loop count i = 0)
Then, with START = 0, END = 255, the average value AV,
The statistic SK is calculated, and “109” and “−27.
Get the value of 4 ". Then, since i = 0, the process proceeds from step S404 to step S405. Step S
In the image feature determination processing of 405, since the statistic SK is less than “−20.0” according to the equation (5), it becomes true, the character flag MF is set to “1”, and S is obtained in step S414.
TART = 0 and END = 109 are set.

Subsequently, in the second processing (i = 1), ST
The average value AV and the statistic SK at ART = 0 and END = 109 are calculated to obtain the values “62” and “8.9”, respectively. Since the statistic SK exceeds “0.1”, the process proceeds from step S406 to step S407, and since i = 1, the process proceeds to step S408. In step S408, since the skew value SK is positive, the flag PF remains "0". Then, the result of the equation (6) is "-
3.08 (= −27.4 / 8.9) ”, which is true, so that the collapsed character flag TF is set to“ 1 ”. Then, in step S410, since the flag PF remains "0", the blur flag KF remains "0". Furthermore, since the skew value SK is positive, STAR is set in step S413.
T = 62 and END = 109 are set.

Subsequently, in the third processing (i = 2), ST
The average value AV and the statistic DK at ART = 62 and END = 109 are calculated to obtain the values “84” and “1.9”, respectively. In this case, since the statistic SK exceeds “0.1”, the process proceeds to steps S407 and S409. Then, since the skew value SK is positive, step S
At 413, START = 84 and END = 109 are set.

Subsequently, in the fourth processing (i = 3), ST
The average value AV and the statistic SK at ART = 84 and END = 109 are calculated to obtain the values “96” and “0.6”, respectively. In this case, since the statistic SK exceeds “0.1”, the processing continues, and the skew value SK is positive,
In step S413, START = 96, END = 109
Is set.

Then, in the fifth processing (i = 4), ST
The average value AV and the statistic SK at ART = 96 and END = 109 are calculated, and “102” and “−0.3” are calculated, respectively.
Is obtained. In this case, the statistic SK is "-0.
Since it is less than 1 ”, the processing continues, and since the skew value SK is negative, START = 96, END in step S414.
= 102 is set.

Subsequently, in the sixth processing (i = 5), ST
The average value AV and the statistic SK at ART = 96 and END = 102 are calculated to obtain the values “98” and “0.3”, respectively. In this case, since the statistic SK exceeds “0.1”, the processing continues, and the skew value SK is positive,
In step S413, START = 98, END = 102
Is set.

Then, in the seventh processing (i = 6), ST
The average value AV and the statistic SK at ART = 98 and END = 102 are calculated to obtain the values “99” and “0.4”, respectively. In this case, since the statistic SK exceeds “0.1”, the processing continues, and the skew value SK is positive,
In step S413, START = 99, END = 102
Is set.

Subsequently, in the eighth processing (i = 7), ST
The average value AV and the statistic SK at ART = 99 and END = 102 are calculated to obtain the values “100” and “0.2”, respectively. In this case, since the statistic SK exceeds “0.1”, the process continues, and the skew value SK is positive. Therefore, in step S413, START = 100, END =
102 is set.

Subsequently, in the ninth processing (i = 8), ST
Average value AV at ART = 100 and END = 102,
The statistic SK is calculated, and “101” and “−0.
You get the value 2 ". In this case, the statistic SK is “−
Since it is less than 0.1 ”, the processing continues, and the skew value SK is negative, so START = 100 in step S414,
END = 101 is set.

Subsequently, in the tenth processing (i = 9), S
Average value A at TART = 100 and END = 101
V and the statistic SK are calculated, and “100” and “0.
You get the value 2 ". In this case, the statistic SK is "0.
However, since the number i of times of threshold value determination processing loop is "9", the process proceeds to step S416 by the determination in step S409, and the threshold value TH is the average value AV "10".
"0" is set, and the threshold value determination process is completed. However,
Since the block in this example has the collapsed character flag TF set to "1", step S30 in FIG.
The determination in step 5 is true, the threshold value is limited in step S306, TH is set to “85 (= 100 × 0.85)”, and after smoothing processing of the threshold value TH in step S308, 2 is set in step S309. Valued. (In this case, "0.85" is set in TP.)
The binarized image is stored in the storage unit 5.

Next, the process of determining the binarization threshold value TH of FIG. 4 in the present embodiment will be described using the example of the histogram shown in FIG.

FIG. 10 shows a histogram of a blurred character image (8-bit input). FIG. 11 shows step S402 in the binarization processing shown in FIG. 4 described above for an image having a histogram as shown in FIG.
FIG. 6 is a diagram showing changes in the values of the respective parameters during the processing shown in S403 and S403. Each parameter value shown in FIG. 11 is indicated by the number of times it passes through steps S402 and S403.

First, the first processing that passes through steps S402 and S403 (threshold determination processing loop count i = 0)
Then, with START = 0, END = 255, the average value AV,
The statistic SK is calculated, and “130” and “−60.
You get the value 2 ". Then, since i = 0, the process proceeds from step S404 to step S405. Step S
In the image feature determination processing of 405, since the statistic SK is less than “−20.0” according to the equation (5), it becomes true, the character flag MF is set to “1”, and S is obtained in step S414.
TART = 0 and END = 130 are set.

Then, in the second processing (i = 1), ST
The average value AV and the statistic SK at ART = 0 and END = 130 are calculated to obtain the values “95” and “−19.3”, respectively. Since the statistical value SK exceeds “0.1”,
From step S406 to step S407, i = 1
Therefore, the process proceeds to step 408. In step S408, since the skew values SK and SK0 are both negative, "1" is set in the flag PF. Then, since the result of the expression (6) is false as "3.11 (= -60.2 / -19.3)", the collapsed character flag TF remains "0".
Then, in the faint character processing of step S410, both the character flag MF and the flag PF are "1", so step S410
In step 704, the formula (7) is calculated, and the result is “3.11 (=
-60.2 / -19.3) "is true, the faint character flag KF is set to" 1 ". Since the blur flag KF is "1", steps S411 to S416
Then, the average value AV of "95" is set to the threshold value TH, and the threshold value determining process ends. Then, after the smoothing process of the threshold value TH in step S308 of FIG. 3, the image is binarized in step S309, and the binarized image is stored in the storage unit 5.

In the "smoothing process", the smoothing process of step S308 of FIG. 3 will be described with reference to FIGS.
Will be explained.

FIG. 12 is a flow chart best showing the configuration of the smoothing process of step S308 of FIG. In FIG. 12, steps S1201 to S1204 are steps for setting various parameters of smoothing processing performed in block units.
A step S1201 sets a vertical smoothing area of a block to be smoothed, a step S120.
In step S1203, the horizontal smoothing area of the block to be smoothed is set. In step S1203, the vertical smoothing step of the block to be smoothed is set. In step S1204, the horizontal smoothing step of the block to be smoothed is set. Then, from step S1205 to step S120
Up to 9, steps S1201 to S1204
This is a step of executing the smoothing of the binarization threshold value in block units based on the above settings. Step S1205
Performs the smoothing processing block image extraction, step S1206 sets the thresholds of the four corners of the block to be smoothed, step S1207 performs the vertical smoothing processing, and step S1208 performs the horizontal smoothing processing. Then, in step S1209, it is determined whether or not there is an unprocessed block for smoothing. If there is an unprocessed block, step S1209 is performed.
In step 1205, the smoothing process is continued, and if there is no unprocessed block to be smoothed, the process ends.

Below, in order to perform the details of each step,
The relationship between the block for calculating the threshold value for each block and the block for performing the smoothing process in the loop of steps S301 to S307 will be described, and then the details of each step of steps S1201 to S1209 will be described.

FIG. 13 shows steps S301 to S3 of FIG.
It shows the unit of the block for calculating the threshold value of the block unit in the loop up to 07, and is 64 from the upper left corner.
Blocks are divided for every 64 pixels, and B11 to B
The numbers are shown in nm and blocks. Hereinafter, the block-by-block threshold calculation loop of steps S301 to S307 is called a block threshold calculation loop, and the resulting threshold is called a block threshold.

FIG. 14 is a diagram showing the relationship between the block threshold for binarization calculated in the block threshold calculation loop and the block serving as the unit of smoothing processing for calculating the threshold in pixel units. . In FIG. 14, a thin solid line is the same as the block division in FIG. 13, and shows a 64 × 64 block division starting from the upper left first pixel. In the block threshold calculation loop, the block threshold is calculated in units of blocks divided by the thin solid line, and thus the block threshold can be considered as a threshold representing the block. Therefore, the center point of the block divided by the thin solid line, that is, the intersection of the thick dotted lines is set as the block threshold value obtained from the block threshold value calculation loop, and in the smoothing process of step S308, the block newly divided by the thick dotted line is used. For each unit, interpolation processing is performed based on the threshold values at the four corners of the block divided by the thick dotted lines to calculate the threshold value in pixel units of the block divided by the thick dotted lines. Hereinafter, the block divided by the thick dotted line is referred to as a smoothing block.

That is, in the smoothing process of step S308, BL1 divided by the thick dotted line in FIG.
1, BL12 ,. ． ． BL1 (m-1), BL1m, B
L21, bl22 ,. ． ． BLn (m-1), BLnm
Is newly defined as a smoothing block for smoothing processing, and a block threshold value as shown in the figure is defined at the intersection of the blocks, that is, the intersection of the thick dotted lines. For example, the thresholds at the four corners of BL11 are TH11, TH
11, TH11, TH11, and the thresholds at the four corners of BL22 are TH11, TH12, TH21, TH22. Then, in the smoothing block, linear interpolation in the vertical direction or the horizontal direction is performed according to the threshold values at the four corners. For example, the smoothing process for BL22 is T
Linear interpolation in the vertical and horizontal directions is performed using four thresholds H11, TH12, TH21, and TH22.

Now, steps S1201 to S1201 in FIG.
Up to 1204 will be described with reference to FIG.

In FIG. 15, TH_TL, TH_T
R, TH_BL, TH_BR represent block thresholds at the four corners of the smoothing block, and TH_TL, TH_TR, TH_B in each smoothing block.
The relationship between the values of L and TH_BR and the block threshold calculated by the block threshold calculation loop is as described above.

A step S1201 sets a vertical smoothing area. The vertical smoothing area is an area for performing interpolation calculation in the vertical direction, and is set by V1 and V2 as shown in FIG. For example, when V1 = 1 and V2 = 64, the vertical direction interpolation calculation is performed on the entire area, and V1 = 1.
7, V2 = 48, in the smoothing block, the interpolation calculation in the vertical direction is not performed from the first row to the 16th row, and the threshold value of the first row is repeatedly used.
From line to line 48, TH_TL, TH_TR, TH
Vertical interpolation calculation is performed using _BL and TH_BR, and vertical interpolation calculation is not performed from the 49th line to the 64th line, and the value of the 49th line is repeatedly used.

A step S1202 sets a horizontal smoothing area. The horizontal smoothing area is an area in which horizontal interpolation calculation is performed.
It is set by H1 and H2, as shown in FIG. For example, when H1 = 1 and H2 = 64, the horizontal direction interpolation calculation is performed on the entire area, and H1 = 1.
7, H2 = 48, in the smoothing block, the interpolation calculation in the horizontal direction is not performed from the first column to the 16th column, and the threshold value of the first column is repeatedly used.
From the column to the 48th column, TH_TL, TH_TR, TH
Horizontal interpolation calculation is performed using _BL and TH_BR, and horizontal interpolation calculation is not performed from the 49th column to the 64th column, and the value of the 49th column is repeatedly used.

Therefore, in FIG. 15, the quadrangle region having (0,0) at the upper left corner and (H1, V1) at the lower right corner is T
The value of H_TL is repeated, (H2,0) is in the upper left corner,
The rectangular area having the lower right corner of (64, V1) is TH_T.
The value of R is repeated, (0, V2) is in the upper left corner, (H1,
In the rectangular area with the lower right corner at 64), the value of TH_BL is repeated, and (H2, V2) is at the upper left corner, (64, 64).
The value of TH_BR is repeated in the rectangular area with the lower right corner of. A square area having (0, V1) at the upper left corner, (H1, V2) at the lower right corner, and (H2, V1) at the upper left corner, (6
4, V2) is the lower right corner of the quadrangle region, only vertical interpolation calculation is performed, and (H1,0) is the upper left corner, and (H2,
Only the interpolation operation in the horizontal direction is performed on the quadrangle region having V1) as the lower right corner, the quadrangle region having (H1, V2) as the upper left corner, and (H2, 64) as the lower right corner. And (H1, V
For a quadrangular area having 1) in the upper left corner and (H2, V2) in the lower right corner, both vertical and horizontal interpolation calculations are performed.

As described above, the smaller the smoothing area in the vertical and horizontal directions is, the smaller the number of interpolation calculations for smoothing can be and the shorter the calculation time for smoothing processing can be. The smaller the area, the steeper the change in the image data at the boundary of the block, so that the block distortion is likely to occur. In the present embodiment, since the area setting is variable, it is possible to set the smoothing area that is optimum for the resolution of the input device or the input image.

A step S1203 sets a vertical smoothing step. The vertical direction smoothing step is a value indicating how many pixels are to be calculated for the interpolation calculation in the vertical direction smoothing area set in step S1201, and is set by VSTEP.
For example, the vertical smoothing step VSTEP is 1
In the case of, the interpolation calculation is performed for each pixel, and in the case of 4, it is performed every four pixels. When the interpolation calculation is performed for every plural pixels, the value obtained by the interpolation calculation is repeatedly used as the value between the values. For example, when V1 = 1, V2 = 64 and the vertical smoothing step VSTEP is 16, the first row, the 17th row
The values of the lines, the 33rd line, and the 49th line are calculated by interpolation calculation from the block thresholds at the four corners. And from the second row 1
The values in the first row are repeated up to the sixth row, and the values in the eighteenth to thirty-second rows are repeated in the seventeenth row.
The values in the 33rd row are repeated for the values from the row to the 48th row, and the values in the 49th row are repeated for the values in the 50th to 64th rows.

A step S1204 sets a horizontal smoothing step. The horizontal smoothing step is a value indicating how many pixels are to be calculated for the interpolation calculation in the horizontal smoothing area set in step S1202, and is set by HSTEP.
For example, the horizontal smoothing step HSTEP is 1
In the case of, the interpolation calculation is performed for each pixel, and in the case of 4, it is performed every four pixels. When the interpolation calculation is performed for every plural pixels, the value obtained by the interpolation calculation is repeatedly used as the value between the values. For example, when H1 = 1, H2 = 64 and the horizontal smoothing step HSTEP is 16, the first column, the 17th column
The values of the column, the 33rd column, and the 49th column are calculated by interpolation calculation from the block thresholds at the four corners. And from the second column 1
The values in the first column are repeated up to the sixth column, and the values in the eighteenth column to the thirty-second column are repeated in the seventeenth column.
The values in the 33rd column are repeated for the values from the column to the 48th column, and the values in the 49th column are repeated for the values in the 50th to 64th columns.

Therefore, the smaller the number of smoothing steps in the vertical and horizontal directions, the less the number of interpolation calculations for smoothing, and the shorter the calculation time for smoothing processing. However, if the smoothing steps are made smaller. As the threshold value is increased, the change in the threshold value of the smoothing area becomes coarser, and thus the block distortion is likely to occur. In the present embodiment, since the area setting is variable, it is possible to set the smoothing step that is optimum for the resolution of the input device or the input image.

Next, from step S1205 to step S
Before describing the loop for performing the interpolation calculation up to 1209, the interpolation calculation method in the vertical direction and the horizontal direction will be described with reference to FIG. 15, and then the interpolation calculation loop will be described.
In FIG. 15, regarding the interpolation calculation in the vertical direction, TH_T
VLi the vertical direction interpolation processing result using L and TH_BL
(I = 1, 2, ..., (V2-V1 + 1) / VSTE
P) and the vertical direction interpolation processing result using HT_TR and TH_BR is VRi (i = 1, 2, ..., (V2-V
1 + 1) / VSTEP), VLi and VRi are VLi = TH_TL + (i-1) ^* (TH_BL-TH_TL) / ((V2-V1 + 1) / VSTEP). ． ． (12-1) VRi = TH_TR + (i-1) ^* (TH_BR-TH_TR) / ((V2-V1 + 1) / VSTEP). ． ． It can be expressed as (12-2). Then, using the VLi and VRi, horizontal interpolation processing of each row is performed. The interpolation result is Hij (i = 1, 2, ..., (V2-V1 + 1) / V
STEP, j = i = 1, 2 ,. ． ． , (H2-H1 +
1) / HSTEP), Hij is Hij = VLi + (j-1) ^* (VRi-VLi) / ((H2-H1 + 1) / HSTEP). ． ． It can be expressed as (12-3). Where (V2-V1 + 1) / V
STEP is the number of interpolation calculations per line in the vertical direction, and (H2-H1 + 1) / HSTEP is 1 in the horizontal direction.
Indicates the number of interpolation calculations per line.

V1 = 1, V2-64, H1 = 1, H2 =
64, VSTEP = 1, HSTEP = 1, TH_TL
= 32, TH_TR = 96, TH_BL = 96, TH_
If BR = 160, the above formula (12-1), (12-
When the threshold value in the smoothing block is calculated from the equations (2) and (12-3), it becomes as shown in FIG.

Next, from step S1205 to step S
The loop processing up to 1209 will be described in detail.
This loop includes BL11 and BL1 shown in FIG.
2 ,. ． ． BL1 (m-1), BL1m, BL21, B
L22 ,. ． ． This is a loop for processing for each smoothing block of BLn (m-1), BLnm. -In step S1205, the image data of BL11 is extracted. -In step S1206, the four corner thresholds are TH_
TL = TH11, TH_TR = TH11, TH_BL =
TH11, TH_BR = TH11 are set. In step S1207, smoothing processing in the vertical direction is performed, but the values of HT_TL and TH_BL are the same,
Since TH_TR and TH_BL have the same value, interpolation calculation in the vertical direction is not performed, and the same value TH11 is repeated. In step S1208, since the values at the left end and the right end are the same for the horizontal interpolation process, the horizontal interpolation calculation is not performed and the same value TH11 is repeated. In step S1209, since there is an unprocessed block, the process proceeds to step S1205.

Next, the smoothing block BL12 is processed. -In step S1205, the image data of the next smoothing block BL12 is extracted. -In step S1206, block thresholds TH_ at four corners
TL = TH11, TH_TR = TH12, TH_BL =
TH11 and TH_BR = TH12 are set. In step S1207, TH_TL and TH_BL,
Since TH_TR and TH_BR are the same value, vertical interpolation calculation is not performed, and TH11 in VLi is
In VRi, TH12 is repeated. In step S1208, the interpolation calculation in the horizontal direction is performed based on the equation (12-3). However, i =
1, 2 ,. ． ． , (V2-V1 + 1) / VSTEP, VLi = TH11 and VRi = TH12 are always satisfied, so that the value of Hij is the same even if i changes. Therefore, after i = 2, the value H1j (j = 1,
2 ,. ． ． , (H2-H1 + 1) / HSTEP) are repeatedly used. In step S1209, since there is an unprocessed block, the process proceeds to step S1205. Hereinafter, the same processing as the smoothing block BL12 is performed by the smoothing blocks BL13, BL14 ,. ． ． ，
Repeated up to BL1m.

Then, the smoothing block BL21 is processed. In step S1205, the image data of the next smoothing block BL21 is extracted.・ Step S12
In 06, block thresholds at four corners TH_TL = TH11,
TH_TR = TH11, TH_BL = TH21, TH_
BR = TH21 is set. In step S1207, VLi and VRi are interpolated based on the equation (12-1) and VRi based on the equation (12-2) to obtain VLi and VRi. In step S1208, TH_TL and TH_TR,
Since TH_BL and TH_BR are the same, VLi and V
The value of Ri is i = 1, 2 ,. ． ． (V2-V1 + 1) /
Since all VSTEPs are the same, only when i = 1, the horizontal interpolation operation is not performed, and the value of VLi is Hij (j = 1, 2, ...
STEP) is used repeatedly. This repetition is repeated for i = 1, 2 ,. ． ． (V2-V1 + 1) / VST
It is done up to EP. In step S1209, since there is an unprocessed block, the process proceeds to step S1205.

Next, the smoothing block BL22 is processed. -In step S1205, the image data of the next smoothing block BL22 is extracted. -In step S1206, block thresholds TH_ at four corners
TL = TH11, TH_TR = TH12, TH_BL =
TH21 and TH_BR = TH22 are set. In step S1207, VLi and VRi are interpolated based on the equation (12-1) and VRi based on the equation (12-2) to obtain VLi and VRi. In step S1208, interpolation calculation in the horizontal direction is performed based on the above equation (12-3) to obtain Hij. In step S1209, since there is an unprocessed block, the process proceeds to step S1205.

Thereafter, the same processing as described above is repeated up to BLnm, and the binarization threshold value of the entire image is determined in step S308.
The smoothing process of is completed.

As described above, according to the threshold value determining method of the present embodiment, the luminance frequency is calculated for each block in the multivalued image,
A binarization threshold value for each block is calculated based on the luminance frequency, and a binarization threshold value for each pixel is calculated by interpolating the binarization threshold value for each block unit, that is, for each block in an image. With, it becomes possible to automatically set an appropriate threshold value between the object and the background density, and further to automatically set the binarization threshold value in pixel units. This makes it possible to properly separate the object from the background for each of the character portion / other portions in the image and obtain a binary image without block distortion.

<< Another Example of Smoothing Process >> In the above embodiment, in order to perform the smoothing process, the smoothing process is performed in the vertical direction and then the smoothing process in the horizontal direction. However, the vertical smoothing process may be performed after the horizontal smoothing process.

Further, in the above-mentioned embodiment, the smoothing block is defined in order to carry out the smoothing process, and the interpolation operation is performed for each smoothing block.
The calculation order is not limited to this, and the smoothing process may be realized by dividing the calculation order into various directions such as top, bottom, left, and right. For example, after the interpolation calculation of the first line of the entire image area is performed, the second line and the third line may be sequentially rasterized. Furthermore, the BL of the smoothing block defined in the embodiment
21, BL22 ,. ． ． , BL2m, BL3
1 ,. ． ． , BLnm are divided into upper and lower parts, and BL11, BL12 ,. ． ． , BL1m on BL21, on BL22 ,. ． ． , BL2m above BL21 below, BL22 below ,. ． ． , BL2m below BL31, above BL32 ,. ． ． , BL3m above BL31 below, BL32 below ,. ． ． , BL3m below ... BLn1 below, BLn2 below ,. ． ． , BLnm and smoothing can also be performed.

At this time, the smoothing parameter is set to V1.
= 33, V2 = 64, H1 = 1, H2 = 64,
Smoothing block lines 1 to 32 and 3
If you divide it into three parts from the 3rd row to the last row of the smoothing block, the upper side of the smoothing block is TH.
Only horizontal smoothing is performed from _TL and TH_TR, and the lower side is TH_TL, TH_TR, TH_BL,
Smoothing in the vertical and horizontal directions is performed from four TH_BRs. In this case, BL11, BL12 ,. ． ． , BL
1m, on BL21 ,. ． ． , BL2m, the smoothing process can be performed using only the threshold values of the results of the first band and the second band in FIG.
under,. ． ． , BL2m below, BL3 above, BL32
Up,. ． ． , BL3m, the first band and the second band in FIG.
The smoothing process can be performed using only the threshold value of the band result. By processing the lower side and the upper side of the smoothing block as a set even after BL31 and below,
By only saving the block threshold of the previous band,
It can be processed in band units shown in. Accordingly, when the present invention is implemented by band processing, smoothing processing can be implemented by a single band without having a plurality of bands, so that it is possible to save the image band memory.

(Other Embodiments) In the above embodiments, the image input is 8-bit multi-valued image data of one pixel single color, but it is not limited to this and a plurality of colors can be used. Good. That is, it is sufficient that the data for binarization has a plurality of bits of information.

Further, the image processing block for calculating the histogram is 64 pixels × 64 pixels,
The block size may be 32 pixels × 32 pixels. Further, the block shape may be square or rectangular. That is, the processing block may be 64 pixels × 96 pixels. Depending on the memory capacity, the entire image may be used as the processing block.

Further, the sampling in the image when calculating the histogram may be all pixels or every few pixels. Further, the calculation of the average AV and the statistic SK does not have to be performed with 8 bits, and may be performed with a small number of bits for speeding up, memory reduction, and the like.

Further, the convergence condition of the statistic SK is set to "± 0.
However, the present invention is not limited to this, and another condition may be set, and the threshold for binarization may be determined using the statistic SK, and there is no limitation. Further, another condition may be set, such as changing depending on the image input device or the image input condition.

Although the character flag MF is set to "-20.0" in the determination of the character block of the expression (5), the present invention is not limited to this, and the determination of the character block is performed using the statistic SK. Therefore, another condition may be set. Further, another condition may be set, such as changing depending on the image input device or the image input condition.

Further, the SR value is used as "3.0" for the judgment of the blurred character block or the blurred character block in the expressions (6) and (7), but the present invention is not limited to this, and the statistic value SK Another condition may be set so as to determine a blurred character block or a blurred character block using. Also,
Other conditions may be set, such as changing depending on the image input device or the image input conditions.

Further, the lower limit value L and the upper limit value H of the threshold value may be changed depending on the image input device and the image input condition.
You may comprise.

Further, the constant TP is used to prevent crushing and is set to "0.85". However, the present invention is not limited to this, and another condition such as a change depending on the image input device or the image input condition may be set. Good.

Further, an object of the present invention is to supply a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to supply a computer (or CPU) of the system or apparatus.
It is needless to say that the above can be achieved by reading out and executing the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, 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, C
DR, magnetic tape, non-volatile memory card, ROM
Can be used.

For example, referring to FIG. 18, as an example,
Corresponds to 1 to 3 in FIG. 1, and the CPU 101 of this device
This is achieved by reading the program code stored in the floppy disk 103 into the memory 102 and executing it.

Further, not only the functions of the above-described embodiments are realized by executing the program code read by the computer, but also the OS (operating system) running on the computer based on the instructions of the program code. It is needless to say that this also includes a case where the above) performs a part or all of the actual processing and the processing realizes the functions of the above-described embodiments.

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

When the present invention is applied to the above-mentioned storage medium, the storage medium stores the program code corresponding to the above-mentioned flowchart. Briefly, the memory map example of FIG. Each module shown will be stored in the storage medium.

That is, for example, the “block processing module” corresponding to the S301 processing block extraction processing of FIG. 3, the “histogram calculation module” corresponding to the S401 histogram calculation processing of FIG. 4, and the S402 average value calculation processing of FIG. "Average value calculation module", Figure 4
4. “Skew value calculation module” corresponding to S403 SK value calculation processing of FIG. 4, “Image feature determination processing module” corresponding to S405 image feature determination processing of FIG. 4, and S416 of FIG.
"Threshold calculation module" for the threshold calculation processing, S304 threshold restriction processing of FIG. 3, or S306 threshold restriction processing of FIG. 3, "smoothing processing module" corresponding to S308 smoothing processing of FIG. 3, and S3 of FIG.
The program code of each module of “binarization processing module” corresponding to 09 simple binarization processing may be stored in the storage medium.

As described above, according to the embodiment, it is possible to perform smooth binary reproduction without block distortion in binarization.

Particularly, according to the present embodiment, the luminance frequency is calculated for each block in the multi-valued image, the binarization threshold value for each block is calculated based on the luminance frequency, and the binary value for each block unit is calculated. By calculating the binarization threshold value for each pixel by interpolating the threshold value, that is, automatically setting an appropriate threshold value between the object and the background density for each block in the image,
Further, it becomes possible to automatically set the binarization threshold value for each pixel. This makes it possible to obtain a binarized image in which the object is appropriately separated from the background for each of the character portion / other portion in the image and the block distortion is not generated.

Further, the block distortion can be removed by the interpolation (smoothing process) of this embodiment.
Further, by adjusting the parameters for smoothing, it is possible to shorten the interpolation processing time for smoothing and realize the interpolation processing according to the characteristics such as the resolution of the input device or the input image. Furthermore, when band processing using an image band memory having the same height as a block is applied to the present invention, smoothing can be realized by only a single band by setting smoothing parameters, and the cost required for the band memory is reduced. Can be suppressed.

Further, by multiplying the calculated value by the effective digit number storage variable determined by the processing environment of the computer, it is possible to maintain the precision below the decimal point even in the integer calculation, and the average value calculation and the skew value calculation are made as one unit. By dividing the calculated value by the effective digit number storage variable obtained for each unit, it is possible to perform the operation without exceeding the integer effective value that the computer can handle. This makes it possible to obtain a high-speed numerical calculation method for image processing while maintaining a constant accuracy.

[0138]

As described above, according to the present invention, the brightness frequency is calculated for each block in a multi-valued image, the binarization threshold value for each block is calculated based on the brightness frequency, and the block unit By interpolating the binarization threshold of
By calculating the binarization threshold, it is possible to automatically set an appropriate threshold between the object and the background density for each block in the image, and it is also possible to automatically set the binarization threshold for each pixel. become. This makes it possible to properly separate the object from the background for each of the character portion / other portions in the image and obtain a binary image without block distortion.

Also, by making it possible to adjust the parameters when performing the interpolation, it is possible to shorten the interpolation processing time and realize the interpolation processing according to the characteristics such as the resolution of the input device or the input image.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing a character recognition process in the present embodiment.

FIG. 3 is a flowchart showing a binarization process in the present embodiment.

FIG. 4 is a flowchart showing a threshold value determining process in the present embodiment.

FIG. 5 is a flowchart showing image feature determination processing according to the present embodiment.

FIG. 6 is a flowchart showing a blurred character process according to the present embodiment.

FIG. 7 is a flowchart showing faint character processing according to the present embodiment.

FIG. 8 is a diagram showing an example of a histogram of a blurred character image according to the present embodiment.

FIG. 9 is a diagram showing a transition example of each variable value in the binarization processing of a blurred character according to the present embodiment.

FIG. 10 is a diagram showing a histogram example of a blurred character image in the present embodiment.

FIG. 11 is a diagram showing a transition example of each variable value in binarization processing of a blurred character according to the present embodiment.

FIG. 12 is a flowchart showing smoothing processing according to the present embodiment.

FIG. 13 shows steps S301 to S307 of FIG.
It is a figure which shows the block in the loop which calculates the threshold value of every block unit up to.

FIG. 14 is a diagram showing a relationship between a smoothing block and a block threshold value.

FIG. 15 is a diagram showing thresholds at four corners of a smoothing block, a vertical smoothing area, and a horizontal smoothing area.

FIG. 16 is TH_TL = 32, TH_TR = 96, TH
It is a figure which shows the interpolation calculation result in a smoothing block when _BL = 96 and TH_BR = 160.

FIG. 17 is a flowchart showing a numerical calculation process.

FIG. 18 is a diagram illustrating an example of a computer program product according to an embodiment of the present invention.

FIG. 19 is a diagram showing an example of a layout of a program module for executing image processing according to the embodiment of the present invention on a predetermined storage medium.

[Explanation of symbols]

1 Image processing device 2 Image input device 3 Image display device 4 Input section 5 memory 6 Luminance frequency accumulation section 7 Image feature discriminator 8 Binarization threshold calculation unit 9 Interpolation processing unit 10 binarization unit 11 Character recognition part 12 Image processing unit 13 Output section 15 Control unit

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroshi Mori 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-7-212591 (JP, A) JP-A-5 -191649 (JP, A) JP 62-297980 (JP, A) JP 63-146173 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 1/40- 1/409 H04N 1/46 H04N 1/60

Claims (8)

(57) [Claims] 1. A brightness frequency is calculated for each block in a multi-valued image, a binarization threshold value for each block is calculated based on the brightness frequency, and an area for interpolating the binarization threshold value for each block is set. and, an image processing method and calculates a binarization threshold of each pixel by to the set region interpolating binarization threshold of the block unit. Wherein a region that does not interpolate binarization threshold of the block unit, the image processing method according to claim 1, wherein the repeatedly using binarization threshold of the block unit. 3. Interpolation Starring the binarization threshold of the block
The image processing method according to claim 1, wherein setting the interval of pixels for performing calculations. 4. performs interpolation operation on the set interval, the threshold of the pixels that are not interpolated operation by the interpolation operation
The image processing method according to claim 3, wherein the calculated threshold value is repeatedly used. 5. A first calculation means for calculating a luminance frequency for each block in a multi-valued image, a second calculation means for calculating a binarization threshold value for each block based on the luminance frequency, and a first calculation means for each block. a first setting means for setting an area for interpolating the binarizing threshold, pixel by interpolating the binarizing thresholds of the Bro <br/> click units to set region by said first setting means And an interpolating unit that calculates the binarization threshold of the image processing apparatus. 6. The block unit is configured by the first setting unit.
In areas not set in the area to interpolate the position of the binarization threshold, the image processing apparatus according to claim 5, wherein the repeatedly using binarization threshold of the block unit. 7. Interpolation Starring the binarization threshold of the block
The image processing apparatus according to claim 5 , further comprising a second setting unit that sets an interval between pixels for which calculation is performed. 8. Interpolation calculation is performed at intervals set by the second setting means, and a threshold value of a pixel not subjected to interpolation calculation is
The image processing apparatus according to claim 7, wherein the threshold value calculated by the interpolation calculation is repeatedly used.