JP3591183B2 - Afterimage detection method and afterimage detection device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an afterimage detection method and an afterimage detection apparatus for detecting an afterimage of at least one line of an image sensor that accumulates electric charge in accordance with irradiated light.
[0002]
[Prior art]
A so-called linear sensor in which an image pickup device such as a CCD is arranged one-dimensionally is provided. The linear sensor is an element formed by combining an image sensor and a shift register arranged one-dimensionally, and transfers an image at each point detected by each image sensor to the shift register in units of one line. One line is sequentially read from the register as an output signal every time. This one-line output signal forms a one-dimensional image.
[0003]
The linear sensor can also sequentially read a two-dimensional image line by line by moving the linear sensor in a direction perpendicular to the one-dimensional direction of the linear sensor. The linear sensor is widely used in such applications as a sensor for reading a document in a facsimile, a scanner, a digital copy, and the like.
[0004]
One of the characteristics of the linear sensor is an afterimage characteristic. In general, a linear sensor converts irradiated light into electric charges in each image sensor, and transfers the electric charges to the shift register via a gate. However, when the transfer time is short or the transfer electric field is weak, the generated charges may not be completely transferred to the shift register within a desired time.
[0005]
In such a case, the charge remaining on each image sensor without being transferred will be mixed in the subsequent transfer. That is, the afterimage means that the output signal of the previous line is mixed with the output signal of one line from the linear sensor. The reasons why the charge is not completely transferred include a problem in the structure of the linear sensor and a factor such as a short time during which the read gate is open.
[0006]
The afterimage characteristics are important characteristic evaluation items for evaluating the performance of the linear sensor. For example, in the case of using a linear sensor for reading a two-dimensional image in a device such as the above-described facsimile, if a linear sensor having a different afterimage characteristic is used for each pixel, the image becomes uneven. In addition, the presence of an afterimage may cause deterioration of characteristics at the time of small exposure.
[0007]
In the evaluation of the afterimage characteristics, an intermittent light source such as a strobe light source is usually used. After irradiating the linear sensor with light for a predetermined time using this light source, one line of electric charge is read out from the linear sensor, and the one line is read out. The after-image characteristic is evaluated by detecting the after-image from the charge of one line read next to the image.
[0008]
FIG. 9 shows a timing chart of a method for detecting an afterimage using such an intermittent light source. In the figure, in order from top to bottom, a readout gate control signal φROG of a fixed cycle for controlling the transfer of one line of charge from the linear sensor, a light source control signal φSTB for controlling light emission of a strobe light, and an output signal V _OUT The waveforms of the respective signals are shown.
[0009]
Here, “ON” and “OFF” on the left side of the waveform of the light source control signal φSTB represent the “ON” and “OFF” potentials of the light source. Further, the output signal V _OUT "V" on the left side of the waveform of _RS "And" V _OS "Represents a" reset level "and an" offset level ", respectively.
[0010]
The linear sensor transfers charges of one line at the timing of the pulse of the readout gate control signal φROG, and the charges of one line are sequentially output. That is, the charges on each of the “A line” and the “B line” in FIG. _OUT "A line output" and "B line output".
[0011]
The light source of the intermittent light emission is controlled by the light source control signal φ by the “A line”. _STB And emits light in response to the pulse of "ON", and irradiates the linear sensor with light for a predetermined time. The linear sensor converts this light into electric charge, and the electric charge of this one line is output signal V _OUT Is output at the next “A line output”. This output signal V _OUT In the "A line output" cycle, the amplitude increases and the offset potential V _OS Above the negative side corresponds to the charge read from the linear sensor.
[0012]
The output signal V _OUT In the "A line output" period, a local decrease in the amplitude is seen in the uniformly increased amplitude portion A3. This local decrease in amplitude occurred because some of the charge stored in the linear sensor was not completely transferred. The charge remaining without being transferred is read out in the next line.
[0013]
In the "B line", the linear sensor is not irradiated with light and no electric charge is accumulated. Therefore, in the "B line output", only the electric charge remaining without being transferred as described above is read. This is the output signal V _OUT This appears as a local increase in the amplitude, as shown by the portion B3 in FIG.
[0014]
As described above, after irradiating the linear sensor with the intermittent light on the “A line”, the charges on this line are transferred and read out by the “A line output”, and the “B line” corresponding to the “B line” not irradiated with the light is read out. Line output ”, and the output signal V of this“ B line output ” _OUT By examining the change in the amplitude of the image, the charge of the afterimage can be detected.
[0015]
Here, enlarged views in the vicinity of the portion A3 and the portion B3 in FIG. 9 are shown in FIGS. 10A and 10B, respectively. Each pulse in the figure corresponds to each sensor constituting the linear sensor. Therefore, in the sensors corresponding to the portion A3 and the portion B3, it can be seen that the amount of charge read out is decreasing or increasing.
[0016]
Next, FIG. 11 shows a timing chart when there is no afterimage in the method of detecting an afterimage using a light source of intermittent light emission. In the figure, the readout gate control signal φROG, the light source control signal φSTB, and the output signal V _OUT The waveforms of the respective signals are shown. The output signal V _OUT At the points A4 and B4, the local decrease and increase of the amplitude as seen at the points A3 and B3 in FIG. 9 when there is the afterimage described above is not seen.
[0017]
12A and 12B are enlarged views of the vicinity of the portion A4 and the portion B4, respectively. Since the pulse amplitude is constant, it can be seen that the charge transferred from each sensor is constant and there is no afterimage.
[0018]
[Problems to be solved by the invention]
As described above, in the conventional method for detecting the afterimage of the linear sensor, a light source of intermittent light emission such as a strobe light source is used.
[0019]
However, such intermittent light sources are generally expensive. The intermittent light source is troublesome to handle and has a short life. In addition, the light source of the intermittent light emission is used exclusively for the evaluation of the afterimage characteristic of the linear sensor, and has few other uses. Therefore, there is a problem in terms of equipment efficiency. Further, the evaluation of the afterimage characteristic of the linear sensor is limited to a place where the light source for the intermittent light emission is provided.
[0020]
In view of the above circumstances, the present invention provides an afterimage evaluation method for evaluating an afterimage characteristic of a linear sensor without using an intermittent light source such as a strobe light source, and a linear image sensor without the intermittent light source. An afterimage evaluation device for evaluating an afterimage characteristic of a sensor is provided.
[0021]
[Means for Solving the Invention]
In order to solve the above-mentioned problem, the afterimage detection method according to the present invention provides a method in which at least one line of an image pickup element that accumulates electric charge in accordance with the amount of light irradiated is irradiated with light for a first accumulation time. A first readout step of sequentially reading out the charges of the first order, and a second readout of sequentially reading out the charges of one line after irradiating the image sensor with light for a second accumulation time different from the first accumulation time. And detecting a charge of an afterimage from the charge of each line read in the first readout step and the second readout step.
[0022]
According to the present invention, after irradiating the image pickup device provided with at least one line for accumulating electric charges according to the irradiated light amount for a first accumulation time, one line is read in a first reading step. Are sequentially read out, and after irradiating the image sensor with light for a second storage time different from the first storage time, the charges of one line are sequentially read out in a second readout step, and an afterimage is formed. In the charge detection step, the charge of one line read in the first read step is compared with the charge of one line read in the second read step to detect the charge of an afterimage. .
[0023]
Further, in the afterimage detection method according to the present invention, the first accumulation time is longer than the second accumulation time, and an afterimage is detected from the charge of one line read in the second reading step. It was done. Further, in the afterimage detection method according to the present invention, the image pickup device includes a solid-state image pickup device.
[0024]
According to the present invention, the charge accumulated in the first accumulation time having a long accumulation time is read out in the first reading step, and the charge of the afterimage is accumulated in the second accumulation time having a short accumulation time. The charges are read out together with the charges in the second reading step, and the charges of the afterimage are detected from the charges of one line read in the second reading step. In addition, a solid-state image sensor is used as the image sensor.
[0025]
In order to solve the above problem, an afterimage detection apparatus according to the present invention includes: a light irradiation unit configured to irradiate at least one line of an imaging element that accumulates electric charge in accordance with the amount of irradiated light with light of a predetermined intensity; Charge readout means for sequentially reading out one line of charge from the image pickup device at a predetermined timing; and one line of charge read out from the image pickup device irradiated by the light irradiation means after the first accumulation time by the charge readout means And an afterimage charge detection unit for detecting an afterimage charge from the charge of one line read by the charge read unit after the second accumulation time.
[0026]
In the present invention, the image pickup element that accumulates electric charges in accordance with the irradiated light provided on at least one line is irradiated with light by light irradiation means, and the electric charge of the one line is read by electric charge reading means. Irradiating the image sensor with light for a first accumulation time to read out one line of charge, and irradiating the imager with light for a second accumulation to read out one line of charge; In this method, after-image charges are detected from these one-line charges.
[0027]
Further, in the afterimage detecting apparatus according to the present invention, the first accumulation time is longer than the second accumulation time. Further, in the afterimage detection apparatus according to the present invention, the afterimage charge detection means detects an afterimage charge from the charge of one line read after the second accumulation time.
[0028]
According to the present invention, the charge accumulated in the first accumulation time having a long accumulation time is read out in the first reading step, and the charge of the afterimage is accumulated in the second accumulation time having a short accumulation time. The charge is read out together with the charge in the second readout step, and the charge of the afterimage is detected from the charge of this one line.
[0029]
In the afterimage detection apparatus according to the present invention, the image pickup device is a solid-state image pickup device, and the light irradiation unit uses a continuous light source.
[0030]
According to the present invention, a solid-state imaging device is used as the imaging device, and a continuous light source is used as the light irradiation unit.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a residual image detection method and a residual image detection device according to the present invention will be described with reference to the drawings.
[0032]
As shown in FIG. 1, the afterimage detection device according to the present invention includes a light irradiation unit 1, a control unit 2, a monitor unit 3, and a sensor unit 10.
[0033]
The light irradiation unit 1 includes a continuous light source such as a fluorescent lamp, and irradiates the sensor unit 10 with light having a predetermined intensity. The sensor unit 10 converts light emitted from the light irradiating unit 1 into electric charges by an image sensor arranged one-dimensionally, and reads out the electric charges line by line according to a clock supplied from the control unit. It is supplied to the monitor unit 3. The monitor unit 3 displays an output signal supplied from the sensor unit on a display screen.
[0034]
Next, FIG. 2 shows the structure of the sensor unit 10. Here, the sensor unit 10 is configured on a single chip by integrating a CCD image pickup device and its peripheral circuits.
[0035]
The sensor unit 10 includes a plurality of one-dimensionally arranged sensors 11, a plurality of dummy sensors 12 disposed at both ends of the one-dimensionally arranged sensor 11, and a charge transfer from the sensor 11. A readout gate 13 for controlling transfer, a CCD analog sensor 14 for receiving charges from the sensor 11 via the readout gate 13, an output amplifier for processing an output signal from the CCD analog shift register 13, and It comprises a sample and hold circuit 15, a first timing generator 16 for giving a reset timing to the CCD analog shift register 14, and a second timing generator 17 for giving a readout gate control timing to the readout gate 13. You.
[0036]
The sensor section includes a reset terminal 51 for providing a reset signal φRS to the CCD analog shift register via the first timing generator 16 as a terminal, and a sample / hold signal φS / H and a sample-and-hold terminal 52 for applying H and an output signal V from the output and sample-and-hold circuit 15 _OUT , A ground terminal 54, a power supply terminal 55, a first clock terminal 56 for supplying a first clock φ1 to the CCD analog shift register 14, and the CCD analog shift register A second clock terminal 57 for supplying a second clock φ2 having a phase different from that of the first clock, and a readout gate control for giving a charge transfer timing to the readout gate 13 via the second timing generator 17 And a readout gate control terminal 58 for transmitting a signal φROG.
[0037]
A predetermined number of the sensors 11 are arranged one-dimensionally, and a predetermined number of the dummy sensors 12 are arranged one-dimensionally at both ends of the arranged sensors. Each of the sensors 11 arranged one-dimensionally converts light irradiated at each irradiated point into electric charges and accumulates the charges. The readout gate 13 converts the electric charge accumulated in the sensor 11 into the CCD analog signal in accordance with the timing at which the readout gate control signal φROG is supplied from the readout gate control terminal 58 via the second timing generator 17. The data is transferred to the shift register 14.
[0038]
The CCD analog shift register 14 is provided so that each element corresponds to each element of the sensor 11 with the readout gate 13 interposed therebetween. The CCD analog shift register 14 receives charges transferred from the sensor 11 line by line via the readout gate 13. Then, the charges of this one line are sequentially read out according to the clock. Here, a two-phase clock of a first clock φ1 supplied from the first clock terminal 56 and a second clock φ2 supplied from the second clock terminal 57 is used. A phase or four phase clock may be used. The sensor 11 and the dummy sensor 12, the readout gate 13, and the CCD analog shift register 14 arranged one-dimensionally constitute a linear sensor as an integral unit. Sometimes you take.
[0039]
The output amplifier and sample hold circuit 15 processes the output signal read from the CCD analog shift 14. That is, the output signal is amplified to a predetermined level, and the output signal is sample-held according to the timing of the sample-hold signal φS / H supplied from the sample-hold terminal 52. The output signal V thus processed _OUT Is supplied to the output terminal 53.
[0040]
The first timing generator 16 adjusts a reset signal φRS supplied from the reset terminal 51 and gives a reset timing to the CCD analog shift register 14. The second timing generator 17 gives a timing to open the readout gate 58 from a readout gate control signal φROG supplied from the readout gate control terminal 58. Although the first timing generator 17 and the second timing generator 17 have independent configurations, they may have an integrated configuration including a portion that generates another timing signal.
[0041]
Subsequently, FIG. 3 shows an example of a clock timing chart showing a time relationship between each signal of a signal supplied to each terminal of the sensor unit 10 and an output signal from the sensor unit and a time relationship of each signal. Show. Here, the output signal V _OUT Does not perform sample hold. From the top to the bottom of the figure, the readout gate control signal φROG, the first clock signal φ1, the second clock signal φ2, the reset signal φRS, and the output signal V _OUT The waveforms of the respective signals are shown. The numbers shown on the left side of the waveforms of the signals indicate the potentials of 5V and 0V.
[0042]
The readout gate control signal φROG controls the readout gate 13 to transfer charges accumulated in accordance with the light irradiated on each element of the sensor 11 to the CCD analog shift register 14 for one line. The timing of transfer as a unit is given via the second timing generator 17. The charge transferred to the CCD analog shift register 14 based on the pulse timing of the readout gate control signal φROG is converted into an output signal V in accordance with a two-phase clock of the first clock φ1 and the second clock φ2. _OUT Are sequentially read out one line. When the charge of one line is read from the CCD analog shift register 14, the charge of one line is again transferred from each element of the sensor 11 to the CCD analog shift register 14 based on the pulse timing of the readout control signal φROG. Will be transferred.
[0043]
The output signal V _OUT Is an output signal of one line which is output from the CCD analog shift register 14 and processed by the output amplifier section and the sample hold circuit 15. However, since the sample hold is not performed here, this output signal V _OUT Is pulsed. Note that this output signal V _OUT With respect to, the upper limit potential on the positive side is the reference potential.
[0044]
The output signal V _OUT The indices “D” and “S” shown above each pulse indicate that each pulse corresponds to the dummy sensor 12 and the sensor 11. That is, this output signal is obtained by reading one line from the CCD analog shift register 14 in the order in which the dummy sensor 11 and the sensor 12 are arranged one-dimensionally. Such an output signal V of one line _OUT The "one line output period" includes a "dummy signal" portion corresponding to the dummy sensor 12 and a "valid pixel signal" portion corresponding to the sensor 11, as shown in FIG. ing.
[0045]
The output signal V _OUT The magnitude of the pulse amplitude corresponds to the amount of charge read. Therefore, the portion where the pulse amplitude is small is optically black, and “optical black” in the figure indicates this.
[0046]
Next, FIG. _OUT 5 shows the respective waveforms of the signal supplied to each terminal of the sensor unit 10 and the output signal from the sensor unit 10 when the sample hold function is used, and the temporal relationship between the signals. FIG. 4 shows a clock timing diagram. Here, from the top to the bottom of the figure, the readout gate control signal φROG, the first clock signal φ1, the second clock signal φ2, the reset signal φRS, the sample / hold signal φS / H, and the output signal V _OUT The waveforms of the respective signals are shown.
[0047]
The output signal V _OUT The sample and hold is processed by the output amplifier and sample and hold circuit 15. That is, the pulse-like signal read from the CCD analog shift register 14 is sampled at the pulse timing of the sample-and-hold signal φS / H, and the next pulse of the sample-and-hold signal φS / H is sampled. Until the timing, the potential obtained by the sampling is held. Therefore, the output signal is pulse-shaped, but is flat at the same level.
[0048]
Next, an example of an embodiment of detecting an afterimage using the above-described afterimage detection method or the above-described afterimage detection method will be described.
[0049]
FIG. 5 shows a timing chart according to such an afterimage detection method. In the figure, as a timing for controlling the readout gate 13 to transfer charges, a readout gate control signal having two lines, an “A line” and a “B line” shorter than the “A line” alternately. φROG and an output signal V supplied from the CCD analog shift register 14 through the output amplifier and sample hold circuit 15. _OUT The waveforms of the respective signals are shown.
[0050]
Here, the sensor 11 of the sensor section 10 is irradiated with light from the light irradiation section in the “A line”. This light is converted into electric charge by the sensor 11, and the electric charge is converted to the CCD analog signal via the readout gate at the timing of the pulse of the readout gate control signal φROG passing through the second timing generator 17. The charges are transferred to the shift register 14 as one line of charges. Then, the charge of this one line is output from the output signal V by the “A line output”. _OUT Is output as
[0051]
The electric charge accumulated in the sensor 11 at the “B line” is transferred in accordance with the timing of the pulse of the readout gate control signal φROG via the second timing generator 17, and the output signal is output at the “B line output”. V _OUT Is output as
[0052]
Here, since the accumulation time of the “A line” in the sensor 11 is longer than the accumulation time of the “B line”, the electric charge accumulated in the “A line” in the sensor 11 is accumulated in the “B line”. Charge. The larger the amount of charge, the more the output signal V _OUT The difference in the amount of charge read between the “A line” and the “B line” depends on the output signal V _OUT Appears as a difference in the amplitude of That is, the output signal V _OUT Are larger in the “A line” than in the “B line”.
[0053]
Here, the output signal V _OUT The amplitude of the output of the “A line” of FIG. Further, the output signal V _OUT Of the “B line” of FIG. 7 locally increases in the portion B1. The local decrease in the amplitude in the portion A1 is because a part of the electric charge accumulated in the linear sensor was not completely transferred. Such charge remaining without being transferred is read out in the next line, and appears as a local increase in amplitude, as shown in a portion B1.
[0054]
In this way, the charge remaining without being transferred is transferred together with the charge of this line when the amount of charge stored in the next line is small. That is, it is possible to transfer and read out the charge remaining as an afterimage on the “A line” where the charge is accumulated for a long accumulation time and the charge accumulated on the “B line” where the accumulation time is short. Therefore, the output signal V of "B line output" _OUT , The charge of the afterimage can be detected.
[0055]
The change in the output amplitude due to the afterimage is also seen in the “A line output”, but in the “B line output”, the output signal V _OUT Is smaller than the “A-line output” because the amplitude is small.
[0056]
Here, FIGS. 6A and 6B are enlarged views of the vicinity of the portion A1 and the portion B1, respectively. Here, “V” in FIG. _RS "Indicates the reset level and" V _OS "" Indicates an offset level. Each pulse in the figure corresponds to each sensor 11 of the linear sensor.
[0057]
The larger the amount of charge transferred and read from the sensor 11, the greater the output signal V _OUT Of the sensor 11 corresponding to the portion A1 has a reduced charge. In the sensor 11 corresponding to the portion B2, the charge has increased. The increase and decrease of the charge in the sensor 11 are due to an afterimage phenomenon in which the charge is not completely transferred and the remaining charge appears in the next line.
[0058]
Next, a timing chart when there is no afterimage is shown in FIG. In the figure, the readout gate control signal φROG and the output signal V _OUT The waveforms of the respective signals are shown. The output signal V _OUT In the point A2 and the point B2, the local decrease and increase in the amplitude as seen at the point A1 and the point B1 in FIG.
[0059]
FIGS. 8A and 8B are enlarged views of the vicinity of the portion A2 and the portion B2, respectively. Each pulse in the figure corresponds to each linear sensor. Since the pulse amplitude is constant, it can be seen that the charge transferred from each sensor is constant and there is no afterimage.
[0060]
【The invention's effect】
As described above, the afterimage detection method and the afterimage detection apparatus according to the present invention can detect an afterimage without using an intermittent light source such as a strobe light source. Since no special light source as described above is used, this method and apparatus are advantageous in terms of cost and reduce the burden on the operator. Furthermore, since the equipment for the light source for the intermittent light emission is not required, the present invention can be implemented without limiting the place.
[0061]
Further, according to the present invention, the charge of the afterimage that has been accumulated during the first accumulation time having a long accumulation time and has not been completely transferred remains together with the charge accumulated during the second accumulation time having a short accumulation time. Reading is performed in the second reading step, and charges of an afterimage are detected from the charges of this one line. Since the charge accumulated in the second accumulation time is smaller than the charge accumulated in the first accumulation time, the amplitude is also small, so that an increase in the amplitude due to the charge of the afterimage can be clearly detected.
[0062]
Further, in the afterimage detection device according to the present invention, a continuous light source is used as a light source of the light irradiation unit. Therefore, the light source is easy to handle, low in cost, and consumes little power.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically illustrating a configuration of an afterimage detection device.
FIG. 2 is a block diagram illustrating an example of a sensor unit configured on one chip.
FIG. 3 is a timing chart showing an example of a waveform of each unit of a sensor unit when a sample hold function is not used.
FIG. 4 is a timing chart showing an example of a waveform of each unit of the sensor unit when a sample hold function is used.
FIG. 5 is a timing chart showing waveforms of an output signal and the like when there is an afterimage;
FIG. 6 is an enlarged view in which a part of a waveform of an output signal when there is an afterimage is enlarged.
FIG. 7 is a timing chart showing waveforms of output signals and the like when there is no afterimage.
FIG. 8 is an enlarged view in which a part of a waveform of an output signal when there is no afterimage is enlarged.
FIG. 9 is a timing chart showing a waveform of an output signal when there is an afterimage by a conventional afterimage detection method.
FIG. 10 is an enlarged view in which a part of a waveform of an output signal when there is an afterimage by a conventional afterimage detection method is enlarged.
FIG. 11 is a timing chart showing a waveform of an output signal when there is no afterimage by a conventional afterimage detection method.
FIG. 12 is an enlarged view of a part of a waveform of an output signal in a case where there is no afterimage by a conventional afterimage detection method.
[Explanation of symbols]
Reference Signs List 1 light irradiation unit, 2 control unit, 3 monitor unit, 10 sensor unit 11 sensor, 12 dummy sensor, 13 readout gate, 14 CCD analog shift register

Claims (9)

A first readout step of sequentially reading out one line of charge after irradiating at least one line of image pickup device that accumulates charge according to the amount of light irradiated for a first storage time;
A second reading step of sequentially reading out charges of one line after irradiating the image sensor with light for a second storage time different from the first storage time;
A residual image detection method, comprising: detecting a residual image charge from each one-line charge read in the first read step and the second read step. 2. The method according to claim 1, wherein the first accumulation time is longer than the second accumulation time. 3. The afterimage detection method according to claim 2, wherein an afterimage is detected from the charge of one line read in the second reading step. 2. The afterimage detection method according to claim 1, wherein the image sensor is a solid-state image sensor. Light irradiating means for irradiating at least one line of the imaging element that accumulates charges according to the amount of light to be irradiated with light of a predetermined intensity;
Charge readout means for sequentially reading one line of charge at a predetermined timing from the image sensor;
From the image pickup device irradiated by the light irradiation unit, one line of charge read by the charge reading unit after a first accumulation time, and one line of charge read by the charge reading unit after a second accumulation time And an afterimage charge detection unit for detecting afterimage charges. 6. The afterimage detection apparatus according to claim 5, wherein the first accumulation time is longer than the second accumulation time. 7. An afterimage detection apparatus according to claim 6, wherein said afterimage charge detection means detects afterimage charges from one line of charges read after said second accumulation time. 6. An afterimage detecting apparatus according to claim 5, wherein said image sensor is a solid-state image sensor. 6. An afterimage detecting apparatus according to claim 5, wherein said light irradiation means uses a continuous light source.

Images