Image processing apparatus

Abstract

To obtain an image processing apparatus that derives, in a relatively short time, a correction value that satisfactorily reduces a noise component caused by spread spectrum.SOLUTION: A data processing unit 22 (a) derives a weighted moving average value of a density variation component of pixel clocks from the difference between a reference board read value while lighting is turned off and black reference data in synchronization with modulation of an SS clock, (b) for every pixel clock, derives the average value of weighted moving average values for a plurality of modulation periods, and (c) and corrects image data on the basis of the average value of the weighted moving average values. Here, when each pixel clock is defined as a target clock, the weighted average of the density variation component of the target clock and the density variation components of predetermined number of peripheral clocks adjacent to the target clock is the weighted moving average value of the target clock, and a weighting factor of the density variation component of the target clock is larger than a weighting factor of the density variation component of the peripheral clock.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). However, noise is generated in line image data due to spectrum spreading, resulting in a decrease in image quality. Therefore, 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) derives a line density variation component for each line from the difference between the reference plate reading value when the illumination is off and the reference plate reading value when the illumination is on, and the black reference data and the white reference data, (b) corrects the line density variation component by dividing the line density variation component by the difference between the white reference data and the black reference data, (c) derives the average of the corrected line density variation 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, and (e) corrects the image data based on the correction value. As a result, the distribution of the density variation 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] In the above-described image processing apparatus, by deriving the average of the corrected line density fluctuation components in a plurality of lines, the noise components included in the correction value are reduced. At this time, the larger the number of lines, the smaller the noise components included in the correction value, but the time required to derive the correction value becomes longer.

[0006] The present invention has been made in view of the above problems, and an object thereof is to obtain an image processing apparatus that derives a correction value that preferably suppresses noise components caused by spectrum diffusion in a relatively short time.

Means for Solving the Problems

[0007] 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 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. Then, the data processing unit (a) derives a weighted moving average value of the density fluctuation components of each pixel clock from the difference between the reference plate reading value at the time of turning off the illumination and the black reference data in synchronization with the modulation of the SS clock, (b) derives an average value of the weighted moving average values for a plurality of modulation periods for each pixel clock, and (c) corrects the image data based on the average value of the weighted moving average values. Here, the weighted average of the density fluctuation component of the target clock and the density fluctuation components of a predetermined number of peripheral clocks adjacent to the target clock when each pixel clock is the target clock is the weighted moving average value of the target clock, and the weighting coefficient of the density fluctuation component of the target clock is larger than the weighting coefficient of the density fluctuation component of the peripheral clock.

Effects of the Invention

[0008] According to the present invention, an image processing apparatus can be obtained that derives a correction value for satisfactorily suppressing noise components caused by spectrum diffusion in a relatively short time.

[0009] 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

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0012] Embodiment 1.

[0013] 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.

[0014] The image reading unit 1 includes an image sensor 11. The image sensor 11 is driven by a drive circuit 11a according to drive signals such as a clamp signal CP, a reset signal RS, a clock CCDCLK, and a shift pulse SH, receives the image of a document or a reference plate, and outputs an electrical signal corresponding to the document image.

[0015] Figure 2 is a side view showing the internal configuration of the image reading unit 1 in Figure 1. As shown in Figure 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.

[0016] 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.

[0017] 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.

[0018] 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, a component memory 37, a weighted moving average calculation circuit 41, an amplitude adjustment coefficient calculation circuit 42, and an amplitude adjustment unit 43.

[0019] 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.

[0020] 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.

[0021] For example, 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.

[0022] The data processing unit 22 operates with a pixel clock IMGCLK generated based on an 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.

[0023] Also, 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.

[0024] Specifically, the data processing unit 22 derives a density fluctuation 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 in synchronization with the modulation of the SS clock, and corrects the image data with the density fluctuation component. Here, the SS component address n is generated in synchronization with the SS clock, and the density fluctuation component is derived for each SS component address n.

[0025] 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.

[0026] 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 a pixel clock IMGCLK.

[0027] The processor 25 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., and operates as various processing units by loading a program from the ROM and 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 sets the offset and gain of the AFE 21.

[0028] 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.

[0029] The correction circuit 32 performs SS component correction and shading correction for suppressing an error component (hereinafter referred to as an SS component) caused by the periodic variation of the SS clock described later on the above-described image data.

[0030] The image processing unit 33 executes predetermined image processing on the image data after correction by the correction circuit 32 as necessary.

[0031] 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.

[0032] Specifically, the correction circuit 32 corrects the image data so as to suppress the SS component using the reference plate reading value obtained by reading the reference plate 16 with the image sensor 11 in the lighting-off state.

[0033] For example, the reference data generation circuit 34 generates black reference data (x) and white reference data (x) described later and writes them into the reference memory 35, and the SS component data generation circuit 36 generates SS component data SS0(n) as a density variation component caused by spectrum diffusion by the following equation.

[0034] SS0(n)=AVEn[reference plate reading value (x) - black reference data (x)]

[0035] n is an SS component address, and has a value that is counted up from 0 to the pixel clock IMGCLK within the modulation period. The SS component address n is generated in synchronization with the pixel clock IMGCLK by the timing signal generation circuit 24 and supplied to the data processing unit 22 (correction circuit 32, SS component data generation circuit 36, etc.).

[0036] AVEn[] indicates the average value for a plurality of predetermined modulation periods for each SS component address n.

[0037] 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 lighting-off state for the main scanning pixel position x.

[0038] 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.

[0039] In this way, for each modulation period, SS component data is derived for each SS component address (that is, pixel clock).

[0040] The weighted moving average calculation circuit 41 derives the weighted moving average value SS1(n) of the above-mentioned density fluctuation component (that is, SS component data SS0(n)) for each pixel clock (that is, for each SS component address n) by the following formula. That is, when each pixel clock is the target clock (SS component address n), the weighted average of the density fluctuation component SS0(n) of the target clock n and the density fluctuation components SS0(i) of a predetermined number k of peripheral clocks i adjacent to the target clock n (i = n - k, ···, n - 1, n + 1, ···, n + k) is defined as the weighted moving average value SS1(n) of the target clock n.

[0041] SS1(n)=(SS0(n - k)+···+SS0(n - 1)+ω0×SS0(n)+SS0(n + 1)+···+SS0(n + k)) / (2k + ω0)

[0042] Here, ω0 is the weight coefficient of SS0(n) (here, ω0 = k = 8). Note that the weight coefficients of SS0(n - k), ···, SS0(n - 1), SS0(n + 1), ···, SS0(n + k) are 1. In this way, in the weighted average, the weight coefficient ω0 of the density fluctuation component SS0(n) of the target clock is set larger than the weight coefficients of the density fluctuation components SS0(i) of the peripheral clocks. Also, for example, ω0 is set the same as k.

[0043] Then, the weighted moving average calculation circuit 41 derives the average value SS1av(n) of the weighted moving average values SS1(n) for a plurality of modulation periods for each pixel clock n.

[0044] The data processing unit 22 corrects the image data based on the average value SS1av(n) of the weighted moving average value SS1(n).

[0045] Here, SS1av(n) is amplitude-adjusted by the amplitude adjustment coefficient calculation circuit 42 and the amplitude adjustment unit 43, and the amplitude-adjusted SS1av(n) is written into the component memory 37. Note that this amplitude adjustment is executed as necessary and may not be executed in some cases. Details of the amplitude adjustment will be described later.

[0046] The correction circuit 32 derives the corrected image data (x) from the uncorrected image data (x) by the following formula based on the black reference data (x) and white reference data (x) in the reference memory 35, SS1av(n) in the component memory 37, etc.

[0047] Corrected image data (x) = (Uncorrected image data (x) - Black reference data (x) - SS1av(n)) / (White reference data (x) - Black reference data (x)) × Maximum output data value

[0048] Here, the white reference data (x) is a value obtained by averaging the pixel values of a predetermined plurality of lines when the reference plate 16 is read in the illumination lighting state for the main scanning pixel position x. The maximum output data value is 1023 when the image data is 10 bits.

[0049] Here, the above-mentioned amplitude adjustment will be described.

[0050] As described above, since the weighted moving average is performed on the SS component data, the waveform of the SS component data is smoothed. Therefore, the amplitude of the waveform of the SS component data may be smaller than the original amplitude. Therefore, the amplitude adjustment is executed to make the amplitude of the waveform of the SS component data the original amplitude.

[0051] The amplitude adjustment coefficient calculation circuit 42 derives (a) the average value of the density fluctuation component SS0(n) for a predetermined number of modulation periods for each pixel clock n, (b) identifies the amplitude SS0amp of the waveform of the average value SS0av(n) of the density fluctuation component SS0(n) in the modulation period, (c) identifies the amplitude SS1amp of the waveform of the average value SS1av(n) of the weighted moving average value in the modulation period, (d) sets the ratio (SS0amp / SS1amp) of the amplitude SS0amp of the density fluctuation component and the amplitude SS1amp of the weighted moving average value as the amplitude adjustment coefficient CA, and (e) adjusts the weighted moving average value with the amplitude correction coefficient CA as follows.

[0052] SS1av(n) after amplitude adjustment = SS1av(n) before amplitude adjustment × CA

[0053] For example, the above-mentioned predetermined number (the number of variation periods when deriving the amplitude adjustment coefficient CA) is larger than the number of modulation periods when deriving the average value of the weighted moving average value, and the amplitude adjustment coefficient CA is derived in advance. That is, in this case, in the ready state of the image processing apparatus or the like, by increasing the number of modulation periods to derive the amplitude adjustment coefficient CA, the noise components in the average values SS0av and SS1av when deriving the amplitude adjustment coefficient CA are reduced, and an accurate amplitude adjustment coefficient CA can be obtained.

[0054] Alternatively, for example, the above-mentioned predetermined number (the number of variation periods when deriving the amplitude adjustment coefficient CA) is made the same as the number of modulation periods when deriving the average value SS1av(n) of the weighted moving average value, and the amplitude adjustment coefficient CA is derived in parallel with the derivation of the average value SS1av(n) of the weighted moving average value. That is, in this case, it is not necessary to derive the amplitude adjustment coefficient CA in advance as described above.

[0055] Next, the operation of the above image processing apparatus will be described.

[0056] The image sensor 11 outputs an electrical signal corresponding to a read image (such as a document 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 the image data along the scanning order.

[0057] First, as described above, by reading the image of the reference plate 16, the average values of the weighted moving average of the reference data and the SS component data are obtained as described above and set in the reference memory 35 and the component memory 37.

[0058] After that, at the time of reading the image of the document, the correction circuit 32 repeatedly performs SS component correction corresponding to each SS address n using the average values of the weighted moving average of the reference data and the SS component data as described above, and executes it on the image data of the document together with shading correction. The image processing unit 33 executes predetermined image processing on the corrected image data and outputs it.

[0059] As described above, according to the first embodiment, the data processing unit 22 derives (a) the weighted moving average value of the density fluctuation component of each pixel clock from the difference between the reference plate reading value at the time of turning off the illumination and the black reference data in synchronization with the modulation of the SS clock, (b) derives the average value of the weighted moving average values for a plurality of modulation periods for each pixel clock, and (c) corrects the image data based on the average value of the weighted moving average values. Here, the weighted average of the density fluctuation component of the target clock and the density fluctuation components of a predetermined number of peripheral clocks adjacent to the target clock when each pixel clock is the target clock is the weighted moving average value of the target clock, and the weighting coefficient of the density fluctuation component of the target clock is larger than the weighting coefficient of the density fluctuation component of the peripheral clock.

[0060] As a result, a correction value that can satisfactorily suppress the noise component caused by spectrum diffusion is derived in a relatively short time.

[0061] FIG. 3 is a diagram for explaining the effect of the weighted moving average of the SS component data. For example, as shown in FIG. 3, when the number of modulation periods for extracting the SS component data is increased by the weighted moving average, the noise component is suppressed in the same manner as when the number of modulation periods for extracting the SS component data is increased. Therefore, the number of modulation periods for extracting the SS component data can be reduced, and the correction value of the image data can be obtained in a relatively short time.

[0062] Embodiment 2.

[0063] In Embodiment 2, the data processing unit 22 applies the correction data for one modulation period of the SS clock within the above-described correction period a predetermined integer (K) number of times to the image data to correct the image data for one correction period. That is, in Embodiment 2, the number of SS component addresses n is the number of pixel clocks for one modulation period.

[0064] FIG. 4 is a diagram for explaining the correction of image data in the image processing apparatus according to Embodiment 2. In Embodiment 2, the correction data for one modulation period of the SS clock (that is, the SS component data corresponding to the SS addresses 0 to N) is generated in advance, and the SS component data corresponding to the SS addresses 0 to N for one modulation period is repeatedly applied to correct the image data (the pixel data sequence along the main scanning direction).

[0065] The modulation period is detected as follows. A predetermined division setting value is cumulatively added for each clock of the pixel clock IMGCLK, and the modulation period is defined as the period until the cumulative sum value of the division setting values becomes equal to or greater than the multiple clock number for the modulation period (= multiple setting value × number of SS clocks for one modulation period) from the initial value of 0. Then, the difference (fractional part) between the value when the cumulative sum value of the division setting values becomes equal to or greater than the multiple clock number and the multiple clock number is set as the initial value of the cumulative sum value of the division setting values for the next modulation period. Here, the division setting value and the multiple setting value are the setting values when generating the pixel clock IMGCLK by dividing and multiplying the SS clock.

[0066] At that time, for example, as shown in FIG. 4 (where K = 3) in a certain modulation period #i, the difference (fraction di) between the time point after one pixel clock from the last SS address n (n = N) for one modulation period and the end point of the modulation period causes an error in the main scanning direction pixel position between the component data (i.e., SS address) and the image data by that fraction di in the next modulation period #(i + 1). However, since that error is always less than one pixel clock, there is no significant decrease in the correction accuracy.

[0067] In Embodiment 2, as described above, the number of pixel clocks is set corresponding to the modulation period, and the data processing unit 22 acquires the value of the image data for each pixel clock. Then, as described above, when the value obtained by multiplying the number of clocks by the clock period does not match the number of clocks that is a multiple of the modulation period, the data processing unit 22 derives the value of the image data for the pixel clock N outside the modulation period (pixel clock N in modulation period #2 in FIG. 4) from the value of the image data for the final pixel clock N - 1 within the modulation period and the value of the image data for the first pixel clock 0 of the next modulation period (here, as the average value of both).

[0068] As a result, the same number of image data for the pixel clock N outside the modulation period as that for the pixel clock N - 1 within the modulation period can be obtained. Therefore, the image data for the pixel clock N outside the modulation period does not decrease, and the SS component data (N) when deriving the average value SS1av(N) of the weighted moving average value SS1(N) of the SS component data (N) does not decrease, and the noise component in the average value SS1av(N) is suppressed to be equivalent to the noise components in the average values SS1av(n) of the other pixel clocks.

[0069] Note that since the other configurations and operations of the image processing apparatus according to Embodiment 2 are the same as those of Embodiment 1, the description thereof is omitted.

[0070] It should be noted that 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

[0071] The present invention is applicable to, for example, scanners, multifunction printers, and the like.

Explanation of Signs

[0072] 11 Image sensor 13a Light source (an example of illumination) 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 the 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 data processing unit: (a) synchronously with the modulation of the SS clock, derives a weighted moving average value of the density fluctuation component of each pixel clock from the difference between the reference plate reading value at the time of turning off the lighting and the black reference data; (b) derives an average value of the weighted moving average values for a plurality of modulation periods for each pixel clock; (c) corrects the image data based on the average value of the weighted moving average values, The weighted average of the density fluctuation component of the target clock and the density fluctuation components of a predetermined number of peripheral clocks adjacent to the target clock when each pixel clock is the target clock is the weighted moving average value of the target clock, The weight coefficient of the density fluctuation component of the target clock is larger than the weight coefficient of the density fluctuation component of the peripheral clock, An image processing apparatus characterized by the above.

2. The data processing unit: (a) derives an average value of the density fluctuation components for a predetermined number of modulation periods for each pixel clock; (b) specifies the amplitude of the waveform of the average value of the density fluctuation components in the modulation period; (c) specifies the amplitude of the waveform of the average value of the weighted moving average values in the modulation period; (d) uses the ratio between the amplitude of the density fluctuation component and the amplitude of the weighted moving average value as an amplitude adjustment coefficient; (e) adjusts the weighted moving average value with the amplitude correction coefficient. The image processing apparatus according to Claim 1, characterized by the above.

3. The predetermined number is larger than the number of modulation periods when deriving the average value of the weighted moving average value, The amplitude adjustment coefficient is derived in advance, The image processing apparatus according to claim 2, characterized in that.

4. The predetermined number is the same as the number of modulation periods when deriving the average value of the weighted moving average value, The amplitude adjustment coefficient is derived in parallel with the derivation of the average value of the weighted moving average value, The image processing apparatus according to claim 2, characterized in that.

5. The number of clocks of the pixel clock is set corresponding to the modulation period, The data processing unit: (a) acquires the value of the image data for each pixel clock; (b) when the value obtained by multiplying the number of clocks by the clock period does not match the number of clocks that is a multiple of the modulation period, the value of the image data for the pixel clock outside the modulation period is derived from the value of the image data for the final pixel clock within the modulation period and the value of the image data for the first pixel clock of the next modulation period, The image processing apparatus according to claim 1, characterized in that.

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