JPH0630258A - Image processor - Google Patents

Abstract

PURPOSE:To prevent the picture quality degradation caused by the read shift of a black level by subtracting a prescribed value, which is held in a setting unit, from shading corrected image information. CONSTITUTION:Based on information obtained by reading a white reference plane stored in a memory 6, a shading correction circuit 4 performs shading correction to image data. When the white density of the information obtained by reading the white reference plane is equal to that of image information obtained by reading an original, the circuit 4 performs the correction so that the value of the corrected image data can be (a). On the other hand, a setting unit 8 is previously provided with the value of ax/100 in respect to the output of a white level for the output of the black level caused by the light leakage of a completely contact sensor. Then, a subtracter 9 subtracts the set value of the setting unit 8 from a value outputted by the circuit 4 and performs the subtraction just for the ratio of the black level. Since the black side of an output image is shifted to the white side just at a certain fixed level, the picture quality degradation caused by the read shift of the black level is prevented.

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 for performing shading correction processing on input image information.

[0002]

2. Description of the Related Art In a method of irradiating an original with light from a light source and reading the reflected light by using a photoelectric conversion element such as a CCD, uneven light quantity on the reading line of the light source and the photoelectric conversion element Variations between bits affect image quality. Therefore, in this type of apparatus, an image processing apparatus is used that stores a white reference waveform in advance and performs shading correction processing on input image information based on the white reference waveform.

Conventionally, as an image processing apparatus for performing such shading distortion correction of input image information, one shown in FIG. 3 is known.

In the image processing apparatus shown in FIG. 3, an analog image signal supplied from a device (not shown) equipped with the image processing apparatus via an input terminal 1 is converted into a digital image signal by an AD converter 2, The digital image signal is supplied to the shading correction circuit 4 via the movable contact 3c and the fixed contact 3a of the switch 3. Further, the memory control circuit 7 stores the white reference waveform in the memory 6 when the white reference surface is read via the movable contact 3c and the fixed contact 3b, and the shading correction circuit 4 stores the white reference waveform stored in the memory 6. The input image data is subjected to shading correction processing based on the above, and then output through the output terminal 5.

Shading correction in the conventional image processing apparatus will be further described with reference to FIGS. 4 and 5.

FIG. 4 shows an image signal when an image of an original is read by a reduction optical system using a CCD (not shown). FIG. 4A shows an image signal when a white reference plane is read, and FIG. B) shows an image signal obtained as a result of performing shading correction by the shading correction circuit 4 after reading a white original (white image information). Also,
A broken line shown in FIG. 4A is an image signal when a black original (black image information) is read, and a broken line shown in FIG. 4B is shading correction by the shading correction circuit 4 after the black original is read. The image signal obtained as a result is shown. As shown in FIG. 4, although shading distortion appears in the image signal when the white reference plane is read,
After the shading correction circuit 4 has performed the shading correction, the shading distortion is corrected.
Further, as shown in FIG. 4, the image signal when a black original is read has a slight output with shading distortion due to the quality of the surface of the original, as shown in FIG. After the shading correction is performed by the circuit 4, the shading distortion of the output is corrected. The output level after this shading correction is very small.

FIG. 5 shows an image signal when the image is read using a perfect contact sensor (not shown). FIG. 5A shows an image signal when the white reference plane is read, and FIG. 5B shows a white original (white). The image signal obtained as a result of performing the shading correction by the shading correction circuit 4 after reading the image information of FIG. A broken line shown in FIG. 5A indicates an image signal when a black original (black image information) is read,
A broken line shown in FIG. 5B indicates an image signal obtained as a result of performing shading correction by the shading circuit 4 after reading a black original.

As shown in FIG. 5, although shading distortion appears in the image signal when the white reference plane is read, after the shading correction circuit 4 has performed shading correction, the shading distortion is corrected. There is. Further, as shown in FIG. 5, the image signal when a black original is read is as shown in FIG.
An output with shading distortion larger than the level shown in (A) is seen. After the shading correction circuit 4 has performed shading correction on this image signal, the shading distortion of the output is corrected, but a black original is compared with the output shown by the broken line in FIG. 4B. The output level when read is quite large.

It is considered that this is due to so-called light leakage when the image information of the original is read by the perfect contact sensor.

As is apparent from FIGS. 4 and 5, in the above-mentioned conventional image processing apparatus, when a perfect contact sensor is used for reading image information of an original, so-called light leakage causes a black output image. The side shifts to the white side by a certain level.

Therefore, even if shading correction is performed,
It has a characteristic that the black side of the output image is shifted to the white side by a certain level, which deteriorates the image quality.

[0012]

As described above, in the conventional image processing apparatus, especially when the perfect contact sensor is used for reading the image information of the original, a black level reading shift occurs due to light leakage or the like. However, even if the shading correction is performed, the image quality is deteriorated.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image processing apparatus capable of preventing the deterioration of the image quality due to the read shift of the black level of the output image due to the leakage of light or the like.

[0014]

In order to achieve the above object, the present invention provides an image processing apparatus for performing shading correction on image information read based on preset correction information. Holding means for holding a predetermined value corresponding to the black level reading shift, and subtracting means for subtracting the predetermined value held by the holding means from the shading-corrected image information. To do.

[0015]

The predetermined value corresponding to the black level reading shift held in the holding means is subtracted from the shading-corrected image information.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the image processing apparatus of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the image processing apparatus of the present invention. In FIG. 1, parts corresponding to those of the conventional device shown in FIG. 3 are designated by the same reference numerals for convenience of explanation.

The image processing apparatus of one embodiment of the present invention shown in FIG. 1 converts a read image signal (for example, an image signal obtained by reading an original by a not-shown perfect contact sensor) supplied from the input terminal 1 into a digital signal. A to D to convert
The converter 2, the image data from the AD converter 2, the shading correction circuit 4 and the memory 6 (for example, E
A switch 3 for selectively supplying to EPROM or RAM,
Setting value data supplied from a setting device 8 from a memory control circuit 7 that controls the memory 6 to store a waveform obtained by reading, for example, a white reference plane in the memory 6, and an output that has been subjected to shading correction in the shading correction circuit 4. It is composed of a subtracter 8 for subtracting.

Here, the shading correction circuit 4 performs shading correction processing on the image data based on information (reference information) obtained by reading the white reference plane stored in the memory 6. At this time, if the information obtained by reading the white reference surface and the image information obtained by reading the document have the same white density (white level), the shading correction circuit 4 determines the value of the image data after shading correction. Is a.

Further, the setter 8 preliminarily sets ax / 100 when the black level output due to light leakage of a perfect contact sensor (not shown) is x (integer) with respect to the white level output.
The value of is set.

FIG. 2 shows an output obtained by shading-correcting an image signal obtained by reading an original with a perfect contact sensor (not shown). In FIG. 2, the broken line shows the output of the black level due to so-called light leakage when the document is read by the perfect contact sensor. As shown in FIG. 2, the set value is the output value a when shading correction is performed by the shading correction circuit 4, and the ratio x / 100 of the output of the black level to the white level due to the light leakage at the time of reading the document. The value is multiplied.

The configuration of the setter 8 that outputs this set value is as follows.
For example, in the case of manual input, the input unit (for example, keyboard, switch, etc.) and a storage unit (for example, EEPROM, RAM with battery backup, etc.) for storing the set value input by this input unit are used, and automatic input In this case, the detection unit for detecting x and the storage unit for storing the setting value according to the detection result from the detection unit may be configured. Alternatively, the set value may simply be stored in advance in the non-volatile memory. In the subtractor 9, the set value ax / 100 is subtracted from the correction output from the shading correction circuit 4 (FIG. 2A), and the subtraction result is the light leakage at the time of reading the original as shown in FIG. 2B. The output on the black side due to is removed.

Next, the operation of the image processing apparatus of the present invention will be further described. First, when reading the white reference plane, the movable contact 3c of the switch 3 is connected to the fixed contact 3b. Then, after that, a reference original is read by a perfect contact sensor (not shown), and an image signal obtained as a result is supplied to the A / D converter 2 through the input terminal 1, and the A / D converter 2 is supplied. Are converted into digital image data by. This digital image data, that is, the reference data, is then transferred to the memory 6 via the switch 3.
Are stored in the memory 6 under the control of the memory control circuit 7.

Next, during normal use, the movable contact 3c of the switch 3 is connected to the fixed contact 3a. After that, the document is read by a perfect contact sensor (not shown), and the image signal obtained as a result is supplied to the A / D converter 2 through the input terminal 1, and the A / D converter 2 outputs a digital image. Converted to data. This digital image data is then supplied to the shading correction circuit 4 via the switch 3, and when the white density is the same as the reference data read from the memory 6, the value after the shading correction becomes the above a. A shading correction process is performed on. Then, the image data subjected to the shading correction processing is supplied to the subtracter 9, and the set value ax / 100 is subtracted by the subtractor 9, and then the device (on which the image processing apparatus is mounted via the output terminal 10). For example, it is output to another circuit (not shown) such as a facsimile). Since this output image is obtained by subtracting the ratio of the black level to the white level due to light leakage as described above, it is an extremely clear image with almost no image quality deterioration.

As described above, in this embodiment, the ratio of the black level to the white level of the output image due to light leakage or the like at the time of reading a document, that is, the light leakage predicted in advance is used. Since the output of the black level is subtracted from the image data after the shading correction, the image quality deterioration of the output image can be significantly reduced and an extremely clear image can be obtained.

In this embodiment, the case where the image data of the original obtained by the perfect contact sensor is processed has been described. However, the image data of the original obtained by the reduction optical system using the CCD is used. Also in the case of processing, the black level output (ax / 100) that should not be originally output as described in FIG. 4 is stored in the setting device 8 in advance, and the original is read by the subtractor 9 to obtain the original. Even if the output of the black level is subtracted from the image data, the deterioration of the image quality of the output image can be significantly reduced as described above, and an extremely clear image can be obtained.

[0026]

As described above, according to the present invention,
Since a predetermined value related to the reading state of the image information held in the holding means is subtracted from the shading-corrected image information, the black side of the output image is read at a black level that is shifted to the white side by a certain level. It is possible to prevent deterioration of image quality due to shift.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing how image data is corrected by the image processing apparatus shown in FIG.

FIG. 3 is a block diagram showing a conventional image processing apparatus.

FIG. 4 is an explanatory diagram showing how image data is corrected by the image processing apparatus shown in FIG.

5 is an explanatory diagram showing a state of correction of image data in the image processing apparatus shown in FIG.

[Explanation of symbols]

 2 A-D converter 3 Switch 4 Shading correction circuit 6 Memory 7 Memory control circuit 8 Setting device 9 Subtractor

Claims (1)

[Claims] 1. An image processing apparatus for performing shading correction on image information read based on preset correction information, wherein a holding unit holds a predetermined value corresponding to a black level reading shift of the image information. An image processing apparatus comprising: a subtraction unit that subtracts the predetermined value held by the holding unit from the shading-corrected image information.