Image processing apparatus

Abstract

To appropriately prevent a density variation due to spread spectrum in image data even if an automatic black correction value of an analog front end varies due to spread spectrum.SOLUTION: An analog front end 21 derives, in automatic black correction, the difference between the average value of output values in an OBP region from an image sensor in automatic black correction periods and a predetermined reference value, and performs black correction in the subsequent automatic black correction period with a black correction value based on the difference. A data processing unit 22 (a) derives a density variation component for a modulation period of spectrum modulation on the basis of a reference board read value while lighting is turned off, and performs correction of image data on the basis of the density variation component, and (b) for every automatic black correction period, corrects the density variation component with an offset value that offsets the variation of the black correction value due to spread spectrum.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image processing apparatus.

Background Art

[0002] In order to suppress unnecessary radiation, an image processing apparatus uses a spectrum-spreading clock generator (SSCG). Since noise is generated in the line image data due to spectrum spreading and the image quality deteriorates, the noise component is extracted, and based on the value of the noise component, pixel data is corrected so that the noise component is suppressed (see, for example, Patent Document 1).

[0003] Specifically, the image processing apparatus: (a) In the analog front end, samples and holds the output signal of the image sensor with a sampling clock modulated by spectrum spreading to generate sampling data; (b) In the channel synthesis circuit, converts the sampling data into image data. Then, the image processing apparatus: (a) For each line, derives a line density fluctuation component from the difference between the reference plate reading value (image data) when the illumination is off and the reference plate reading value (image data) when the illumination is on, and the black reference data and the white reference data; (b) Corrects the line density fluctuation component by dividing the line density fluctuation component by the difference between the white reference data and the black reference data; (c) Derives the average of the corrected line density fluctuation components in a plurality of predetermined lines; (d) Generates a correction value for the image data by multiplying the average by the difference between the white reference data and the black reference data; (e) Corrects the image data based on the correction value. Thereby, the distribution of the density fluctuation component in the main scanning direction is specified without being affected by the uneven light distribution of the illumination.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When automatic black correction is performed in the analog front end, the difference between the average value of the output values of the OBP (Optical Black Pixel) region of the image sensor in each automatic black correction cycle and the reference value is derived, and black correction in the next automatic black correction cycle is performed using this difference.

[0006] Therefore, since the output values of the OBP region also vary due to the above-described spectrum diffusion, when the modulation period of the spectrum diffusion and the automatic black correction cycle are not the same, the average value of the output values of the OBP region varies for each automatic black correction cycle due to the spectrum diffusion.

[0007] FIG. 4 is a diagram for explaining the output values of the OBP region and the density distribution of the image data in the document reading region obtained when the period of the horizontal synchronization signal of the image sensor and the multiple of the modulation period of the spectrum diffusion are shifted by one pixel clock. FIG. 5 is a diagram for explaining the output values of the OBP region and the density distribution of the image data in the document reading region obtained when the period of the horizontal synchronization signal of the image sensor and the multiple of the modulation period of the spectrum diffusion are shifted by two pixel clocks.

[0008] For example, as shown in FIGS. 4 and 5, the automatic black correction cycle is fixed because it is the number of lines set in the analog front end, but depending on the modulation period of the spectrum diffusion, the period until the multiple of the modulation period matches the multiple of the period of the horizontal synchronization signal of the image sensor varies.

[0009] Therefore, the average value of the output values of the OBP region in each automatic black correction cycle varies depending on the modulation period of the spectrum diffusion and the phase difference between the modulation period and the automatic black correction cycle.

[0010] FIG. 6 is a diagram for explaining the variation of SS component data due to automatic black correction. As described above, due to spectral diffusion, the average value of the output value in the OBP region varies for each automatic black correction cycle. Accordingly, due to the variation of the correction value of automatic black correction due to spectral diffusion, the image data (read value) used for deriving the SS component data also varies, and the SS component data also varies as shown in FIG. 6, for example.

[0011] As described above, since the automatic black correction value of the analog front end varies due to spectral diffusion, it is difficult to appropriately suppress the density variation due to spectral diffusion in the image data.

[0012] The present invention has been made in view of the above problems, and an object thereof is to obtain an image processing apparatus that can appropriately suppress the density variation due to spectral diffusion in image data even if the automatic black correction value of the analog front end varies due to spectral diffusion.

Means for Solving the Problems

[0013] The image processing apparatus according to the present invention includes an image sensor that detects an image of a document or a reference plate, illumination that irradiates light onto the document or the reference plate, an SSCG circuit that generates an SS clock obtained by modulating a reference clock with a spectrum spread having a predetermined modulation period, an analog front end that sample-holds an output signal of the image sensor with a sampling clock generated from the SS clock to generate sampling data, a channel synthesis circuit that converts the sampling data into image data, and a data processing unit that processes the image data with a pixel clock generated based on the SS clock. The analog front end performs automatic black correction, and in the automatic black correction, a difference between an average value of output values of an OBP region of the image sensor in each automatic black correction period and a predetermined reference value is derived, and black correction in the next automatic black correction period is performed with a black correction value based on the difference. Then, the data processing unit (a) derives a density fluctuation component for a modulation period of the spectrum modulation based on a reference plate reading value when the illumination is turned off, and corrects the image data based on the density fluctuation component, and (b) corrects the density fluctuation component with an offset value that cancels a variation in the black correction value due to the spectrum spread for each automatic black correction period.

Advantages of the Invention

[0014] According to the present invention, an image processing apparatus can be obtained that appropriately suppresses density fluctuations due to spectrum spread in image data even when the automatic black correction value of the analog front end varies due to spectrum spread.

[0015] The above or other objects, features, and advantages of the present invention will become more apparent from the following detailed description together with the accompanying drawings.

Brief Description of the Drawings

[0016]

Figure 1

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DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0018] FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to an embodiment of the present invention. In this embodiment, the image processing apparatus shown in FIG. 1 is an image reading apparatus such as a scanner or a multifunction device, and includes an image reading unit 1 and a signal processing unit 2.

[0019] The image reading unit 1 includes an image sensor 11. The image sensor 11 is driven by a driving circuit 11a according to driving signals such as a clamp signal CP, a reset signal RS, a clock CCDCLK, and a shift pulse SH, receives an image of a document or a reference plate, and outputs an electrical signal corresponding to the document image.

[0020] FIG. 2 is a side view showing the internal configuration of the image reading unit 1 in FIG. 1. As shown in FIG. 2, the image reading unit 1 includes, in addition to the image sensor 11, a contact glass 12, carriages 13, 14, an imaging lens 15, a reference plate 16, and a document cover 17. The contact glass 12 is installed on the upper surface of the main body of the image reading unit 1, and the document is placed thereon. The carriage 13 is installed so as to be movable in the sub-scanning direction by a drive source (not shown). The carriage 13 has a light source 13a (illumination) that outputs irradiation light to the document or the reference plate and a mirror 13b. The light source 13a is, for example, a plurality of light-emitting diodes arranged along the main scanning direction. The light emitted from the light source 13a is reflected by the reference plate 16, the document placed on the contact glass 12, etc., according to the position of the carriage 13. The mirror 13b is an optical system that reflects the reflected light from the reference plate 16, the document, etc., and emits it in a predetermined direction toward the carriage 14. The carriage 14 reflects the light from the mirror 13b with the mirrors 14a, 14b and emits it to the imaging lens 15. The imaging lens 15 forms an image of the light from the carriage 14 on the image sensor 11.

[0021] The image sensor 11 receives the reflected light of the light emitted from the light source 13a through a predetermined optical system (here, the mirrors 13b, 14a, 14b and the imaging lens 15). The image sensor 11 outputs an electrical signal corresponding to the amount of received light for a plurality of pixels for each line. In this embodiment, a CCD (Charge Coupled Device), a CIS (CMOS Image Sensor), etc. are used as the image sensor 11.

[0022] The reference plate 16 is a plate-shaped member that is arranged along the main scanning direction on the top surface inside the apparatus and is used to acquire black and white reference data.

[0023] Returning to FIG. 1, the signal processing unit 2 includes an analog front end (AFE) 21, a data processing unit 22, an SSCG circuit 23, a timing signal generation circuit 24, and a processor 25. The data processing unit 22 includes a channel synthesis circuit 31, a correction circuit 32, an image processing unit 33, a reference data generation circuit 34, a reference memory 35, an SS component data generation circuit 36, and a component memory 37.

[0024] The analog front end (AFE) 21 is a circuit that performs sample and hold, AGC (Automatic Gain Control), and A / D (Analog to Digital) conversion.

[0025] The AFE 21 samples and holds the output signal of the image sensor 11 at a timing specified by a sampling clock generated from an SS clock described later, generates output data, and outputs it.

[0026] In this embodiment, the AFE 21 operates as a sample and hold unit that sample and holds the output signal of the image sensor 11, and performs sample and hold in the CDS (Correlated Double Sampling) method. Specifically, the AFE 21 samples two values according to a reset sampling clock SHR and a data sampling clock SHD, and outputs the difference between the two values.

[0027] Also, the AFE 21 performs automatic black correction. In automatic black correction, the AFE 21 derives the difference between the average value of the output values of the OBP region of the image sensor in each automatic black correction cycle and a predetermined reference value for each predetermined automatic black correction cycle, and performs black correction in the next automatic black correction cycle with a black correction value based on the difference. That is, black correction is performed so that the black level becomes the reference value, and the image data after black correction is supplied to the data processing unit 22.

[0028] The data processing unit 22 operates based on the pixel clock IMGCLK generated based on the SS clock described later, converts the output data into image data, and performs predetermined data processing on the image data. The pixel clock IMGCLK is generated by multiplying and dividing the SS clock.

[0029] In addition, the data processing unit 22 corrects the image data so as to suppress the SS component caused by the periodic variation of the SS clock.

[0030] Specifically, the data processing unit 22 synchronizes with the modulation of the SS clock, derives the density variation component for one modulation period from the difference between the reference plate reading value at the time of turning off the above-described illumination and the black reference data, and corrects the image data with the density variation component. Here, the SS component address n is generated in synchronization with the SS clock, and the density variation component is derived for each SS component address n.

[0031] The SSCG circuit 23 oscillates a reference clock with a fixed period, and generates a clock (SS clock) obtained by modulating the reference clock with spectrum spreading having a predetermined modulation period. For example, the SSCG circuit 23 modulates a 40 MHz reference clock with a modulation period of 2000 clock cycles and a modulation rate of center spread ±1% to generate an SS clock.

[0032] The timing signal generation circuit 24 generates a drive signal supplied to the drive circuit 11a and a clock signal (sampling clocks SHR, SHD, a clock ADCLK specifying the timing of A / D conversion, etc.) supplied to the AFE 21 based on the SS clock. For example, the timing signal generation circuit 24 multiplies and / or divides the SS clock with a predetermined multiplication setting value and / or division setting value to generate the above-described drive signal and clock signals such as the pixel clock IMGCLK.

[0033] The processor 25 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. It operates as various processing units by loading a program from the ROM or a storage device (not shown) into the RAM and executing it with the CPU. Here, the processor 25 operates as a controller 25a. The controller 25a performs settings such as the offset and gain of the AFE 21.

[0034] Also, in the data processing unit 22, the channel synthesis circuit 31 changes the order of the output data of the AFE 21 and outputs image data as RGB data along the scanning order.

[0035] The correction circuit 32 performs SS component correction and shading correction to suppress an error component (hereinafter referred to as the SS component) caused by the periodic variation of the SS clock described later on the above-mentioned image data.

[0036] The image processing unit 33 executes predetermined image processing on the image data after correction by the correction circuit 32 as needed.

[0037] The reference data generation circuit 34 generates reference data based on the image data when the reference plate 16 is read and stores it in the reference memory 35. The SS component data generation circuit 36 generates SS component data (that is, data indicating the SS component) based on the image data and the reference data when the reference plate 16 is read and stores it in the component memory 37. The correction circuit 32 corrects the image data using these reference data and component data.

[0038] Specifically, the correction circuit 32 performs shading correction using the first reference plate reading value obtained by reading the reference plate 16 with the image sensor 11 in the lighting-off state and the second reference plate reading value obtained by reading the reference plate 16 with the image sensor 11 in the lighting-on state, and also corrects the image data so as to suppress the SS component with the correction value based on the first reference plate reading value.

[0039] For example, the reference data generation circuit 34 generates black reference data (x) and white reference data (x) described later, writes them into the reference memory 35, the SS component data generation circuit 36 generates SS component data (n) described later as the density fluctuation component caused by spectrum diffusion, writes it into the component memory 37, and the correction circuit 32 derives the corrected image data (x) from the uncorrected image data (x) based on the black reference data (x) and white reference data (x) in the reference memory 35, the SS component data (n) in the component memory 37, etc. as described later.

[0040] SS component data (n) = AVEn[first reference plate reading value (x) - black reference data (x)]

[0041] Corrected image data (x) = (uncorrected image data (x) - black reference data (x) - black SS component data (n)) / (white reference data (x) - black reference data (x)) × maximum output data value

[0042] Here, n is the SS component address, which has a value that is counted up from 0 to the pixel clock IMGCLK within the modulation period. Note that the SS component address n is generated by the timing signal generation circuit 24 in synchronization with the pixel clock IMGCLK and supplied to the data processing unit 22 (such as the correction circuit 32 and the SS component data generation circuit 36). The number of SS component addresses n is, for example, the number of pixel clocks for the modulation period of SSCG and indicates the phase within the modulation period.

[0043] AVEn[] indicates the average value for a plurality of predetermined modulation periods for each SS component address n.

[0044] The black reference data (x) is a value obtained by averaging the pixel values of a plurality of predetermined lines when the reference plate 16 is read in the illumination off state for the main scanning pixel position x.

[0045] The white reference data indicates the light distribution of illumination in the main scanning direction (i.e., the light quantity distribution of illumination in the main scanning direction). The white reference data (x) is a value obtained by averaging the pixel values of a plurality of predetermined lines when the reference plate 16 is read in the illumination lighting state for the main scanning pixel position x.

[0046] When the image data is 10-bit data, the maximum output data value is 1023.

[0047] In this way, the correction circuit 32 of the data processing unit 22 corrects the image data based on the density fluctuation component (SS component data) for each pixel clock (SS component address). At this time, the correction circuit 32 of the data processing unit 22 corrects the density fluctuation component (SS component data) with an offset value that cancels out the variation of the black correction value due to spectral diffusion for each automatic black correction cycle.

[0048] Specifically, in the data processing unit 22, (a) the phase detection circuit 41 causes the (a1) AFE 21 to perform black correction with the black correction value fixed to a predetermined value during a predetermined offset setting period, (a2) specifies the sub-scanning direction variation period due to spectral modulation of the first reference plate reading value during the offset setting period, (a3) specifies the automatic black correction cycle based on the variation of the density peak value of each line of the first reference plate reading value, (b) the offset amount detection circuit 42 sets an offset value corresponding to the phase difference between the sub-scanning direction variation period and the automatic black correction cycle, and (c) the correction circuit 32 corrects the density fluctuation component (SS component data) read from the component memory 37 with the derived offset value, and corrects the image data based on the corrected density fluctuation component (SS component data).

[0049] Note that the sub-scanning direction variation period (start point and end point) due to spectral modulation is detected based on the periodicity of the first reference plate reading value. Also, although the density peak values within each automatic black correction cycle are substantially the same, the density peak values are different between automatic black correction cycles. Therefore, the line where the density peak value changes is detected as the boundary (start point and end point) between automatic black correction cycles.

[0050] At this time, the offset amount detection circuit 42 derives an offset value based on the average value of the density fluctuation component in the automatic black correction cycle.

[0051] FIG. 3 is a diagram for explaining the average value of the density fluctuation component caused by spectral diffusion in the automatic black correction cycle. FIG. 3 shows a case where the automatic black correction cycle for a certain SS component address (a certain pixel clock) has a time length that is 1.5 times the sub-scanning direction fluctuation cycle caused by spectral modulation.

[0052] For example, as shown in FIG. 3, even when the correction target value of the automatic black level correction is constant (for example, zero), due to the phase difference between the automatic black correction cycle and the sub-scanning direction fluctuation cycle caused by spectral modulation (that is, the start and end points of the multiple cycle (here, the double cycle) of the automatic black correction cycle and the start and end points of the multiple cycle (here, the triple cycle) of the sub-scanning direction fluctuation cycle caused by spectral modulation), the above-mentioned average value changes. Therefore, an offset value corresponding to this average value (that is, the phase difference) is set. Note that the correspondence relationship between this average value (phase difference) and the offset value is specified in advance based on experiments and the specifications of the AFE 21.

[0053] Although the time length of the multiple cycle of the automatic black correction cycle and the time length of the multiple cycle of the sub-scanning direction fluctuation cycle caused by spectral modulation are the same, since the automatic black correction and the spectral diffusion are not synchronized, there may be a certain phase difference. Therefore, due to this phase difference, the correction amount of the automatic black correction fluctuates for each automatic black correction cycle. Since this fluctuation repeats for each multiple cycle (here, the double cycle) of the above-mentioned automatic black correction cycle, the above-mentioned offset value is derived and set in advance for each automatic black correction cycle within this multiple cycle.

[0054] Next, the operation of the above image processing apparatus will be described.

[0055] The image sensor 11 outputs an electrical signal corresponding to a read image (such as a manuscript image or an image of the reference plate 16) for each line. The AFE 21 samples, holds, generates, and outputs the output signal of the image sensor 11 at a timing specified by a sampling clock generated from the SS clock by the timing signal generation circuit 24. The channel synthesis circuit 31 changes the order of the output data of the AFE 21 and outputs image data along the scanning order.

[0056] First, as described above, by reading the image of the reference plate 16, reference data and SS component data are derived as described above and set in the reference memory 35 and the component memory 37.

[0057] Also, as described above, offset values for each automatic black correction cycle within the doubling cycle during the above-described automatic black correction period are derived.

[0058] Thereafter, at the time of reading the image of the manuscript, the correction circuit 32 repeatedly corrects the SS component data with the offset value of each automatic black correction cycle as described above, and uses the reference data and the corrected SS component data to repeatedly perform SS component correction corresponding to each SS address n, and executes it on the image data of the manuscript together with shading correction. The image processing unit 33 executes and outputs predetermined image processing on the corrected image data.

[0059] As described above, according to the above embodiment, the analog front end 21 derives the difference between the average value of the output values of the OBP region of the image sensor in each automatic black correction cycle and a predetermined reference value in automatic black correction, and performs black correction in the next automatic black correction cycle with a black correction value based on the difference. Then, the data processing unit 22 (a) derives a density fluctuation component for the modulation period of the spectrum modulation based on the reference plate reading value when the illumination is turned off, and corrects the image data based on the density fluctuation component, and (b) corrects the density fluctuation component with an offset value that cancels the variation of the black correction value due to spectrum diffusion for each automatic black correction cycle.

[0060] As a result, even if the automatic black correction value of the analog front end 21 fluctuates due to spectrum diffusion, the density fluctuation due to spectrum diffusion in the image data is appropriately suppressed.

[0061] Various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing the intended advantages. That is, it is intended that such changes and modifications be included within the scope of the claims.

Industrial Applicability

[0062] The present invention is applicable to, for example, scanners, multifunction printers, etc.

Explanation of Signs

[0063] 11 Image sensor 13a Light source (an example of illumination) 16 Reference plate 21 Analog front end (AFE) 22 Data processing unit 23 SSCG circuit 31 Channel synthesis circuit

Claims

1. An image sensor that detects an image of a document or a reference plate, Lighting that irradiates light onto the document or the reference plate, An SSCG circuit that generates an SS clock in which a reference clock is modulated by spectrum diffusion with a predetermined modulation period, An analog front end that sample - holds an output signal of the image sensor with a sampling clock generated from the SS clock to generate sampling data, A channel synthesis circuit that converts the sampling data into image data, And a data processing unit that processes the image data with a pixel clock generated based on the SS clock, The analog front end performs automatic black correction. In the automatic black correction, an average value of output values of an OBP region of the image sensor in each automatic black correction period is derived, and a difference from a predetermined reference value is derived. Black correction in the next automatic black correction period is performed with a black correction value based on the difference. The data processing unit: (a) Derives a density fluctuation component for a modulation period of the spectrum modulation based on a reference plate reading value when the lighting is turned off, and corrects the image data based on the density fluctuation component; (b) Corrects the density fluctuation component with an offset value that cancels a variation in the black correction value caused by the spectrum diffusion for each automatic black correction period. An image processing apparatus characterized by the above.

2. The analog front end fixes the black correction value to a predetermined value and performs the black correction during a predetermined offset setting period. The data processing unit: (a) Identifies a sub - scanning direction variation period caused by the spectrum modulation based on the reference plate reading value during the offset setting period; (b) Identifies the automatic black correction period based on a variation in density peak values of each line of the reference plate reading value; (c) Sets the offset value corresponding to a phase difference between the sub - scanning direction variation period and the automatic black correction period. The image processing apparatus according to claim 1, characterized by the above.

3. The image processing apparatus according to claim 2, wherein the data processing unit derives the offset value based on an average value of the density fluctuation component in the automatic black correction cycle.

Images