JPH04135388A - Picture signal processor - Google Patents

Abstract

PURPOSE:To accelerate speed for signal processing and to simplify the configuration of the device by reading out fixed pattern noise at the equal shutter speed from plural unit memories corresponding to the shutter speed of a picture signal to be inputted to a subtracting means, and outputting the noise to the subtracting means. CONSTITUTION:When the shutter speed is switched to 1/240S at time T4, the picture signal photographed at the shutter speed 1/240S is transmitted to a subtracter 15. On the other hand, a shutter speed mode signal is turned to an L level, and the fixed pattern noise stored in a memory 12 is selected by a selector 14, transmitted to the subtracter 15 and subtracted so as to output the picture signal removing the fixed pattern noise. Thus, even when light is not shielded each time the shutter speed is changed, the fixed pattern noise contained in the picture signal can be removed, the speed for signal processing can be accelerated, and the configuration of the device can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image signal processing device for removing fixed pattern noise in a camera system using an amplified image sensor.

[Conventional technology]

Conventionally, in camera systems using amplified image sensors, the image signal read out from the image sensor contains fixed pattern noise unique to the sensor, so it is necessary to remove this noise in order to improve image quality. Ta. On the other hand, fixed pattern noise is characterized in that it changes in response to changes in the camera's electronic shutter speed.

Therefore, in the past, the fixed pattern noise was removed from the image signal using the signal processing device shown in FIG. 5, and changes in the fixed pattern noise depending on the shutter speed were dealt with. This signal processing device stores fixed pattern noise specific to the image sensor in a memory 2, inputs the image signal read from the image sensor 1 and the fixed pattern noise stored in the memory 2 to a subtracter 3, and is configured to remove fixed pattern noise from the image signal.

In the signal processing device configured in this way, when the power is turned on to the system, the shutter speed mode signal generated when switching the shutter speed rises and is transmitted from the image sensor 1 in a light-shielded state. The read data is stored in the memory 2. Here, since the image signal level when light is blocked is "0", the data written to the memory 2 at this time corresponds to fixed pattern noise in the dark. The data written in the memory 2 retains its state until the next shutter speed is changed. Then, when the shutter speed is changed, the shutter speed mode signal rises again,
The fixed noise pattern at that shutter speed is shaded and newly written in the same manner as described above.

In this way, each time the shutter speed is changed, light is blocked and the fixed pattern noise data in the memory 2 is rewritten, and the subtracter 3 is used to remove the fixed pattern noise.

[Problem to be solved by the invention]

The above-described image signal processing device must perform light shielding and extract fixed pattern noise every time fixed pattern noise changes in accordance with a change in shutter speed. Therefore, if the shutter speed changes many times, it is necessary to block the light each time, which may slow down the processing speed, and furthermore, it is necessary to provide a special mechanism such as a complicated mechanical shutter for blocking the light. There was a need.

The present invention was made in view of the above-mentioned circumstances, and it is possible to remove fixed pattern noise contained in an image signal without blocking light every time the shutter speed changes, thereby increasing the signal processing speed. It is an object of the present invention to provide an image signal processing device that can increase speed and simplify the configuration of the device.

[Means to solve the problem]

In order to achieve the above object, an image signal processing device according to the present invention includes: an image sensor that converts a subject image photographed at a predetermined shutter speed into an image signal including fixed pattern noise according to the shutter speed; a memory means in which fixed pattern noise of the sensor is accumulated; and subtracting the fixed pattern noise read out from the memory means from the image signal read out from the image sensor, and outputting an image signal from which the fixed pattern noise has been removed. An image signal processing device comprising a subtraction means,
The memory means includes a plurality of unit memories in which each fixed pattern noise corresponding to each of a plurality of shutter speeds used is stored, and the plurality of fixed pattern noises are stored in accordance with the shutter speed of the image signal input to the subtraction means. The fixed pattern noise having the same shutter speed is read out from one of the memories and outputted to the subtraction means.

[For production]

According to the present invention, each fixed pattern noise corresponding to each of a plurality of shutter speeds is stored in advance in a plurality of unit memories, and the same fixed pattern noise is selected from among the plurality of memories according to the shutter speed of the image signal input to the subtraction means. The fixed pattern noise of the shutter speed is read out and used for subtraction by the subtraction means. Therefore, even if the shutter speed changes, subtraction can be performed using fixed pattern noise corresponding to the shutter speed without blocking light.

〔Example〕

Examples of the present invention will be described below.

FIG. 1 is a block diagram of an image signal processing device according to a first embodiment of the present invention. In this embodiment, a plurality of (two in this embodiment) memories 1 and 12 are connected in parallel to the image signal output side of the imager 10, each storing a fixed pattern noise corresponding to the shutter speed. One memory 1 stores fixed pattern noise when the shutter speed is 1/60S, and the other memory 12 stores fixed pattern noise when the shutter speed is 1/24O8. When the shutter speed is 1/60S, H level and 1/2 are stored in each memory 11 and 12.
A shutter speed mode signal indicating an L level at 4O3 is input to each read enable terminal RE.

In addition, the write enable terminal WE of each memory 11 and 12
A synchronizing pulse signal is inputted from the synchronizing pulse generating circuit 13. The synchronizing pulse generation circuit 13 outputs an H level when the light is blocked and a shutter speed mode signal is at the H level, depending on the light blocking signal and the shutter speed mode signal, which indicate an H level when light is blocked and an L level when not light blocked.
A synchronization pulse signal that rises to a level is output to one memory 11, and a synchronization pulse signal that rises to an H level is output to the other memory 11 when the light shielding signal is at an H level and the shutter speed mode signal is at an L level. Both memories 11
．． The output of 12 is led to a selector 14. The selector 14 takes in the shutter speed mode signal as a selection signal, and inputs a memory output corresponding to the selection signal to the subtracter 15.

The subtracter 15 is configured to subtract the fixed pattern noise data input from the selector 14 from the image signal input from the imager 10 to the subtracter 15.

Next, the operation of this embodiment will be explained with reference to FIG.

At the same time as the power is turned on (time T1), light is blocked, and the image signal read from the imager 10 at the time of light blocking is output as dark fixed pattern noise.

At the same time, a synchronization pulse signal corresponding to the shutter speed mode signal rises, and the read fixed pattern noise is written into the memory to which the synchronization pulse signal is applied to the write enable terminal WE. In this embodiment, since the shutter speed mode signal is at H level, that is, 1/60S, the synchronization pulse given to the memory 11 rises, and the fixed pattern noise (A) at the shutter speed of 1/60S is written to the memory 11. . Then, at time T2, when the shutter speed is switched to 1/24O8 and the shutter speed mode signal goes to L level, the fixed pattern noise (
B) is written. When the light shielding signal goes to L level, the synchronization pulse signal input to the write enable terminal WE of memory 11.12 goes to L level, so memory 11.12
is used in ROM. The fixed pattern noise A, B written in each memory 11.12 is controlled by inputting a shutter speed mode signal to the gate enable terminal RE of each memory 11.12. memory 11
．． Fixed pattern noises A and B written in 12, respectively.
are given to the selector 14, respectively. Selector 1
4, the selector 14 selects fixed pattern noise according to the shutter speed based on the supplied selection signal.
is output to the subtracter 15.

For example, between time T3 and time T4, the shutter speed mode signal is at H level, that is, the shutter speed is 1/60S. At this time, the fixed pattern noise (A) written in the memory 11 is selected, and the fixed pattern noise (A) is output from the selector 14. This fixed pattern noise (A) is input to the subtracter 15.

On the other hand, an image signal taken at a shutter speed of 1/60 S and read out from the imager 10 is input to the subtracter 15. As a result, fixed pattern noise having the same shutter speed as the currently input image signal is input to the subtracter 15, and subtraction is performed using such fixed pattern noise to remove the fixed pattern noise. The resulting image signal is output.

Next, when the shutter speed is switched to 17240S at time T4, the image signal photographed at the shutter speed of 1/24O8 is sent to the subtracter 15. On the other hand, the shutter speed mode signal becomes L level, and memory 1
The fixed pattern noise (B) stored in No. 2 is selected by the selector 14 and sent to the subtracter 15, where it is subtracted in the same manner as described above and an image signal from which the fixed pattern noise (B) has been removed is output.

As described above, according to this embodiment, immediately after power is turned on, fixed pattern noise of two types of shutter speeds is stored in advance in the two memories 11 and 12, and the fixed pattern noise is fixed according to the shutter speed of the target image signal. Since the pattern noise is read out and removed from the image signal, even if the shutter speed is changed, the fixed pattern noise at that shutter speed can be read out immediately without blocking light, greatly increasing the signal processing speed. It can be made faster.

In addition, since there is no need to block light every time the shutter speed changes and capture fixed pattern noise data in the dark, capturing fixed pattern noise data when the power is turned on is as simple as attaching a cap to the lens of the camera system. is sufficient, the conventional mechanical shutter mechanism for shielding light can be omitted, and the device can be downsized.

Next, a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. As in the first embodiment, the shutter speed used is in two modes: 1/60S and 1/24O8, and the shutter speed mode signal is 1/24O8.
It is set to H level at 60S, and set to L level at 1/24O8. Also, the light shielding signal is H! when light is shielded. It becomes a novel, and becomes an LI novel when light is not shielded.

In this embodiment, the output of the imager 20 is input to one input terminal of an adder 21 and one input terminal of a subtracter 22, respectively. Memories 23 and 34 in which fixed pattern noises having different shutter speeds are stored are connected in parallel to the output side of the adder 21. The synchronization pulse generation circuit 25 outputs a synchronization pulse signal that becomes H level to the read enable terminal of one memory 23 only when the light shielding signal is at H level, and when the light shielding signal is at H level and the shutter speed mode signal is L + /Bevel, a synchronizing pulse signal that becomes H level is output to the read enable terminal of the other memory 24.

Each memory output is provided to a selector 26, respectively.

The selector 26 selects and outputs one input according to the shutter speed mode signal.

Selector output is D type flip-flop circuit 27
and 1/n circuit 28, respectively. The D-type flip-flop circuit 27 outputs the previously input selector output to the other input terminal of the adder 21 in accordance with the input of the clock signal, and is reset by a reset signal input every time the shutter speed mode is switched. Further, the 1/n circuit 28 converts the selector output into 1/n
This is a circuit for dividing by n, where n is inputted with the number of fixed pattern noises to be added. The subtracter 22 has this 1/n
The output of the circuit 28 and the image signal read out from the imager 20 are input, and from this image signal 1/n circuit 2
An image signal obtained by dividing 8 outputs (averaged fixed pattern noise) is output.

Next, the operation of this embodiment configured as above will be explained.

At time T11, the system is powered on, and at the same time, the light shielding signal rises to H level. Since the shutter speed mode signal is at H level from time Tll to T14,
During this period, fixed pattern noise (A) with a shutter speed of 1/60S is added multiple times, and the integrated fixed pattern noise (A) is stored in one memory 23.

That is, since the shutter speed mode signal is at H level, the synchronization pulse signal applied to the write enable terminal WE of one memory 23 is at H level. At time T11, the dark fixed pattern noise (a) read from the imager 20 is written into the memory 23 as it is through the adder 21. Next, at time T12, the imager 2
Fixed pattern noise (b) is read from 0 and added to adder 2.
It is input to one input terminal of 1. At this time, adder 21
The fixed pattern noise (a), which has been held in the flip-flop circuit 27 through the selector 26, is input to the other input terminal of the adder 21 at the clock time T12.

As a result, the sum of the fixed pattern noises (a) and (b) added by the adder 21 is stored in the memory 23, and is input to the flip-flop circuit 27 through the selector 26. At time T13, fixed pattern noise (
c) and data h are added and stored in the memory 23.

In this way, the three fixed patterns and the added value of noise at the shutter speed of 1/60S are stored in the memory 23.

Next, fixed pattern noise (B)' is captured at a shutter speed of 1/24O8. At time T14, when the shutter speed changes to 1/240S and the shutter speed mode signal goes to L level, the reset signal rises, the synchronization pulse signal of the write enable terminal WE of the other memory 24 rises, and the mode is switched. During the period from T14 to T17, fixed pattern noise is added to the other memory 24 in the same manner as described above.

In this way, the shutter speed 1.0 is stored in the other memory 24. /24 The sum of three fixed pattern noises in the OS is accumulated.

The selector 26 is supplied with the added values stored in the memories 23 and 24, respectively, and the added value of the fixed pattern noise of the mode selected according to the shutter speed mode signal is inputted to the 1/n circuit 28. The 1/n circuit 28 outputs to the subtracter 22 the average value of fixed pattern noise obtained by dividing the input signal by the number of additions n. On the other hand, an image signal taken at the same shutter speed as the fixed pattern noise outputted from the 1/n circuit 28 is read out from the imager 20 and supplied to the subtracter 22 . Therefore, the subtracter 22 performs subtraction using the average value of a plurality of fixed pattern noises, and outputs an image signal subtracted by such fixed pattern noise.

In this way, according to this embodiment, fixed pattern noise of two types of shutter speeds is stored in advance in two memories 23 and 24.
Since the fixed pattern noise is stored and read out in accordance with the shutter speed of the target image signal, the same effects as in the first embodiment can be obtained. Furthermore, in this embodiment, a plurality of fixed pattern noises read out multiple times from the imager 20 are stored in each memory 23 and 24, and this accumulated value is subtracted by the averaged fixed pattern noise. As a result, it is possible to perform noise removal processing using fixed pattern noise with higher accuracy, and the S/N ratio of image data can be further improved.

In addition, the above 1. In the second embodiment, the case where two shutter speeds are used has been described, but there is no limit to the number of shutter speeds as long as the number of memories is changed according to the number of shutter speeds used.

〔Effect of the invention〕

As detailed above, according to the present invention, fixed pattern noise contained in image signals can be removed without blocking light every time the shutter speed changes, thereby increasing signal processing speed. Accordingly, it is possible to provide an image signal processing device that can simplify the configuration of the device.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a first embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of the same embodiment, Fig. 3 is a block diagram of a second embodiment of the present invention, and Fig. 4 is a block diagram of the same embodiment. FIG. 5 is a block diagram of a conventional image signal processing device, and FIG. 6 is a diagram explaining the operation of the conventional example. 10.20... Imager 11, 12, 23°24
...Memory, 13.25...Synchronization pulse generation circuit,
14.26...Selector 15.22...Subtractor.

Claims (1)

[Claims] an image sensor that converts a subject image photographed at a predetermined shutter speed into an image signal including fixed pattern noise according to the shutter speed; and a memory means in which the fixed pattern noise of the image sensor is stored.
and subtraction means for subtracting the fixed pattern noise read out from the memory means from the image signal read out from the image sensor and outputting an image signal from which the fixed pattern noise has been removed, the image signal processing device comprising: The memory means includes a plurality of unit memories in which each fixed pattern noise corresponding to each of the plurality of shutter speeds used is accumulated, and the plurality of units are stored in accordance with the shutter speed of the image signal input to the subtraction means. An image signal processing device characterized in that fixed pattern noise having the same shutter speed is read out from a memory and outputted to the subtraction means.