Imaging apparatus

Details Imaging apparatus Imaging apparatus

2000-08-24

2004-07-06

Vu, Ngoc-Yen (Department: 2612)

Television

Camera, system and detail

Combined image signal generator and general image signal...

C348S250000, C348S297000, C348S312000, C348S622000, C382S265000, C708S320000

Reexamination Certificate

active

06760067

ABSTRACT:

BACKGROUND OF THE INVENTION
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 “recursive NR circuit”), 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 X−2 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 “0”. 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 X−2 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 “0” 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.
SUMMARY OF THE INVENTION
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 “1” 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 si

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