JP4377082B2 - Image processing apparatus and image reading apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus and an image reading apparatus.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. 6-311359 discloses a background removal device that removes the background of image data after shading correction and before image processing. This not only removes the image data below the threshold value as the background, but also gradually reduces the threshold value, thereby reducing the sense of discomfort in the image around the threshold density portion.
[0003]
[Problems to be solved by the invention]
When performing the background removal, it is conceivable to realize a background removal function by detecting the background level from the analog image data with a peak hold circuit and feeding back the value to the reference value of the A / D converter. .
[0004]
However, this technique has the following problems (1) and (2) because the background is removed by detecting the background level with an analog amount and feeding it back to the reference voltage for A / D conversion.
[0005]
(1). The reading density changes depending on the brightness of the document due to the black offset level and the offset of the amplifier or the like.
[0006]
For example, when the gain of the peak hold circuit (P / H) is A, and the value after black offset subtraction with the digital amount after A / D is considered,
Output after background level A / D-Output after black level A / D = (background level + black level + offset voltage) / (A / D reference voltage)
-(Black level + offset voltage) / (A / D reference voltage)
= ((D + Vb + Voff)-(Vb + Voff)) / A (D + Vb + Voff)
= D / A (D + Vb + Voff)
D: Original background reading value (analog amount)
Vb: Black offset level Voff: It becomes an offset of an amplifier or the like, and it can be seen that the digital read value after the background removal changes depending on the background density D of the document. For this reason, there has been a problem that the degree of background change changes depending on the background density.
[0007]
(2). Since it is normalized by A / D according to the background level of the document, the read density of the image changes depending on the background level.
[0008]
In the technique disclosed in Japanese Patent Laid-Open No. 6-311359, the background is detected from the image data after shading correction and the image data is viewed with a threshold value. Since γ greatly changes, the image near the threshold changes due to the influence of the subsequent image processing, and a sense of incongruity occurs. In the technique disclosed in Japanese Patent Laid-Open No. 6-311359, it is attempted to reduce the uncomfortable feeling by laying down γ somewhat in the vicinity of the threshold value, but it cannot be completely eliminated.
[0009]
An object of the present invention is to obtain an image having no sense of incongruity around a threshold value while preserving image density when removing the background level of a document.
[0010]
An object of the present invention is to make it possible to easily detect the influence of changes in the background level due to image processing at a later stage.
[0011]
An object of the present invention is to correctly convey background level information to the subsequent stage without being affected by a filter.
[0012]
[Means for Solving the Problems]
The invention according to claim 1 is a background detection unit that detects a background level of the document from image data obtained by reading the document, and a threshold generation unit that generates a first threshold based on the detected background level; and clip means for clipping the created image data of more than the first threshold value and the value of the first threshold value, the image data and one or more types to the first threshold wherein the clip is made read the original Image processing means for performing the image processing, and background removal means for removing the background level of the document from the image data after the image processing using a second threshold , the background removal means and scalp data extracting means for detecting a third threshold value from the image data processed, the image processing comprises an offset means, the creating a second threshold value by subtracting a predetermined value from the third threshold value It is the location.
[0013]
Therefore, the background level is detected from the image data after shading correction, the image is clipped to the corresponding threshold value, and the background is removed from the image after the image processing, thereby saving the image density. It is possible to obtain an image without a sense of incongruity around the threshold.
[0014]
According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the level of the first threshold after the clipping is added to image data obtained by reading a document before the image processing, and the image Combining means is provided that makes it possible to set the first threshold together with the first threshold by making data the target of the image processing.
[0015]
Therefore, by adding the threshold information detected before the image processing to the image data, it is possible to easily detect the influence of the change in the background level due to the image processing at the subsequent stage.
[0016]
According to a third aspect of the present invention, in the image processing apparatus according to the second aspect, the synthesizing unit adds the first threshold value more than a filter matrix size used in the image processing unit.
[0017]
Therefore, by making the detected threshold information larger than the filter size used in the subsequent stage, the background information can be correctly transmitted to the subsequent stage without being affected by the filter.
[0018]
According to a fourth aspect of the present invention, there is provided a photoelectric conversion element that reads an image of a document, and an image processing apparatus according to any one of the first to third aspects that processes image data read by the photoelectric conversion element. An image reading apparatus provided.
[0019]
Therefore, there exists an effect | action and effect similar to the invention as described in any one of Claims 1-3.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described.
[0021]
First, the basic idea of the technique used in this embodiment will be described. As is clear from the description of the problem to be solved by the invention, there are the following two problems to be solved by this technique.
-The image density changes after removing the background.
-When storing the density, the image is uncomfortable near the threshold.
[0022]
The essence of image discomfort due to the image data being cut at the threshold value is due to the occurrence of unnatural data inflection points in the image data around the threshold value. Therefore, it can be said that a sense of incongruity occurs to be emphasized more. FIG. 1 shows an example of data change after MTF correction when data is changed with a threshold and when it is normal.
[0023]
In order to suppress that sense of incongruity,
<Countermeasure 1> By changing γ around the threshold of the above-described prior art method, it is possible to suppress an abrupt change in data around the threshold and to adversely affect an image due to MTF correction or smoothing of an image processing function at a later stage. Hold down.
[0024]
However, since γ is changed around the threshold, there is a problem that image density cannot be stored around the threshold.
[0025]
<Countermeasure 2>
As shown in FIG. 1 as (1), by clipping data that is equal to or greater than the threshold value to the threshold value, it is possible to mitigate the influence that occurs in the subsequent stage. However, since the background that is the original purpose is not skipped as it is, some measures are required.
[0026]
Therefore, in the present embodiment described below, the background level is detected from the image data after shading correction, threshold 1 is created based on the data, and data greater than that value is clipped to the threshold 1 value. By performing background removal (= cut by threshold) from the image-processed data, it is possible to preserve the background density even after the background removal processing and provide an image that does not feel uncomfortable around the threshold.
[0027]
FIG. 2 is a block diagram showing an electrical connection of the digital copying machine 1 including the image processing apparatus and the image reading apparatus according to the embodiment of the present invention. First, the original image data photoelectrically converted by the CCD 2 that is a photoelectric conversion element is subjected to predetermined signal processing by the signal processing unit 3, A / D converted by the A / D converter 4, and then in the shading unit 5. Black side and white side shading correction is performed and output as image data Drd0 in which uneven illumination and uneven sensitivity of the CCD 2 are corrected. This data Drd0 is input to the background detection unit 6 of the next stage to detect the background level, and the image processing unit 7 performs processing such as MTF correction, filtering processing, scaling processing, and γ conversion, and the skin removal removal unit In 8, the background level of the original is removed. The image data that has been subjected to these processes is modulated by the optical writing unit 9 and is converted into an exposure beam corresponding to the image data by the laser diode 10 to form an image by electrophotography. The image memory 11 stores image data processed by the image processing unit 7, and the CPU 12 controls each unit of the digital copying machine 1.
[0028]
As shown in FIG. 3, in the background detection unit 6, if the background removal mode is set, the background detection block 21 that is the background detection means detects the background level Dba, and the offset is the threshold value generation means from the value. The unit 22 obtains a threshold value Dth1 obtained by subtracting the offset, compares the image data Drd0 with the threshold value Dth1 by the clipping circuit 23 serving as clipping means, clips all the image data of Drd0> Dth1 to the value of Dth1, and outputs it as Drd1. To do. Then, m pixels are added to the head of the image data of the next line by the synthesizing unit 24 which is a synthesizing unit, and the result is output as Drd2 to the image processing unit 7 which is the next stage image processing unit (see FIG. 4). ). Further, the gate signal BaGATE indicating the data position to which the background data is attached is simultaneously output (Drd1 and Drd2 are only different in the image format, and the image characteristics are not changed).
[0029]
In the background detection block 21, smoothing filter is applied by the filter 25 in order to remove the influence of noise, and the peak hold circuit 26 is used to hold the peak in the subsequent data so that the background level Dba can be detected with high accuracy. .
[0030]
If the background level Dba itself is used as a threshold value, background noise may be output.
1. Subtract some offset.
That is,
Dth1 = Dba−offset2. A certain percentage of image data is subtracted.
That is,
Dth1 = Dba × (1-α)
3. Above 1.2. Combine.
That is,
Dth1 = Dba.times. (1-.alpha.)-By using a method such as offset, the threshold value Dth1 is obtained to eliminate the influence of noise of the background data.
[0031]
Thereafter, in the clip circuit 23, as shown in FIG. 5, the threshold value Dth1 and the image data Dwr0 obtained as described above are respectively input to A and B of the comparator 27 and controlled as shown in FIG. The image data equal to or higher than the threshold value Dth1 can be clipped to the threshold value Dth1.
[0032]
When the H level signal is input from the CPU 12, the OR circuit 29 always sets the input signal S to the selector 28 to "1", and the background removal mode is canceled.
[0033]
The detected threshold value Dth1 is set to the number of pixels m larger than the filter size of the image processing unit 7 in the subsequent stage, so that the data is not changed due to the influence of the data outside the gate in the central portion asserted at the gate. The background density can be preserved.
[0034]
In this example, the method using the gate signal BaGATE is adopted as described above. However, the same effect can be obtained by determining in advance how many pixels are added to the head of the image data. . However, even if the filter size is different between models, the background area is clarified by the gate signal, so that the algorithms of the image processing unit 7 and the background removal unit 8 can be shared. It is designed to output.
[0035]
As described above, if the background portion is clipped at the front stage of the image processing unit 6, the background data can be easily detected by the subsequent background removal unit 8 without handling the background data. There is a concern that the cost may increase because the background detection block 21 is provided at two locations.
[0036]
Drd2 output from the background detection unit 6 is subjected to necessary processing (MTF correction, scaling processing, γ conversion, etc.) by the image processing unit 7, output as Dwr0, and input to the background removal unit 8.
[0037]
As shown in FIG. 7, the background removal unit 8 serving as the background removal means detects the threshold value Dth1 ′ after image processing from the background data extraction unit 31 based on Dwr0 and the gate signal BaGATE, and the Dth1 ′ itself is used as the threshold value. Depending on the image processing, the background noise may be amplified and output, so the following operation is performed in the offset unit 32 at the next stage.
[0038]
1. Subtract some offset.
That is,
Dth2 = Dth1′−offset2. A certain percentage of image data is subtracted.
That is,
Dth2 = Dth1 ′ × (1-α)
3. Above 1.2. Combine.
That is,
Dth2 = Dth1 ′ × (1−α) − It is desirable to obtain the Dth2 by using a method such as an offset so as to eliminate the influence of noise of the background data.
[0039]
Thereafter, the threshold value Dth2 and the image data Dwr0 obtained as described above are input to A and B of the comparator 33, respectively, and controlled as shown in FIG. An image without a sense of incongruity can be provided.
[0040]
Further, when the H level signal is input from the CPU 12, the input signal S to the selector 35 is always "1" by the OR circuit 34, and the background removal mode is canceled.
[0041]
Further, FIGS. 9 and 10 show the effects of image γ and data changes.
[0042]
First, the read data Drd has the following characteristics.
[0043]
FIG. 9A shows the γ characteristics of document information and read data Drd. FIG. 10A shows the read data viewed in the main scanning direction with the background detection level Dba added.
[0044]
On the other hand, when clipped by the background detection unit 6,
FIG. 9B shows γ characteristics of the read data Drd0 before clipping and the read data Drd1 (= Drd2) after clipping at that time. FIG. 10 (b) shows a result obtained by adding the background detection level Dba and the threshold Dth1 to the read data at that time viewed in the main scanning direction. Thus, it can be seen that the image data is clipped.
[0045]
Thereafter, MTF correction, γ processing, and the like are performed by the image processing unit 7, and the γ characteristics of the read data Drd and the post-image processing data Dwr0 as shown in FIG. 9C are obtained. Further, as shown in FIG. 10C, the background detection level Dba ′ is added after image processing to the data after image processing viewed in the main scanning direction.
[0046]
From this, it can be understood that γ has been converted, the threshold level has been changed, and the image information level has been changed.
[0047]
Next, the data Dwr1 subjected to the background removal function becomes the γ characteristic of the read data Drdtp background removal data Dwr1 as shown in FIG. Further, as shown in FIG. 10D, the threshold level Dth2 is added to the data after the background removal processing viewed in the main scanning direction.
[0048]
Thereby, the effect is understood from the fact that the background level is removed and the level of the image information is stored.
[0049]
Further, it can be said that the difference between (c) and (d) in FIG. 9 is a function of the γ conversion itself. Therefore, by providing a γ conversion function at the end of the image processing unit 7, the γ function can be shared and realized at a manufacturing cost.
[0050]
Furthermore, the order of image processing is generally changed according to the image mode and the magnification. Therefore, the background removal unit 8 may be able to realize higher image quality by changing the function and order of the image processing performed by the image processing unit 7 according to various conditions such as the mode.
[0051]
【The invention's effect】
According to the first aspect of the present invention, the background level is detected from the image data after the shading correction, the image is clipped to the corresponding threshold value, and the background is removed from the image after the image processing is performed. Thus, it is possible to obtain an image having no sense of incongruity around the threshold value while maintaining the image density.
[0052]
The invention according to claim 2 is the image processing apparatus according to claim 1, wherein the threshold information detected before the image processing is added to the image data, whereby the influence of the fluctuation of the background level due to the image processing is It can be easily detected at a later stage.
[0053]
According to a third aspect of the present invention, in the image processing apparatus according to the second aspect, the detected threshold information is not affected by the filter by making the detected threshold information larger than the filter size used in the subsequent stage, so that the background level It becomes possible to convey information correctly to the subsequent stage.
[0054]
The invention according to claim 4 has the same operations and effects as the invention according to any one of claims 1 to 3.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining processing performed by a digital copying machine according to an embodiment of the present invention;
FIG. 2 is a block diagram showing electrical connection of the digital copying machine.
FIG. 3 is a block diagram of a background detection unit of the digital copying machine.
FIG. 4 is a timing chart illustrating processing performed by the digital copying machine.
FIG. 5 is a block diagram of a clip circuit of the background detection unit.
FIG. 6 is an explanatory diagram illustrating processing performed by a clip circuit.
FIG. 7 is a block diagram of a background removal unit of the digital copying machine.
FIG. 8 is an explanatory diagram illustrating a process performed by the background removal unit.
FIG. 9 is an explanatory diagram illustrating processing performed by the digital copying machine.
FIG. 10 is an explanatory view of the same.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image reading apparatus, image processing apparatus 2 Photoelectric conversion element 7 Image processing means 8 Background removal means 21 Background detection means 22 Threshold creation means 23 Clip means 24 Composition means

Claims (4)

A background detection means for detecting a background level of the document from image data obtained by reading the document;
Threshold creating means for creating a first threshold based on the detected background level;
And clip means for clipping the created image data of more than the first threshold value and the value of the first threshold value,
Image processing means for performing one or more types of image processing on the image data obtained by reading the original and the first threshold value on which the clip is made;
A background removal means for removing the background level of the document using a second threshold value from the image data after the image processing ,
The background removing means
Background data extraction means for detecting a third threshold value from the image data after the image processing;
An image processing apparatus comprising: offset means for subtracting a predetermined value from the third threshold value to create a second threshold value . The first threshold level after the clipping is added to the image data obtained by reading the document before the image processing, and the image data is used as the object of the image processing, so that the first threshold is also added. The image processing apparatus according to claim 1, further comprising a synthesis unit that can be set as a target of image processing. The synthesis means includes
The image processing apparatus according to claim 2, wherein the first threshold is added to a size equal to or larger than a filter matrix size used in the image processing unit. A photoelectric conversion element for reading an image of a document;
An image reading apparatus comprising: the image processing apparatus according to claim 1, which processes image data read by the photoelectric conversion element.

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