JPH11284848A - Original image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct proper shading correction even when shading data are a prescribed value or below without increasing a capacity of a ROM required for shading arithmetic operation. SOLUTION: Even under a limited condition where only shading data requiring a capacity of a ROM more than 128/255 are objects for shading arithmetic operation, when actual shading data Dsh1 are 127/255 or below, not only the shading data Dsh1 but also original image data Dg of a corresponding pixel are multiplied by a multiple of α, and a ROM 5 is used as shading data of 128/255 or over substantially by using the shading data Dsh2 and original image data Dg1 that are results of multiple of α. As a result, proper shading correction conducted even to the shading data Dsh1 of 127/255 or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital copying machine,
The present invention relates to a document image reading apparatus that reads a document image such as a digital scanner as digital data using a photoelectric conversion element such as a CCD line sensor and performs post-processing such as copying.

[0002]

2. Description of the Related Art In general, it is widely known that in this type of original image reading apparatus, shading correction is applied to original image data in consideration of variations in light sources, variations in sensitivity of each pixel of a photoelectric conversion element, and the like. I have. in this case,
Most commonly, a reference white plate disposed outside the original reading range is read by a CCD through an imaging optical system prior to reading the original image.
The shading data for each pixel, which has been digitally converted through a read A / D converter by a line sensor or the like, is acquired and stored in the RAM in advance. At the time of actual reading of the original image, the reading A /
Original image data for each pixel, which has been digitally converted through the D converter, is corrected using the ROM. Here, the ROM stores shading corrected data (calculation results necessary for shading correction) for correcting the document image data by using the respective shading data and the respective document image data as addresses. Specifically, assuming that the data to be handled is 8-bit data, when the reference white board is read, the data is shading-corrected data for making the final output values of all pixels 255, and the original image data is D _G. If the shading data is D _SH , the final image data GD undergoes the shading correction of GD = (D _G / D _SH ) × 255.

With respect to such shading correction, various improvements have been made conventionally. For example, Japanese Utility Model Laid-Open Publication No. 1-387575 (Utility Model Registration No. 25277)
According to the publication No. 90, the shading-corrected data stored in the ROM becomes enormous, and the large-capacity ROM must be used.
The ROM stores only shading-corrected data corresponding to shading data that exceeds 1/2 of the maximum digital output signal in the digital conversion of the A / D converter (128/255 or more in the case of 8-bit data). As a result, the required ROM capacity can be reduced to half, thereby achieving cost reduction. This generally means that the maximum value of the shading data is originally set so as to be a value near the maximum digital output signal of the A / D converter. This is because it is considered that there is not much shading data below 1/2 of the maximum digital output signal of the converter. If the obtained shading data is less than 1/2 of the maximum digital output signal, the data in the ROM cannot be used as it is, so that the original image data is simply doubled and the pseudo shading is performed. By performing the correction, it is possible to maintain the low capacity of the ROM.

[0004] Incidentally, the size of the shading data is made to be 128/255 or more, for example, by adjusting the orientation distribution of the light source.

According to Japanese Patent Application Laid-Open No. 9-224156, shading correction is performed by subtracting a value corresponding to the noise from the shading data so as to eliminate the influence of the noise when the background density is detected by the background removal function. I have to. That is, when the shading data is obtained by reading the reference white plate and when the background density of the document is detected, the reading means inputs the data to the reading A / D converter and the A / D converter.
Under basic configuration to obtain a digital value by giving read data peak value in the peak detecting means to the reference input of the D converters, because they contain noise component V _N in the actual original image data the noise component V _N only during operation by reducing only the shading data output correction value D _OFF so as to suppress the noise component V _N of background removal function is prevented appear as data.

[0006] Figure 3 shows a configuration example of a shading correction circuit 1 for the mean value circuit 2 in each pixel in the main scanning direction based on the original image data D _g of In the shading data generated period is input Calculate the average value,
The average value is stored in the memory 3 for all pixels as shading data _Dsh for each pixel. This memory 3 is composed of a FIFO (First-In First-Out). Thereafter, the shading data D read from the memory 3
_The subtractor 4 subtracts the output correction value D _off from _sh to obtain corrected shading data D _sh1 . Here, the shading data D for the output correction value D _off
noise component V _N is prevented appear in the data by reducing the _sh. Thereafter, the read original image data D _g
And the shading data _Dsh1 obtained from the subtractor 4 of the corresponding pixel are searched in the ROM 5 as an address, and the calculation result stored in the ROM 5 is converted into the final image data G as the post-shading data.
D is output to perform shading correction. Here, the output correction value D given from the CPU or the like
_“off” is a general value that is set to a value of about “5” only when the background is removed, and is set to “0” in other cases.

According to Japanese Patent Application Laid-Open No. 9-224156, correction of shading data and correction of original image data are performed as a noise removal function when the background removal function is turned on. Since the dynamic range change that cannot be performed by the γ correction function can be performed, an image desired by the user can be reproduced more by using the function of changing shading data regardless of whether the background removal function is on or off.

[0008]

According to a method realized by switching a calculation ROM in order to switch a shading calculation so that an image desired by a user can be reproduced more, it is necessary to have a large number of ROMs. However, according to the method of subtracting the fixed value of the output correction value D _off from the shading data as in the example of Japanese Patent Application Laid-Open No. 9-224156, it is possible to realize the method at low cost only by switching the operation. However, since a certain fixed value is subtracted from the shading data, the shading data may become data of 1/2 or less of the maximum digital output signal in digital conversion (127/255 or less in the case of 8-bit data). . In this case, even if the orientation distribution of the light source is adjusted, the shading data after subtraction is 12
It is difficult to keep it below 7/255. As a result, the condition for reducing the capacity of the operation ROM by half is not satisfied, and the ROM required for shading operation is not satisfied.
The capacity is doubled.

[0009] In this respect, when the shading data is reduced to half or less of the maximum digital output signal in the digital conversion using the method described in Japanese Utility Model Application Laid-Open No. 1-387575 (Japanese Utility Model Registration No. 2527790). If the value obtained by doubling the original image data is used as the data after the shading correction, the ROM capacity for storing the calculation result required for the shading correction can be reduced by 1 /.
2 can be maintained. However, although this method originally performs shading correction in a pseudo manner,
This is simply doubling the original image data, which may be far from the actual shading correction, and is not a proper countermeasure.

An object of the present invention is to provide a document image reading apparatus capable of performing appropriate shading correction even when shading data is equal to or less than a predetermined value without increasing a ROM capacity required for shading calculation. .

Another object of the present invention is to provide a document image reading apparatus capable of realizing the above object with a simple configuration.

[0012]

According to the first aspect of the present invention,
Prior to reading the document image, the reference white plate disposed outside the document reading range is read by the reading means, and digitally converted shading data for each pixel is obtained and stored in the memory. When reading the document image, the reading means reads the document. In a document image reading apparatus that corrects digitally converted document image data for each pixel according to corresponding shading data, when the shading data is equal to or less than a predetermined value, both the shading data and the corresponding document image data are used. Shading correction is performed using data multiplied by a predetermined number.

Therefore, RO required for shading calculation
Even under limited conditions by targeting only shading data whose M capacity exceeds a predetermined value, if the actual shading data is less than a predetermined value, not only the shading data but also the original image of the corresponding pixel The data is also multiplied by a predetermined amount at the same time, and by using the multiplied shading data and the original image data, the ROM can be used as the shading data substantially equal to or more than the predetermined value. Can also perform proper shading correction.

According to a second aspect of the present invention, prior to reading a document image, a reference white plate disposed outside the document reading range is read by a reading means, and digitally converted shading data for each pixel is acquired and stored in a memory. When reading a document image, in a document image reading apparatus which corrects the document image data of each pixel read and converted by the reading means in accordance with the corresponding shading data, a reference white board is read and obtained for each pixel. And a multiplier for multiplying both the shading data stored in the memory and the original image data obtained by reading the original image by a predetermined number, and the maximum digital output signal in the digital conversion when the shading data for each pixel is converted into a digital signal. And a comparator for determining whether it is equal to or less than 1/2 of When the judgment result is less than 1/2, the shading data and the original image data multiplied by a predetermined number by the multiplier are selected, and when the judgment result is not less than 1/2, the shading data and the original image stored in the memory are read and obtained. A selector for selecting the original document image data, shading data in which shading corrected data corresponding to each shading data having a value exceeding 1/2 of the maximum digital output signal in the digital conversion are stored and selectively output by the selector. A ROM from which shading-corrected data stored with the document image data as an address is read.

Therefore, the shading data for each pixel is １ ／ of the maximum digital output signal in digital conversion.
A comparator determines whether or not the following is true. Based on the result of the determination, a selector is used to determine whether the shading data and the original image data have been multiplied by a predetermined number through a multiplier or data that has not been multiplied by a predetermined number without passing through the multiplier. Select with RO
With a simple configuration that only reads out the shading-corrected data from M, one of the maximum digital output signals
Appropriate shading correction can be realized for shading data of / 2 or less.

According to a third aspect of the present invention, in the document image reading apparatus according to the second aspect, when the most significant bit data of the shading data is "0", the shading data is 1 / the maximum digital output signal. It is determined that it is 2 or less.

Therefore, it is only necessary to check the most significant 1-bit data of the shading data, so that the comparator can be easily constructed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. The same parts as those shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, the maximum digital output signal is “255” (=
11111111).

First, FIG. 1 shows an example of a mechanical configuration of a document image reading apparatus according to the present embodiment, in which a contact glass 12 on which a document 11 to be read is placed is provided. The end of the contact glass 12 is covered with a main body cover 14 including a scale 13 for positioning such as A4 and B4, and a reference white plate 15 is incorporated at a reference position. A reading optical system is provided below the contact glass 12. This reading optical system
Light source 1 for slit exposure of 11 originals and 15 reference white plates
6, first to third mirrors 17, 18, and 19 that sequentially receive the reflected light from the original 11 surface and the reference white plate 15, a one-dimensional array-shaped CCD 20 that receives the reflected light, and the reflected light to the CCD 20. And an imaging lens 21 for converging and forming an image. Here, the light source 16 and the first mirror 17
Are set so as to perform sub-scanning at the speed ratio of 2: 1 in the same direction as the first traveling body and the second and third mirrors 18 and 19 as the second traveling body.

FIG. 2 shows a schematic configuration of a signal processing system including the shading correction circuit 31. First, the read data read by the one-dimensional array CCD 20 is converted into digital data by an A / D converter 33 through signal processing by a signal processing circuit 32 such as waveform shaping, sample hold, amplification, etc., and is converted into a shading correction circuit. 31 is input.
Here, the CCD 20, the signal processing circuit 32, and the A / D converter 33 constitute a reading unit 34.

On the other hand, as in the case of FIG. 3, the shading correction circuit 31 includes an average value circuit 2, a memory 3, a subtractor 4, and a ROM 5, and also performs subtraction obtained from the subtractor 4. Shading data D for each pixel
predetermined multiple (alpha times) multipliers 35 are provided to the data D _g for each pixel obtained from _sh1 and A / D converter 33. Here, α is set to 2, and binary data can be simply processed and shifted by one bit. Further, a comparator (comparator) 3 for determining whether or not the value of the shading data D _sh1 for each pixel after the subtraction obtained from the subtractor 4 is equal to or smaller than a predetermined value.
6 are provided. More specifically, if the value of the shading data D _sh1 determines whether a 127/255 or less, if the value of the most significant bit (MSB) of the shading data D _sh1 is "0" 127 / 255
It is determined that it is below, and if it is “1”, it is determined that it is 128/255 or more. Further, the shading data D _sh1 , A / D for each pixel after subtraction obtained from the subtractor 4
Data D _g for each pixel obtained from the converter 33 and shading data D multiplied by a predetermined value obtained from the multiplier 35
A selector (selector) 37 for inputting _sh2 and document image data _Dg1 is provided. In this selector 37, any data is used as the shading data D _sh3 ,
The comparator 3 determines whether to output the original image data D _g2.
6 is selected by the output COMP. Here, the selector 37
If the output COMP of the comparator 36 is 128/255 or more, the shading data D _sh3 = D
_sh1, make a selection consisting original image data D _g2 = D _g, in the case of that the output COMP from the comparator 36 is 127/255 or less shading data D _sh3 = D _sh2, comprising the document image data D _g2 = D _g1 selected Is set to do.

The maximum digital output signal “25” in the digital conversion by the A / D converter 33 is stored in the ROM 5.
5 ”(= 111111111)
8/255 or higher) shading corrected data corresponding to the shading data D _sh3 of is stored, the selector 37 by the stored shading corrected shading data D _sh3 and the document image data D _g2 which is selectively outputted as an address It is configured to read data. Therefore, 12
Data corresponding to 7/255 or less shading data is not stored.

In such a configuration, the shading data _Dsh for each pixel, which is obtained by reading the reference white plate 15 by the reading means 34 and digitized before acquiring the image of the document 11, is stored in the memory 3, and is stored in the memory 3. basic operation that correcting the original image data D _g for each pixel and read digital conversion by the reading means 34 when reading of the document image to the corresponding shading data D _sh is conventional. The processing to remove the influence of noise component by using the shading data D _sh1 that during background elimination subjected to subtraction processing in the shading data D _sh subtracter 4 by using the output correction value D _off given appropriately from CPU38 also JP This is performed in the same manner as in the case of Japanese Unexamined Patent Publication No. 9-224156. As a result, in reality, as described above, the shading data D _sh1 after the subtraction is 127/255.
The following may occur.

Therefore, in the present embodiment, proper shading correction is performed by the configuration of the shading correction circuit 31 as described above even when the shading data D _sh1 after the subtraction is 127/255 or less.

That is, when the shading data D _sh1 is 12
The shading calculation in the case of 7/255 or _{less, GD = INT [(D g} × α) / (D sh1 × α) × 255] INT []: Function displays an integer value of the maximum 255 GD: shading after data D _g : Original image data D _sh1 : Shading data (after subtraction) α: Arbitrary predetermined multiple, and the shading data is 128/2
ROM5 can be used where the value is 55 or more.
Can be used as it is. The above calculation can be rewritten as GD = INT [(D _g1 / D _sh2 ) × 255], and can be easily realized only by using the data passed through the multiplier 35. Therefore, even in the case of the shading data of 127/255 or less, the shading correction can be appropriately performed using the ROM 5 based on the shading data of 128/255 or more. Conversely, as usual, the shading data D _sh1 after the subtraction is 128/2.
If it is 55 or more, the conventional processing of GD = INT [(D _g / D _sh1 ) × 255] may be performed.

As described above, according to the present embodiment, with respect to the shading data D _sh stored in the memory 3,
Shading data D obtained by subtracting the output correction value D _off
the value of the _sh1 determines whether a 127/255 or less in the comparator 36, in the case of 127/255, there in _{GD = INT [(D g1 /} D sh2) × 255] 128/255 or For example, the output COMP of the comparator 36 determines whether the output through the multiplier 35 or the output before the output is passed by the selector 37 so that GD = INT [(D _g / D _sh1 ) × 255]. It is only necessary to perform switching for inputting data to the ROM 5, and an extremely simple configuration is sufficient.

In this embodiment, the output correction value D _{off is obtained} from the shading data D _sh stored in the memory 5.
The value of the shading data D _sh1 obtained by subtracting the minute is 127
/ 255 Although the whether the following was configured to determine the comparator 36, the shading data D _sh before subtraction may be equal to or less than a predetermined value using. That is, the magnitude may be determined using a value that allows for the output correction value D _off . In this case, the light source 16
Can be relaxed.

[0028]

According to the first aspect of the present invention, when the shading data is equal to or less than a predetermined value, shading correction is performed using data obtained by multiplying both the shading data and the corresponding original image data by a predetermined value. Even under limited conditions, only the shading data for which the ROM capacity required for shading calculation exceeds a predetermined value is used. The original image data of the corresponding pixel is also multiplied by a predetermined value at the same time, and by using the multiplied shading data and the document image data, the ROM can be used as the shading data substantially equal to or more than the predetermined value. Appropriate shading correction for all shading data It can be carried out.

According to the second aspect of the present invention, there is provided a memory for storing shading data for each pixel obtained by reading a reference white plate, and shading data stored in the memory and original image data obtained by reading an original image. , And a comparator for determining whether or not the shading data for each pixel is equal to or less than の of the maximum digital output signal in digital conversion. In the following cases, the shading data and the original image data multiplied by a predetermined value are selected by the multiplier, and if not less than 1/2, the shading data stored in the memory and the original image data obtained by reading the original image are selected. And the shading data having a value exceeding 1/2 of the maximum digital output signal in the digital conversion. RO shading corrected data stored in the shading data and original image data as an address response to shading corrected data is selectively outputted by the selector stored is read
M, the comparator determines whether or not the shading data for each pixel is equal to or less than 1/2 of the maximum digital output signal in the digital conversion, and multiplies the shading data and the original image data based on the determination result. Select the data that has been multiplied by a predetermined amount through a multiplier or the data that has not been multiplied by a predetermined number without passing through a multiplier,
With a simple configuration that only reads the shading corrected data from the
Appropriate shading correction can be realized for shading data of 2 or less.

According to the third aspect of the present invention, in the document image reading apparatus according to the second aspect, when the most significant bit data of the shading data is "0", the comparator outputs the shading data of the maximum digital output signal. Since it is determined that it is 1/2 or less, it is sufficient to check only the most significant 1-bit data of the shading data, and the comparator can be easily configured.

[Brief description of the drawings]

FIG. 1 is a front view illustrating a mechanical configuration example of a document image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram mainly showing a shading correction circuit;

FIG. 3 is a block diagram illustrating a configuration example of a conventional shading correction circuit.

[Explanation of symbols]

 3 Memory 5 ROM 11 Original 15 Reference white plate 34 Reading means 35 Multiplier 36 Comparator 37 Selector

Claims (3)

[Claims] 1. Prior to reading a document image, a reference white plate disposed outside a document reading range is read by a reading means, and digitally converted shading data for each pixel is acquired and stored in a memory. In a document image reading apparatus which is configured to correct the document image data of each pixel read and converted by the reading means in accordance with the corresponding shading data, when the shading data is equal to or less than a predetermined value, the shading data is corrected. A document image reading apparatus wherein shading correction is performed using data obtained by multiplying the corresponding document image data by a predetermined number. 2. Prior to reading a document image, a reference white plate disposed outside the document reading range is read by a reading means, and digitally converted shading data for each pixel is obtained and stored in a memory, and the document image is read. In a document image reading apparatus which sometimes corrects document image data of each pixel read and converted by the reading means in accordance with the corresponding shading data, shading data of each pixel which is obtained by reading the reference white plate A multiplier that multiplies both the shading data stored in the memory and the original image data obtained by reading the original image by a predetermined number; and a shading data for each pixel that is 1 / the maximum digital output signal in the digital conversion. A comparator for determining whether the number is 2 or less; When the result is less than 1/2, the shading data and the original image data multiplied by the multiplier by a predetermined number are selected. When the result is not less than 1/2, the shading data and the original image stored in the memory are read and obtained. A selector for selecting the selected original image data, and shading in which shading corrected data corresponding to each shading data having a value exceeding 1/2 of the maximum digital output signal in the digital conversion is stored and selectively output by the selector. A ROM from which shading corrected data in which data and document image data are stored as addresses is read. 3. The comparator according to claim 2, wherein when the most significant bit data of the shading data is “0”, the comparator determines that the shading data is equal to or less than の of the maximum digital output signal. Original image reading device.