JP3974236B2 - Image processing apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus and an image processing method for electronically reading a document, performing image processing, and outputting processed image information.
[0002]
[Prior art]
It has been conventionally known that an image processing apparatus detects a background density from an input image and removes the background density based on the detected background density. In the background density detection, since the detection level varies depending on the state of the document, it has been proposed to add an offset value to the background density in order to absorb the width of the variation (Japanese Patent Laid-Open No. 3-68270).
In another prior art, the background is detected based on the low density by density detection with respect to the threshold value in the region of interest and the density continuity by density variation detection, and the background is removed. It has been proposed to set a predetermined threshold value by adding a predetermined offset value to the maximum background density (Japanese Patent Laid-Open No. 6-217140).
[0003]
In addition, in an image processing apparatus, there are conventionally known several methods for detecting the transmittance of an original and adjusting an output image according to the value. For example, a method of detecting the transmittance of a document and adjusting the voltage charged to the photosensitive band of the image forming apparatus according to the value (Japanese Patent Laid-Open No. 1-318460), detecting the transmittance of the document, Accordingly, a method of adjusting the developing voltage of the image forming apparatus (Japanese Patent Laid-Open No. 2-53082), calculating the transmittance of the document with a thickness sensor, and adjusting the light quantity of the halogen lamp that irradiates the document according to the value There is a method (JP-A-4-346366).
[0004]
[Problems to be solved by the invention]
In the conventional technique for detecting the background density and removing the background based on the offset value, the offset value is a predetermined constant value, and the user's instruction such as density adjustment instruction or double-sided document instruction is used. On the other hand, since it was not an optimum value, there was a problem that, for example, when the density was adjusted in the background removal mode, characters with low density were not reproduced.
An object of the present invention is to solve the problems of the prior art when performing background removal, to set an offset value that matches a user's instruction, and to obtain an image processing apparatus that can perform appropriate background removal.
In the conventional techniques for detecting the transmittance of an original and adjusting the output image according to the detected value, it is necessary to change values such as phenomenon, charging, exposure, etc. of the image forming apparatus. Since a circuit or the like is required, the cost reduction of the apparatus has been hindered.
SUMMARY An advantage of some aspects of the invention is that it provides an image processing apparatus that can adjust an output image without changing values such as development, charging, and exposure of the image forming apparatus.
[0005]
[Means for Solving the Problems]
The present invention is an image processing apparatus for processing an input image from the reading means for reading a document image, a background detecting means for detecting the background level of a document, a density setting means for setting the density information of the output image, the density an offset value setting unit concentration of the set concentration indicator information setting means sets the background level offset value as the offset value of the higher background level is reduced, the the detected background level by the background detection unit offset and removing means for background elimination with respect to the input image based on the background level offset value set by the value setting means, for adjusting the density of the image after background removal by the removing means in response to said concentration indicator information And adjusting means.
The offset value setting means includes information on whether the original is a single-sided original or a double-sided original, information on whether the reading means is a moving original or a fixed original, and attribute information of the instructed original (that is, the original is a photograph, The offset value is set based on any one of the parameters such as text, or a mixture of photos and text) or a combination thereof.
[0006]
Further, the present invention is an image processing apparatus for processing an input image from the reading means for reading a document image, a background detecting means for detecting the background level of a document, the transmission rate detecting means for detecting a transmission of a document, an offset value setting means for setting the background level offset value as the offset value of the background level higher detected transmittance is increased by the transmission detector, said the background level detected by said background detecting means offset characterized by providing a removal means for background elimination with respect to the input image based on the offset value set by the value setting means.
Further, the present invention is an image processing apparatus for processing an input image from the reading means for reading a document image, a background detecting means for detecting the background level of the document, be read of the read means background level when the moving document Offset value setting means for setting the offset value to be high and setting the background level offset value to be low for a fixed document, the background level detected by the background detection means, and the offset value setting means According to another aspect of the present invention, there is provided removal means for removing a background from the input image based on the background level offset value.
[0007]
[Action]
Oite the inventions for setting an offset value according to the density instruction information, the background level detected by the background detection unit, the output image based on the offset value set in accordance with the concentration indicator information by setting means The background is removed by the removing means. The adjusting means adjusts the density in accordance with the density instruction information with respect to the image after the background removal.
As a result, when the background is removed and the density is specified to be high, the offset value can be set to be smaller as the density level of the density instruction is higher as illustrated in FIG. The density part can also be reproduced.
Further, the offset value setting means sets the offset value for a double-sided document as high as shown in FIG. 2A, for example, according to information on whether the document is a single-sided document or a double-sided document. Can be prevented.
Further, appropriate background removal can be performed by setting a high offset value in the case of a moving document, for example, as shown in FIG.
Also, depending on whether the document attribute is a photo, text, or a mixture of both, for example, as shown in FIG. 2A, the offset value for a photo is low, the offset value is high for a character, By setting it in the middle, the photo is reproduced to a low density, and the character is not reproduced the roughness of the low-quality original.
[0008]
Has a transmittance detection means for detecting an original transmittance, Oite the inventions for setting an offset value according to the detected document transmission, the original transmission by background level and setting means detected by the background detection unit Based on the offset value set accordingly, the removing means performs background removal on the output image. As illustrated in FIG. 5B, when the original transmittance is high, the show-through of the original can be prevented by increasing the offset value.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention.
The image processing apparatus according to the present embodiment inputs image information read by a reading unit (not shown) that reads an original image, and corrects gradation characteristics, and an input tone correction unit 1 for correcting the tone characteristics. An image processing unit 2 that performs various processes such as MTF (modulation transfer function) correction, image editing, and image compression and accumulation on the input image that has been subjected to gradation correction in step S3, A user interface unit 4 for performing various instructions and display such as a background detection unit 3 for detecting the background density, a density button for density adjustment, a document mode specifying button for specifying document attributes, and an offset to the background density An offset setting unit 5 for setting a value, a background removal value based on the background density detected by the background detection unit 3 and the offset value set by the offset setting unit 5 The background removal unit 6 that performs background removal on the image that has been obtained and processed by the image processing unit 2 and the density of the image after the background removal according to the density instruction information (density adjustment stage) designated by the user interface 4 A density adjustment unit 7 that performs adjustment and an output gradation correction unit 8 that performs output gradation correction on an image from which the background has been removed are provided.
[0010]
In the operation of the image processing apparatus configured as described above, first, the input image is subjected to tone correction by the input tone correction unit 1 for converting, for example, an image read as reflectance into L *, and the image processing unit. 2 and the background detection unit 3. The background detection unit 3 detects the background density value (bkg_orig) for each scanning line. The average of the densities of pixels in a predetermined density range for each predetermined pixel range on each scanning line is taken as the background density value. In the case of processing in real time, the background density value detected in the scanning line one to several lines before the scanning line on which the background removal is performed is used for the background removal. Instead of detecting for each scanning line, data on the entire surface of the document may be obtained in advance by pre-scanning, and the background density value may be determined based on the data on the entire surface of the document. The background detection method is known (see, for example, JP-A-3-68270), and any known detection method may be employed in the present invention.
[0011]
As shown in FIG. 2C, the offset setting unit 5 includes a standard offset value table 51, a conversion table 52 for obtaining a coefficient corresponding to the density adjustment stage, and a standard offset value obtained from the standard offset value table 51. (Off) and a multiplier 53 for multiplying the density adjustment stage coefficient. For the offset value (offset) set here, an offset reference value (off) is obtained from the table index of the standard offset value table 51, and the multiplier 53 multiplies the correction coefficient from the density adjustment stage obtained in the conversion table 52. Is obtained.
An example of the contents of the standard offset value table 51 is shown in FIG. This table shows (1) whether the document reading unit is a document fixed type or a document moving type, (2) whether the document to be read is a single-sided document or a double-sided document, and (3) the document attribute is It is a table in which standard offset values are associated with information such as whether they are photographs, characters, or a mixture of photographs and characters.
As shown in the figure, in the case of a double-sided document, a so-called show-through occurs in which the printed matter on the back side is seen through the front, so that the offset standard value is set higher than that of the single-sided document so as to eliminate this.
When the method of the original reading unit is the original moving type, noise is more likely to occur than in the original fixing type, so the standard offset value is set higher than that of the original fixing type. For the photo mode in which the original is a photograph, there is no difference in the standard offset value depending on whether or not the original is fixed so as not to impair fine gradation expression.
In the photo mode and the character mode, the character mode has a higher standard offset value. The mixed mode is set between the photo mode and the character mode.
[0012]
By providing the standard offset value table 51 having the above configuration with the above-mentioned information of (1) document fixing / moving, (2) single-sided / double-sided, and (3) photo / text / mixture as index conditions, The corresponding offset standard value (off) is retrieved. The document fixing / movement information is given to the standard offset value table 51 when the system detects that the document is placed on a document feeder (not shown). Photo / character / mixed information and single-sided / double-sided information are extracted from the contents designated by the user by the user interface unit 4.
[0013]
The conversion table 52 to the coefficient contains the contents of the first and second columns in the table of FIG. 2B, and the density adjustment stage (in this example, 7 levels between 3 to 3 to light to 3). Is a table composed of coefficients for correcting the standard offset value corresponding to. When the user designates the density adjustment stage through the user interface unit 4, a coefficient corresponding to the designated density adjustment stage is taken out and sent to the multiplication unit 53. The coefficient is set to 1 when the density adjustment stage is “normal”, and the coefficient value is made smaller as “darker 1”, “darker 2”, “darker 3” become darker, “lighter 1”, “lighter 2”, The coefficient value is set to be larger as the thickness becomes “thin 3”. Therefore, when “high density” is designated while performing background removal, it is possible to reproduce the low density portion of the document.
[0014]
The multiplier 53 multiplies the standard offset value (off) obtained in the standard offset value table 51 by the coefficient obtained in the table 54 to calculate an offset value. For example, as shown in the third column of the table of FIG. 2B, “Dark 3” in the density adjustment stage is obtained by multiplying the offset reference value (off) by “0” and the offset value = 0. If the density adjustment stage is “thin 3”, then offset = off × 1.6. This offset value is sent to the background removal unit 6.
[0015]
In the present embodiment, the example in which the offset setting unit 5 is configured with a lookup table and a calculation unit has been described. However, the offset setting unit 5 may be configured as one lookup table.
[0016]
The background removal unit 6 obtains a background removal value (bkg_orig + offset) by adding the offset value (offset) determined by the offset setting unit 5 and the background density value (bkg_orig) detected by the background detection unit 3. The density below the background removal value is set to 0 (white), and the contrast is adjusted for density higher than that.
The background removal value is subjected to mask function processing to limit the value to a specific range. In this example, 0 = <background removal value = <255.
[0017]
FIG. 3 schematically shows the relationship between the input image, bkg_orig, and offset. By performing background removal at a level obtained by adding an offset value (offset) to the background detection result (bkg_orig), show-through and other low-level noise components can be removed.
[0018]
The density of the image data after the background removal by the background removal unit 6 is adjusted by the density adjustment unit 7 in accordance with an instruction from a user interface (not shown).
Thereafter, the output gradation correction unit 8 corrects the output gradation and outputs the result.
[0019]
According to the present embodiment, it is possible to reproduce the low density portion of the document when “high density” is designated while performing background removal.
Further, in this embodiment, when the original is a double-side original, the offset value is set to be large, so that show-through can be reduced. In this embodiment, the offset value is controlled according to the attribute of the document, and if the attribute is “photo”, the offset value is set to be small so that it is reproduced to a low density, and if the attribute is “character”, the offset is set. By setting the value to be large, the roughness of the low-quality document is not reproduced.
Further, when there are a plurality of document reading units such as a document fixing type or a document moving type, it is possible to perform the background removal method appropriately in accordance with the characteristics.
[0020]
(Second embodiment)
FIG. 4 is a diagram showing the configuration of the second embodiment. The main difference from the first embodiment is that the offset is controlled based on the transmittance of the document.
That is, in FIG. 4, the input tone correction unit 1, the image processing unit 2, the background detection unit 3, the user interface unit 4, the offset setting unit 5, the background removal unit 6, the density adjustment unit 7, the output tone correction unit 8, and the like The corresponding elements of the first embodiment have substantially the same functions, and the corresponding elements are denoted by the same reference numerals. The offset setting unit 5 and the output tone correction unit 8 are slightly different in function from the first embodiment, and the document transmittance detection unit 9 is not provided in the first embodiment. The document transmittance detecting unit 9 can detect, for example, by measuring a passing light amount by arranging a light source on one side of the document and an optical sensor on the other side at any position where the document passes.
[0021]
FIG. 5C shows a configuration of the offset setting unit 5 in the second embodiment. The document transmittance detector 9 detects the transmittance of the document. In this example, as shown in FIG. 5B, the transmittance is classified into three stages, and a coefficient for correcting the standard offset value is set correspondingly. That is, the transmittance is divided into three stages, ie, no document transparency, low document transmittance, and high document transmittance. Corresponding coefficients are assigned 0, 1, 1.6, and the document transmittance detector 9 Is converted into a coefficient by the conversion table 54. The coefficient of the original without transparency is 0, and therefore the offset value is also 0. When the document transmittance is low, the coefficient is 1, so that the offset value matches the standard offset value. When the document transmittance is high, the coefficient is 1.6, so that the offset value becomes large. As described above, since the offset value is increased when the document transmittance is high, the show-through of the document can be prevented.
The multiplier 55 multiplies the standard offset value output from the standard offset value table 51 by the coefficient output from the table 54 and sends the offset value fset) to the background removal unit 6. The function of removing the background using the background density value (bkg_orig) and the offset value (off) is the same as that of the first embodiment.
[0022]
The output tone correction unit 8 has a plurality of output tone correction patterns, and the output tone correction pattern is determined based on the value obtained by the document transmittance detecting means in the last output tone correction unit 8 of the input image. Select.
The characteristics of the read image differ depending on the original reading method. In general, the platen is white when the document is fixed, and the back platen color is black when the document is moved. Therefore, the gradation pattern to be selected also changes depending on the original reading method.
[0023]
FIG. 6A shows the relationship between the original transmittance and the output gradation pattern to be selected. FIGS. 4B to 4D are diagrams showing input / output characteristics of the output gradation pattern.
First, when the original reading method is the original fixing type, when the original transmittance is 0 (no transmission), a through gradation pattern, that is, gradation correction having the same input / output characteristics as shown in FIG. When a pattern not to be performed is selected and the document transmittance is low, a low transmittance gradation correction pattern for correcting, for example, in a low density region as shown in FIG. Sometimes the through tone pattern is selected.
When the original reading method is the original moving type, the through gradation pattern shown in FIG. 6B is selected for both no original transparency and low original transparency, and when the original transparency is high, the original transparency is shown in FIG. Select a tone emphasis pattern. When the back platen color is black, the original transmissivity is high. For example, when a tracing paper original is scanned, the background becomes gray, resulting in an unclear figure or text image. A clear output image can be obtained by performing gradation correction with such a characteristic that becomes more black.
As a result, gradation correction can be performed by selecting an appropriate output gradation correction pattern according to the document transmittance obtained by the transmittance detection means, and the background removal value offset according to the document transmittance described above. Since the value can be controlled, the show-through of the original can be prevented.
[0024]
【The invention's effect】
According to the present invention, when the background is removed and the density is specified to be high, the offset value is set to be smaller as the density level of the density instruction is higher as illustrated in FIG. 2B. Therefore, it is possible to reproduce the low density part.
Further, according to the present invention, the offset value in the case of a double-sided document is set high as illustrated in FIG. 2A, for example, in accordance with information on whether the document is a single-sided document or a double-sided document. Can prevent reflection.
Further, according to the present invention, appropriate background removal is performed by setting a high offset value in the case of a moving document, for example, as shown in FIG. Can do.
Further, according to the present invention, depending on whether the document attribute is a photo, text, or a mixture of both, for example, as shown in FIG. If it is high and mixed, it is set in the middle so that the photo is reproduced to a low density and the text does not reproduce the roughness of the low-quality original.
[0025]
According to the configuration having the transmittance detecting means for detecting the document transmittance according to the present invention and setting the offset value according to the detected document transmittance, the document transmittance is high as illustrated in FIG. 5B. Sometimes, by increasing the offset value, the show-through of the document can be prevented. Further, by selecting and correcting an appropriate output gradation pattern by the output gradation correcting means based on the original transmittance, conventionally, the image forming apparatus has been controlled by values such as development, charging, and exposure. Since it can be performed by digital image processing, it is possible to simplify a control circuit for values such as development, charging, and exposure of those image forming apparatuses.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2A is a content example of a standard offset value table, FIG. 1B is a diagram showing a relationship between a density adjustment stage and an offset value. ) Is a diagram showing a configuration example of the offset setting unit 5. FIG. 3 is a diagram showing the relationship between the background detection result and the offset.
FIG. 4 is a block diagram showing a second embodiment of the present invention. FIG. 5A is an example of the contents of a standard offset value table, FIG. 4B is a diagram showing the relationship between document transmittance and offset value, and FIG. ) Is a diagram showing a configuration example of the offset setting unit 5;
FIGS. 6A and 6B are diagrams for explaining a method for determining an output gradation correction according to an original transmittance, wherein FIG. 6A is a gradation pattern to be selected according to an original transmittance, and FIGS. ) Is a diagram showing a characteristic example of a gradation pattern.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Input gradation correction part, 2 ... Image processing part, 3 ... Background detection part, 4 ... User interface part, 5 ... Offset setting part, 6 ... Background removal part, 7 ... Density adjustment part, 8 ... Output gradation correction Section 9: Document transmittance detection section.

Claims (8)

An image processing apparatus for processing an input image from the reading means for reading an original image,
A background detection means for detecting the background level of the document;
Density setting means for setting density instruction information of the output image;
An offset value setting means for setting the background level offset value so that the offset value of the background level becomes smaller as the density of the density instruction information set by the density setting means is higher ;
And removing means for background elimination with respect to the input image based on the background level offset value set by the detected background level the offset value setting means by the background detection unit,
The image processing apparatus is characterized by providing an adjustment means for adjusting the density of the image after background removal by the removing means in response to the density instruction information. Said offset value setting means, and characterized in that the document is set so that sometimes the background level offset value is one-sided document becomes low, the original is set so that the background level offset value becomes high when a double-sided document The image processing apparatus according to claim 1. Said offset value setting means, when a document attribute is a character set as the background level offset value increases, that document attributes set to the background level offset value becomes low when a photograph The image processing apparatus according to claim 1, wherein the image processing apparatus is characterized in that: An image processing apparatus for processing an input image from the reading means for reading an original image,
A background detection means for detecting the background level of the document;
A transmittance detecting means for detecting the transmittance of the document;
An offset value setting means for setting the background level offset value as the offset value of the background level higher detected transmittance is increased by the transmission detector,
And removing means for background elimination with respect to the input image based on the offset value set by the detected background level the offset value setting means by the background detection unit
The image processing apparatus characterized by a provided. An image processing apparatus for processing an input image from the reading means for reading an original image,
A background detection means for detecting the background level of the document;
An offset value setting means reads the target of the reading means is set so that background level offset value is high when the moving original document, when a fixed document set to background level offset value is low,
An image comprising: a background level detected by the background detection means; and a removal means for performing background removal on the input image based on the background level offset value set by the offset value setting means. Processing equipment. In an image processing method for processing an input image from a reading means for reading a document image,
  A background detection step for detecting the background level of the document;
  A density setting step for setting density instruction information of the output image;
  An offset value setting step for setting the background level offset value so that the offset value of the background level decreases as the density of the density instruction information set in the density setting step increases;
  A removal step of performing background removal on the input image based on the background level detected by the background detection step and the background level offset value set by the offset value setting step;
  An adjustment step of adjusting the density of the image after the background removal by the removal step according to the density instruction information;
An image processing method comprising: In an image processing method for processing an input image from a reading means for reading a document image,
  A background detection step for detecting the background level of the document;
  A transmittance detecting step for detecting the transmittance of the document;
  An offset value setting step for setting the background level offset value such that the higher the transmittance detected by the transmittance detection means, the higher the background level offset value;
  A removal step of performing background removal on the input image based on the background level detected by the background detection step and the offset value set by the offset value setting step;
An image processing method comprising: In an image processing method for processing an input image from a reading means for reading a document image,
  A background detection step for detecting the background level of the document;
  An offset value setting step for setting the background level offset value to be high when the reading target of the reading unit is a moving document, and to set the background level offset value to be low when the document is a fixed document;
  A removal step of performing background removal on the input image based on the background level detected by the background detection step and the background level offset value set by the offset value setting step;
An image processing method comprising:

Images