JP2005094161A - Apparatus and method for image reading - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading apparatus and an image reading method capable of performing highly accurate gradation adjustment by accurately determining a suitable sampling point while using a simple and inexpensive gray scale. <P>SOLUTION: Average values of a plurality of pixels in a main scanning direction and a sub-scanning direction are calculated for each density of the gray scale on the basis of the value of an output electric signal for each pixel in the case where each density reference region of the gray scale is read by an image sensor (S1-S6). These average values are compared with the ideal value of the output electric signal of the image sensor which is set for each density of the gray scale (S7). A sampling point at which both the values approximate is determined (S8-S11). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus and an image reading method provided in an image forming apparatus such as a copying machine or a facsimile.

Conventionally, as shown in Patent Document 1, a gray reference plate having a plurality of gradations is read while changing sampling points in order to improve the gradation performance at the time of image reading by an image reading apparatus provided in a copier, a printer, or the like. There has been proposed an image reading apparatus that discriminates and sets sampling points at which the gradation is optimal.
Japanese Patent Laid-Open No. 10-336452

  However, in the image reading apparatus disclosed in Patent Document 1, it is necessary to prepare a gray reference plate (FIG. 3 of Patent Document 1) having a plurality of gradations. This gray reference plate is expensive and cumbersome because the user has to manage the original document that becomes the gray plate.

  The present invention has been made in order to solve the above-described problems, and it is possible to accurately determine an appropriate sampling point and perform high-precision gradation adjustment using a simple and inexpensive gray scale. An object of the present invention is to provide an image reading apparatus and an image reading method.

In order to achieve the above object, according to the first aspect of the present invention, there is provided an image sensor that optically reads an image by a plurality of pixels and converts the image into an electric signal, and an output signal process that processes an electric signal output from the image sensor. An image reading apparatus comprising: a circuit; a timing signal generation circuit that generates a timing signal for driving the output signal processing circuit; and a timing signal phase adjustment unit that adjusts a phase of the timing signal generated by the timing signal generation circuit Because
Storage means for storing a value of an output electric signal for each pixel when a gray scale composed of a reference region having a plurality of densities extending in the main scanning direction is read by the image sensor;
An average value calculating means for calculating an average value of output signals from a plurality of pixels of the image sensor for each density of the gray scale based on a value of an electric signal for each pixel stored in the storage means;
An ideal value storage means for storing an ideal value of an electric signal to be output from the image sensor for each of a plurality of levels of density,
The timing signal phase adjusting unit is configured to calculate an average value calculated for each density of the gray scale by the average value calculating unit for each sampling point at which the output electric signal from the pixel of the image sensor is collected, Each ideal value stored in the ideal value storage means corresponding to the density is compared to determine a sampling point that approximates both values, and the output signal processing circuit is driven at this sampling point. In addition, the phase of the timing signal generated by the timing signal generation circuit is adjusted.

  In this configuration, the gray scale composed of a reference region consisting of a plurality of levels of density extending in the main scanning direction of the image sensor is read by the image sensor, and the value of the output electrical signal of each pixel of the image sensor is stored in the storage means. Based on the value of the output electric signal for each pixel stored in the storage means, the average value calculating means calculates the average value of the output electric signal from the plurality of pixels of the image sensor for each density of the gray scale. To do. Then, the average value calculated for each density and the ideal value stored in the ideal value storage means corresponding to each density are compared to determine the sampling point at which both values are approximated. The phase of the timing signal generated by the timing signal generation circuit is adjusted so that the output signal processing circuit is driven at the sampling point.

  According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the average value calculating unit is based on a value of an electric signal for each pixel stored in the storage unit. The average value of a plurality of pixels in the main scanning direction is calculated for each density of the gray scale.

  In this configuration, based on the value of the electric signal for each pixel stored in the storage unit, the average value calculation unit calculates the average value of the plurality of pixels in the main scanning direction of the image sensor reading the same reference area, The average value is used for comparison with the ideal value.

  The invention according to claim 3 is the image reading apparatus according to claim 1, wherein the average value calculating means is based on the value of the electrical signal for each pixel stored in the storage means. The average value of a plurality of pixels in the main scanning direction and the sub scanning direction of the image sensor reading the same reference area is calculated for each density of the gray scale.

  In this configuration, based on the value of the electric signal for each pixel stored in the storage means, the average value of the average value of a plurality of pixels in both the main scanning direction and the sub-scanning direction of the image sensor reading the same reference area is averaged. The calculation means calculates and uses the average value to compare with the ideal value.

According to a fourth aspect of the present invention, there is provided the image reading apparatus according to any one of the first to third aspects, wherein a reading position confirmation mark provided at a predetermined position with respect to the gray scale is provided. Based on the read pixel position of the image sensor, the image sensor includes a determination unit that determines a pixel group of the image sensor that has read each gray scale reference region,
The average value calculation means calculates an average value of the output signals of the pixel group determined by the determination means.

  According to this configuration, the pixel of the image sensor that has read each density reference region of the gray scale based on the position of the pixel of the image sensor that has read the reading position confirmation mark provided at a predetermined position with respect to the gray scale. The determination unit determines the group, and the average value determination unit calculates the average value of the output signals of the pixel group.

Further, according to the invention described in claim 5, when the gray scale composed of the reference area composed of a plurality of densities extending in the main scanning direction of the image sensor is optically read by the image sensor composed of a plurality of pixels. Compares the value of the output electrical signal from the image sensor with the ideal value of the electrical signal that should be output from the image sensor for each of the multiple reference densities, and the optimal sampling point that approximates both values. An image reading method for determining
Based on the value of the output electrical signal for each pixel when each density reference area of the gray scale is read by the image sensor, an average value of a plurality of pixels is calculated for each density of the gray scale, and these are calculated. The average value obtained is compared with the ideal value of the output electric signal of the image sensor set for each density of the gray scale, and the sampling point where both values are approximated is discriminated.

  In this configuration, an average value of output signals of a plurality of pixels of the image sensor is calculated for each density of the gray scale, and the average value is used for comparison with the ideal value.

  As described above, according to the first aspect of the invention, the following effects can be obtained. For example, when the gray scale printed on the recording paper by the pattern generator output is read for each density by the image sensor, the value of the output signal for each pixel arranged in parallel in the main scanning direction is halftone dot The value of the output signal differs depending on whether a reference area with the same density is read, depending on whether a certain part is read or a part without halftone dots. Therefore, even if the value of the output signal of the image sensor is used as it is and an appropriate sampling point is determined by comparison with the ideal value of the electrical signal to be output from the image sensor, accurate gradation adjustment cannot be performed. However, according to the present invention, since the average value of the output signals from the plurality of pixels of the image sensor is compared with the ideal value, a gray scale in which a plurality of gray densities are expressed by halftone printing is used. Even in such a case, it is possible to accurately determine an appropriate sampling point. Thus, accurate gradation adjustment can be performed while using a simple and inexpensive gray scale printed on recording paper by the pattern generator output.

  According to the second aspect of the present invention, the average value of the plurality of pixels in the main scanning direction of the image sensor reading the same reference area based on the value of the electrical signal for each pixel stored in the storage means. Is calculated by the average value calculation means, and the average value is used for comparison with the ideal value, so that an appropriate sampling point can be accurately determined.

  According to the invention described in claim 3, both the main scanning direction and the sub-scanning direction of the image sensor reading the same reference area based on the value of the electrical signal for each pixel stored in the storage means Since the average value calculation means calculates the average value of a plurality of pixels at and compares the average value with the ideal value, an appropriate sampling point can be determined more accurately.

  According to the invention of claim 4, each density reference region of the gray scale is based on the position of the pixel of the image sensor that has read the reading position confirmation mark provided at a predetermined position with respect to the gray scale. Since the determination means determines the pixel group of the image sensor that has read the image, and the average value determination means calculates the average value of the output signal of the pixel group, regardless of the position where the user sets the clay scale in the image sensor, It is possible to accurately specify the pixel group of the image sensor that has read the density reference region and calculate the average value of the output signals of the pixel group. Thereby, the user can perform gradation adjustment with high accuracy by a simple operation.

  According to the fifth aspect of the present invention, the average value of the output signals of the plurality of pixels of the image sensor is calculated for each gray scale density, and the average value is used for comparison with the ideal value. So, for example, even if the tone is adjusted using the gray scale printed on the recording paper by the pattern generator output, whether each pixel of the image sensor has read the portion with the halftone dot, It is possible to accurately determine an appropriate sampling point regardless of whether a portion without a halftone dot is read. Thus, it is possible to perform highly accurate gradation adjustment while using a simple and inexpensive gray scale printed on recording paper by the pattern generator output.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram of an image reading apparatus showing an embodiment of the present invention. The image reading apparatus 1 includes a CCD 2, an AFE (analog front end) circuit 3, an A / D conversion circuit 4, a shading correction circuit 5, an image processing circuit 6, a timing generation circuit 7, a phase adjustment circuit 8, and a control unit 10. ing.

  The CCD 2 is an example of an image sensor referred to in the claims, and receives a document or grayscale reflected light irradiated by a document irradiation light source (not shown), performs photoelectric conversion, and corresponds to the amount of received light (document reflected light amount). An electrical signal is output for each of ODD and EVEN for each of R, G, and B.

  The AFE circuit 3 includes a sample hold circuit 31 and an amplifier circuit 33. The sample hold circuit 31 samples and holds the electric signal output from the CCD 2 in synchronization with the sample clock. The amplifier circuit 33 amplifies the electrical signal output from the CCD 2 to a level suitable for A / D conversion by the A / D conversion circuit 4.

  The A / D conversion circuit 4 converts the analog signal of each density sent from the AFE circuit 3 into a digital signal in synchronization with the A / D clock. The shading correction circuit 5 performs shading correction on the image data converted into the digital signal by the A / D conversion circuit 4 based on reference correction data such as orientation characteristics of the original irradiation light source and CCD pixel sensitivity prepared in advance. To do.

  The image processing circuit 6 includes a combining circuit 61 that combines the ODD signal and the EVEN signal. The image processing circuit 6 performs necessary image processing such as MTF (modulator transfer function) correction, edge enhancement, scaling, and binarization, and the image data processed by the image processing circuit 6 is output to a printer unit or the like. The

  The control unit 10 controls operation of the entire image reading apparatus 1. The control unit 10 controls the operation of the imaging system such as the CCD 2, the AFE circuit 3, the A / D conversion circuit 4, the shading correction circuit 5, and the image processing circuit 6, and further adjusts the phase of the sample clock when adjusting the gradation. On the other hand, the value of the electrical signal of the CCD 2 (the read value of the CCD 2) after the shading correction by the shading correction circuit 5 is compared with an ideal value (details will be described later) held in advance in the storage unit 105. The control unit 10 is connected to a memory 106 that stores a value of an output electric signal for each pixel when the gray scale is read by the CCD 2.

  Further, the control unit 10 determines a sampling point where the reading value of the CCD 2 is close to an ideal value, and gives an instruction to optimize the phase of the timing signal so that sampling is performed at this sampling point at the time of actual image reading. This is sent to the adjustment circuit 8 and the timing signal generation circuit 7. In comparison between the read value of the CCD 2 and the ideal value, the average value of the read values of a plurality of pixels in the main scanning direction and the sub scanning direction of the CCD 2 is used, and the control unit 10 also calculates the average value.

  The timing generation circuit 7 generates a timing signal necessary for timing control of a series of operations by the imaging system, such as a sample clock signal input to the AFE circuit 3 and an A / D clock signal input to the A / D conversion circuit 4. And consists of a collection of logic circuits configured to obtain optimum timing for each process. The generation and output of the timing signal by the timing generation circuit 7 is controlled by instructions from the control unit 10 and the phase adjustment circuit 8.

  The phase adjustment circuit 8 is configured such that a delay amount is set by a plurality of gate circuits arranged in parallel or an RCL circuit in which each constant is variable, and is controlled based on an instruction from the control unit 10.

  Next, a description will be given of a process for setting sampling points so that the gradation is optimal in the image reading apparatus 1 according to the present invention. 2 is a flowchart showing a flow of the sampling point setting process, FIG. 3A is a diagram showing a gray scale used for the sampling point setting process, FIG. 2B is a partially enlarged view of a reference area of the gray scale, and FIG. FIG. 5 is a diagram showing the change over time of the output of one pixel from the CCD at the time of gray scale reading, and FIG. 5 is a diagram comparing the ideal value and the actual reading characteristic regarding the relationship between the gray scale reflectance and the average value of the output of the CCD 2. It is. 3A schematically shows the density difference of each reference area by hatching in order to clarify the figure, but FIG. 3A is formed on the recording paper by the pattern generator output. In addition, a reference area consisting of a plurality of densities is intended.

  The sampling point setting process in which the gradation is optimized by the image reading apparatus 1 according to the present invention is a gray scale comprising a plurality of density reference areas formed on a recording sheet by a pattern generator output (FIG. 3A). Is read by the CCD 2 and the average value of the read values of the plurality of pixels obtained by reading the same reference area (reference area of the same color and the same density) among the plurality of pixels of the CCD 2 is calculated. The sampling point at which the gradation is optimal is determined by comparison with the ideal value for each of the multiple levels of the density of the electrical signal to be output from.

  In the case of the CCD 2 that performs reading in a plurality of channels, the following processing for obtaining an average value and determining an appropriate sampling point is performed for each channel. For example, as shown in FIG. 1, in the case of reading by two channels consisting of ODD and EVEN, the following processing is performed for each of ODD and EVEN to determine the optimum sampling point. In case of reading by 4 channels consisting of forward and backward ODD and EVEN, the optimum sampling point is determined by performing the following processing for each of forward-ODD, forward-EVEN, backward-ODD and backward-EVEN. To do.

  When the gray scale set at the reading position by each CCD 2 is irradiated by the original irradiation lamp (S1) and the reflected light from the gray scale is read by the CCD 2 (S2), each pixel of the CCD 2 collected at a certain sampling point. Each reading value (value of the output electric signal) is stored in the memory 106 (S3).

  The read value of one pixel of the CCD 2 draws a different waveform shape in each of the reset period, feedthrough period, and image output period as shown in FIG. 4, for example. In particular, the waveform of the average value during the image output period changes according to the amount of reflected light from the gray scale input to the CCD 2. For example, when the gray scale is read, the average value of the output values from the CCD 2 changes as waveform A → waveform B → waveform C as the gray density increases, and the white reference region is read. Draws the waveform D. However, when the gray scale formed by halftone printing is read by the CCD 2 as in this embodiment, the read value of each pixel of the CCD 2 is a reference area having the same density depending on whether or not the pixel of the CCD 2 reads the black dot portion. Even when reading is greatly different.

  Sampling of the read values of the pixels of the CCD 2 is performed within the image output period. In the image output period, the sample clock signal instructing execution of sampling becomes high for 30 n seconds, for example, and sampling is performed and held at the falling edge. In addition, sampling is set to be possible at points 1 to 6 in an image output period as shown in FIG. And the phase adjustment of a timing signal is set so that it can adjust at the timings 1-6 shown in FIG. Note that the sampling point and timing signal phase adjustment range are appropriately changed according to the required gradation performance and the like.

  Subsequently, the position of the reading position confirmation mark m is determined based on the reading value of each pixel (S4). For example, when there is a pixel group of the CCD 2 that outputs a reading value having the same density as the reading position confirmation mark m, the pixel group has a range equivalent to the area of the reading position confirmation mark m in the main scanning direction and the sub scanning direction. It is determined that the reading position confirmation mark m has been detected. The position of the pixel group that has read the reading position confirmation mark m is set as the position of the reading position confirmation mark m.

  Next, the control unit 10 determines the position of each grayscale (each color) reference region based on the position of the reading position confirmation mark m determined in S4 (S5). As shown in FIG. 3A, the reading position confirmation mark m is located at a certain distance in the main scanning direction of the CCD 2 from the side edge of the white reference area that is first read in the gray scale. Thus, the sub-scanning direction is provided at the same position as the white reference area. The other color reference area of the gray scale has the same position in the main scanning direction as the white reference area, and the position and the distance from the white reference area are determined for each reference area. The relative positional relationship between the reading position confirmation mark m and the white reference region, and the relative positional relationship between the white reference region and the reference regions of other colors are stored in the storage unit 105. Based on these pieces of information stored in the storage unit 105, the position of the pixel group that has read each density reference area is determined from the position of the pixel group of the CCD 2 that has read the reading position confirmation mark m.

  When the position of the pixel group that has read each density reference region is determined as described above, the average value of the read values of the plurality of pixels of the CCD 2 that has read the same reference region is calculated for each density (S6). ). That is, the average value of the read values of the pixel group in the main scanning direction and the sub-scanning direction of the CCD 2 that has read the reference region of each density is calculated for each density. Then, each average value is compared for each density with an ideal value predetermined for each density (S7).

  For example, as shown in FIG. 5, the average value of the read values of a plurality of pixels obtained by reading the white reference area of the CCD 2 with respect to the ideal characteristic in which the ideal value from the brightest white part and the ideal value of the darkest black part are connected by a straight line. Then, the sum of the deviations (differences) in the average values of the read values of the plurality of pixels obtained by reading the reference regions having different gray densities is calculated. The total sum of the deviations is used as an evaluation value for comparison with other sampling points.

  Subsequently, the sampling point is changed to the next point (YES in S8 and S9), and the same reading, comparison, and evaluation value calculation are performed (S1 to S7). When the reading, comparison, and evaluation value calculation at all sampling points are completed (NO in S9), the evaluation values at the respective sampling points are compared to determine the sampling point whose evaluation value is closest to the ideal value (S10). The phase of the sample clock signal is adjusted so that the read value from each pixel of the CCD 2 is sampled at the sampling point at the time of actual image reading such as when printing is performed (S11).

  Therefore, at the time of actual document reading by the image reading apparatus 1, in the case of reading by two channels consisting of ODD and EVEN, the reading value from each pixel of the CCD 2 is obtained at the sampling point determined for each of ODD and EVEN by the above processing. Sampled. The ODD and EVEN reading values are subjected to A / D conversion by the A / D conversion circuit 4 and shading correction by the shading correction circuit 5, and then the ODD signal and EVEN signal are output by the image processing circuit 6. The combined image is subjected to necessary image processing such as MTF correction, edge enhancement, scaling, and binarization, and the image processed image data is output to a printer unit or the like. In the case of reading with 4 channels consisting of forward and backward ODD and EVEN, A / D conversion and shading correction are applied to forward-ODD, forward-EVEN, backward-ODD and backward-EVEN respectively. Thereafter, the signals are combined in the image processing circuit 6 to perform necessary image processing and output to the printer unit or the like.

  By performing the above processing, it is possible to accurately determine an appropriate sampling point even when a simple and inexpensive gray scale printed on recording paper by pattern generator output is used. High gradation adjustment can be performed.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above embodiment, the position of each density reference area of the gray scale is determined based on the position of the reading position confirmation mark m read by the CCD 2, but the gray scale is printed at a predetermined position of the CCD 2. The position information of each density reference area when the prepared document is set is stored in the storage unit such as the storage unit 105, and is stored in the storage unit as long as the document is set at the predetermined reading position of the CCD 2. The position of each density reference region may be determined based on the information that has been set.

  In the above embodiment, when the average value of each pixel of the CCD 2 is calculated, the average value is calculated from all the pixels in the area corresponding to the reference area in the main scanning direction and all the pixels in the area corresponding to the reference area in the sub-scanning direction. A.) All pixels in the area corresponding to the reference area only in the main scanning direction, b.) All pixels in the area corresponding to the reference area only in the sub-scanning direction, c.) Main scanning Only any pixel corresponding to the reference area in the direction, d.) Only any pixel corresponding to the reference area in the sub-scanning direction, e.) Any plurality corresponding to the reference area in the main scanning direction and the sub-scanning direction An average value of only the pixels may be obtained, and an appropriate sampling point may be determined based on the average value.

  In the above embodiment, the configuration of the image reading apparatus 1 according to the present invention is shown in FIG. 1, and the evaluation method of the read value and the ideal value of the CCD 2 during the phase adjustment processing is described with reference to FIG. However, the configuration of the image reading apparatus 1 and the evaluation method of the read value and the ideal value of the CCD 2 are not limited to those shown in the above embodiment.

1 is a block diagram of an image reading apparatus showing an embodiment of the present invention. It is a flowchart which shows the process which sets a sampling point so that a gradation property becomes optimal. (A) is a figure which shows the gray scale used for the sampling point setting process of FIG. 2, (b) is the elements on larger scale of the reference | standard area | region of a gray scale. It is the figure which showed the time-dependent change of the output of 1 pixel from CCD at the time of gray scale reading. It is the figure which compared the ideal value and the actual reading characteristic about the relationship between a gray scale reflectance and CCD output.

Explanation of symbols

1 Image reader 2 CCD (image sensor)
3 AFE circuit (output signal processing circuit)
31 Sample hold circuit (output signal processing circuit)
33 Amplifier circuit (output signal processing circuit)
4 A / D conversion circuit (output signal processing circuit)
5 Shading correction circuit (output signal processing circuit)
61 Synthesis Circuit 7 Timing Generator (Timing Signal Generator)
8 Phase adjustment circuit (timing signal phase adjustment means)
10 Control unit (average value calculation means, determination means)
105 Storage unit (ideal value storage means)
106 Memory (storage means)

Claims (5)

An image sensor that optically reads an image by a plurality of pixels and converts it into an electrical signal, an output signal processing circuit that processes an electrical signal output from the image sensor, and a timing signal for driving the output signal processing circuit An image reading apparatus comprising: a timing signal generation circuit to be generated; and timing signal phase adjustment means for adjusting a phase of the timing signal generated by the timing signal generation circuit,
Storage means for storing a value of an output electric signal for each pixel when a gray scale composed of a reference region having a plurality of densities extending in the main scanning direction is read by the image sensor;
An average value calculating means for calculating an average value of output signals from a plurality of pixels of the image sensor for each density of the gray scale based on a value of an electric signal for each pixel stored in the storage means;
An ideal value storage means for storing an ideal value of an electric signal to be output from the image sensor for each of a plurality of levels of density,
The timing signal phase adjusting unit is configured to calculate an average value calculated for each density of the gray scale by the average value calculating unit for each sampling point at which the output electric signal from the pixel of the image sensor is collected, Each ideal value stored in the ideal value storage means corresponding to the density is compared to determine a sampling point that approximates both values, and the output signal processing circuit is driven at this sampling point. In addition, the phase of the timing signal generated by the timing signal generation circuit is adjusted.   The average value calculating means calculates an average value of a plurality of pixels in the main scanning direction for each density of the gray scale based on a value of an electric signal for each pixel stored in the storage means. The image reading apparatus according to claim 1.   The average value calculating means is an average value of a plurality of pixels in the main scanning direction and the sub-scanning direction of the image sensor reading the same reference area based on the value of the electric signal for each pixel stored in the storage means. The image reading apparatus according to claim 1, wherein the value is calculated for each density of the gray scale. Based on the position of the pixel of the image sensor that has read the reading position confirmation mark provided at a predetermined position with respect to the gray scale, the pixel group of the image sensor that has read each density reference area of the gray scale. A determination means for determining,
The image reading apparatus according to claim 1, wherein the average value calculation unit calculates an average value of output signals of the pixel group determined by the determination unit. When the gray scale composed of a reference area consisting of a plurality of densities extending in the main scanning direction of the image sensor is optically read by the image sensor consisting of a plurality of pixels, the value of the output electric signal from the image sensor and the value stored in advance An image reading method for comparing an ideal value of an electrical signal to be output from an image sensor for each of a plurality of reference densities and determining an optimal sampling point that approximates both values,
Based on the value of the output electrical signal for each pixel when each density reference area of the gray scale is read by the image sensor, an average value of a plurality of pixels is calculated for each density of the gray scale, and these are calculated. And comparing the average value obtained with the ideal value of the output electric signal of the image sensor set for each density of the gray scale, and determining a sampling point where both values approximate to each other Reading method.

Images