KR20010002853A - Method for correction shading function in scanner - Google Patents

Abstract

PURPOSE: A method for correcting shading of scanner is provided to execute shading correction of high capacity with memory of small capacity by calculating and storing shading data using simple hardware logic. CONSTITUTION: The method for correcting shading of scanner corrects distortion of shading waveform through pattern data of l line quantity gained by scanning standard pattern. The method for correcting shading of scanner includes two steps. The first step is to detect brightness information corresponding to a first pixel of the pattern data as the first prescribed bit number and to store it.(S3) The second step is to detect brightness information corresponding to other pixels except the first pixel of the pattern data and store them by calculating different element of result value of the first prescribed bit number detected from the front pixel and result value of the first prescribed bit number detected from the next pixel.(S4)

Description

Scanner shading correction method {METHOD FOR CORRECTION SHADING FUNCTION IN SCANNER}

The present invention relates to a shading correction method of a scanner, and more particularly, to obtain and correct shading data in order to perform a process of correcting a shading waveform distortion caused by an optical path and an uneven response characteristic of a sensor. The present invention relates to a shading correction method of a scanner that can efficiently manage memory by improving a method of controlling the same.

A scanner is a device that detects data recorded on an original in units of read width (1 line or 1 band) and converts the data into an electrical signal. That is, a shuttle scanner as an example of the scanner will be described. As shown in FIGS. 1 and 2, an image is installed in the document 101 while being spaced apart from the effective reading area of the document 101 by a predetermined distance. Provides driving force for scanning head 102 for scanning information, guide rail 103 for guiding the left and right reciprocating motion of scanning head 102, and scanning head 102 for reciprocating left and right A conveyance belt which is simultaneously mounted to a carriage return motor 104, a carriage return motor 104 and a scanning head 102, and transmits a driving force of the carriage return motor 104 to the scanning head 102. 105, the pickup roller 107 which picks up the original 101 loaded on the cassette 106 and puts it on the document feed path, and the originals picked up by the pickup roller 107 are effective for the scanning head 102. Drive roller 108 to transfer to the reading area, and the scanning operation is finished A discharge roller 109 for discharging the document 101, and is included in the flow trace of the scanning head 102 and attached to a point outside the effective reading area of the scanning head 102, so that the scanning head 102 can read it. It consists of a reference sheet 110 in which a reference pattern of a predetermined form is recorded.

Then, the detailed structure of the scanning head 102, the lamp 111 is provided at its end so that the light emitted from the lamp 111 is irradiated to the document 101. In addition, a photoelectric conversion element (using a "charge coupled device (CCD)" 112) for detecting the light reflected from the document 101 and converting the light reflected from the document 101 into electrical data is provided inside the scanning head 102. And a lens 113 for focusing the reflected light between the lamp 111 and the photoelectric conversion element 112 so that the light reflected from the document 101 reaches a predetermined region of the photoelectric conversion element 112. Here, the lamp 111, the photoelectric conversion element 112 and the lens 113 has an integrated structure.

Meanwhile, as shown in FIG. 3, the shuttle scanner has a scanning width that can be scanned at a time. The mono type can scan horizontally 1 [Pixel] × vertical 128 [Pixel]. The color type is configured to scan horizontal 1 [Pixel] x vertical 160 [Pixel]. That is, by one scanning operation, the scanning head 102 continuously scans from the first pixel to the last pixel by 1 [Pixel] x 128 [Pixel] (in the case of monochromatic type).

A process of scanning a document by a general shuttle scanner having such a configuration will be described below with reference to FIG. 4.

The general scanning head 102 scans the reference sheet 110 on which the white pattern is printed due to the nonuniformity of the lamp 111 and the nonuniformity of sensitivity per pixel of the photoelectric conversion element 112 within the read width section. In either case, the output of the scanning head 102 becomes a non-uniform waveform ("A" portion) in a state where distortion occurs in the shading waveform, as shown in FIG.

Correcting to set this to the correct white reference value ("B" part) is called shading correction. This process is equally applicable to the calibration process to set the black reference value. In normal image processing, the shading phenomenon is a phenomenon occurring in an imaging tube such as a videoconductor, a cathode ray tube (CRT), and the like, in which brightness varies depending on the screen portion of the imaging tube. This is caused by non-uniformity of the target or secondary redistribution from the target to the target, which improves the distorted image quality by providing the adjusting electron lens. Recently, however, the concept limited to the display device has been applied to an image input device such as an image scanning device in an extended concept having the same meaning.

In other words, shading correction corrects the darkening or deformation of the edges of the screen due to the characteristics of the lens system when digitalizing general documents, aerial photographs, etc. to generate digital image data for computers. The method of correcting the density so that the entire screen has the same brightness by determining the conversion function of the density for each divided area, and the method of obtaining shading data during dummy scanning and performing shading correction through it have.

Here, a method of acquiring shading data and performing shading correction through pseudo scanning is mainly adopted. In this case, the shading correction operation of this method is first applied to the reference sheet 110 attached to the device while the lamp is turned on. Is first scanned to calculate white shading data for converting a waveform such as "A" of FIG. 4 into a flat white reference value such as "B". Next, the reference sheet 110 attached to the apparatus is scanned while the lamp is turned off, and black shading data for converting the detected shading waveform into a flat black reference value is calculated. Thereafter, scanning the document 101 and applying the white and black shading data to the scanned real data, respectively, to compensate, thereby obtaining image information almost identical to the image recorded on the document 101.

On the other hand, when the scanning operation command is received, the originals 101 loaded on the cassette 106 are sequentially picked up one by one by the pickup roller 107 and supplied to the driving roller 108 side. The driving roller 108 transfers the document 101 transferred to the pickup roller 107 to the readable area of the scanning head 102. Accordingly, the transferred document 101 is located in the readable area of the scanning head 102, and at this time, the scanning head 102 scans the image recorded in the document 101 in band units for the document 101. ) Is detected. Then, when the scanning operation for one band is finished, the document 101 is discharged to the outside by the drive roller 108 and the discharge roller 109.

Conventionally, in order to perform shading correction, shading data for each pixel should be stored for one line amount. For example, when scanning letter paper having a resolution of 600 DPI and 5K pixels per line with a monochromatic scanner, one line of white and black shading data for shading correction is represented by Equation 1 below. Likewise, it becomes 100 Kbit.

Here, 10 bits represents the number of data bits (2 ^ 10) when dividing the brightness value of each pixel in 1024 steps, and arithmetic coefficient 2 represents the number of cases where shading data should be calculated for white and black, respectively.

If the scanner is a multi-color scanner, all the shading data for each color should be stored, so the data amount of the shading data necessary for the shading correction operation is 300 Kbit as shown in Equation 2 below.

Here, arithmetic coefficient 3 represents the number of cases where each shading data is detected for three primary colors of red, blue, and green.

However, according to the conventional shading correction method, the following problem (s) occur.

That is, conventionally storing both 10-bit white shading data of the digitized output of the photoelectric conversion element with the lamp turned on and 10-bit black shading data of the digitized output of the photoelectric conversion element with the lamp off. As a result, an excessive amount of memory of 300 Kbit is required. Thus, the price of the scanner rises.

Accordingly, an object of the present invention is to solve such problem (s), and an object of the present invention is to calculate and store shading data using simple hardware logic, thereby performing high-performance shading correction with a small amount of memory. It provides a method of shading correction of a scanner.

1 is a schematic structural diagram of a typical shuttle scanner,

2 is a schematic structural diagram showing a feed path of an original,

3 is a view showing a scanning area in which a scanning head of a conventional shuttle scanner can scan at one time;

4 is a voltage waveform diagram obtained by the photoelectric conversion element of the scanning head,

5 is a schematic block diagram of a shading correction apparatus for a scanner applied to the present invention,

6 is a flowchart illustrating an operation of the shading correction method of the scanner according to the present invention.

<Description of the code | symbol about the principal part of drawing>

201: Scanning control unit 202 ROM

203: RAM 204: lamp

205: lamp driving unit 206: optical module unit

207: photoelectric conversion element 208: step motor unit

209: analog / digital converter 210: shading memory

211: shading correction unit 212: shading correction unit

In order to achieve the above object (s), a feature of the present invention is a shading correction method of a scanner for correcting a distortion of a shading waveform through one line of pattern data obtained by scanning a reference pattern: Detecting and storing brightness information corresponding to a pixel with a first predetermined number of bits; The brightness information corresponding to the remaining pixels other than the first pixel of the pattern data is detected by calculating a difference component between the result of the first predetermined number of bits detected from the previous pixel and the result of the first predetermined number of bits detected from the next pixel. And store it.

Here, the brightness information for each pixel is separately detected and stored for the white reference value and the black reference value, respectively.

Further, the difference component may include: a 1-bit increment value indicating an increase or decrease of the result value of the first predetermined number of bits detected from the next pixel with respect to the result value of the first predetermined number of bits detected from the previous pixel; And a size value of the second predetermined number of bits indicating a magnitude corresponding to a difference between the result value of the first predetermined number of bits detected from the previous pixel and the resultant value of the first predetermined number of bits detected from the next pixel.

The second predetermined number of bits is a number of bits capable of expressing size information within a range of 5% from the total number of grades of brightness information for each pixel that can be expressed through the first predetermined number of bits.

Hereinafter, exemplary embodiment (s) of the present invention will be described in detail with reference to the accompanying drawings. First, in adding reference numerals to the elements of each drawing, it should be noted that the same elements are denoted by the same reference numerals as much as possible even if they are displayed on different drawings. In addition, in the following description there are shown a number of specific details, such as components of the specific circuit, which are provided only to help a more general understanding of the present invention that the present invention may be practiced without these specific details. It is self-evident to those of ordinary knowledge in Esau. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

FIG. 5 is a schematic block diagram of a shading correcting apparatus of a scanner applied to the present invention, and FIG. 6 is a flowchart illustrating an operation process of the shading correcting method of the scanner according to the present invention.

Referring to FIG. 5, the scanning control unit 201 generates a timing signal for performing a series of scanning operations according to a program stored in a ROM 202 and manages the overall system operation.

The ROM 202 stores programs and reference data having a certain flow so that the scanning control unit 201 can control the scanning system in a predetermined order. The RAM 203 stores temporary data generated while the scanning control unit 201 controls the system.

The lamp 204 outputs light of a predetermined intensity to read the image information of the original with the amount of reflected light. The lamp driver 205 receives a control signal from the scanning controller 201 and turns on and off the lamp 204 at an appropriate time for driving the lamp 204.

The optical module unit 206 reflects the light output from the lamp 204 to the document, and forms an optical path so that the reflected light is incident on the photoelectric conversion element 207. The step motor unit 208 receives the driving signal from the scanning control unit 201 and moves the optical module unit 206 along the sub-scanning direction of the original with a predetermined resolution.

The photoelectric conversion element 207 photoelectrically converts light incident through the optical module unit 206 into an electrical analog signal proportional to the amount of light. The analog / digital converter 209 converts an analog image signal into digital image data corresponding to a preset number of bits.

The shading memory 210 stores image data digitized by the analog / digital converter 209, and in particular, the shading data detected for the shading correction operation is stored.

The shading correction controller 211 reads the shading data stored in the shading memory 210 for each pixel unit, and applies shading data corresponding to each pixel to the image data stored in the shading memory 210 to correct the shading data. The correction operation for each pixel unit is controlled.

The shading correction unit 212 applies and corrects shading data in each pixel unit according to a control operation of the shading correction controller 211 and outputs the image data stored in the shading memory 210.

Referring to Figure 6 with respect to the operation of the present invention having such a configuration as follows.

When the scanning operation command is received by the user (S1), the scanning control unit 201 drives the lamp 204, the optical module unit 206, the photoelectric conversion element 207, and the like to perform a scanning operation. Switch the system. The scanning control unit 201 scans the reference pattern attached to the predetermined position of the scanner (S2). Accordingly, the photoelectric conversion element 207 converts the reflected light incident through the optical module unit 206 into an electrical signal proportional to the amount of light to obtain an analog image signal. At this time, each pixel in the photoelectric conversion element 207 is driven at a preset timing according to the sensor driving clock provided from the scanning control unit 201, and the photoelectric conversion element 207 has a constant number of analog images according to the preset resolution. Output the signal. The scanning control unit 201 controls the lighting and turning off state of the lamp 204 and simultaneously controls the amount of light reflected in proportion to the original density to be incident on the photoelectric conversion element 207 via the optical module unit 206. Accordingly, the incident reflected light is converted into an analog voltage signal proportional to the intensity of light according to the characteristics of the photoelectric conversion element 207 and output.

Thereafter, the analog / digital converter 209 converts the analog image signal converted by the photoelectric conversion element 207 into digital image data having a predetermined number of bits (for example, 10 bits). Here, although the gray level of the image binarized in the form of black and white is preferably represented by 10 bits as shown in the present invention, the number of bits allocated to each application field can be added or subtracted. When performing the analog / digital conversion, the more bits are assigned to the pixels, the more precise and detailed the pixels can be represented. On the other hand, the relatively large memory area must be allocated, and the computational amount increases exponentially during signal processing. It is well known that is delayed.

The shading memory 210 is detected by scanning a reference pattern (white pattern) recorded on a reference sheet during dummy scanning, and corresponds to the pixel position of the pattern data digitized by the analog / digital converter 209. To the address to be stored. Here, the pseudo scanning refers to an operation in which the photoelectric conversion element 207 scans a reference pattern of a reference sheet provided on the opposite surface. In this case, a white paper or a white roller may be used as the reference pattern in addition to the white panel.

Subsequently, the shading correction controller 211 reads pattern data for each pixel stored in the shading memory 210 for each address by a pseudo scanning process, and calculates a predetermined maximum brightness value in pixel units to shade corresponding to each pixel position. The data is calculated, and the calculated shading data for each pixel is provided to the shading memory 210. In addition, the shading correction controller 211 outputs the shading data for each pixel stored in the shading memory 210 in correspondence with the scanning data output from the analog / digital converter 209 for each pixel position in the process of scanning the actual document. do.

That is, when the reference pattern is scanned, the brightness difference between adjacent pixels does not exceed approximately 5%. Therefore, the value of the first pixel among the result values of the digitized pattern data of one line scanned by the reference pattern corresponds to the first pixel. Only the 10-bit shading data is stored in the shading memory 210, and only the size of the difference between the brightness value and the difference value of the brightness value between the previous pixel and the current pixel is stored for each pixel (S3). At this time, the data structure for the remaining pixels is composed of one bit (0: increase, one decrease) representing the brightness value, and a five-bit magnitude value (0 to 31) representing the magnitude of the difference component.

When the shading correction function is expressed by Equation 3, Equation 3 below.

Here, Ire (X) is the shading correction function for the X-th pixel for each line, I (X) is actual data for the X-th pixel for each line, and Sw (X) is the shading indicating the white reference value of the previous pixel. It is an operation value of data and the difference component thereof, and Sb (X) represents shading data representing the black reference value of the binary pixel and an operation value of the difference component thereof.

Here, Sw (X) and Sb (X) may be replaced with Equations 4 and 5 below.

Sw (X) = Sw (X-1) + W_MEMORY DATA (X)

Sb (X) = Sb (X-1) + B_MEMORY DATA (X)

Here, W_MEMORY DATA (X) is a white difference component value corresponding to the X-th pixel position, and B_MEMORY DATA (X) represents a black difference component value corresponding to the X-th pixel position.

Further, Sw (1) and Sb (1) are information stored in a temporary register in the shading memory 210 for the first pixel, and Sw (2) and Sb (2) are white and black shading for the second pixel, respectively. Represents the data.

Thereafter, when all of the shading data of one line is stored (S5), the scanning control unit 201 performs a scanning operation on the actual document (S6).

As a result, when the shading data is stored in the shading memory 210 through the above process, since the storage capacity is reduced by 4 bits for each pixel as compared with the conventional method, the shading data is reduced by approximately 40% from the capacity of the overall shading memory 210. Can be reduced.

As can be seen from this process, the more finely divided (10 bits or more) the step for the brightness value of the scanning data is more effective because the storage capacity of the memory is further reduced.

As described above, although the specific embodiment (s) have been described in the detailed description of the present invention, various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiment (s) but should be defined by the claims below and equivalents thereof.

As a result, according to the shading correction method of the scanner according to the present invention, the following advantages occur.

In other words, by calculating and storing shading data using simple hardware logic, high-performance shading correction can be performed even with a small amount of memory. Therefore, a low cost scanner can be manufactured.

Claims (4)

In the shading correction method of a scanner for correcting the shading waveform distortion through the one-line pattern data obtained by scanning the reference pattern: Detecting and storing brightness information corresponding to the first pixel of the pattern data as a first predetermined number of bits; And The difference component between a result value of the first predetermined number of bits detected from a previous pixel and brightness values corresponding to the remaining pixels except the first pixel of the pattern data and a result value of the first predetermined number of bits detected from a next pixel. Comprising the step of detecting and storing the shading correction method of the scanner. The method of claim 1, wherein the brightness information for each pixel is A shading correction method for a scanner, characterized in that the white reference value and the black reference value are individually detected and stored. The method of claim 1, wherein the tea component, A one-bit increment value indicating an increase or decrease of the result value of the first predetermined bit number detected from the next pixel with respect to the result value of the first predetermined number of bits detected from the previous pixel; And A scanner comprising a magnitude value of a second predetermined number of bits indicating a magnitude corresponding to a difference between a result value of the first predetermined number of bits detected from the previous pixel and a result value of the first predetermined number of bits detected from a next pixel Shading correction method. The method of claim 3, wherein the second predetermined number of bits, And a number of bits capable of expressing size information within a range of 5% from the total number of grades of brightness information for each pixel that can be expressed through the first predetermined number of bits.