JPH1032681A - Color image reader and its adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the color image reader and its adjustment method in which unbalanced color is corrected and an image signal with excellent color reproducibility is obtained through simple adjustment. SOLUTION: A plurality of different color LEDs 11R, 11G, 11B are sequentially emitted to light an object and an image of the object is picked up by a CCD sensor 22 and the picked-up image signal is received by each color image signal in the color image reader, which is provided with a lighting adjustment means 14 to adjust the light emission time of each LED for each color in addition to an LED emission circuit 13 to emit each color LED. The lighting adjustment means 14 adjusts the light emission time of each color LED so that the image pickup signal level of each color light obtained by a CCD sensor 22 is made equal to correct unbalanced color and to obtain an image signal with excellent color reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus using an image pickup device having a photoelectric conversion function, such as a CCD, and more particularly to illuminating by sequentially switching a plurality of light sources of different color lights to perform imaging with each color light. The present invention relates to a color separation type color image reading apparatus which reads a color-separated image, and an adjustment method thereof.

[0002]

2. Description of the Related Art As a color image reading apparatus of a color separation system, an image pickup optical system is provided with red (R), green (G), and blue (B) image pickup elements, respectively.
R, R, and R
Generally, a method of obtaining an image signal in which G and B colors are separated is generally used. However, in this method, a total of three expensive CCD sensors to be used as image pickup devices corresponding to each color light are required, which makes the image reading apparatus expensive and hinders downsizing. For this reason, in recent years, R,
The subject is illuminated by sequentially turning on and off the respective color light sources of G and B, and the subject is imaged by one light receiving element at the timing of lighting of each color light source, so that the respective color light signals of R, G and B can be time-divided. Has been proposed.

FIG. 5 is a diagram conceptually showing this method.
The R, G, and B LEDs 100R, 100G, and 100B are selected by the selector 101 and sequentially connected to the power supply 102 to emit light, thereby illuminating the subject A. Also, lens 1
04 and the CCD sensor 103 serving as an image sensor, an image of the object A is captured, and the obtained image signal is captured in accordance with the light emission timing of the LED. It can be read as a signal. In this system, R, G, and B image signals separated by one light receiving element can be obtained, which is advantageous in terms of cost reduction and miniaturization.

[0004]

In such a color image reading apparatus of the color separation system, C as an image sensor is used.
The spectral characteristics of the CD sensor and the light emission luminance of each color LED are problematic. That is, the CCD sensor has a spectral sensitivity characteristic as shown in FIG. 6, and there is a difference in sensitivity for each emission wavelength of the LED that emits each color light of R, G, and B, in other words, the light reception signal level. . Therefore, if R,
Even when the subject is illuminated with the same illuminance by the G and B color LEDs, the level of the imaging signal output from the same CCD sensor will be different, resulting in a loss of color balance and reproduction of the subject color. Becomes difficult. Further, in practice, even if the same color power is supplied to the R, G, and B LEDs, the light emission luminances thereof are different, so that it is difficult to illuminate the subject with the same illuminance. Shall be remarkable.

To solve such a problem, it is conceivable to control the accumulation time of the CCD sensor to make the image signal level of each color light uniform. However, as described above, in the method of performing imaging with one CCD sensor while switching the illumination with each of the R, G, and B color lights at high speed,
In order to control the change of the accumulation time at the time of individual light reception, extremely high-precision timing control is required, and the circuit configuration therefor becomes complicated and expensive. Also, C
The adjustment work for controlling the accumulation time of the CD sensor with high precision is actually extremely difficult, and it is difficult to realize it. Further, if a configuration for making the emission luminance of each color LED uniform is added, the configuration becomes more complicated and expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color image reading apparatus capable of correcting such a color balance loss and obtaining an image signal with good color reproducibility by simple adjustment, and an adjustment method therefor. is there.

[0007]

SUMMARY OF THE INVENTION The present invention provides an illuminating means for illuminating a subject while sequentially switching a plurality of different color lights, and an imaging means for taking an image of the subject and taking an image signal as an image signal of each color light. And an illumination adjusting means for adjusting the illumination time of each color light for each color light. The illumination adjustment unit is configured to perform adjustment so that the image signal level of each color light in the image sensor is equalized. For example, a red LED, a blue LED, and a green LED that respectively emit red, blue, and green color lights are respectively arranged as illumination means, and a CCD sensor that captures an image of a subject illuminated with each color light is provided as an imaging means. LED
Are individually adjusted in accordance with the spectral sensitivity characteristics of the CCD sensor.

The adjusting method according to the present invention is also directed to a color image reading apparatus which irradiates a subject with a plurality of different color lights in order and fetches an image signal of the subject taken by an image sensor as the color light signal. And irradiating each color light to the color-drawn reference chart, and adjusting the irradiation time of each color light so that the respective image signal levels of the image sensor for each color light at that time become equal. .

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the embodiment of the present invention. The image reading device is an LED that illuminates the subject A with R, G, and B color light.
An illuminating unit 10; a CCD imaging unit 20 for imaging an illuminated subject to obtain an image signal;
And a control unit 30 for controlling the D imaging unit 20.

The LED illuminating section 10 is provided with an LED array 12 in which a plurality of red, green, and blue LEDs 11R, 11G, and 11B for emitting R, G, and B color lights are arranged in a matrix. . The LEDs of the respective colors are sequentially supplied with power under the control of the LED light emitting circuit 13, and are configured to emit light in a time-division manner. Also, an LED adjustment circuit 1 for controlling power supply to each color LED and correcting the color balance of the R, G, B image signals obtained by the CCD image pickup unit 20.
4 are provided.

The CCD imaging unit 20 is provided with the LE
An imaging lens 21 for forming an image of a subject A illuminated by the D illumination unit 10 and an imaging element 22 for photoelectrically converting the subject image formed by the imaging lens 21 are provided. Here, a CCD sensor, which is a charge storage type photoelectric conversion element, is used as the image sensor 22. A photoelectric conversion output corresponding to the amount of light of a subject image formed on the CCD sensor 22 by the imaging lens 21 is output. It is configured to be obtained as a signal level of an imaging signal. Also,
A CCD drive circuit 23 is connected to the CCD sensor 22, and the CCD drive circuit 23 controls the output timing of an image signal.

The control section 30 has a built-in reference clock generator 31 here, and outputs the reference clock C generated here to the CCD driving circuit 23 and the LED light emitting circuit 13.
To synchronize the timing between the LED illumination unit 10 and the CCD imaging unit 20, and
R, G, B LEDs 11R, which are sequentially lit at 0,
The CCD sensor 22 is operated to read image signals of R, G, and B color lights in accordance with the illumination timings of 11G and 11B.

FIG. 2 is a block diagram functionally showing the internal configuration of the LED light emitting circuit 13 and the LED adjusting circuit 14. The LED light emitting circuit 13 includes a power supply 15 and each color LED.
And three electronic switches 16 interposed therebetween.
R, 16G, and 16B, and the selector 17 switches each of the electronic switches 16R, 16G, and 16G based on a reference clock C input from the control unit 30.
The power supply 1 is turned on and off sequentially.
5 are sequentially supplied to the LEDs of each color, and
The ED emits light. At this time, the power supply time for each color LED is one clock cycle time of the reference clock C at the maximum.

On the other hand, the LED adjustment circuit 14 adjusts the color balance of R, G, and B in the image pickup signal. Here, the light amounts of the red, green, and blue LEDs, that is, the LEDs 11R, 11G, 11B has a function of controlling the light emission time of the LED 11B. For this purpose, three timers 18R, 18
G and 18B are provided. These timers are configured to supply the power from the LED light emitting circuit 13 to the corresponding LED of the color light only when the timer is on, and the timer on time is controlled by the attached manually adjustable variable resistor 1.
It is configured to be able to be adjusted by 9R, 19G, 19B. In addition, the maximum time of this timer ON is
At least one cycle time of the reference clock is required.

Next, an image reading operation and an adjusting method by the image reading apparatus having the above-described configuration will be described. First, in order to adjust the RGB color balance, a reference chart including an RGB reference density color pattern is prepared as the subject A, and imaging is performed on the reference chart. First, the timer on time of each of the timers 18R, 18G, 18B is set to the maximum value by the variable resistors 19R, 19G, 19B of each LED adjustment circuit 14. As a result, as shown in the timing chart of FIG.
7 turns on the electronic switches 16R, 16G, and 16B sequentially for one clock in synchronization with the fall of the reference clock C, thereby turning on the LEDs 11R, 11G, and 11B of each color.
Power from the LED light emitting circuit 13 is supplied to the LED adjusting circuit 1
4 for one clock cycle time.
As a result, each of the LEDs 11R, 11G, and 11B emits light sequentially for the same time, and illuminates the reference chart A. Then, the subject is imaged by the CCD sensor 22 and an image signal is captured in synchronization with the reference clock C, so that the image signals corresponding to the LEDs of the respective colors can be read as R, G, and B image signals, respectively. It becomes possible.

In this case, each color LED 11R, 11G, 1
Since the light emission luminances of the LEDs 1B are different and the light emission times of the LEDs of the respective colors are equal, the illuminance of the illumination of the reference chart A varies, and the CCD sensor 22 has a spectral sensitivity characteristic as shown in FIG. Each of the R, G, and B image signals obtained from the sensor 22 has a difference in signal level. In this case, G,
The signal level is reduced in the order of B and R, and as a result, the color balance in the imaging signal is deteriorated.

Therefore, each timer 1 of the LED adjustment circuit 14
8R, variable resistors 19R attached to 18G, 18B,
The timer ON time is adjusted by manually adjusting 19G and 19B. FIG. 3B is a timing chart showing an example of this. Here, based on the above-described spectral sensitivity characteristics of the CCD sensor, the timer ON time of the R timer 18R having a low signal level is the longest, and the G timer 1
The 8G timer ON time is set to be the shortest.
As a result, the power supply from the LED light emitting circuit 13 is time-limited by each of the timers 18R, 18G, and 18B, and the light emitting time of the LEDs 11R, 11G, and 11B of each color has a difference as shown in FIG. Time to do
R, B, and G become shorter in this order.

Accordingly, in the CCD sensor 22, the order in which the reference chart A is illuminated, that is, R, B,
The imaging time, that is, the charge accumulation time, is shortened in the order of each color of G, and the imaging signal level of each color light of R, B, and G is reduced in this order. Therefore, by appropriately setting the ratio of the time-on time of the timer of each color to the image signal level of each color light of the CCD sensor shown in FIG. 3A, the image signal level of each color from the CCD sensor is obtained. Is made uniform. For this reason, after performing the adjustment, by capturing an image of a desired subject, the color balance in the image capture signal is corrected, and an image signal with good color reproducibility can be obtained.

As described above, even in the color image reading apparatus using one CCD sensor, the color balance of the image pickup signal from the CCD sensor is adjusted by adjusting the light emission time of each color LED, thereby improving the color reproducibility. Can obtain an image signal. The light emission time of the LED can be adjusted by a timer that can set the time as in this embodiment, so that the circuit configuration is not complicated, and the adjustment is performed by using a variable resistor. It can be easily performed because only adjustment is required.

FIG. 4 is a view showing another embodiment of the present invention, in which parts equivalent to those in FIG. 1 are denoted by the same reference numerals. In this embodiment, the R, G, B images captured by the CCD sensor 22 are used.
Level sensor 24 for detecting the image signal level of each color light of
Is provided, and the signal level of each color light detected by the level sensor 24 is stored in the memory 25. Then, based on the stored signal level, the corresponding LED of each color
In response to the above, the timer-on time of each timer built in the LED adjustment circuit 14 'is feedback-controlled so that each color L
The ED emission time is controlled. In this case, LED
If a timer circuit whose time constant is variable by digital data, that is, a timer ON time is used as a timer in the adjustment circuit 14 ', the timer ON time of each color timer can be controlled using the signal level data read from the memory 25 as it is. it can. Therefore, in this embodiment, if the reference chart A is imaged, the control of the light emission time of each color LED is automatically realized, so that the manual adjustment as in the above-described embodiment becomes unnecessary.

The present invention is not limited to the configuration of each of the above embodiments.
Needless to say, the configuration of the illumination unit, the configuration of the control unit, and the like can be changed as appropriate.

[0022]

As described above, according to the present invention, the illuminating means for illuminating a plurality of different color lights for illuminating the object is provided with means for adjusting the illumination time of each color light, thereby enabling image pickup. Even if the signal level of the imaging signal obtained from each color light varies due to the spectral sensitivity characteristics of the means, by adjusting the illumination time of each color light,
The signal levels of the imaging signals of the respective color lights can be made equal.
As a result, it is possible to correct the color balance in the image pickup signal and obtain an image signal with good color reproducibility, and to simplify the circuit configuration therefor, and to easily perform the adjustment. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of an LED drive circuit and an LED adjustment circuit.

FIG. 3 is a timing chart showing a relationship between a light emitting time of an LED and an image signal level of a CCD sensor.

FIG. 4 is a block diagram of another embodiment of the image reading apparatus of the present invention.

FIG. 5 is a diagram showing a conceptual configuration of a color image reading apparatus of a color separation system.

FIG. 6 is a diagram illustrating spectral sensitivity characteristics of a CCD sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 LED illumination part 11R, 11G, 11B LED 13 LED light emission circuit 14, 14 'LED adjustment circuit 15 Power supply 20 CCD imaging part 21 Shooting lens 22 CCD sensor 23 CCD drive circuit 24 Level sensor 25 Memory 30 Control part 31 Reference clock generator

Claims (6)

[Claims] 1. A color image reading apparatus comprising: illuminating means for illuminating a subject while sequentially switching a plurality of different color lights; and imaging means for taking an image of the subject and capturing an imaged image signal as an image signal of each color light. A color image reading apparatus, comprising: an illumination adjusting means for adjusting an illumination time of each color light for each color light. 2. The color image reading apparatus according to claim 1, wherein the illumination adjusting means adjusts the image pickup signal level of each color light in the image pickup device to be equal. 3. A illuminating means includes a red LED, a blue LED, and a green LED, which respectively emit red, blue, and green color lights, and a CCD sensor for imaging a subject illuminated with each color light as an imaging means. 3. The color image reading apparatus according to claim 2, wherein the illumination adjusting means individually adjusts the light emission time of each color LED in accordance with the spectral sensitivity characteristic of the CCD sensor. 4. The illumination adjusting means is provided with a timer for setting a light emission time for each LED of each color, and the set time of each timer can be adjusted manually.
Color image reading device. 5. The color image reading apparatus according to claim 3, further comprising: means for detecting a signal level of an image pickup signal of each color light; and means for feedback-adjusting a timer setting time so that the detection levels become equal. 6. A color image reading apparatus which irradiates a subject with a plurality of different color lights while sequentially switching the color light, and captures an image signal of the subject by an image sensor as the color light signal. A method of irradiating each color light to a chart and adjusting an irradiation time of each color light so that an image pickup signal level of each image light for each color light at that time becomes equal. .