JPH06105142A - Picture reader - Google Patents

Abstract

PURPOSE:To prevent the occurrence of an undesirable phenomenon such as a black stripe or void onto an output picture by implementing shading correction using backup data when a back plate becomes dirty. CONSTITUTION:Dirt may be caused on a back plate 1 which is frequently in contact with an original G. When dirt is caused on the back plate, shading correction data obtained based on read scanning of the plate 1 are improper and a phenomenon such as black stripe or void takes place in an output picture of the original G. In this case, a changeover switch 12 is selected to connect a ROM 11 to a shading correction circuit 6 in place of a RAM 10. Although shading correction data stored in the ROM 11 are not always in matching with the actual status of distribution of a reflected luminous quantity, the data are not the improper data caused when the plate 1 becomes dirty. Thus, the occurrence of undesirable event is avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus applied to a facsimile machine or the like, and more particularly to an image reading apparatus having an image signal shading correction function.

[0002]

2. Description of the Related Art In an image reading apparatus applied to a facsimile apparatus or the like, it is difficult to equalize the amount of light projected from a linear light source onto a document. Generally, the central portion of the document in the main scanning direction is located at both end sides. It tends to be brighter than. Therefore, if the original image is read and scanned by a CCD sensor or the like and the image signal is output as it is, the central portion of the output image is often whiter than both ends. In this case, the output image is different from the actual document image and is not appropriate. Therefore,
Conventionally, an image reading apparatus having a shading correction function has been proposed as a means for solving such a problem. That is, this apparatus preliminarily scans and scans the white back plate before starting to scan and scan a desired document, so that the amount of reflected light in the main scanning direction is unequal based on the sampled image signal. It seeks the distribution state. Then, by correcting the image signal of the original image so as to eliminate the initial improper distribution state, image data close to the actual original image is obtained.

[0003]

The above shading correction process is premised on that the image signal sampled by the reading scan of the back plate is a proper image signal, and the back plate is contaminated. In this case, proper shading correction data can no longer be obtained. If the shading correction is performed based on such inappropriate data, as shown in FIGS. 6A and 6B, a black image portion called a so-called black band appears in the output image on the recording paper K. A phenomenon called "blurring" or "whiteout" occurs. However, in the past, the actual situation has been that no suitable means for eliminating such an unreasonable phenomenon has been adopted. As a result, conventionally, it is inconvenient because there is no effective measure for eliminating the black band and the like other than removing the dirt on the back plate by removing the cover of the image reading unit.

The present invention has been proposed in view of the above points, and even when the back plate is dirty, the black output image does not require the troublesome work of cleaning the back plate. It is an object of the present invention to provide an image reading device that can easily prevent an unfavorable situation such as occurrence of a band.

[0005]

An image reading apparatus according to the present invention, which has been proposed to achieve the above object, has storage means for storing backup data for performing shading correction of an image signal. The signal shading correction processing selects one of the data stored in the storage unit and the shading correction data obtained based on the image signal obtained by scanning the back plate. Is configured to run.

[0006]

In the image reading apparatus according to the present invention having the above-mentioned configuration, the shading correction data obtained based on the image signal obtained by scanning the back plate and the backup data separately stored in the storage means are provided. The shading correction processing of the image signal can be performed using the data on any one of the sides. Therefore, in the normal time when the back plate is not contaminated, by using the shading correction data based on the reading scanning of the back plate, it is possible to perform an appropriate shading correction process that immediately corresponds to the actual reflected light amount. Then, when the back plate becomes dirty and black bands or white spots occur in the output image, shading correction using the backup data can be performed. In the shading correction using such backup data, since the shading correction can be executed regardless of whether the back plate is dirty or not, even if the back plate is still dirty, black stripes, white spots, etc. can be properly displayed. A resolved output image can be obtained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of a main part of a hardware configuration of an image reading apparatus according to the present invention. The image reading apparatus shown in the figure receives a linear light source 2 for projecting light on a document G arranged on the front side of the back plate 1, receives reflected light from the document G, and scans an image of the document G. It is equipped with a CCD sensor 3 for operating. In the subsequent stage of the CCD sensor 3, a gain control circuit 4 for giving a predetermined gain to an analog image signal output from the CCD sensor 3, a clamp circuit 5 for changing a reference level of an input waveform of the image signal, and a shading correction described later. A shading correction circuit 6 that executes processing, a binary converter (binarization circuit) 7, a peak detection circuit 8, and a pulse width modulation circuit 9 are provided. In addition to these, a RAM 10 for storing data for shading correction obtained by reading and scanning the back plate 1, a ROM 11 for storing backup data for shading correction,
Further, a manual type changeover switch 12 such as a dip switch for changing over and connecting either one of the RAM 10 and the ROM 11 to the shading correction circuit 6 is also provided.

Of the above, the peak detection circuit 8 is a CCD
When an image signal sampled by reading and scanning the white back plate 1 by the sensor 3, that is, a sampling image signal as shown in FIG. 2, is input, shading correction data is calculated based on the input image signal. . As this shading correction data, for example, as shown in FIG. 3, a voltage peak value D at a predetermined position in the main scanning direction of the sampling image signal is applied, and the value D corresponds to, for example, the A4 width of the CCD sensor 3. In this case, the values are obtained for each of the 1728 pixels in the main scanning direction, and these values are calculated as digitized shading correction data. The RAM 10 is a memory for storing the shading correction data transmitted from the peak detection circuit 8.
Each time the shading correction data is transmitted from the device, the previously stored shading correction data is rewritten with new data. RO
M11 is data in which backup data for shading correction is stored in advance. As a specific example of the backup data, an average shading correction obtained by the manufacturer by reading and scanning the white back plate 1 with no stain Data or theoretically calculated data is applied.

The shading correction circuit 6 corrects the shading of the image signal obtained by scanning the original G, that is, the correction for eliminating the distortion of the image signal due to the uneven distribution of the amount of reflected light in the main scanning direction. RAM10 processing
Alternatively, it is executed based on the data for shading correction stored in any of the ROMs 11. That is, as the shading correction process using the data stored in the RAM 10, first, the waveform of the voltage peak just shown in FIG. 3 is inverted from the shading correction data stored in the RAM 10 as shown in FIG. 4B. A control signal (voltage signal) having the selected shape is created. Then, when the image signal of the original image as shown in FIG. 4A is obtained by reading and scanning the original G, the image signal is multiplied by the voltage signal of FIG. The voltage is controlled so that the image signal is corrected. According to the voltage control of the image signal, the image signal of the original image in which the variation of the reflected light amount in the main scanning direction is canceled can be obtained.

Further, the shading correction circuit 6 includes an RO
Even when the shading correction processing of the image signal of the original is executed using the data stored in M11, basically the same image signal control processing as that in the case of using the data of the RAM 10 is performed. Binary converter 7
The image signal of the original image whose shading correction has been completed by the shading correction circuit 6 is sliced at a desired threshold value,
The conversion processing is performed into a binary image signal of "0" and "1" (black and white).

Next, a usage example of the image reading apparatus having the above configuration,
The operation will be described. First, in the linear light source 2 configured by arranging a large number of light emitting elements in a line, the amount of light emitted from each part is easily changed over time due to long-term use. First, it is desirable to obtain shading correction data according to the actual light emission state of the linear light source 2 in advance. Therefore, at normal times, the changeover switch 12 may be set so that the shading correction circuit 6 is connected to the RAM 10. By reading and scanning the white back plate 1 prior to reading and scanning the original G, the peak detection circuit 8 creates the latest shading correction data corresponding to the variation in the actual light projection amount of the linear light source 2, and the RAM 10 is used. Can be stored in. Then, according to the setting state of the changeover switch 12 described above, the shading correction processing of the image signal of the document can be appropriately performed based on the latest shading correction data stored in the RAM 10.

On the other hand, dirt may be attached to the back plate 1 which is repeatedly contacted with the original G, and when such a situation occurs, shading obtained based on the reading scanning of the back plate 1 is performed. The correction data becomes improper, and the output image of the original G has a phenomenon of black bands or white spots. So in this case,
It suffices to switch the changeover switch 12 and connect the ROM 11 to the shading correction circuit 6 instead of the RAM 10. The shading correction data stored in the ROM 11 may not always match the actual state of the distribution state of the reflected light amount, but the back plate 1
It is not unwarranted data that would be obtained if there was dirt on the. Therefore, if the shading correction processing is executed based on the data stored in the ROM 11, even if the back plate 1 is dirty, an undesired phenomenon such as a black band or a blank area in the output image of the document G is irrelevant. It is possible to surely avoid the occurrence of.

When performing shading correction using the backup data stored in the ROM 11,
It is not necessary to read and scan the back plate 1 in advance to obtain a sampling image signal. Therefore, the changeover switch 12 is R
When connected to the OM 11 side, it is preferable to perform soft control so that reading scanning of the back plate 1 is not executed. Step 100 of the flowchart of FIG.
Reference numerals 105 to 105 show an operation procedure when the shading correction processing is switched and executed.

The image reading apparatus according to the present invention is applied not only to a facsimile apparatus but also to a scanner or the like connected to a computer or the like.
It does not matter about its specific use.

[0015]

As can be understood from the above description, according to the image reading apparatus of the present invention, the shading correction is executed on the basis of the shading correction data obtained by the reading scan of the back plate at normal times. By doing so, an appropriate original image can be obtained, but when the back plate becomes dirty, shading correction is performed using the backup data, so that an undesired phenomenon such as a black band or white spots appears in the output image. A special effect is obtained in that it can be easily prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a main part of a hardware configuration of an image reading apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing an example of an image signal sampled by reading scanning of a back plate.

FIG. 3 is an explanatory diagram showing an example of a case where shading correction data is created based on a sampling image signal.

FIG. 4A is an explanatory view showing an example of an image signal of a document,
FIG. 6B is an explanatory diagram showing an example of an inverted control signal for shading correction.

FIG. 5 is a flowchart showing an example of an operation procedure when switching and executing shading correction processing.

6A and 6B are perspective views showing a case where a black band and white spots occur in an output image.

[Explanation of symbols]

 1 back plate 2 linear light source 3 CCD sensor 6 shading correction circuit 7 binary converter 8 peak detection circuit 10 RAM 11 ROM 12 changeover switch

Claims (1)

[Claims] 1. A storage means for storing backup data for performing shading correction of an image signal, wherein the shading correction processing of the image signal scans the data stored in the storage means and a back plate. An image reading apparatus, characterized in that it is configured such that either one of the data and the shading correction data obtained based on the image signal can be selected and executed.