Source: {"pile_set_name": "USPTO Backgrounds"}

1. Field of the Invention
The present invention generally relates to an imaging apparatus, and particularly to an imaging apparatus having a picture memory function to simultaneously achieve a recursive noise reduction circuit (hereinafter, referred to simply as xe2x80x9crecursive NR circuitxe2x80x9d), and long time accumulation (accumulation sensitivity increase) of CCD.
2. Description of the Related Art
Conventionally, such a recursive NR circuit has been used in a video system in order to reduce noise using a memory. However, semiconductor memories have recently developed to have large capacity at low cost, so that a memory and a recursive NR circuit have been incorporated in an imaging apparatus. Thus, the imaging apparatus have had the combination with various functions using memories.
For example, JP-A-5-23612 describes various functions using a recursive NR circuit and a memory system. Particularly, in the second noise reduction mode, the noise reduction effect is achieved by the recursive NR circuit and the accumulation sensitivity increase over 2-field periods.
Such a conventional imaging apparatus will be described with reference to FIG. 38. FIG. 38 is a schematic block diagram of a conventional imaging apparatus.
The imaging apparatus shown in FIG. 38 includes: a CCD 101 for converting a light image into an electrical image signal; a CDS 102 for sampling the electrical image signal; an A/D circuit 103 for converting the sampled image signal into a digital signal; a recursive NR circuit 104 that performs the recursive filtering process to the digital image signal in the time-axis direction to reduce the noise component of the image signal; a digital process circuit 105 that performs the necessary signal process to the recursive-filtered image signal; a D/A circuit 106 that converts the processed image signal into an analog signal to be output; a field memory 107 for storing an output signal of the recursive NR circuit 104; a field memory control circuit 108 for controlling the field memory 107; and a microcomputer 109 for controlling the whole imaging apparatus.
The field memory control circuit 108 delays the output signal of the recursive NR circuit 104 by one vertical scanning period, and outputs this delayed signal to the recursive NR circuit 104 as a cyclic signal.
The microcomputer 109 controls the cyclic coefficient of the recursive NR circuit 104, and controls the field memory control circuit 108 to write to and read from the field memory 107.
The CCD 101 is controlled by a charge reading pulse from a timing control circuit 110. The accumulation sensitivity increase is achieved when the microcomputer 109 controls the accumulation time that is input to the timing control circuit 110.
FIG. 39 is a timing chart showing the operation timing of this imaging apparatus in the normal operation.
As illustrated in FIG. 39, in the normal operation, the timing control circuit 110 outputs the charge reading pulse to the CCD 101 every vertical scanning period, so that the image signal is output from the CCD 101.
When an image signal x is output from the CCD 101, the cyclic coefficient K which is input from the microcomputer 109 to the recursive NR circuit 104 is set to be k. The recursive NR circuit 104 performs the arithmetic operation using the image signal x and an output signal Xxe2x88x922 of the field memory 107 to output the result as an output signal X. The output signal X is written to the field memory 107.
When an image signal x+1 is output from the CCD 101, the cyclic coefficient K which is input from the microcomputer 109 to the recursive NR circuit 104 is set to be xe2x80x9c0xe2x80x9d. Consequently, the output signal X of the field memory 107 is output from the recursive NR circuit 104 as the output signal X as it is. At this time, the output signal X of the recursive NR circuit 104 is not written to the field memory 107.
FIG. 40 is a timing chart showing the operation timing of this imaging apparatus in a 2-times accumulation sensitivity increase operation.
As illustrated in FIG. 40, when the accumulation sensitivity is increased twice, the timing control circuit 110 outputs the charge reading pulse to the CCD 101 every two vertical scanning periods. Therefore, the CCD 101 accumulates charges for two vertical scanning periods, and outputs the accumulated charges as an image signal.
When an image signal x is output from the CCD 101, the cyclic coefficient K which is input from the microcomputer 109 to the recursive NR circuit 104 is set to be k. The recursive NR circuit 104 performs the arithmetic operation using the image signal x and an output signal Xxe2x88x922 of the field memory 107 to output the result as an output signal X. The output signal X is written to the field memory 107.
When an image signal x+1 is output from the CCD 101, the timing control circuit 110 outputs no charge reading pulse, and hence the CCD 101 outputs no image signal.
Therefore, the cyclic coefficient K which is input from the microcomputer 109 to the recursive NR circuit 104 is set to be xe2x80x9c0xe2x80x9d so that the output signal X of the field memory 107 is output from the recursive NR circuit 104 as the output signal X as it is. In addition, the output signal X of the recursive NR circuit 104 is not written to the field memory 107.
Thus, the accumulation sensitivity can be increased twice, and at the same time the recursive NR can be achieved. Both of the sensitivity increase and the noise reduction can be attained.
In the above conventional imaging apparatus, however, the recursive NR is performed using the field memory 107, and the noise reduction operation by the recursive NR in the normal operation is performed by circulation of only one-field signal of the interlaced signal with the other-field signal not used. As a result, the vertical resolution is deteriorated. In addition, when the normal operation is changed to the accumulation sensitivity increase operation or when the accumulation sensitivity increase operation is changed to the normal operation, uncomfortable feeling occurs in the recursive NR operation.
It is an object of the invention to provide an imaging apparatus that has functions to use the both-fields signals of the interlaced signal for the recursive noise reduction in the normal operation, and to prevent the uncomfortable feeling in the recursive NR when the accumulation time of CCD (the accumulation sensitivity increase operation) is changed.
In order to achieve the above object, an imaging apparatus according to the first aspect of the invention includes:
imaging means for accumulating an image signal by an n-times long time accumulation (n is an integer of xe2x80x9c1xe2x80x9d or more);
timing control means for controlling to read out the image signal stored in the imaging means according to the n-times long time accumulation;
memory means for storing the image signal read out by the timing control means for one frame period or more;
memory control means for controlling the memory means; and
recursive noise reduction means for performing a noise reduction process on the basis of the image signal read out from the imaging means and the one-frame-period-or-more delayed image signal read out from the memory means to generate a noise-reduction processed image signal, wherein
when the imaging means performs a 2n-times long time accumulation, in a vertical scanning period in which the image signal is output from the imaging means, the memory control means writes to the memory means the image signal generated by the recursive noise reduction means, and the recursive noise reduction means outputs the generated image signal as an output signal as it is; and
in a vertical scanning period in which the image signal is not output from the imaging means, the memory control means inhibits the writing of the image signal generated by the recursive noise reduction means to the memory means, and the recursive noise reduction means outputs the image signal read out from the memory means, as the output signal as it is.
This imaging apparatus may use the memory means such as a frame memory, and performs the recursive noise reduction process to the both-fields signal of the interlaced signal in the normal operation. Thereby, it is possible to reduce noise without deteriorating the vertical resolution. Further, even if the imaging means such as a CCD performs the 2n-times long time accumulation (or the accumulation sensitivity increase), it is possible to make the recursive noise reduction means operate properly.
In an imaging apparatus according to the second aspect of the invention, when the long time accumulation in the imaging means changes from one-time to 2n-times, after 2n vertical scanning periods from this change, the recursive noise reduction means outputs the image signal from the imaging means as the output signal as it is, without performing the noise reduction process.
In this imaging apparatus, even when the long time accumulation in the imaging means changes from one-time to 2n-times, after 2n vertical scanning periods from this change, the recursive noise reduction means outputs the image signal from the imaging means as the output signal as it is, without performing the noise reduction process. Thereby, it is possible to prevent the recursive noise reduction means from the erroneous operation. Further, it is possible to change the one-time accumulation sensitivity increase operation to the 2n-times accumulation sensitivity increase operation without any uncomfortable feeling.
In an imaging apparatus according to the third aspect of the invention, when the long time accumulation in the imaging means changes from 2m-times (m is an integer of xe2x80x9c1xe2x80x9d or more, mxe2x89xa0n) to 2n-times, after 2n vertical scanning periods from this change, the recursive noise reduction means outputs the image signal from the imaging means as the output signal as it is, without performing the noise reduction process.
In this imaging apparatus, even when the long time accumulation in the imaging means changes from 2m-times to 2n-times, after 2n vertical scanning periods from this change, the recursive noise reduction means outputs the image signal from the imaging means