JP3373876B2 - Image processing device - 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 capable of forming an image in which a background portion of an image is removed based on density information read from an original.

[0002]

2. Description of the Related Art Generally, when making a copy of an original image, if the original image has a density on the background, if the original is read and output as it is, an overall darker output image is produced. Operations such as lowering are required. However, in the case of a manuscript whose background density differs depending on the image position, such as a cut and pasted manuscript such as a newspaper or a magazine, the background cannot be completely processed by a method in which unique processing is performed on the entire manuscript.

In this respect, as disclosed in Japanese Patent Laid-Open No. 3-68270, there is a method in which a background portion is successively detected in a minute area so that an original having a different background density can be positioned. More specifically, a background detection unit for detecting a background of an original by presetting a density range that is assumed to be a background and taking a one-dimensional average value of input pixel densities within the density range by appropriate sampling. A background removing means for comparing the background density detected by the background detecting means with the input pixel density and forcibly correcting the pixels having a background density or less to white density pixels and outputting the pixels having a background density or more as they are. It is a thing.

Further, as disclosed in Japanese Patent Laid-Open No. 3-294567, a density change and a density area in a target area are detected and each is compared with a predetermined fixed threshold value, and only when both are within the threshold value. There is one in which the attention area is used as a background portion to perform background processing.

[0005]

However, in the former publication method, since only the low density of the background is used as the background detection means, for example, in the case of the original 1 as shown in FIG. Text area A with low density and background area B with high density
There may be a case where erroneous recognition occurs in the background detection.
Therefore, during the copying process of the original document 1 as described above, the copy 2 as shown in FIG. 1B is obtained, and the character portion A having a low density is erroneously removed or the background portion B having a high density is removed. It will be inseparable.

In the latter publication method, since the threshold value for detecting the density information area in the attention area is fixed (can be set from the outside), the background density is set to an outside of the allowable range (threshold value). On the other hand, we cannot deal with it.

Therefore, even in the case of a document having a different background background density or a document having a low density character part or a high density background part, it is desirable to be able to perform an appropriate background removal process in real time. To be done.

[0008]

According to a first aspect of the present invention, an image reading unit for reading the density information of an original and a variation of the pixel density in a region of interest of the density information read by the image reading unit are within a predetermined range. And a density area detecting means for detecting that the pixel density in the area of interest of the density information read by the image reading means is below a predetermined threshold density, and the image reading means.
Enter the maximum value detected from the read density information.
Has a pitch, the attention area based on the detection result of the these concentrations fluctuation detecting means and the density region detection means detects whether a background portion, its every time it is the background portion is detected <br The maximum value of the density information in the area
If it is not detected that the background part is
Held in the latch by not changing the contents of
And background density determining means for determining the concentration of background portion of the region of interest by the content, the land which is determined by the background density determining means
A background removing unit configured to compare the skin density with the pixel density of the region of interest and forcibly convert pixels having a background density lower than or equal to a predetermined white density pixel.

According to a second aspect of the present invention, in addition to the first aspect of the invention, there is provided threshold setting means for adding a predetermined offset value to the maximum background density detected in the preprocessing line to set a predetermined threshold value. Provided.

Further, in the invention described in claim 3, in addition to the invention described in claim 2, detection area control means for limiting the detection area of the maximum background density in the pretreatment line is provided.

According to the invention described in claim 4,
In addition to the above-described invention, a threshold value setting means for setting a predetermined threshold value by adding a predetermined offset value to the maximum background density detected in the previous attention area of the current processing line is provided.

According to a fifth aspect of the present invention, in addition to the first aspect of the present invention, a storage unit for storing the respective maximum background density values detected in a plurality of preceding processing lines and the maximum background density are stored in the storage section. And a threshold value setting means for setting the density value subjected to the weighting calculation as a predetermined threshold value.

[0013]

According to the first aspect of the present invention, the background density of the original is sequentially detected for a predetermined area of the density information read from the original, so that even if the originals have different background densities in real time, the real-time background density is detected. It is possible to perform an appropriate background removal process. Further, when detecting the background portion, not only the range of the density information in the attention area but also the degree of variation of the density information is detected, so that more appropriate background removal processing can be performed. That is, not only the low density of the background portion but also the continuity of the density information is detected by the density variation detecting means, so that the more accurate background portion detection, that is, the background density detection becomes possible. Therefore, even in the case of a document that includes low density character areas or high density background areas,
At the time of the copying process, a copy having the background removed properly can be obtained.

In the inventions according to claims 2, 4, and 5,
Since the threshold value for the density region detecting means can be changed in real time by the threshold value setting means in accordance with the original, in addition to the operation according to the invention of claim 1, when an original having an extremely high background density is targeted. In addition, it is possible to perform an appropriate background removal process. Particularly, in the invention of claim 5,
Considering the maximum background density of multiple preceding processing lines,
Since the threshold value is set through the weighting calculation, the influence on the threshold value setting can be minimized even if extreme density information is input for some reason.
A more appropriate background removal process becomes possible.

Further, in the invention described in claim 3, in addition to the invention described in claim 2, since the area for detecting the background portion is limited by the detection area control means, the background density from the image area in the document is reduced. It is possible to reduce the possibility of false detection as much as possible.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. This embodiment corresponds to the invention described in claim 1, and schematically, as shown in FIG. 1, a scanner section (image reading means) 3 for optically reading a document image and converting it into digital density information. A range check unit (density variation detection unit) 4 that compares the dynamic range of the attention area with a predetermined threshold value from the density information read by the scanner unit 4
And a logical product of the detection results of the level check unit (density region detection means) 5 for comparing the maximum value in the region of interest with a predetermined threshold value and the range check unit 4 and the level check unit 5. Based on the result, the background density determination unit (background density determination means) 6 having a function of latching the maximum value of the attention area, and the determined background density and the pixel density of the attention area are compared with each other. The background removal unit (background removal means) 7 for forcibly converting the following pixels into white density pixels is configured.

The configuration of each part will be described below in order. First,
The scanner unit 3 is configured as shown in FIG. That is, the original 8 set on the contact glass (not shown) is exposed and illuminated by the fluorescent lamp 9, and the reflected light from the original 8 is reflected by the first, second and third mirrors 10, 11, 12 and the imaging lens 13. After that, an image is formed on the light receiving surface of the CCD 14. Here, the CCD 14 has a line sensor structure,
Two-dimensional reading is performed by arranging the CCD 14, the mirrors 10, 11, and 12, the imaging lens 13 and the like arranged in one line in the main scanning direction along the original 8 in the sub scanning direction. The image density of the original 8 is converted into an electric signal by the CCD 14, amplified by the amplifier 15, and then corrected by the signal correction unit 16.
Then, signal correction such as shading correction, dark current correction, and density setting is performed, and the A / D converter 17 converts the density information (white level 0 to black level 255) of 8 bits per pixel.

The range check unit 4 for detecting the dynamic range of the density information of the target region (one-dimensional in the main scanning direction = one line) of the original 8 when the density information is input from the scanner unit 3 is shown in FIG. It is configured as shown in. In the following description, the range of the attention area is 8 pixels. First, a maximum value detector 18 and a minimum value detector 19 to which density information is serially input from the scanner unit 3 are provided. Here, the maximum value detector 18 for detecting the maximum value max in the density information is configured as shown in FIG. 4, for example. That is, the density information is used as the previous density information via the latch 20 on the one hand, and is directly input to the comparator 21 as the current density information on the other hand for comparison, and the density information on the latch 20 side is larger. If this comparator 21
Is newly held in the latch 20. However, it is assumed that the initial value 0 is given to the latch 20. Carry the octal counter 22 with this operation repeatedly.
The output of the latch 20 is latched every 8 pixels by the signal 23
The maximum value max of a predetermined area is output to the outside.

The minimum value detector 19 is also constructed similarly to the maximum value detector 18. For example, referring to FIG. 4, the maximum density information 255 is given to the latch 20 as an initial value, and when the density information from the scanner unit 3 is smaller than the content on the latch 20 side, the comparator The output of 21 may be activated and held in the latch 20.

The maximum value max and the minimum value min detected by the maximum value detector 18 and the minimum value detector 19 are input to the subtractor 24, and the difference between the two is in the range range = ma.
Calculated as x −min. This range range is input to the comparator 25, compared with a predetermined threshold value rthr, and range ≦ r
In the case of thr, the output rflag of the comparator 25 is configured to be active. By such processing,
It is detected whether the dynamic range of the density information of the predetermined area of interest is equal to or smaller than a predetermined threshold value rthr. That is,
It is detected whether the variation of the pixel density of the attention area of the density information read by the scanner unit 3 is within a predetermined range.

Next, the level check unit 5 which receives the density information from the scanner unit 3 and detects the range of the density information of the attention area of the original 8 is constructed as shown in FIG. 5, for example. First, a maximum value detector 26 to which density information is serially input from the scanner unit 3 is provided. The maximum value detector 26 may have the structure shown in FIG. The maximum value max detected by the maximum value detector 26 is calculated by the comparator 25.
It is configured to be activated to the output lflag of the comparator 27 when max ≤lthr and is compared with a predetermined threshold value lthr. By such processing, the maximum value max of the density information of the predetermined area of interest is set to the predetermined threshold lthr.
The following is detected.

Next, an example of the structure of the background density determination unit 6 is shown in FIG.
Shown in. The background density determination section 6 inputs the detection output rflag of the range check section 4 and the detection output lflag of the level check section 5 to the AND gate 28 to detect whether the attention area is the background section. , If detected, the output dflag of the AND gate 28 is latched 2
Give to 9. The latch 29 holds the maximum value of the region of interest obtained by passing the density information from the scanner section 3 through the maximum value detector 30 each time the output dflag becomes active. The background part is not detected and AND
Latch 2 when the output dflag of the gate 28 is at L level
The content of 9 does not change. That is, the latch 29 holds the maximum value of the background area every time the background area is detected. The content of the latch 29 thus obtained is output as the background density dgnd in the attention area. If the background portion is not detected at the beginning of the main scan, the preset predetermined background density initial value dinit is held in the latch 29.

FIG. 7 shows a structural example of the background removing section 7. The background removal unit 7 uses the background density dgnd determined by the background density determination unit 6 to perform background removal processing of the density information of the attention area. First, the density information from the scanner unit 3 is held in the shift register 31 in order to give a delay until the background density is determined as described above. Further, predetermined density information (for example, density minimum value 0 =
An 8-bit register 32 holding white density information) is prepared. The contents of the shift register 31 and the contents of the 8-bit register 32 are input to the selector 33, and any information is output according to the select signal. Here, the selection signal of which one is selected is determined by the output of the shift register 31 and the output of the comparator 34 which compares the background density dgnd of the background density determination unit 6. That is, when the density information held in delay by the shift register 31 is larger than the background density dgnd, the shift register 31
The density information stored in the selector 33 is directly output from the selector 33. However, when the density information is smaller than the background density dgnd, the density information stored in the 8-bit register 32 is replaced and output from the selector 33. To be done. That is, a pixel having density information equal to or lower than the background density dgnd is forcibly converted to a white density pixel.

In this manner, the background portion is removed in the main scanning direction of the original 8 by sequentially performing the above processing on the serial density information of the original 8 output from the scanner section 3. The processing is completed for one line, and the same is done for the next line. However, in the sub-scanning direction, the detected background density value is not held, and the initialization is sequentially performed at the leading end of the main scanning for each line.

As described above, according to the present embodiment, the background density of the original 8 is successively detected for the attention area of the predetermined range having the density information read from the original 8, so that the background density is positionally different. Appropriate background removal processing can be performed in real time even on a document. Further, when detecting the background portion, not only the range of the density information in the attention area but also the degree of variation of the density information is detected, so that more appropriate background removal processing can be performed. That is, not only the low density of the background portion but also the continuity of the density information is detected by the range check unit 4, so that more accurate background portion detection, that is, background density detection can be performed. Therefore, as shown in FIG. 8 (FIGS. 21 (a) and the same), even when the document 8 containing a high background portion B lower text part A and concentration density, during its replication process, suitable positively As a result, a copy that has been subjected to the background removal processing can be obtained, and the character portion A having a low density can be surely reproduced, while the background portion B having a high density can be removed.

In this embodiment, the range check unit 4
In the above, the difference in the density of the attention area is detected by the difference between the maximum value and the minimum value of the attention area.
However, the present invention is not limited to this, and another parameter may be used to detect the variation in the concentration. Further, as the processing of the background removing unit 7, pixels having a density equal to or lower than the background density are forcibly converted to 0, but the white density equal to or lower than the background density is 0.
The density information of other levels may be set to the white level.

Next, a second embodiment of the present invention will be described with reference to FIGS. 9 and 10. The same parts as those shown in the above-mentioned embodiments are designated by the same reference numerals (the same applies to the following embodiments). The present embodiment corresponds to the invention according to claim 2, and further includes a threshold setting unit (threshold setting unit) 36 for sequentially changing and setting a predetermined threshold lthr for the level checking unit 5 based on the output of the background density determining unit 6. It was done. This threshold setting unit 3
In general, 6 takes in the background density dgnd of the pre-processing line, detects and holds the maximum background density in the pre-processing line, and adds a predetermined offset value to this maximum background density to obtain the level. Threshold for the next processing line in the check unit 5
It is output as LTHR.

The threshold value setting unit 36 is specifically shown in FIG.
It is configured as shown in 0. First, the background density dgnd by the background density determination unit 6 is input via the latch 37 on the one hand, and the comparator 38 is directly input on the other hand, and the directly input background density dgnd is the output of the latch 37. When it is larger than this, the background density dgnd of this time is held in the latch 37 by the output of the comparator 38. By repeating the above-mentioned processing, the CARRY signal from the counter 39 causes the latch 4
Hold at 0. As a result, the maximum background density of the pretreatment line is maintained. The output of the latch 40 is input to the adder 41, added with a predetermined offset value, and output to the level check unit 6 as a threshold LTHR for the current processing line.

However, 0 is given to the latch 37 as an initial value at the beginning of the line, 100 is given to the latch 40 as an initial value for the leading line, and 20 is given as the offset value of the adder 41. Shall be given.

As a result, the level check unit 5 uses the threshold LTHR set by the threshold setting unit 36 to perform the level check of the density information as described above. This time,
An initial value of 120 is used as the threshold value LTHR in the processing of the first line, and a value obtained by adding an offset value to the maximum background density detected in the preprocessing line is used as a new threshold value LTHR in the processing of the second and subsequent lines. When the background is not detected in the pre-processing line, the background density of the previous processing line is used.

Subsequent processing is the same as in the case of the first embodiment, and a description thereof will be omitted.

According to this embodiment, since the threshold value setting unit 36 is provided, the threshold value LTHR for detecting the density information area is changed in real time according to the condition of the original 8. In addition to the effects of the embodiment, an appropriate background removal process can be performed even in the case of a document 8 having an extremely high background density.

A third embodiment of the present invention will be described with reference to FIG. The present embodiment corresponds to the invention described in claim 4, and a threshold setting unit 42 as shown in FIG. 11 is used instead of the threshold setting unit 36 of the embodiment. That is, the threshold setting unit 36 of the above embodiment sets the threshold LTHR based on the maximum background density in the pre-processing line, but the threshold setting unit 42 of the present embodiment sets the maximum of the current processing line of interest. The threshold LTHR is set based on the background density.

First, the background density dg by the background density determination unit 6
nd is input through the latch 43 on the one hand, and the comparator 44 is directly input on the other hand. When the background density dgnd input directly is larger than the output of the latch 43, the output of the comparator 44 is output. Thus, the background density dgnd of this time is held by the latch 43. By repeating such processing, the maximum background density of the current processing line is held by the latch 43. The output of the latch 43 is input to the adder 45, a predetermined offset value is added, and the threshold value for the attention area in the current processing line is added.
It is output to the level check unit 6 as LTHR.

However, 100 is given as an initial value to the latch 43 at the beginning of each line, and the adder 4
As an offset value of 5, for example, 20 is given.

As a result, the level check unit 5 uses the threshold LTHR set by the threshold setting unit 42 to perform the level check of the density information as described above. This time,
When processing the first region of interest in the line, set the threshold value LTHR to 1
An initial value of 20 is used, and a value obtained by adding an offset value to the maximum background density detected in the previous attention area is used as a new threshold value LTHR at the time of processing of the next attention area and thereafter. If the background is not detected in the previous attention area,
The background density of the previous region of interest is used. As a result, the same effect as in the above embodiment can be obtained.

A fourth embodiment of the present invention will be described with reference to FIG. In the present embodiment, a threshold setting unit 46 having the configuration shown in FIG. 12 is used instead of the threshold setting unit 36 of the above-described embodiments. This threshold setting unit 46 is shown in FIG.
For the threshold value setting unit 36 shown in FIG.
The average value calculation circuit 47 which receives the output of is added to the preceding stage of the adder 41. Thus, the average of the maximum background density detected in the pre-processing line and held in the latch 40 and the maximum background density detected in the current processing line and held in the latch 37 is calculated as an average value. The threshold value LTHR of this time is calculated by the circuit 47, and the adder 41 adds a predetermined offset value to the background density which is the average value.
Is set to be variable. Here, the average value calculation circuit 47 can be realized by a combination of, for example, a 2-input adder and a shift register.

In this case, the latch 37 is given an initial value of 100 at the beginning of the line, the latch 40 is given an initial value of 100 at the beginning line, and the offset value of the adder 41 is set to 20, for example.
Shall be given.

As a result, the level check unit 5 uses the threshold LTHR set by the threshold setting unit 46 to perform the level check of the density information as described above. This time,
An initial value of 120 is used as the threshold value LTHR when processing the first attention area of the first line, and at the time of processing after the next attention area, the maximum background density detected in the previous attention area and the initial value 100 of the latch 40. The value obtained by adding the offset value to the average value is used as a new threshold value LTHR,
At the time of processing after the line, the maximum background density detected in the preprocessing line and held in the latch 40 is used for the average value calculation instead of the initial value 100. If the background is not detected in the area of interest or the preprocessing line,
Further, the background density of the previous region of interest or the previous processing line is used. As a result, the same effect as in the above embodiment can be obtained.

A fifth embodiment of the present invention will be described with reference to FIG. The present embodiment corresponds to the invention described in claim 5, and a threshold setting unit 48 having a configuration as shown in FIG. 13 is used instead of the threshold setting unit 36 of the above-described embodiment. The threshold setting unit 48 is the threshold setting unit 3 shown in FIG.
A latch (storage unit) 49 for holding the maximum background density of the pre-processing line and a storage unit and a latch (storage unit) 49 for holding the maximum background density of the pre-processing line are provided on the output side of these units. The calculation unit 50 is provided which sets a threshold value LTHR by performing a predetermined weighting calculation process based on the maximum background densities of a plurality of (two in this case) preceding process lines. The arithmetic unit 50 includes a shift register 51 for shifting the maximum background density of the pre-pre-processing line held in the latch 49, and a shift register 52 for shifting the maximum background density of the pre-processing line held in the latch 40. ,
An input / output side of the shift register 52 is connected to an input side thereof, and an adder 54 for outputting a weighted average value using the output of the difference unit 53 and the output of the shift register 51 as input, It is connected to an adder 41 that sets a threshold value LTHR by adding a predetermined offset value to the output of the adder 54.

In such a configuration, when the maximum background density of the pre-pre-processing line and the maximum background density of the pre-processing line are weighted, for example, the maximum background density of the pre-pre-processing line is "1", and the pre-processing is performed. "3" for the maximum background density of the line
Latch 4
A value obtained by shifting the maximum background density output of the pre-preprocessing line from 9 to the least significant bit side by the shift register 51 by 2 bits and the maximum background density output of the preprocessing line from the latch 40 by 2 bits by the shift register 52. This can be realized by adding the value shifted by the least significant bit side by the adder 54 with the value obtained by subtracting the maximum background density output of the preprocessing line by the differentiator 53. Adder 41
Then, a predetermined offset value is added to the weighted average value calculated by the adder 54 to obtain a threshold value in the region of interest.
It is output to the level check unit 5 as LTHR.

In this case, 100 is given to the latch 37 as an initial value at the beginning of the line, and the latch 40,
49, for example, 10 is set as the initial value in the leading line.
It is assumed that 0 is given and 20 is given as an offset value of the latch 49.

With such a configuration, according to the detected values of the maximum background density of the pre-processing line and the pre-pre-processing line,
The threshold LTHR for level check will be changed,
The same effect as that of the above-described embodiment can be obtained. In particular, in this embodiment, since the threshold value LTHR for the level check is changed by the weighting calculation of the maximum background density for the preceding plural processing lines, the density information in the same processing line is all extremely extreme for some reason. Even if an input with a high density is made, the influence on the threshold setting can be minimized and the background part detection processing can be continued. For example, in the case where the density information for one line is input such that all the density is 0, in the next processing line,
Further, the threshold LTHR is determined by weighting the background densities of the lines before that, so that the false detection of the background detection is minimized.

Regarding the threshold value setting sections 36, 42, 46 and 48 of the second to fifth embodiments, specific numerical examples of the initial value of the threshold value and the offset value are merely examples, and may be set to arbitrary numerical values as appropriate. Good. Further, the weighting operation between the pre-processing line and the pre-pre-processing line in the threshold value setting unit 48 is not limited to the averaging at the ratio of 1: 3, and the averaging may be performed at an appropriate ratio. Not limited to this, the number of target lines may be increased and averaging may be performed.

Further, a sixth embodiment of the present invention will be described with reference to FIGS. This embodiment corresponds to the invention described in claim 3, and in addition to the invention described in claim 2 as shown in FIG. 9, the background density latching operation of the threshold value setting unit 36 is performed according to the area in the processing line. A region control unit (detection region control means) 55 for permitting / prohibiting is added.

The area control section 55 outputs an area signal to the threshold setting section 36 while it corresponds to a predetermined area in one line, and the threshold setting section 36 outputs the area signal only while the area signal is active. The new background density is allowed to be latched and is configured as shown in FIG. First, two counters 56 and 57 that start the counting operation in synchronization with the line synchronization signal are provided, and latches 58 and 59 that are triggered when a predetermined number of pixels are counted and output H level are provided. These counters 5
The numerical values for the predetermined number of pixels set to 6 and 57 are different. An inverter 60 is connected to the output side of the latch 58. The output of the latch 58 and the output of the latch 59 inverted by the inverter 60 are input to the OR gate 61 so that a predetermined area signal can be obtained.

In such a configuration, for example, the counter 56 starts the counting operation in synchronization with the line synchronizing signal as shown in FIG. 16D, and when counting for a predetermined number of pixels, the latch 58 is triggered and the H level is set. Output a signal. The output of the latch 58 is inverted by the inverter 60 and becomes an output as shown in FIG. Similarly,
The counter 57 also starts the counting operation in synchronization with the line synchronization signal, and when counting for a predetermined number of pixels, triggers the latch 59 to output a signal as shown in FIG. 16C.
Therefore, the logical sum output by the OR gate 61 is as shown in FIG.
The area signal is as shown in (c).

The area signal thus obtained is output to the threshold value setting section 36 and used as an operation enable signal of the latch 37 for holding the maximum value of the background density dgnd output from the background density determination section 6. (Active at H level). Therefore, the area signal is, for example, as shown in FIG.
In the case of the waveform as shown in FIG. ₅ , the background density determination unit 6 does not perform the background density latching operation in the area E ₁ , and the maximum background density in the area E ₂ or E ₃ is held in the latch 37 of the threshold value setting unit 36. It is used for various threshold settings.

Therefore, according to the present embodiment, in addition to the effect of the second embodiment, since the area for detecting the background portion is limited by the area control unit 55, the background density can be changed from the image area in the original 8. The possibility of erroneous detection can be reduced as much as possible. For example, by setting an area E having a high possibility of being a background portion for the original 8 as shown in FIG. 17 as a detection area, a portion having a low density in the image area may be erroneously detected as a background density. Is prevented, and appropriate background removal processing becomes possible.

In this embodiment, the area controller 55
Then, the threshold setting unit 3 is provided at the front end and the rear end of the line
Although the region signal for 6 is enabled, the region signal may be enabled only at one of the leading end and the trailing end in the line, or the region signal may be enabled for another region. . Further, not only in the main scanning direction but also in the sub scanning direction, the region signal may be similarly generated and enabled.

Further, a seventh embodiment of the present invention will be described with reference to FIGS. In this embodiment, the threshold setting unit 36
(Or, the threshold value setting unit 42, 46, 48 may be used.) The threshold value control unit 62 which receives the threshold value and initializes this threshold value to a predetermined value when the value exceeds a predetermined limit value. Is added.

The threshold control unit 62 is constructed as shown in FIG. First, a comparator 63 is provided which receives information on the maximum background density of the pre-processing line from the threshold setting unit 36. The comparator 63 compares a predetermined limit value held in advance in the register 64 with the maximum background density of the preprocessing line, and outputs the output as a select signal of the selector 65. Here, the maximum background density of the pre-processing line and a predetermined initial value held in advance in the register 66 are input to the selector 65, and one of the levels is used as a correction value of the threshold value according to the select signal. Is output to.

The correction value of the threshold value obtained from the threshold value control unit 62 in this way is used when the output of the threshold value setting unit 36 is smaller than the limit value held in the register 64 of the threshold value control unit 62. Although it is the same as the output of 36, if it is larger than the limit value, it becomes the initial value held in the register 66, and after the threshold value setting processing by the threshold value setting unit 36, the threshold value of the level check unit 5 becomes It is reset to the initial value. This makes it possible to continue the appropriate background removal processing.

In the present embodiment, the threshold control unit 62 corresponds to the threshold setting unit 36, so that the threshold control is performed by monitoring the maximum background density in the pre-processing line, but another threshold setting unit 42 is used. , 46, and 48, the initialization control can be performed similarly.

The eighth embodiment of the present invention will be described with reference to FIG. In this embodiment, the threshold control unit 62 of the above embodiment is used.
Instead, when the threshold value set by the threshold value setting unit 36 does not change over a certain processing unit time, the threshold value is subtracted by a predetermined amount so that the threshold value is attenuated at a predetermined rate. Threshold control unit 6 for resetting the threshold as a value
7 is provided.

Here, the threshold controller 67 is, for example, as shown in FIG.
It is configured as shown in 0. First, the threshold setting unit 36
There is provided a shift register 68 which receives the maximum background density information of the pre-processing line from the above and holds the information of eight lines. The local skin density information held in the shift register 68 is input to the comparator 69, and is used to detect whether or not the background skin density information for 8 lines is all the same. The output of the comparator 69 is used as a switching signal for the selector 70. Preselection line maximum background density information and a value obtained by subtracting a predetermined value held in the register 71 by the subtracter 72 from the density information are input to the selector 70, and the selector 69 switches the value. Either one is output to the level check unit 5 as a correction value of the threshold according to the signal.

As a result, when there is no change in the maximum background density of the pre-processed 8 lines, the selector 70 selects the value obtained by subtracting a predetermined amount by the subtractor 72 from the maximum background density of the pre-processed line as the corrected threshold value. And output to the level check unit 5. When there is a change in the maximum background density in the 8 lines, the maximum background density of the pre-processed line is output as in the above-described processing.

The correction value of the threshold value thus obtained is calculated for each processing line, and after the threshold value is set by the threshold value setting unit 36, it is reset by the level check unit 5 as the corrected threshold value. This makes it possible to continue the appropriate background removal processing.

Note that, from the first line to the seventh line, it is assumed that the shift register 68 is given an appropriate initial value as the background density.

Further, in the present embodiment, the threshold value control unit 67 corresponds to the threshold value setting unit 36, so that the threshold value control is performed by monitoring the maximum background density in the pre-processing line, but another threshold value setting unit 42 is used. , 46, and 48, the attenuation control can be similarly performed. Further, the attenuation processing in the threshold control unit 67 is not limited to the subtraction method of a predetermined amount from the threshold value, and the attenuation processing may be performed by a method such as multiplication by a predetermined multiplier. Further, for example, in the example shown in FIG. 20, a predetermined amount of subtractive attenuation processing is applied to the threshold value when there is no change in the background density in all eight lines. Even if it falls within the range, a predetermined attenuation process may be performed.

In each of the above-mentioned embodiments, the density information is black and white 8 bits, but R, G, B or Y, M,
By performing the same operation for each color information of C and BK, it is possible to apply to a full-color image processing apparatus. Further, the example in which the density information of the document 8 is optically read by the scanner unit 3 has been described, but the invention is applied to a device for reading and inputting the density information of the document by another method such as inputting from a recording medium. Will also be possible.

[0062]

According to the first aspect of the present invention, the density fluctuation detecting means for detecting that the fluctuation of the pixel density in the attention area of the density information of the document read by the image reading means is within a predetermined range, A density area detecting means for detecting that the pixel density in the attention area of the density information read by the image reading means is below a predetermined threshold density; and the image reading means
The maximum value detected from the density information read in is input.
A latch is provided, and it is detected whether or not the attention area is the background portion based on the detection results by the density variation detection means and the density area detection means, and each time the background area is detected. <br /> The maximum value of the density information of the area is held in the latch.
If it is not detected that the background part is
Held in the latch by not changing the contents of
And background density determining means for determining the concentration of background portion of the region of interest by the content, the land which is determined by the background density determining means
By providing a background removal unit that compares the skin density with the pixel density of the region of interest and forcibly converts the pixels of the background density or lower to a predetermined white density pixel, the region of interest having density information is sequentially examined for the region of interest. Since the background density of the original is detected, it is possible to perform real-time proper background removal processing even if the original has a different background density. Not only the range of, but also the degree of variation of the density information, that is, since it is configured to detect the continuity of the density information, it is possible to perform a more appropriate background removal process, more accurate background detection, that is, The background density can be detected, and even in the case of a document that includes a low-density character portion or a high-density background portion, it is possible to obtain a copy with the background removed properly during the copying process. That.

In addition, according to the invention described in claim 2, there is provided threshold setting means for adding a predetermined offset value to the maximum background density detected in the preprocessing line to set a predetermined threshold. According to a fourth aspect of the invention, there is provided threshold setting means for adding a predetermined offset value to the maximum background density detected in the previous attention area of the current processing line to set a predetermined threshold value. According to the method, the storage unit stores the maximum background density values detected in the plurality of preceding processing lines, and the operation unit that performs a predetermined weighting operation on these maximum background density values. The threshold value setting means for setting the calculated density value as a predetermined threshold value is provided so that the threshold value for the density area detecting means can be changed in real time according to the original by the threshold value setting means. Description In addition to the effects of the present invention, even when a document having an extremely high background density is targeted, an appropriate background removal process can be performed. In particular, according to the invention of claim 5, a plurality of preceding process lines Since the maximum background density of is taken into consideration and the threshold value is set through the weighting calculation, even if extreme density information is input for some reason, the effect on the threshold value setting should be minimized. This makes it possible to perform more appropriate background removal processing.

Further, according to the invention of claim 3, in addition to the invention of claim 2, detection area control means for limiting the detection area of the maximum background density in the pretreatment line is provided to detect the background area. Since the area to be performed is limited, the possibility that the background density is erroneously detected from the image area in the document can be reduced as much as possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of the scanner unit.

FIG. 3 is a block diagram showing a configuration of a range check unit.

FIG. 4 is a block diagram showing a configuration of the maximum value detector.

FIG. 5 is a block diagram showing a configuration of a level check unit.

FIG. 6 is a block diagram showing a configuration of a background density determination unit.

FIG. 7 is a block diagram showing a configuration of a background removal unit.

FIG. 8 is an explanatory view showing the original manuscript.

FIG. 9 is a block diagram showing a second embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a threshold setting unit.

FIG. 11 is a block diagram showing a third embodiment of the present invention.

FIG. 12 is a block diagram showing a fourth embodiment of the present invention.

FIG. 13 is a block diagram showing a fifth embodiment of the present invention.

FIG. 14 is a block diagram showing a sixth embodiment of the present invention.

FIG. 15 is a block diagram showing the configuration of the area control unit.

FIG. 16 is a timing chart showing the operation.

FIG. 17 is an explanatory diagram showing an example of a target document.

FIG. 18 is a block diagram showing a seventh embodiment of the present invention.

FIG. 19 is a block diagram showing the configuration of the threshold control unit.

FIG. 20 is a block diagram showing an eighth embodiment of the present invention.

FIG. 21 is an explanatory view of a document and a copy showing a conventional example.

[Explanation of symbols]

3 Image reading means 4 Concentration fluctuation detection means 5 Concentration area detection means 6 Background density determination means 7 Background removal means 8 manuscript 36 threshold setting means 42 threshold setting means 48 threshold setting means 55 Detection area control means

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Claims (5)

(57) [Claims] 1. An image reading unit for reading the density information of a document, and a density fluctuation detecting unit for detecting that the fluctuation of the pixel density in a region of interest of the density information read by the image reading unit is within a predetermined range. The density area detection means for detecting that the pixel density in the area of interest of the density information read by the image reading means is below a predetermined threshold density, and the maximum detected from the density information read by the image reading means.
It has a latch to which a large value is input , detects whether or not the attention area is the background portion based on the detection results of the density variation detection means and the density area detection means, and determines that it is the background portion.
Whenever is detected, the maximum value of the density information of the area
It is held in the latch and it is not detected that it is the background part
In this case, the contents of the latch are not changed,
And background density determining means for determining the concentration of background portion of the region of interest by the content held in the pitch, and background density determined by the background density determining means interest
An image processing apparatus comprising: a background removing unit that compares a pixel density of a region and forcibly converts a pixel having a background density or less into a predetermined white density pixel. 2. The image processing apparatus according to claim 1, further comprising threshold setting means for setting a predetermined threshold value by adding a predetermined offset value to the maximum background density detected in the pre-processing line. . 3. The image processing apparatus according to claim 2, further comprising detection area control means for limiting a detection area of the maximum background density in the preprocessing line. 4. A threshold value setting means for setting a predetermined threshold value by adding a predetermined offset value to the maximum background density detected in the previous attention area of the current processing line. Image processing device. 5. A weighting is provided, comprising: a storage unit that stores each maximum background density value detected in a plurality of preceding processing lines; and an operation unit that performs a predetermined weighting operation on these maximum background density values. The threshold value setting means for setting the calculated density value as a predetermined threshold value is provided.
The image processing device described.