Image Processing Device

Abstract

To provide an image reading apparatus which executes monochrome scanning using light with proper color balance ratios.SOLUTION: A driving circuit 26 drives light sources 12R, 12G, 12B. The light sources 12R, 12G, 12B emit light of a plurality of colors. An image sensor 11 is configured to scan an image on the basis of the light sequentially emitted by the light sources 12R, 12G, 12B. A controller 27a is configured to supply to the driving circuit 26 a command of light-emitting pulse widths of the light sources 12R, 12G, 12B. The controller 27 corrects the light-emitting pulse widths in monochrome scanning, on the basis of a rising time and a falling time of driving currents conducted through the light sources 12R, 12G, 12B by the driving circuit so that the light-emitting pulse widths may by equal to light-emitting pulse widths based on predetermined color balance ratios of the respective colors.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image processing device. [Background technology]

[0002] One image reading device detects the peak value and peak position of the read value of a white reference plate when the light source is on, adjusts the light intensity so that the peak value matches a target value, and sets the light intensity amplification factor based on the read value and peak value at the peak position when the light source is off (see, for example, Patent Document 1).

[0003] Another image reading device turns on light sources of multiple primary colors in sequence, reads the light from those light sources in sequence, and adjusts the width limit value of the pulse width modulation of each light source based on the difference between the reference data value obtained based on the light when the light is off and the reference data value obtained based on the light when the light is on (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-030971 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-216934 Summary of the Invention [Problem to be solved by the invention]

[0005] When performing monochrome reading with a light source switching image sensor module (such as a CIS (Contact Image Sensor) module), the controller uses a drive circuit to make each RGB (red, green, blue) light source emit light so that the light intensity is in accordance with a specified color balance ratio (for example, R light intensity: G light intensity: B light intensity = 3:6:1). For example, by making each RGB light source emit light at a constant light intensity level with a pulse width that corresponds to the color balance ratio of that color, the desired amount of light is emitted from each light source.

[0006] However, due to the response characteristics of the drive circuit and light source (e.g., LED (Light Emitting Diode)), even if the controller supplies a pulse width command to the drive circuit according to the color balance ratio, the pulse width of the light actually emitted from the light source may not conform to the color balance ratio. In particular, during monochrome scanning, if the color balance ratio of a certain color is low, there is a possibility that light of that color will not be emitted.

[0007] The present invention has been made in view of the above problems, and has as its object to provide an image reading device that performs monochrome reading with light having an appropriate color balance ratio. [Means for solving the problem]

[0008] The image reading device according to the present invention includes a plurality of light sources that emit light of a plurality of colors, an image sensor that reads an image based on the light emitted from the plurality of light sources in order, a drive circuit that drives the light sources, and a controller that supplies a command for the light emission pulse width of the light sources to the drive circuit. In the case of monochrome reading, the controller determines a light emission pulse width based on a predetermined color balance ratio for each of the plurality of colors. The light The light emission pulse width is corrected based on the rise time and fall time of the drive current conducted to the light source by the drive circuit so that: Here, the rise time is the time required for the drive current to rise to a predetermined first value, and the fall time is the time required for the drive current to fall to a predetermined second value. [Effects of the Invention]

[0009] According to the present invention, an image reading device that performs monochrome reading with light having an appropriate color balance ratio can be obtained.

[0010] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1]FIG. 1 is a block diagram showing the configuration of an image processing device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating the pulse width command signal during monochrome reading. [Figure 3] FIG. 3 is a diagram illustrating the rise time and fall time of the drive current. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] 1 is a block diagram showing the configuration of an image processing device according to an embodiment of the present invention. In this embodiment, the image processing device shown in FIG. 1 is an image reading device such as a scanner or a multifunction peripheral, and includes an image reading unit 1 and a signal processing unit 2.

[0014] The image reading unit 1 includes an image sensor 11 and light sources 12R, 12G, and 12B. The image sensor 11 is, for example, a CIS sensor, and is driven by a drive circuit 11a in accordance with drive signals such as a start pulse signal SP and a clock CLK, receives an original image, and outputs RGB electrical signals corresponding to the RGB original image through mutually different channels.

[0015] Image sensor 11 receives light emitted in sequence from multiple light sources 12R, 12G, and 12B and reflected from a target object such as a document via a predetermined optical system, and reads the image of the target object. Image sensor 11 outputs electrical signals corresponding to the amount of light received for multiple pixels for each line. Light sources 12R, 12G, and 12B are LEDs that emit light of multiple colors (here, the three primary colors of RGB).

[0016] The signal processing unit 2 includes an analog front end (AFE) 21, a channel combining circuit 22, a peak detecting unit 23, an image processing unit 24, a timing signal generating circuit 25, a driving circuit 26, and a processor 27.

[0017] 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. The AFE 21 samples and holds the output signal of the image sensor 11 at the timing specified by the sampling clock.

[0018] The channel synthesis circuit 22 changes the order of the output data of the AFE 21 and outputs the image data as RGB data in the scanning order.

[0019] The peak detection unit 23 detects the maximum and minimum pixel values ​​on each line for each of the RGB colors.

[0020] The image processing unit 24 performs predetermined image processing on the image data after shading correction, as necessary.

[0021] The timing signal generating circuit 25 generates a drive signal for the drive circuit 11a, a drive signal for the drive circuit 26, and the like.

[0022] FIG. 2 is a diagram illustrating the pulse width command signal during monochrome reading.

[0023] As shown in FIG. 2, for example, the drive circuit 26 drives the light sources 12R, 12G, and 12B with pulse width modulation signals (i.e., pulse signals with pulse widths) PWM_R, PWM_G, and PWM_B of each color, which are delayed by a predetermined amount in synchronization with the start pulse signal SP, thereby conducting drive currents to the light sources 12R, 12G, and 12B and causing the light sources 12R, 12G, and 12B to emit light in sequence.

[0024] The processor 27 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 programs from the ROM or a storage device (not shown) into the RAM and executing them on the CPU. Here, the processor 27 operates as a controller 27a.

[0025] The controller 27a supplies a command for the light emission pulse width of the light sources 12R, 12G, and 12B to the drive circuit 26. In this embodiment, the controller 27a uses a timing signal generation circuit to supply a command signal for the light emission pulse width (i.e., a pulse width modulation signal) to the drive circuit 26.

[0026] Furthermore, the controller 27a adjusts the amount of light (here, adjusts the light emission pulse width) during color reading based on the maximum and minimum values ​​for each of the RGB colors detected by the peak detection unit 23.

[0027] FIG. 3 is a diagram illustrating the rise time and fall time of the drive current. 3 illustrates the waveforms of the pulse width modulation signal (drive signal) PWM_B of the light source 12B for blue (B) and the drive current LED_B of the light source 12B. The same applies to colors other than blue (R, G).

[0028] 3, due to the characteristics of the drive circuit 26, a delay occurs in the rise of the drive current LED_B corresponding to the rise of the pulse width modulation signal (drive signal) PWM_B, and the rise of the drive current LED_B becomes gradual. Here, the time required for the drive current LED_B to rise to a predetermined threshold TH1 is defined as rise time Trise(B), and the time required for the drive current LED_B to fall to a predetermined threshold TH2 is defined as fall time Tfall(B), and the rise time Trise(B) and fall time Tfall(B) are determined in advance by experiment or the like. Note that these rise time and fall time may be set intentionally to suppress crosstalk.

[0029] Furthermore, in the case of monochrome reading, the controller 27a performs a color balance calculation based on a predetermined color balance ratio for each of the plurality of colors. lightThe light emission pulse width of each color is corrected based on the rise time and fall time of the drive current conducted to the light sources 12R, 12G, and 12B by the drive circuit so that: Note that the color balance ratio during monochrome reading is different from the color balance ratio during color reading.

[0030] Specifically, the controller 27a derives the light emission pulse widths Tpwm(mono_R), Tpwm(mono_G), Tpwm(mono_B) for each of the RGB colors during monochrome reading, for example, according to the following formula, from (a) the light emission pulse widths Tpwm(color_R), Tpwm(color_G), Tpwm(color_B) during color reading set by the above-mentioned light intensity adjustment, (b) the total light emission pulse widths for all of the multiple colors during monochrome reading, (c) the color balance ratios CB(mono_R), CB(mono_G), CB(mono_B), (d) rise times Trise(R), Trise(G), Trise(B), (e) fall times Tfall(R), Tfall(G), Tfall(B), etc.

[0031] Tpwm(mono_R)=(Tpwm(color_R)-Trise(R)+Tfall(R))×Rate(R)+Trise(R)-Tfall(R)

[0032] Tpwm(mono_G)=(Tpwm(color_G)-Trise(G)+Tfall(G))×Rate(G)+Trise(G)-Tfall(G)

[0033] Tpwm(mono_B)=(Tpwm(color_B)-Trise(B)+Tfall(B))×Rate(B)+Trise(B)-Tfall(B)

[0034] Here, Rate(R), Rate(G), and Rate(B) are conversion rates from the light emission pulse width during color reading to the light emission pulse width during monochrome reading, and are calculated according to the following formula based on the total value (fixed value) of the light emission pulse width during monochrome reading, the light emission pulse width during color reading, and the color balance ratio.

[0035] Rate(R)=(Tpwm(mono_R)+Tpwm(mono_G)+Tpwm(mono_B)) / Tpwm(color_R)×CB(mono_R)

[0036] Rate(G)=(Tpwm(mono_R)+Tpwm(mono_G)+Tpwm(mono_B)) / Tpwm(color_G)×CB(mono_G)

[0037] Rate(B)=(Tpwm(mono_R)+Tpwm(mono_G)+Tpwm(mono_B)) / Tpwm(color_B)×CB(mono_B)

[0038] Next, the operation of the image processing device will be described.

[0039] First, the controller 27a adjusts the amount of light during color reading, and sets the light emission pulse widths Tpwm(color_R), Tpwm(color_G), and Tpwm(color_B) during color reading.

[0040] Next, using the pre-specified color balance ratios CB(mono_R), CB(mono_G), CB(mono_B) for monochrome reading, the total value of the light emission pulse widths for monochrome reading, and the above-mentioned rise times Trise(R), Trise(G), Trise(B) and fall times Tfall(R), Tfall(G), Tfall(B), the controller 27a adjusts the light intensity for monochrome reading, and derives and sets the light emission pulse widths Tpwm(mono_R), Tpwm(mono_G), Tpwm(mono_B) for monochrome reading as described above, separately from the light emission pulse widths Tpwm(color_R), Tpwm(color_G), Tpwm(color_B) for color reading.

[0041] During color reading, the controller 27a uses the timing signal generating circuit 25 and the driving circuit 26 to cause the light sources 12R, 12G, and 12B to emit light with light emission pulse widths Tpwm(color_R), Tpwm(color_G), and Tpwm(color_B), thereby reading the color image.

[0042] On the other hand, during monochrome reading, the controller 27a uses the timing signal generating circuit 25 and the driving circuit 26 to cause the light sources 12R, 12G, and 12B to emit light with light emission pulse widths Tpwm(mono_R), Tpwm(mono_G), and Tpwm(mono_B), thereby reading the monochrome image.

[0043] As described above, according to the embodiment, the drive circuit 26 drives the light sources 12R, 12G, and 12B, which emit light of multiple colors. The image sensor 11 reads an image based on the light emitted sequentially from the light sources 12R, 12G, and 12B. The controller 27a supplies a command for the light emission pulse width of the light sources 12R, 12G, and 12B to the drive circuit 26. In the case of monochrome reading, the controller 27a corrects the light emission pulse width based on the rise time and fall time of the drive current conducted to the light sources 12R, 12G, and 12B by the drive circuit so that the light emission pulse width is based on a predetermined color balance ratio for each of the multiple colors.

[0044] As a result, the light emission pulse width is set taking into consideration the rise time and fall time of the drive current, so that even if there is a color with an extremely low color balance ratio in RGB during monochrome reading (for example, blue (B) when CB(mono_R)=3 / 10, CB(mono_G)=6 / 10, CB(mono_B)=1 / 10), the light source of that color will not be turned off, and monochrome reading will be performed with light of an appropriate color balance ratio.

[0045] 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 its intended advantages. In other words, it is intended that such changes and modifications be included within the scope of the claims.

[0046] For example, in the above embodiment, the controller 27a may advance the start time of the light emission pulses of each color when adjusting the light intensity for color reading by the above-mentioned rise times Trise(R), Trise(G), and Trise(B), respectively, thereby increasing the reading light intensity. [Industrial Applicability]

[0047] The present invention is applicable to, for example, scanners, multifunction peripherals, and the like. [Explanation of symbols]

[0048] 11 Image sensor 12R,12G,12B light source 26 Drive circuit 27a Controller

Claims

1. a plurality of light sources that emit light of a plurality of colors; an image sensor that reads an image based on light emitted sequentially from the plurality of light sources; a driving circuit for driving the light source; a controller that supplies a command for a light emission pulse width of the light source to the drive circuit; the controller, in the case of monochrome reading, corrects the light emission pulse width based on a rise time and a fall time of a drive current conducted to the light source by the drive circuit so that the light is based on a predetermined color balance ratio for each of the plurality of colors; the rise time is the time required for the drive current to rise to a predetermined first value; the fall time is the time required for the drive current to fall to a predetermined second value; An image reading device characterized by:

2. 2. The image reading device according to claim 1, wherein the controller advances the start time of a light emission pulse when adjusting the amount of light for color reading by the rise time.

3. 2. The image reading device according to claim 1, wherein the controller derives the light emission pulse width during monochrome reading from (a) the light emission pulse width during color reading, (b) the total value of the light emission pulse widths during monochrome reading for all of the multiple colors, (c) the color balance ratio, (d) the rise time, and (e) the fall time.

Images