JP4414276B2 - Image reading device - Google Patents

Description

  The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus that reads an image using an image sensor such as a document reading apparatus in a digital copying machine or a facsimile machine, or an image scanner for peripheral devices of a personal computer.

  Conventionally, a large number of image sensors are arranged in a straight line, and a carriage equipped with a color image sensor including three line image sensors such as CCDs that read each of the three primary colors is moved in parallel to the document surface. An image reading apparatus that reads an image of a document is known.

  For example, in the case of a flat bed type image reading apparatus, an original table made of a transparent plate such as glass for placing an original is provided on the upper surface of a box-type casing, and a driving device is provided inside the casing. Is provided with a carriage that moves parallel to the document table. The carriage is equipped with a light source and the color imaging means described above. The light emitted from the light source is reflected on the surface of the original on the original table and is condensed on the color imaging means by the condenser lens.

  In such a line image sensor, a phenomenon is known in which a certain amount of output value is output even when no light is incident on the signal output from each photoelectric conversion element. It has been. The output voltage in this case is referred to as dark output voltage. At the time of original image reading, the dark output voltage of the photoelectric conversion element is added to each image data voltage and output. Therefore, in order to obtain a true image signal voltage, the dark output voltage is obtained from the output voltage of the photoelectric conversion element. It is necessary to perform correction processing (dark output correction processing) of subtracting the minutes.

  As a technique relating to such dark output correction, a method of correcting line by line using a light shield element is known. For example, as described in Patent Document 1 (Japanese Patent Laid-Open No. 60-41363) and Patent Document 2 (Japanese Laid-Open Patent Application No. 2-17969), a plurality of light shield elements are provided outside the effective image area of the image sensor. (Dummy photoelectric conversion element) is formed in a light-shielded state so that a dark output voltage can always be obtained, and the original image in the effective image area is line-by-line based on the dark output value obtained from these light shield elements. It is intended to perform dark output correction of the photoelectric conversion element.

JP 60-41363 A Japanese Patent Laid-Open No. 2-179069

  The image data read by the image reading apparatus is subjected to γ conversion in the subsequent image processing unit. By this γ conversion, the data on the black side is converted into a conspicuous direction. In this case, particularly in the color image reading apparatus, in the case of the above-described correction method in units of lines, when the black level detection value in RGB is changed so as to be different in the sub-scanning direction, for example, an achromatic document is used. There is a problem that a line that is colored when read is generated, and an image on a horizontal stripe appears.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image reading apparatus capable of improving black level detection accuracy and reducing horizontal stripes.

In order to solve the above-described problems and achieve the object, the present invention provides a color image sensor that optically reads a document and converts it into image data, and a black level in the main scanning direction and the sub-scanning direction of the color image sensor. Each black level detection value is calculated in the detection range, and the black level detection value in the black level detection range in the sub-scanning direction is a value obtained by averaging pixel values in the black level detection range in the main scanning direction of a plurality of lines. A black subtraction value calculation means for calculating a black subtraction value based on the calculated black level detection value; and a black level correction means for subtracting the black subtraction value from the image data. The means compares the black level detection value of the black level detection range in the main scanning direction with the black level detection value of the black level detection range in the sub scanning direction for each line, and the difference is a threshold value. In the above case, the black level detection value of the black level detection range in the main scanning direction is set as the black subtraction value. A subtraction value is used.

Further, according to a preferred aspect of the present invention, the color image sensor is an RGB color image sensor, and the black subtraction value calculation means averages RGB image data and performs the black level detection value in the color mode. It is desirable to calculate

  According to the present invention (Claim 1), a color image sensor that optically reads a document and converts it into image data, and a line cycle changing unit that changes a line cycle of the color image sensor between a color mode and a monochrome mode. A black level detection range setting means for setting a black level detection range in the main scanning direction and the sub scanning direction of the color image sensor, and a black level detection value in each of the black level detection ranges in the main scanning direction and the sub scanning direction. And a black subtraction value calculation means for calculating a black subtraction value based on the calculated black level detection value, and a black level correction means for subtracting the black subtraction value from the image data. Level detection accuracy can be improved, and horizontal streaks can be reduced.

The black subtraction value calculating means compares, in line units, the black level detection value in the black level detection range in the main scanning direction and the black level detection value in the black level detection range in the sub scanning direction, and the difference is a threshold value. In the above case, the black level detection value in the black level detection range in the main scanning direction is set as the black subtraction value. In the case where the black level detection value is not equal to or more than the threshold value, the black level detection value in the black level detection range in the sub scanning direction is set as the black subtraction value. Therefore, it is possible to reduce the horizontal streak without side effects.

According to the present invention (Claim 2 ), the color image sensor is an RGB color image sensor, and the black subtraction value calculation means averages the RGB image data and performs the black level detection value in the color mode. Therefore, the black level detection accuracy can be increased by increasing the number of black level detection pixels, and the fluctuation of the black level in RGB can be made the same tendency, and the horizontal color streak can be reduced. Become.

  Hereinafter, an image reading apparatus according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

  FIG. 1 is a block diagram showing a configuration of an image forming apparatus 1 to which an image reading apparatus according to the present invention is applied. As shown in FIG. 1, the image forming apparatus 1 includes an image reading unit (scanner unit) 100 that reads image data of a document, and an image processing unit 200 that performs image processing on the image data read by the image reading unit 100. The printer unit 300 outputs the image data processed by the image processing unit 200 to paper or the like.

  FIG. 2 is a cross-sectional view illustrating a mechanical configuration of the image reading unit 100 according to the present embodiment. As shown in FIG. 2, the image reading unit 100 includes a contact glass 101 on which a document 111 is placed as a document table, a first carriage 102 including a document exposure illumination lamp 121 and a first reflection mirror 122, and a second carriage 102. A second carriage 103 including a reflection mirror 131 and a third reflection mirror 132, a CCD linear image sensor (hereinafter referred to as "CCD") 105, a lens unit 104 for forming an image on the CCD 105, and a sensor on which the CCD 105 is mounted. A housing 106 includes a board 106, a connection cable 107 for connecting the sensor board 106 and the signal processing board 108, a signal processing board 108, and a white reference plate 109 for correcting various distortions due to a reading optical system and the like. It is prepared for.

  In the image reading apparatus 100 configured as described above, when the original 111 is placed and fixed on the contact glass 101 and read, the first carriage 102 moves forward (in the direction of arrow A) at a constant speed, and the second carriage 103 Moves forward following the first carriage 102 at a speed half that of the first carriage 102, whereby the document 111 on the contact glass 101 is optically scanned. After the reading of the original is completed, the first carriage 102 and the second carriage 103 return to the home position (position shown in FIG. 1). The first carriage 102 and the second carriage 103 are driven by a motor drive system (not shown).

  FIG. 3 is a block diagram illustrating an electrical configuration of the image forming apparatus 1 according to the present embodiment. The image reading unit 100 includes the CCD 105 described above and a signal processing circuit 140 mounted on the signal processing board 108 described above. The CCD 105 is composed of a color 3-line CCD in which three rows of CCD sensors covered with RGB filters are arranged. The CCD 105 is a two-phase output method in which the output is divided into two systems of odd phase (ODD) and even phase (EVEN), and a light-shielded photoelectric element is provided outside the effective image area. ing.

  The signal processing circuit 140 samples the analog waveform signal portion of the R, G, B analog image data output from the CCD 105 and adjusts the gain thereof with a built-in amplifier, and then converts the R, G, B analog image signal to A. / D-converted and output to the image processing unit 200 as 8-bit digital RGB image data. Since the CCD 105 is a color 3-line CCD, the signal output from the CCD 105 has a positional deviation of 4 lines at the same magnification of 3 lines. That is, there is a positional deviation of 8 lines between RB.

  The image processing unit 200 includes an inter-line correction unit 201, a shading correction unit 202, a dot correction unit 203, an image area separation unit 204, a scanner γ unit 205, a filter unit 206, a color correction unit 207, and a variable correction unit 207. A magnification unit 208, a printer γ unit 209, and a gradation processing unit 210 are provided.

  The line-to-line correction unit 201 stores 8 lines of R signal and 4 lines of G signal for R, G, and B image data input from the image reading unit 100, and delays by storing 4 lines of G signal. And the corrected R, G, B image data is output to the shading correction unit 202.

  The shading correction unit 202 corrects the density unevenness of the optical system and the sensitivity variation of the CCD 105 for the input R, G, B image data, and outputs the corrected R, G, B image data to the dot correction unit 203. To do.

  The dot correction unit 203 cannot correct the R, G, B image data to be input by the inter-line correction unit 201 because only the inter-line correction unit 201 may not be aligned during zooming. The positional deviation of one line or less is corrected with reference to surrounding pixels, and the corrected R, G, B image data is output to the scan γ unit 205 and the image area separation unit 204.

  The image area separation unit 204 determines whether each pixel of the R, G, and B image data is a character area or a picture area in order to perform optimal processing that matches the image characteristics in the subsequent image processing. An area determination signal (for example, character area “0” / design area “1”) indicating a character area and a picture area is filtered by a filter unit 206, a color correction unit 207, a scaling unit 208, a printer γ unit 209, and a gradation. The data is output to the processing unit 210.

  The scanner γ unit 205 performs linear color correction on the R, G, B image data by the subsequent color correction unit 207 because the input R, G, B image data has linear characteristics with respect to the reflectance. Are converted into characteristics that improve the correction accuracy of the image and output to the filter unit 206.

  The filter unit 206 performs filter processing on the input R, G, B image data based on the region determination signal, and outputs the R, G, B image data after the filter processing to the color correction unit 207. Specifically, the filter unit 206 performs a smoothing process on the R, G, and B image data in order to enhance the edge for sharpening the character region and smooth the pattern region.

  The color correction unit 207 converts the input R, G, and B image data into C, M, Y, and K signals based on the region determination signal and outputs them to the scaling unit 208. Since the sensitivity and ink characteristics of the CCD 105 are different from ideals, the color correction parameters are adjusted in the copying machine so as to correct the difference from the original.

  The scaling unit 208 performs scaling processing in the main scanning direction on the input C, M, Y, and K signals, and outputs them to the printer γ unit 209. In this case, by using the convolution method, the scaling process can be performed while maintaining the MTF of the reading optical system, and the resolution of the image data can be maintained. The sub-scanning direction is performed by controlling the scanning speed in the sub-scanning direction.

  The printer γ unit 209 performs γ conversion on the input C, M, Y, and K signals to match the original and the copy density based on the area determination signal, and outputs the result to the gradation processing unit 210. Specifically, the printer γ unit 209 performs processing so that the difference between the spectral characteristics of the document and the toner, the gray balance, and the top density become appropriate in order to finally match the copy density with the document.

  The gradation processing unit 210 binarizes or multi-values the input C, M, Y, and K signals (8 bits) based on the region determination signal and outputs them to the printer unit 300. Specifically, the gradation processing unit 210 binarizes or multi-values the character area for the C, M, Y, and K signals (8 bits), and the pattern area. Dither processing or error diffusion processing is performed.

  The printer unit 300 prints input C, M, Y, and K signals on a sheet via the LD writing unit 301.

  FIG. 4 is a detailed block diagram of the image reading unit 100 for explaining the configuration of the signal processing circuit 140 according to the present embodiment. The signal processing circuit 140 includes a sample hold circuit 141, a black level correction circuit 142, two amplifier circuits 143, two ADCs (A / D converters) 144, a multiplex circuit 145, a timing generation circuit 146, I / F147.

  First, the CCD 105 outputs analog image data Ve (odd number lines) and Vo (even number lines) to the sample hold circuit 141 in synchronization with the drive pulse input from the timing generation circuit 146. The sample hold circuit 141 and the analog image data Ve and Vo are sampled and held by the sample pulses input from the timing generation circuit 146, respectively, and the image data is output as a continuous analog signal and output to the black level correction circuit 142.

  The black level correction circuit 142 corrects variations in the dark output level of the CCD 105 by subtracting the black subtraction value from the input R, G, B image data, and outputs the result to the amplification circuit 143. A detailed method for calculating the black subtraction value will be described later. The amplifying circuit 143 adjusts the output of the odd and even pixels of each color image data to a certain level, and then outputs it to the ADC 144. The ADC 144 converts the analog image data Ve and Vo into digital image data and outputs the digital image data to the multiplex circuit 145. The multiplex circuit 145 outputs the image data obtained by multiplexing the output of the image data of the odd and even pixels to the subsequent image processing unit 200 via the I / F 147. Signals necessary for driving the CCD 105 and other circuits are generated by the timing generation circuit unit 146.

  FIG. 5 is a timing chart for explaining the reading timing in the main scanning direction during black and white (in black and white mode), and FIG. 6 is a timing chart for explaining the reading timing in the main scanning direction during color (in color mode). Is shown. In the present embodiment, description will be made on the assumption that the reading speed in color is different from the reading speed in black and white. In general, in the case of a color copying machine, the color copying speed is structurally slower, so that the reading speed can be slowed accordingly.

  5 and 6, TG is a signal for transferring the charge accumulated in the photodiode by the transfer gate signal of the CCD 105 to the CCD register, and is generated in a line cycle. φ1 is a drive pulse for transferring charges in the CCD register section. VOUT indicates an analog signal output output from the CCD 105, and includes an empty transfer portion of a dummy signal, an optical black portion where a light receiving portion is shielded, and an effective photocell portion that is actually read. The TG and φ1 signals are generated by the timing generation circuit 146.

  First, the black reading detection timing setting will be described. As shown in FIG. 5, in the black-and-white reading mode, the timing generation circuit 146 sets various timings so that the line cycle T1 is reached. At this time, the black reading detection range (black level detection range in the main scanning direction) is set in the signal portion of the optical black portion (96 pixels).

  Next, as shown in FIG. 6, in the color reading mode, the timing generation circuit 146 sets various timings so that the line period becomes T2. Since the color has a longer line cycle, there are more empty transfer portions after the effective pixel area in the VOUT output. In the color reading mode, by setting the black reading detection range (black level detection range in the main scanning direction) in the empty transfer unit as shown in FIG. 6, more detection pixels are set than in the black and white reading mode. As will be described later, a value obtained by averaging pixel values detected in the black level detection range in the main scanning direction is used as the black level detection value. Thus, the black level detection value can be calculated without being affected by noise as the number of detection pixels increases.

  FIG. 7 is a diagram showing an example of the configuration of the black level correction circuit 142 of FIG. As shown in FIG. 7, the black level correction circuit 142 includes a black level detection unit 401 and a black level correction control unit 402. In FIG. 7, image data D <b> 1 is input to a black level detection unit 401 and a black level correction control unit 402. In the black level detection unit 401, a first black level detection value obtained by averaging pixel values in a black level detection range in the sub-scanning direction (a black level detection range in a plurality of lines in the main scanning direction), and a black level in the main scanning direction. A second black level detection value obtained by averaging pixel values in the detection range (black level detection range in the main scanning direction of the target line) is calculated, and the first black level detection value and the second black level are calculated in units of lines. The level detection value is compared, and if the difference is equal to or larger than the set value (threshold value), the second black level detection value is set as the black subtraction value D2 and the black level detection value is set as the black subtraction value D2. Output to the level correction control unit 402.

  FIG. 8 is a diagram illustrating an example of the first black level detection value and the second black level detection value. In FIG. 8, the horizontal axis indicates the position in the sub-scanning direction (line position), the vertical axis indicates the image data level (black level), and the broken line portion indicates the first black level detection value (black processed by averaging in the sub-scanning direction). The level detection value) and the solid line portion indicate the second black level detection value (the black level detection value averaged in the main scanning direction).

  The black level correction control unit 402 aligns the phases of the black subtraction value D2 and the image data D1 input from the black level detection unit 401, subtracts the black subtraction value D2 from the image data D1, and sets the result as image data D3. Output. By performing such black level correction, it is possible to reduce horizontal streaks associated with black level fluctuations. In this embodiment, the black level correction circuit 142 is provided in the image reading unit 100, but may be provided in the subsequent image processing unit 200.

  The black level detection in the color reading mode is the same, and the three RGB signals are input to the black level detection unit 401 and the black level correction control unit 402 and processed in the same manner. In this case, in addition to a method of processing the three signals in parallel in different systems, there is a method of reducing noise by averaging the three signals of RGB to calculate a black level detection value. In this case, since it is necessary for RGB to detect the black level detection value from the data after the inter-line correction processing, the black level detection unit 401 and the black level correction control unit 402 are the inter-line correction unit 201 of the image processing unit 200. It is necessary to provide in the latter stage.

  As described above, the image reading apparatus according to the present invention outputs in the dark when reading an image using an image sensor such as a document reading apparatus in a digital copying machine or a facsimile machine or an image scanner for a peripheral device of a personal computer. It can be widely used in devices that perform correction.

1 is a block diagram illustrating a configuration of an image forming apparatus to which an image reading apparatus according to the present invention is applied. It is sectional drawing which shows the mechanical structure of the image reading part which concerns on a present Example. 1 is a block diagram illustrating an electrical configuration of an image forming apparatus according to an embodiment. It is a block diagram which shows the structure of the signal processing circuit which concerns on a present Example. 6 is a timing chart for explaining the reading timing in the main scanning direction during black and white. 6 is a timing chart for explaining the reading timing in the main scanning direction during color. It is a figure which shows an example of a structure of a black level correction circuit part. It is a figure which shows an example of the 1st black level detection value and the 2nd black level detection value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 100 Image reading part (scanner part)
101 Contact Glass 102 First Carriage 103 Second Carriage 104 Lens Unit 105 CCD
106 sensor board 107 connection cable 108 signal processing board 109 white reference plate 110 housing 111 document 121 illumination lamp 122 first reflection mirror 131 second reflection mirror 132 third reflection mirror 140 signal processing circuit 141 sample hold circuit 142 black level correction circuit 143 Amplification circuit 144 ADC (A / D converter)
145 Multiplex circuit 146 Timing generation circuit 147 I / F
DESCRIPTION OF SYMBOLS 200 Image processing part 201 Interline correction part 202 Sheding correction part 203 Dot correction part 204 Image area separation part 205 Scanner gamma part 206 Filter part 207 Color correction part 208 Scaling part 209 Printer gamma part 210 Tone processing part 300 Printer part 301 LD writing section

Claims (2)

A color image sensor that optically reads a document and converts it into image data;
A black level detection value is calculated for each of the black level detection ranges in the main scanning direction and the sub scanning direction of the color image sensor . A black subtraction value calculating means for calculating a black subtraction value based on the calculated black level detection value, which is a value obtained by averaging pixel values in a black level detection range;
Black level correction means for subtracting the black subtraction value from the image data;
With
The black subtraction value calculation means compares, in line units, the black level detection value in the black level detection range in the main scanning direction and the black level detection value in the black level detection range in the sub scanning direction, and the difference is a threshold value. In the above case, the black level detection value in the black level detection range in the main scanning direction is set as the black subtraction value. An image reading apparatus characterized by having a subtraction value. The color image sensor comprises an RGB color image sensor,
The image reading apparatus according to claim 1, wherein the black subtraction value calculating means calculates the black level detection value by averaging the RGB image data in the color mode.

Images