JPH07121135B2 - Imaging device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image pickup apparatus such as an electronic camera, and more particularly to white balance adjustment of the image pickup apparatus.

[Prior Art] Three types of white balance adjustment in an image pickup apparatus are conventionally known: a manual type, a feedback type automatic adjustment type, and an automatic adjustment type using a colorimetric sensor, a so-called automatic tracking type. Of these methods, the white balance adjustment is performed by adjusting the gains of the red signal R, the green signal G, and the blue signal B from the imaging system to a predetermined value with a manual volume. Feedback so that is a predetermined ratio (R: G: B = 1: 1: 1)
A loop is used to set the gain for them, and then the white balance is adjusted by shooting with the gain that has been set. Is a colorimetric sensor that is arranged independently of the image pickup system to ensure correct light source information. Is supplied to the circuit of the image pickup system to adjust the white balance.

Among these methods, the automatic adjustment method using the colorimetric sensor is considered to become the mainstream in the future from the viewpoint that it is easy and the white balance can be adjusted at any time. .

A silicon photo diode, a photoconductive substance or the like is used as a colorimetric sensor in the conventional automatic tracking type white balance adjustment. Further, solid-state image pickup devices such as CCD, MOS, SIT and the like are often used as sensors of the image pickup system.

In that case, both the colorimetric sensor and the imaging system sensor show some differences in spectral sensitivity characteristics due to differences in physical properties, structure, etc. Depending on the light source used, such as when using a light source with a bright line spectrum, white・ The balance will be lost.

Therefore, it is desirable to use CCD, MOS, SIT, etc. of the same type as the image sensor for the white balance colorimetric sensor, but since these elements have a narrow dynamic range, conventional colorimetric systems If the sensor is simply replaced with these elements, it is not possible to compensate for all the changes in external light.

[Problems to be Solved by the Invention] As described above, in the conventional white balance adjusting device, the solid-state image sensor of the same type as the image sensor is used in the colorimetric sensor due to the lack of the dynamic range of the sensor. However, there is a problem that the spectral sensitivity characteristics of both sensors are deviated, and the white balance is lost depending on the light source used.

In view of these problems, it is an object of the present invention to provide an image pickup apparatus that can accurately adjust the white balance without losing the white balance regardless of which light source is used. Is.

[Means for Solving the Problems] In order to achieve this object, according to the present invention, an imaging system element, a colorimetric sensor using an element having the same characteristics as the imaging system element, and an imaging system element An image pickup device having means for limiting the accumulation of electric charges in the color sensor is used.

[Operation] By doing so, it is possible to appropriately control the period in which the charge is accumulated in the colorimetric sensor and the period in which the image capturing element is irradiated with light and the charge is accumulated in the image capturing element. Therefore, even when the color of the light source changes abruptly, the charge amounts accumulated in both the image pickup system sensor and the colorimetry system sensor can always be made equal to each other, and the spectral sensitivity characteristics of both sensors are prevented from shifting. It becomes possible.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a circuit block diagram for explaining the first embodiment of the present invention, and FIG. 2 is a timing diagram for explaining the operation of this circuit. In FIG. 1, 1 is a pattern for limiting incident light, 2 is a shutter, 3 is a solid-state image sensor that stores optical information as electric charges and converts it into an electric signal, and 4,5 are red signals R of the image sensor 3, respectively. , A red signal amplifier for amplifying the output of the blue signal B, a blue signal amplifier, 6 is a processing unit for deriving a color difference / luminance signal from the outputs of the amplifiers 4 and 5 and the output of the green signal G of the image sensor, and 8 is the color of the light source. A colorimetric sensor for colorimetry, 7 a pattern for limiting the incident light of the colorimetric sensor, 9 a control voltage deriving section for deriving a voltage for controlling the amplifiers 4, 5 from the output of the colorimetric sensor 8, and 10 an image sensor. 3. A pulse generator that sends a timing pulse to each block such as the colorimetric sensor 8.

Step motors 11 and 12 drive the prints 1 and 2, respectively, and are driven by the output e of the pulse generator 10.

CCDs, MOSs, SITs, and other solid-state image sensors can be used for the image sensor 3 and the colorimetric sensor 8. However, the elements used for both are of the same type and have the same substrate and electrode configurations. It is desirable to use devices that are equal to and have exactly the same characteristics.

Next, the operation of this imaging device will be described. First, prior to the accumulation of signals in the colorimetric sensor 8 and the image pickup device 3, the step motors 11 and 12 bring the patterns 1 and 7 into a predetermined state by a pulse e as shown in FIG. The incident light limited by the print 1 and the shutter 2 is converted into an electric signal of a red signal R, a green signal G, and a blue signal B by the image sensor 3. At this time, the second
As shown in the figure, the pulse a is sent from the pulse generator 10 to the image sensor 3, and charges are accumulated only during the charge accumulation period. A pulse b is sent to the shutter 2 and the shutter 2 is opened only during the high period.

Therefore, the charges accumulated in the image sensor 3 correspond to the incident light during the period when the shutter 2 is open. Also, the third,
4 and 5 are diagrams for explaining the colorimetric sensor 8 in more detail. FIG. 3 is a block diagram of the colorimetric sensor, and FIG.
FIG. 5 is an energy level diagram of the MOS capacitor when cut at -B, and FIG. 5 is a timing pulse diagram necessary for operation.

In FIG. 3, reference numeral 13 is a block for detecting a red component of incident light and converting it into an electric charge, and reference numerals 14 and 15 are conversion portions for a green component and a blue component. Reference numeral 16 is an amplifier unit that converts the electric charge corresponding to the red component of incident light into a voltage, and 17 and 18 are amplifier units for the green component and the blue component similarly.

In FIG. 4, reference numeral 23 designates a light receiving region corresponding to 13, 14, 15 and converts incident light into electric charges 29. Reference numeral 22 is a drain that absorbs excess charges that have overflowed from 23. 24 and 27 are portions where the energy level changes in order to transfer the signal charge, and are changed by applying a pulse cd to the electrodes 41 and 32. Reference numerals 25, 26, 27 and 28 constitute an amplifier A (floating diffusion amplifier) for changing electric charge into voltage, 25 is a floating diffusion section, and 26 is a buffer for the output of the floating diffusion section 25. , 27 are reset gates for discarding charges accumulated in the floating diffusion section 25, and 28 is a drain. Reference numeral 30 is a light-shielding portion that blocks light other than 23.

Next, the operation will be described with reference to FIGS.

In FIG. 5, a indicates a signal applied to the image sensor 3, the signal is transferred from the image sensor 3 in the period T ₁ , and the signal is accumulated in the image sensor 3 in the period T _2. Controlled to be performed.

c and d represent the levels of the signals applied to the electrodes 31 and 32 shown in FIG. 4, respectively, and out represents the output out shown in FIG.

In the accumulation period T _{2 in} FIG. 5, the energy level of the sensor is in the state of (1) shown in FIG. 4, and the incident light is converted into the charges 29. In the transfer period, the pulse d becomes high, and the electrode 32 causes the energy level of the reset gate 27 to reach the fourth level.
As shown in FIG. 2B, the charges generated by the thermal excitation accumulated in the floating diffusion portion 25 are absorbed by the drain 28 and reset. The reference numerals (1) to (6) shown in FIG. 4 correspond to the reference numerals (1) to (6) shown in FIG. By the above operation, the output out shown in FIG. 5 becomes the reset potential. In (3), the pulse d becomes low level, and the energy level of the reset gate 27 rises.

Next, at (4), the pulse c becomes high level, and the electrode 31
As a result, the energy level of the portion 24 is lowered, and the charges are transferred to the floating diffusion portion 25. As a result, the output out becomes the signal potential.

Next, in (5), the pulse c becomes low level and the pulse d becomes high level, which is equal to the state of (2), so that the signal charge is absorbed by the drain 28. Therefore, the output becomes the reset potential.

Further, in (6), the state returns to (1), and the charge starts to be accumulated in 23 again. The signal level thus obtained is the difference between the signal potential and the no-signal potential, as shown in the output of FIG.

In this way, the colorimetric sensor 8 receives the light limited by the pattern 7 and outputs the red, green, and blue components R _w , G _w , and B _{w of the} light. Furthermore, from the outputs R _w , G _w , B _{w of the} colorimetric sensor 8,
The control voltage introduction portion 9, prompts the _{R c = G w / R w} B c = G w / B w, R c is the red signal amplifier 4, the B _c to green light amplifier 5 is fed respectively, R ' = R × R _c B ′ = B × B _c is output. The R ', G, B'signals are input to the process unit 6 and converted into a luminance signal and a color difference signal.

As described above, the pulses c and d are sent from the pulse generator 10 to the colorimetric sensor 8, and the same period as the charge accumulation period in the image sensor 3 becomes the accumulation period. That is, the accumulation period of the station sensor 8 coincides with the period during which light is incident on the image sensor by the shutter 2, that is, the accumulation period T ₂ of the image sensor 3.
Further, since the sensors having the same characteristics are used for both the image sensor 3 and the colorimetric sensor 8 and the exposure periods are the same, the accumulated charge amounts are the same. Therefore, even if the color of the light source changes abruptly, the charge amounts accumulated in both the image pickup system sensors 3 and 8 of the colorimetry system are always the same and are not affected thereby.

Further, in the image pickup system, the light is limited by the pattern 1 to compensate for the lack of the dynamic range of the image pickup element 3. Therefore, if the imprint value of the imprint 1 and the imprint value of the imprint 7 are set to the same value, the light amount of the colorimetric sensor 8 will not exceed the dynamic range of the element. That is, the pattern values of the patterns 1 and 7 are set to the same value by the pulse e from the pulse generator 10 by the stepper motors 11 and 12 that control the patterns.

In the present embodiment, the pattern is provided on the front surface of the colorimetric sensor 8. However, the sixth example of eliminating the pattern is described below.
This will be described with reference to FIGS. FIG. 6 is a circuit block diagram for explaining another embodiment of the present invention, and FIG. 7 is a pulse waveform diagram for explaining the operation of this circuit. In FIG. 6, reference numeral 33 is an integrator for integrating the outputs R _c and B _C of the control voltage deriving unit 9 for a certain period. The other structure of FIG. 6 is the same as that of FIG.

Next, the operation of this imaging device will be described. The pulse f is sent from the pulse generator 10 to the image pickup device 3, and the incident light of the pulse f during the charge accumulation period is converted into charges and accumulated. A pulse g is sent to the shutter 2, and the shutter is opened only during the high period. Therefore, the charges accumulated in the image sensor 3 correspond to the incident light during the period when the shutter 2 is open.

On the other hand, the pulse c and the pulse d are applied to the colorimetric sensor 8, and the pulses c and d are, as shown in FIG. 7, several times during the charge accumulation period in the image sensor 3 by the pulse f. , The transfer period comes in. If the pulses c and d are pulses having continuous charge storage periods like the pulse f,
Since the colorimetric sensor 8 of this embodiment is not provided with a pattern unlike the colorimetric sensor of the embodiment of FIG. 1, more electric charge than the amount of electric charge that can be accumulated in the sensor 8 is generated and saturated. Things happen. Therefore, in the present embodiment, a plurality of transfer periods are provided while the shutter 2 is open, the output signal is read out and sent to the integrator 11.

Here, the number of times of providing the transfer period is determined by the value of the pattern 1. That is, if the print value is small, increase the number of times,
By shortening one accumulation period, decreasing the number of times when the print value is large, and lengthening one accumulation period,
It is possible to prevent the charge of the colorimetric sensor from exceeding the dynamic range, that is, to prevent the charge from being saturated. Furthermore, the output for each accumulation period is made into 11 integrators. A pulse i of g is sent to the integrator 11
Since the integrator integrates only during its high period, a control signal corresponding to the incident light accumulated during the period when the shutter 2 is opened is obtained. Note that by making the transfer period as short as possible, it is possible for the colorimetric sensor 8 to detect almost all the incident light during the period in which the shutter 2 is open as electric charges.

[Effects of the Invention] As is clear from the above description, according to the present invention, the image pickup element and the colorimetric sensor are provided with elements having the same characteristics,
Furthermore, the dynamic range of the colorimetric sensor is exceeded by limiting the charge accumulation by adding the same pattern as the image sensor to the colorimetric sensor or dividing the charge accumulation period into the colorimetric sensor. In addition, no matter what light source is used, such as a light source with a bright line spectrum or a light source with flicker, the white balance is not lost and highly accurate white balance adjustment is possible.

[Brief description of drawings]

FIG. 1 is a circuit block diagram for explaining the first embodiment of an image pickup device according to the present invention, FIG. 2 is a pulse waveform diagram for explaining the operation of this circuit, and FIG. 3 is a configuration of a colorimetric sensor. 4 is an energy level diagram when the sensor shown in FIG. 3 is cut along the line AB, FIG. 5 is a timing chart for explaining the operation, and FIG. 6 is a second embodiment. FIG. 7 is a pulse waveform diagram for explaining the operation of this circuit. In the figure. 1,7: Print, 2: Shutter 3: Image sensor, 8: Colorimetric sensor 10: Pulse generator, 11: Integrator

Claims (3)

[Claims] 1. An imaging system element, a colorimetric sensor using an element having the same characteristics as those of the imaging system element, and means for limiting the accumulation of charges in the imaging system element and the colorimetric sensor to substantially the same state. An imaging device comprising: 2. An image pickup device according to claim 1, wherein a print is provided on the front surface of the image pickup device and the front surface of the colorimetric sensor so that the print values of both prints coincide with each other. apparatus. 3. A charge accumulation period in a colorimetric sensor,
It is characterized in that it is divided into a plurality of periods according to the imprint value of the imprint provided on the front surface of the imaging system element, and the output of the colorimetric sensor in each period is integrated during the period when the shutter of the imaging system is open. The imaging device according to claim (1).