JPH0818873A - Video camera - Google Patents

Abstract

PURPOSE:To surely correct a white level defect caused by a temperature rise or the like by comparing position information of a defective picture element obtained in the defective picture element detection mode with position information of a defective picture element stored already and storing newly only new position information to a defective picture element position storage means. CONSTITUTION:A white level defect correction circuit 7 keeps closing an iris 2 after application of power to prevent incident light onto a solid-state image pickup element 4. Furthermore, in order to easily detect a white level defect, the gain of an AGC circuit 5 is increased. A signal is read from each picture element of the solid-state image pickup element 4 synchronously with a pulse of a synchronizing signal generating circuit 3 while keeping a closing iris and the increased gain. Then the signal level is compared with a threshold level and the white level defect correction circuit 7 gives position information of the picture element from which a higher level of signal is obtained than the threshold level to a microprocessor 11. When the received position information is not in the memory 10 in comparison with the position information having been stored in the past in the memory 10 and the information is not in the memory 10, the information is stored in the memory 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera using a solid-state image sensor, and more particularly to a video camera having a function of correcting pixel defects of the solid-state image sensor by signal processing.

[0002]

2. Description of the Related Art As a conventional technique for correcting a pixel defect of a solid-state image pickup device, there is, for example, one described in Japanese Patent Laid-Open No. 2-235480. The technology disclosed in this prior application is such that a solid-state imaging device including a solid-state imaging device is provided with a non-volatile memory and an input terminal for inputting data to be written in the non-volatile memory. The address data of the defective portion is detected, the address data of the defective portion is written in the nonvolatile memory through the input terminal, and the pixel defect is corrected by the memory data.

[0003]

The solid-state image pickup device converts light energy into an electric signal, but has a property of converting thermal energy into an electric signal. The signal component converted into an electric signal by this heat energy is called dark current. Since the dark current is generated by thermal energy, it has a strong temperature dependency, and the white defect is caused by the dark current abnormally increasing as compared with other pixels due to a pixel defect. Therefore, at the time of inspection before shipment, even for white scratches that were below the detection level that required pixel defect correction, the white scratch level increased due to the temperature rise,
May exceed acceptable levels.

However, in the prior art disclosed in the above-mentioned prior application, correction of white scratches whose level has risen due to such temperature rise has not been considered at all.

The present invention has been made in view of the above points,
The purpose thereof is to frequently detect white defects due to pixel defects of the solid-state image pickup element and to reliably correct white defects caused by temperature rise.

[0006]

In order to achieve the above object, a video camera according to the present invention comprises a defective pixel detecting means for detecting a defective pixel of a solid-state image sensor, and a defective pixel for storing position information of the detected defective pixel. When the signal of the defective pixel recognized by the position storage means and the position information obtained by the pixel position storage means is input, the signal corresponding to this defective pixel is replaced with the signal of the peripheral pixel of the defective pixel or the calculated value. And a defective pixel detection mode for detecting a defective pixel of the solid-state image sensor, which is activated in association with an appropriate operation, and the position of the defective pixel detected in the defective pixel detection mode. The data is compared with the already stored position data every time, and only the new position data is added to the defective pixel position storage means and stored.

[0007]

For example, when the power switch is turned on or when the power switch is turned off, the video camera automatically enters the defective pixel detection mode, and the position information of the defective pixel obtained by this defective pixel detection mode has already been obtained. The position information of the stored defective pixel is compared, and only the new position information is newly added and stored in the defective pixel position storage means. Therefore, all the position information of the white defects that have occurred so far are stored, and all the white defects corresponding to the position information are corrected.

[0008]

The present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a block diagram showing the main configuration of a video camera according to the first embodiment of the present invention. In FIG.
Is a lens, 2 is an iris, 3 is a synchronizing signal generation circuit, 4 is a solid-state image sensor, 5 is an automatic gain control circuit (AGC circuit),
6 is an analog-digital conversion circuit (A / D conversion circuit),
Reference numeral 7 is a white defect correction circuit, 8 is a signal processing circuit, 9 is a digital-analog conversion circuit (D / A conversion circuit), 10 is a memory, and 11 is a microprocessor.

In the above-mentioned structure, the optical signal incident from the lens 1 is converted into an electric signal by the solid-state image sensor 4, and if the brightness of the subject is within the range required for AGC processing (the iris 2 is fully opened). (When the luminance signal level does not reach the predetermined value despite the state), the AGC circuit 5 performs a variable amplification process appropriately according to the brightness of the subject,
Next, the A / D conversion circuit 6 converts each pixel into a digital signal.

A normal signal passes through the white defect correction circuit 7 and is subjected to a known appropriate process that complies with the video signal standard such as color separation, white balance and γ correction in the signal processing circuit 8, and then D The signal is converted into an analog signal by the / A conversion circuit 9 and output as a luminance signal Y and a chroma signal C. Further, the signal from the defective pixel is recognized by the white defect correction circuit 7 based on the position information stored in the memory 10, and the signal corresponding to this defective pixel is detected by the white defect correction circuit 7 in the peripheral pixels of the defective pixel. Replace with signal or calculated value and output.

Next, the operation of detecting white defects and the correction operation based thereon will be described with reference to the flow chart of FIG. 2 and FIGS. In this embodiment, white flaws are detected after the power is turned on and before an image is output.

As shown in FIG. 2, after the power is turned on (step ST1), the white defect correction circuit 7 keeps the iris 2 closed to prevent the incident light to the solid-state image pickup device 4 (step ST).
2). In addition, the gain of the AGC circuit 5 is increased to facilitate the detection of the white flaw (step ST2). In this embodiment, since the white flaw detection is performed after the digital signal is formed, it is necessary to perform the amplification process in the analog signal system before the A / D conversion in order to reduce the quantization error due to the digitization. is there. In addition, a gain setting mode dedicated to white defect detection is prepared, and in this gain setting mode dedicated to white defect detection,
The gain may be set to exceed the gain variable width of the normal operation.

After keeping this state (iris closed and gain up), the signal from each pixel of the solid-state image pickup device 4 is read in synchronization with the pulse of the synchronizing signal generating circuit 3. FIG. 3 shows an example of the color filter arrangement of the solid-state image sensor 4, which is composed of four colors A, B, C, and D.
Then, the color signal corresponding to this color filter is read in synchronization with the horizontal and vertical drive pulses generated by the synchronization signal generation circuit 3, but since the iris 2 is closed, the output from the solid-state image sensor 4 is , Only the dark current described above. This dark current is shown in FIG. The dark current amount of a normal pixel does not vary so much, but a very large level of dark current (corresponding to A ₁₃ in FIG. 4) is obtained from a pixel having a pixel defect. Since this is a white defect, comparison is performed at a certain threshold level, and the white defect correction circuit 7 sends to the microprocessor 11 the position information of the pixel for which a signal larger than the threshold level is obtained. The microprocessor 11 examines whether the position information input just now is the same as the position information stored in the memory 10 in the past. As a result, if the input position information does not exist in the memory 10, it is stored in the memory 10 (step ST
3 to ST6).

By the above operation, the storage processing of the position information of all pixels in which white defects occur in the memory 10 is completed,
The processing flow of FIG. 2 exits the white defect pixel detection loop (steps ST3 to ST6) and becomes the normal image output processing (steps ST7 and ST8). That is, while the gain control of the iris 2 and the AGC circuit 5 is interlocked with each other to perform proper automatic exposure, a signal is read from the solid-state image sensor 4 in synchronization with the pulse of the synchronizing signal generating circuit 3. The position information of the pixel to be read out is continuously checked, and the signal is corrected when it coincides with the position of the white defect pixel stored in the memory 10 (steps ST9 to ST11).

As described above, the level of white scratches depends on the temperature, and in a video camera, the temperature inside the set rises due to continuous energization, and they are noticeable when used at high temperatures. On the other hand, as to how to use the video camera, since the power is frequently turned on and off, in the first embodiment, the power is turned on again while the solid-state image pickup device 4 is in the high temperature state, and the white defect pixel detection loop described above. Since the position information of the white scratches is stored in the memory 10, the white scratches generated by the temperature rise can be corrected.

If the detection time in the defective pixel detection mode is set to N fields, the output level of the defective pixels can be increased N times as compared with the case of the detection time of 1 field, and the defective pixel detection rate can be increased. Can be raised.

Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, white defects are detected when the power is off, the position information of the white defects is stored in the memory, and the white defects are corrected based on the stored position information when the power is turned on next time. FIG. 5 is a flowchart when the power switch of this video camera is turned off. The configuration of this embodiment is similar to that of FIG.

In this embodiment, first, the power switch is turned off.
Is detected (step ST21), the iris 2 is closed (step ST22) and the AG
The gain of the C circuit 5 is increased (step ST23). The dark current at this time is shown in FIG. Although only A ₁₃ was the white defect that exceeded the threshold level when the power was turned on, it is assumed that the white defect also occurred in the pixel of B ₁₁ due to the temperature rise of the solid-state image sensor 4. Then, the position information of B ₁₁ is sent to the microprocessor 11 and it is determined whether or not it has been stored in the memory 10 in the past. Since the position information of B ₁₁ is not stored, it is stored in the memory 10. The position information of A ₁₃ is
Since it was stored when the power was turned off previously, it is not stored at this time (steps ST24 to ST27). By the above operation, the memory 1 for the position information of a new pixel in which a white defect occurs
The storing process to 0 is completed, the AGC circuit 5 is returned to the normal gain, and the power is turned off (steps ST28 and ST29).
If the temperature of the solid-state imaging device 4 immediately before the power is turned off is 60 ° C., it means that all the positional information of the white flaws generated at 60 ° C. or less has been learned at this time.

Therefore, when the temperature of the solid-state image pickup device 4 is 60 ° C. or less when the power is turned on next time, the position information of the white scratches that can occur at that time is stored in the memory 10, and all the corrections are made. Since it will be lost, you can shoot well without white scratches. Further, even if a new white defect occurs due to the temperature of the solid-state imaging device 4 being 60 ° C. or higher, or a white defect occurs due to aging, if the power is turned off at that time, the new white defect is also learned. Therefore, when the power is turned on, all white scratches will be corrected under the use condition of the temperature equal to or lower than the detected temperature.

[0020]

As described above, according to the present invention, it is possible to more surely perform white defect correction due to a pixel defect of a solid-state image pickup device by a video camera alone.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main configuration of a video camera according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a processing flow of white defect correction at power-on according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a color filter arrangement of a solid-state image sensor.

FIG. 4 is an explanatory diagram of dark current output of the solid-state image sensor at room temperature.

FIG. 5 is a flowchart showing a processing flow of white defect correction when the power is turned off according to the second embodiment of the present invention.

FIG. 6 is an explanatory diagram of a dark current output of the solid-state imaging device at high temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 lens 2 iris 3 synchronization signal generation circuit 4 solid-state image sensor 5 AGC circuit 6 A / D conversion circuit 7 white flaw correction circuit 8 signal processing circuit 9 D / A conversion circuit 10 memory 11 microprocessor

Claims (4)

[Claims] 1. A solid-state image sensor for converting incident light into an electric signal, defective pixel detection means for detecting a defective pixel of the solid-state image sensor, and defective pixel position storage means for storing position information of the detected defective pixel. When the signal of the defective pixel recognized by the position information obtained by the pixel position storage means is input, the signal corresponding to the defective pixel is replaced with the signal of the peripheral pixel of the defective pixel or the calculated value. A video camera having a signal replacement means, having a defective pixel detection mode for detecting a defective pixel of the solid-state imaging device, the position data obtained in the defective pixel detection mode, the position already stored every time A video camera characterized in that only new position data is added to the defective pixel position storage means and stored in comparison with the data. 2. The output level of a defective pixel according to claim 1, wherein the detection time in the defective pixel detection mode is N fields.
A video camera characterized by being N times as many as in the field. 3. The video camera according to claim 1, wherein the defective pixel detection mode is automatically activated by turning on or off a power switch. 4. The automatic gain control circuit according to claim 1, wherein, in the defective pixel detection mode, the gain of the automatic gain control circuit for amplifying the output of the solid-state imaging device is set to a value higher than a gain variable width of normal operation. Characteristic video camera.