JPH0473675B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a solid-state imaging device for a video camera.

Conventional configurations and their problems There are various types of solid-state image sensors, but here we will discuss them.
A photodiode called a MOS image sensor
Taking an image sensor using a MOS field effect transistor as an example, the occurrence of a white spot defect or a black spot defect will be explained in detail.

FIG. 1 is an example showing the operating principle of a MOS type image sensor. That is, a large number of photodiodes 1, which are photosensitive elements, are arranged in a matrix, and a horizontal shift register 2, a vertical shift register 3, horizontal changeover switches 41, 42, 43, . Switches 51, 52, . . . 5m are provided. As is well known, the horizontal shift register 2 is driven by a start pulse and a horizontal clock pulse synchronized with a horizontal synchronizing signal, and switches 41, 42,
43...4n are sequentially opened and closed to operate all the switches within one horizontal scanning time. On the other hand, the vertical shift register 3 is driven by a start pulse synchronized with the vertical synchronization signal and a clock pulse synchronized with the horizontal synchronization signal, and the switch 5
1, 52,...5m are sequentially opened and closed, and all switches are operated within one vertical scanning time.

By operating these two types of switches, the charge stored in the photodiode is sequentially supplied to a load circuit composed of a resistor 6 and a power supply 7, and is taken out as a voltage signal.

Here, if the photodiode 1A is destroyed for some reason and the substrate and cathode are short-circuited, the signal from the photodiode 1A always reaches the signal saturation point and becomes extremely large.

Further, a large signal voltage is also generated when leakage occurs in the photodiode and the dark current of the photodiode is abnormally large.

These are collectively referred to as white spot defects of the image sensor, and the level of the latter varies depending on the operating temperature, operating voltage, etc. of the image sensor.

Further, if the situation is opposite to the above, a black spot defect occurs, but the black spot defect is not very noticeable on the screen.

FIG. 2a shows the state of a black dot defect in the horizontal line signal, and FIG. 2b shows the state of a white dot defect in the horizontal line signal. The shaded area in FIG. 2 indicates the amount of signal generated in the photodiode 1 depending on the amount of received light.

FIG. 3 shows an example in which such black spot defects and white spot defects are replaced and corrected with the signal amount of the picture element one picture element before.

The operation of the conventional example shown in FIG. 3 will be explained below with reference to FIG. 4. The solid-state image sensor 8 is driven by a pulse generation circuit 9, and pulses in a synchronous relationship with the solid-state image sensor 8 are supplied to a first sample-and-hold circuit 10 and a second sample-and-hold circuit 11. FIG. 4a shows the signal state of a horizontal line with a defect, and position D is a black spot defect. 4b shows the first sample and hold pulse, c shows the output of the first sample and hold circuit 10, d shows the second sample and hold pulse, and e shows the output of the second sample and hold circuit 11.

The first sample and hold pulse is passed through the defect position memory circuit 12 to the first sample and hold circuit 1.
0, and the defect position memory circuit 12 is
1st sample hold pulse (4th pulse) at defect location
(see Figure b). Therefore, since the output of the first sample and hold circuit 10 does not sample and hold the defective position as shown in FIG. be done. When this signal is passed through the second sample and hold circuit 11 with the second sample and hold pulse shown in d, the defective position D is corrected with the signal c, which is the previous pixel signal, as shown in Figure 4e. be done. The conventional example shown in FIG. 3 is effective for black-and-white video camera devices, and defective parts other than edge parts can hardly be identified.

However, the subject of the video camera often has many edges, which makes it easy to see defects in the solid-state image sensor.

Purpose of the Invention The present invention is intended to solve the above-mentioned conventional drawbacks, and to correct white spot defects or black spot defects that occur in a dotted manner on the screen due to a defect occurring in a part of a solid-state image sensor, and to correct the defect location. The purpose is to remove the horizontal correlation error signal that occurs at the correction location.

Structure of the Invention The present invention includes a solid-state image sensor, a pulse generation circuit for driving the solid-state image sensor, a defect position memory circuit operated by the pulse generation circuit, and a defect position memory circuit connected to the output of the solid-state image sensor and operated by the output of the defect position memory circuit. a second sample and hold circuit connected to the output of the first sample and hold circuit and operated by a pulse generation circuit; and a delay means and a subtraction means connected to the output of the second sample and hold circuit. an error detection circuit; a switch circuit connected to the output of the subtraction means of the correlated error detection circuit and operated by the defect position storage circuit; and a subtracter for subtracting the output of the switch circuit and the output of the delay means of the correlated error detection circuit. This solid-state imaging device is capable of making white dot defects and black dot defects that occur in dots on the screen due to a defect occurring in a portion of the solid-state imaging device less noticeable.

DESCRIPTION OF EMBODIMENTS FIG. 5 shows a block diagram of a solid-state imaging device according to a first embodiment of the present invention. In FIG. 5, the same numbers as in FIG. 3 are the same. In FIG. 5, 14 is a horizontal correlation error detection circuit, and this horizontal correlation error detection circuit is composed of a delay circuit 15 as a delay means and a subtracter 16 as a subtraction means. Further, 18 is a switch circuit, and 19 is a subtracter.

The operation of the solid-state imaging device of this embodiment configured as described above will be described below with reference to the main waveform diagram of FIG. 6 and FIG. 7.

In the embodiment shown in FIG. 5, the same numbers as in the conventional example shown in FIG. 3 are the same or have equivalent functions, and a to e in FIG. It shows. FIG. 6a shows the state of a black spot defect in a horizontal line signal, where position D is the defect position, and the shaded area shows the amount of signal generated in the photodiode 1 depending on the amount of light received. In order to correct the defective position at position D using the previous pixel signal, the defective position memory circuit 12 generates a sample-holding pulse for defective position D as shown in the first sample-holding pulse b. can be stopped. Therefore,
The output of the first sample and hold circuit is the signal of the previous picture element c as shown in Figure 6c.
Sample and hold is performed up to the signal position. When this signal is passed through the second sample and hold circuit 11 with the sample and hold pulse shown in FIG. 6d, the C signal, which is the previous picture element signal, is applied to the defective position D as shown in FIG. 6e. Corrected. However, as shown in the screen of FIG. 7a, if there is a change between a white object and a black object shown by diagonal lines between the defective position D of photodiode 1 and the previous picture element C, the part shown in FIG. 7A When enlarged and shown in FIG. 7b, in example n, a white output corresponding to one picture element is generated. This operation shows the signal amounts at f, g, and h in FIG. 6, where O indicates the black level and 1 indicates the white level, and the white level by one picture element is generated more in the n column portion. In order to remove the error signal for one picture element, the delay circuit 15 delays the signal for one picture element, and one output is the signal of n column and n-1
Column signals are shown as j and k, and the other output is the i signal of the horizontal correlation error detection circuit 14. This n
When g before the column signal passes through the delay circuit 15 and k after passing through the delay circuit 15 are passed through a subtracter, an output l from the horizontal correlation error detection circuit 14 is obtained.

The other output of the defective position memory circuit 12 is a switch pulse delayed by approximately two picture elements, and the sixth
The switch circuit 18 is operated as shown in FIG.

There is no particular problem in the part where there is horizontal correlation, but
In the case as shown in FIG. 7a where no horizontal correlation can be obtained, the horizontal correlation error signal (FIG. 6l) is switched by the switch circuit 18 only at the defective position. By passing the output signal of the switch circuit 18 and the local output of the horizontal correlation error detection circuit 14 through the subtracter 19, the signal shown in FIG. 6k becomes the signal shown in FIG. The correlated error signal is removed, and the horizontal correlated error signal at the defect location disappears, as shown in FIG. 7c.

As described above, according to this embodiment, a horizontal correlation error signal is detected by the signal horizontal correlation error detection circuit, and only the portion at the defective position is switched by the switch circuit, so that the signal is connected to the other output of the horizontal correlation error detection circuit. By passing the output of the switch circuit through a subtracter, the horizontal correlation error signal at the defect position is removed.
A smooth luminance signal can be obtained. Although this embodiment shows an example using correlation in the horizontal direction, it goes without saying that the same effect can be obtained in the vertical direction as well. Further, it is easily possible to carry out the same function by performing digital signal processing using a field memory, a frame memory, etc., and correcting the defect by incorporating information around the defect position in the image.

Effects of the Invention The solid-state imaging device of the present invention includes a defect correction means for correcting defects in the solid-state image sensor, a correlation error detection circuit connected to the defect correction means, and a defect position storage circuit connected to one of the outputs of the correlation error detection circuit. By providing a switch circuit that operates according to However, the correlated error signal generated at the defective part can be removed and a smooth screen can be obtained, which has a great practical effect.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of an example of a MOS solid-state image sensor.
FIG. 2 is a waveform diagram of an example of a defective state of a horizontal line signal, FIG. 3 is a circuit diagram of an example of a conventional defect correction circuit, FIG. 4 is a waveform diagram of the main part of the conventional example, and FIG. FIG. 6 is a circuit diagram of an element of one embodiment, FIG. 6 is a waveform diagram of essential parts of the present invention, and FIG. 7 is a diagram showing a screen state. 8... Solid-state imaging element, 9... Pulse generation circuit,
12...Defect position memory, 14...Horizontal correlation error detection circuit, 18...Switch circuit, 19...Subtractor.

Claims (1)

[Claims] 1. A solid-state image sensor, a pulse generation circuit for driving the solid-state image sensor, a defect position storage circuit operated by the pulse generation circuit, and a defect position storage circuit connected to the output of the solid-state image sensor and operated by the output of the defect position storage circuit. a first sample and hold circuit, a second sample and hold circuit connected to the output of the first sample and hold circuit and operated by the pulse generation circuit, and a delay means and a subtraction means connected to the output of the second sample and hold circuit. a switch circuit connected to the output of the subtraction means of the correlation error detection circuit and operated by the output of the defect position memory; and a switch circuit that connects the output of the switch circuit and the delay means of the correlation error detection circuit. What is claimed is: 1. A solid-state imaging device comprising: a subtracter for subtracting an output from a subtracter; and obtaining a luminance signal from the output of the subtracter.