Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1995-05-23
2002-02-12
Lee, Richard (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C348S607000, C382S250000
Reexamination Certificate
active
06347118
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing apparatus which encodes and outputs an image signal which was inputted from an image pickup section.
2. Description of the Related Art
The typical examples for the above-described image processing apparatus are an electronic camera and a video camera. In an electronic camera, the controls such as the shutter speed, focus, zoom, and diaphragm (lens aperture) controls are performed in the lens unit. A gain control is performed in the image pickup section by processing a signal, which was photoelectrically converted and outputted from a CCD. These controls, i.e., the diaphragm and gain controls, are called the automatic exposure control (which is referred to as AE below). The gain control is performed by a voltage control amplifier (referred to as VCA) and clamping circuit (referred to as CL). A video signal which is outputted from the image pickup section is converted to a digital signal by an A/D converter and stored in memory. Then, the digital signal which was read out from the memory is compressed and encoded respectively by a quantizer and coder, and then outputted as coded output.
However, in conventional image processing, the aforementioned controls and the adjustment for the brightness level are complicated which causes apparatus to be quite large. In addition, since noise removal is not enough, there is the drawback that an efficiency of coding is decreased. A few other drawbacks in the conventional apparatus are further described below.
In an image processing apparatus, which adjusts a brightness level, the following arrangement is well known. First, a video signal is inputted to the A/D converter and converted to a digital signal. The digital signal is stored in the memory. Then, the brightness level which was inputted through a microprocessor (CPU) is added by an adder to every pixel of the video signal which was being stored in the memory. However, since the brightness level needs to be added to each pixel of image data, there are the drawbacks that the number of adding operation is increased, buffer quantity for data which relates to the addition is increased, and the apparatus becomes both complicated and quite large.
FIG. 19
is a block diagram illustrating the arrangement of a conventional electronic camera. The reference numeral
10
is a lens unit comprising a photograph lens, shutter, and diaphragm. The CCD image pickup device
12
converts a subject image picked up by the lens unit
10
into an electrical signal. The image pickup processing circuit
14
performs a well-known camera signal processing operation such as a gamma correction on the output of the image pickup device
12
and outputs a standard type video signal. The image pickup processing circuit
14
adjusts the gain so that white and black peak levels will be within a predetermined range. The A/D converter
16
digitizes the output of the image pickup processing circuit
14
and the output is temporarily stored in the memory
18
. The image data which was read from the memory
18
is either modulated or coded if necessary, and recorded on a recording medium.
The system controller
28
drives a shutter of the lens unit
10
by the shutter drive circuit
30
and also drives a focusing lens and zooming lens by the lens drive circuit
32
. Furthermore, the system controller
28
directly controls a diaphragm. Instructions for photographing and the like are inputted to the system controller
28
in a manner such that a user operates the operation section
34
. The display section
36
displays the state of operation.
The system controller
28
calculates the white and black peak levels in a screen (or a predetermined area) from the output of the A/D converter
16
(or the memory
18
) and controls the gain of the image pickup processing circuit
14
so that the levels will be at a predetermined level.
On the other hand, in an electronic camera which electromagnetically records a still image and a moving image, e.g. an electronic still camera and video camera, the method such that an image is compressed and stored using a recording medium in digital recording has recently been of interest. In this method, because of the digital recording, image deterioration by duplication is decreased and many images can be recorded in a small recording capacity because of compression recording.
However, in the above-described electronic camera in the case of photographing at a low light intensity or at a high shutter-speed, the S/N ratio of the output signal of the image pickup device
12
deteriorates, and if the image is compressed as it is, the quality of the image decreases. Furthermore, there is another drawback such that the compressing efficiency is decreased, since a high-frequency component of an image having a deteriorated S/N ratio is large.
Furthermore, in the case where an image source to be compressed is a reproduction image of a video tape recorder or an output of a TV tuner, the image does not have a sufficient S/N ratio. If such an image is compressed as is, not only is the quality of the image decreased, but also the efficiency of compression is decreased.
As an example, a block diagram of the gain adjustment arrangement in the conventional image processing apparatus is shown in FIG.
20
. An analog video signal is inputted to an input terminal and the voltage control amplifier (VCA)
14
a
amplifies the analog video signal to reach a predetermined white peak level and the clamping circuit
14
b
clamps a DC level so that the analog video signal reaches a predetermined black peak level.
The output of the clamping circuit
14
b
is converted to a digital signal by the A/D converter
16
and stored in the memory
18
.
The system controller
28
comprising a microcomputer seeks white and black peak levels from the output of the memory
18
and controls the gain of the VCA
14
a
and the clamping level of the clamping circuit
14
b
so that the dynamic range of the A/D converter
16
is fully utilized. For example, if the range of the A/D converter
16
is set from “0” to “FF” (hexadecimal notation), the video signal of white and black peaks shown in
FIG. 5A
is expanded to the video signal shown in FIG.
5
B.
However, in the conventional apparatus, since the white and black peaks are detected from the signal after the A/D conversion, there is a drawback such that the processing of the gain adjustment is susceptible to noise, impulse noise in particular. That is, there is a drawback such that false peak levels are detected and the dynamic range of the A/D converter
16
cannot be efficiently utilized.
This drawback has also arisen when the image data stored in the memory is compressed.
The apparatus which performs AE control is shown in FIG.
21
. As shown in the diagram, the image is converted to an electrical signal in the lens unit
10
and the solid state pickup device
12
(which is referred to as CCD below), and then converted to a video signal in the image processing circuit
14
. It is further converted to a digital signal in the A/D converter
16
and stored in memory
18
. It is then compressed by the image data compressor
20
and the coded output is outputted.
Finally, the AE operation is described. The video signal which was obtained in the CCD
12
and the image processing circuit
14
is converted to a digital signal by the A/D converter
25
through the LPF (low-pass filter)
23
and the SW (switch)
24
. Then, the digital signal is integrated by the integrator
26
and inputted into the system controller
28
. While the output of the integrator
26
is supervised optimize the inputted light quantity of the CCD
12
, the system controller
28
controls an amplifier gain of the iris, or diaphragm, control and image processing circuit
14
and performs automatic exposing.
However, in this conventional apparatus, since the LPF
23
, SW
24
, A/D converter
25
, and integrator
26
are necessary for AE, there are drawbacks that
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