JPS63169882A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To prevent the production of lateral stripe noise even when a defect is present in a solid-state image pickup element by providing plural light-shielded picture elements to the solid-state image pickup element, using the mean value of the picture element output at a black reference level to apply black level correction of a video signal. CONSTITUTION:An optical black part is provided to each line of plural picture elements and solid-state image pickup element 1. In reading data of each line from a memory 3, the optical black picture element data are all added by an adder circuit 13, and the result of addition is latched in a pre-stage latch circuit 14. Then the mean value is stored in a post-stage latch circuit 12. Then the output of the picture element receiving light is read and outputted from the memory 3, then the output from the memory 3 and the mean data of the latch circuit 12 are subtracted by a subtraction circuit 11. Thus, the effect of picture element defects of the solid-state image pickup element 1 and of noise are almost removed and lateral stripe noise is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state imaging device having a function of correcting a black level of a video signal.

(Prior art) In recent years, high-speed and
Many digitized solid-state imaging devices have been announced due to lower prices, higher integration of semiconductor memories, and lower prices. FIG. 5 shows a typical example of the conventional device. In Fig. 5, 1 is a solid-state image sensor such as a CCD (charge-coupled device), and in the solid-state image sensor 1, an optical image from a manuscript, microfilm, etc. is converted into an electric charge, and this electric charge is further converted into a voltage. Afterwards, it is output in series. Solid-state image sensor 1
The output of is input to the ^/D converter 2 and is converted into ^/D. The A/D converted digital video data is temporarily stored in the memory 3. The data stored in the memory 3 is then subjected to necessary signal processing such as black level correction, filtering, or gamma correction by a signal processing circuit 4, and then output.

The CPU (control unit) 5 rewrites the data in the memory 3 for each field to create a moving image, and when the rewriting is stopped, it becomes a still image.

6 is a drive circuit that drives the solid-state image sensor 1.

The memory 3 stores data of all pixels of the solid-state image sensor 1,
The stored data is sequentially processed by the signal processing circuit 4, and the black level correction processing at that time will be described next.

FIG. 6 shows part of the video data read out from the memory 3 mentioned above. However, this data χ. □,
Although χgel...xacn is originally digital data, it is shown in analog form in this figure for convenience. usually,
Since dark current is generated in the solid-state image sensor 1, some pixels on the solid-state image sensor 1 are shielded from light so that the output of the light-shielded pixels (generally called optical black) becomes the black level in the video output. image processing, that is, black level correction processing. Generally, the pixels to be shaded are the first few pixels of each horizontal line. In the example in Figure 6, optical black is the first pixel χ0 of each horizontal line.
41.

FIG. 7 shows an example of a conventional black level correction circuit that performs the above-mentioned black level correction processing. In this figure, 11 is a subtraction circuit, and 12 is a latch circuit. At the beginning of every H (horizontal period), X0B1, which is the data in the optical black section, is read out from the memory 3 in advance and latched into the latch circuit 12, and all the data in that H, that is, X. a
+s Xac+...X latched from xacn. I
Black level correction is performed by subtracting the value of ll.

[Problem that the invention seeks to solve]

However, in this case, if there is a pixel defect in the optical black part or noise from output amplification of the solid-state image sensor 1 is included, there is a drawback that an error occurs in black level correction. That is, X is optical black data. There was a drawback that all 10 minutes of the image data were raised or lowered depending on the value of B1, resulting in horizontal stripe noise.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a solid-state imaging device having a black level correction function that eliminates the above-mentioned drawbacks and eliminates black level correction errors that cause horizontal stripe noise.

[Means for solving problems]

In order to achieve such an object, the present invention provides a solid-state imaging device that processes and outputs a video signal obtained by converting the output of a solid-state imaging device from analog to digital, in which a plurality of light-shielded pixels are provided in the solid-state imaging device, The present invention is characterized in that it includes a black level correction circuit that corrects the black level of a video signal by using the average value of output values output from pixels as a black reference level.

[Effect]

According to the present invention, the solid-state image sensor is provided with a plurality of light-shielded pixels, and the average value of the pixel output is used as the black reference level to correct the black level of the video signal. horizontal stripe noise does not occur even if

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of a black level correction circuit 10 according to an embodiment of the present invention. In this figure, 13 is an addition circuit that sequentially adds data output from a plurality of light-shielded pixels (optical black portion) provided in the solid-state image sensor l. 1
Reference numeral 4 designates a latch circuit for performing the addition, and reference numeral 15 designates a shift register that shifts and averages the addition result in the addition circuit 13 in the LSB (least significant digit) direction according to the number of additions. The data averaged by the shift register 15 is latched by the latch circuit 12 and used for black level correction processing.

FIG. 2 shows an example of the output of the solid-state image sensor 1 used in combination with the circuit shown in FIG. In the example shown in FIG. 2, eight pixels are provided in the optical black section.

Next, the operation of the circuit of this embodiment shown in FIG. 1 will be explained with reference to FIG.

When reading the data of each line from memory 3, first,
Optical black pixel data χ. Bl,X0B2
. . . all roBa are added by the adder circuit 13, and the addition result is latched into the latch circuit 14 at the previous stage. Next, the binary data latched in the latch circuit 14 is shifted and divided three times in the LSD direction by the shift register 15, and the average value of χoa+ −X oea obtained as a result is stored in the latch circuit 12 at the subsequent stage. . Next, when the outputs Xac, . . .

The output of the latch circuit 12 is a plurality of optical black pixel data X. Since it is the average value of B, ~Xoma, the effects of pixel defects and noise of the solid-state image sensor 1 are almost eliminated, and horizontal stripe noise is eliminated.

FIG. 3 shows a modification of the embodiment of the present invention shown in FIG. 1, in which black level correction processing similar to that in FIG. In this example, among the outputs of the A/D converter 2, the output corresponding to the optical black portion (X oat - The average value is latched into the subsequent latch circuit 12, and the average value of the output of the optical black section latched by the latch circuit 12 is subtracted from the ^/D output corresponding to the pixels of the video period section by the subtraction circuit 11. The subtraction result is stored in the memory 3, only the black level corrected output of the video period part. In this way, by providing the black level correction circuit 10 before the memory 3, the capacity of the memory 3 can be saved.

FIG. 4 roughly shows the embodiment of FIG. 3 in which the input potential of the A/D converter 2 is controlled to an optimum value in order to make maximum use of the dynamic range of the A/D converter 2. An example of improvement is shown. In FIG. 4, 16 is a clamp circuit, 17 is a reference potential generation circuit that generates a reference potential for the clamp circuit 16, 18 is a black reference data generation circuit that generates black reference data, and 19 is a latch circuit 12 for the black reference data. A comparator 20 is a clamp capacitor interposed between the solid-state image sensor 1 and the A/D converter 2.

The black level correction circuit 10 is the same as that shown in FIG. 3, and a comparator 19 compares the average value data of the optical black portion created in the same manner as that shown in FIG. 3 with the black reference data. The reference potential applied to the clamp circuit 16 via the reference potential generation circuit 17 is controlled so that the data difference falls within a predetermined range. Now, if the black reference data is 0, the case where the average value data is 0 is the most A/
Although the dynamic range of the D converter 2 is effectively used, there is also the possibility that the clamp level is too low, causing blackouts. Therefore, good results can be obtained if the difference between the average value data and the black reference data is determined to be within the input range of the A/D converter 2, for example, between 1/20 and 0.

In this embodiment, 8 optical black pixels are provided, and division is performed by shifting three times with the shift register 15, but the invention is not limited to this, and especially if there are a plurality of optical black pixels, Of course, the number of pixels may be any number. Generally, division can be performed by shifting n times if the numerator is 20. However, even if more than 2n pixels are provided, it is sufficient to average only the 2n pixels. In addition, in this embodiment, the shift register 15
is used to find the average value, but there is no need to use a shift register; for example, if the output wiring from the addition side is shifted and connected to the latch circuit 12 except for the n bits of the lower digits, similar processing can be performed. Needless to say, this can be done.

(Effects of the Invention) As explained above, according to the present invention, a solid-state image sensor is provided with a plurality of light-shielded pixels, and the average value of the pixel outputs is used as a black reference level to correct the black level of a video signal. Since this is done, it is possible to obtain the remarkable effect that horizontal stripe noise does not occur even if there is a defect in the solid-state image sensor.

Furthermore, by providing the black level correction circuit according to the present invention in the front stage of the memory, it is possible to eliminate the need for a memory area for storing the optical black portion, and to make full use of the dynamic range of the A/D converter. In this way, the input potential of the A/D converter can be controlled to an optimal value.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of one embodiment of the present invention, FIG. 2 is an explanatory diagram showing the output state of the solid-state image sensor of FIG. 1, and FIG. 3 is a circuit of another embodiment of the present invention. FIG. 4 is a block diagram showing a circuit configuration of still another embodiment of the present invention. FIG. 5 is a block diagram showing an example of a circuit configuration of a conventional device. FIG. 6 is a conventional solid-state image sensor. FIG. 7 is a block diagram showing the configuration of a conventional black level correction circuit. DESCRIPTION OF SYMBOLS 1...Solid-state image sensor, 2.-ADD converter, 3...Memory, lO...Black level correction circuit, 11...Subtraction circuit, 12.14...Latch circuit, 13... Adder circuit, 15...Shift register, 16...Clamp circuit, 19...Comparator.

Claims (1)

[Scope of Claims] 1) In a solid-state imaging device that processes and outputs a video signal obtained by converting the output of a solid-state imaging device from analog to digital, the solid-state imaging device is provided with a plurality of light-shielded pixels; 1. A solid-state imaging device, comprising: a black level correction circuit that corrects the black level of the video signal by using an average value of output values output from the video signal as a black reference level. 2) A solid-state imaging device according to claim 1, further comprising a circuit that adjusts the output potential of the solid-state imaging device according to the average value.